General Description
The DS2784 operates from 2.5V to 4.6V for integration in
battery packs using a single lithium-ion (Li+) or Li+ poly-
mer cell. Available capacity is reported in mAh and as a
percentage. Safe operation is ensured with the included
Li+ protection function and SHA-1-based challenge-
response authentication.
Precision measurements of voltage, temperature, and
current, along with cell characteristics and application
parameters are used to estimate capacity. The available
capacity registers report a conservative estimate of the
amount of charge that can be removed given the current
temperature and discharge rate.
In addition to the nonvolatile (NV) storage for cell compen-
sation and application parameters, 16 bytes of EEPROM
memory is made available for the exclusive use of the
host system and/or pack manufacturer. This facilitates
battery lot and date tracking or NV storage of system or
battery usage statistics.
A 1-Wire® interface provides serial communication at
16kbps or 143kbps to access data registers, control
registers, and user memory. Additionally, 1-Wire com-
munication enables challenge-response pack authentica-
tion using SHA-1 as the hash algorithm in a hash-based
message authentication code (HMAC) authentication
protocol.
Applications
●Health and Fitness Monitors
●Digital Still, Video, and Action Cameras
●Medical Devices
●Handheld Computers and Terminals
●Handheld Radios
●Home and Building Automation, Sensors
●Smart Batteries
●Power Tools
Features
●Precision Voltage, Temperature, and Current
Measurement System
●Available Capacity Estimated from Coulomb
Count, Discharge Rate, Temperature, and Cell
Characteristics
●Estimates Cell Aging Using Learn Cycles
●Uses Low-Cost Sense Resistor
●Allows for Calibration of Gain and Temperature
Coefficient
●Li+ Safety Circuitry—Overvoltage, Undervoltage,
Overcurrent, Short-Circuit Protection
●Programmable Safety Thresholds for Overvoltage
and Overcurrent
●Authentication Using SHA-1 Algorithm and 64-Bit
Secret
●32-Byte Parameter EEPROM
●16-Byte User EEPROM
●Maxim 1-Wire Interface with 64-Bit Unique ID
●Tiny, Pb-Free, 14-Pin TDFN Package Embeds Easily
in Battery Packs Using Thin Prismatic Cells
19-4636; Rev 5; 1/17
Ordering Information appears at end of data sheet.
Modes and commands are capitalized for clarity.
1-Wire is a registered trademark of Maxim Integrated Products,
Inc.
1K 150 1K
1K1K
DC
SNS
5.1V
PK-
DATA
PK+
150
VSS
DS2784
RSNS
PLS
DQ
0.1µF 0.1µF
PIO
VDD
VIN
CP
CTG
CC
DS2784 1-Cell Fuel Gauge with FuelPack,
Protector, and SHA-1 Authentication
Simple Fuel Gauge Circuit Diagram
Voltage Range on PLS Pin Relative to VSS ..........-0.3V to +18V
Voltage Range on CP Pin Relative to VSS ...........-0.3V to +12V
Voltage Range on DC
Pin Relative to VSS ...............................-0.3V to (VCP + 0.3V)
Voltage Range on CC
Pin Relative to VSS .........................VDD - 0.3V to VCP + 0.3V
Voltage Range on All
Other Pins Relative to VSS ............................... -0.3V to +6.0V
Maximum Voltage Range on
VIN Pin Relative to VDD ........................................ VDD + 0.3V
Continuous Sink Current, PIO, DQ ....................................20mA
Continuous Sink Current, CC, DC......................................10mA
Operating Temperature Range ........................... -40°C to +85°C
Storage Temperature Range ............................ -55°C to +125°C
Lead Temperature (soldering,10s) .................................. ±300°C
Soldering Temperature (reflow) ....................................... +260°C
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VDD (Note 1) +2.5 +4.6 V
Supply Current
IDD0 Sleep mode 1 4
µA
IDD1 Sleep mode, VDD = 2.5V 0°C to +50°C 0.4 1.5
IDD2 Active mode 85 125
IDD3 Active mode during SHA computation 300 500
Temperature Accuracy -3 +3 °C
Temperature Resolution 0.125 °C
Temperature Range -128.000 +127.875 °C
Voltage Accuracy, VIN
4.0 ≤ VIN ≤ 4.6, VIN ≤ VDD + 0.3V -30 30 mV
2.5 ≤ VIN ≤ 4.6V, VIN ≤ VDD + 0.3V -50 +50
Voltage Resolution, VIN 4.88 mV
Voltage Range, VIN 0 4.6 V
Input Resistance, VIN 15 MΩ
Current Resolution 1.56 µV
Current Full Scale -51.2 +51.2 mV
Current Gain Error -1 +1 % full
scale
Current Offset (Notes 2, 3, 4) -15 +25 µV
Accumulated Current Offset (Notes 2, 3, 4) -360 0 µVh/day
Time Base Error 0°C ≤ TA ≤ +50°C -2 +2 %
-3 +3
CP Output Voltage VCP ICC + IDC = 0.9μA 8.50 9.25 10.00 V
CP Startup Time tSCP CE = 0, DE = 0, CCP = 0.1μF, Active mode 200 ms
Output High: CC, DC VOHCC
VOHDC IOH = -100μA (Note 5) VCP -
0.4 V
Output Low: CC VOLCC IOL = 100μA VDD +
0.1 V
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Absolute Maximum Ratings
Electrical Characteristics
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
(VDD = 2.5V to 4.6V, TA = 0°C to +50°C, unless otherwise noted. Typical values are at TA = +25°C.)
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Output Low: DC VOLDC IOL = 100µA 0.1 V
DQ, PIO Voltage Range -0.3 +5.5 V
DQ, PIO Input-Logic High VIH 1.5 V
DQ, PIO Input-Logic Low VIL 0.6 V
DQ, PIO Output-Logic Low VOL IOL = 4mA 0.4 V
DQ, PIO Pullup Current IPU Sleep mode, VPIN = VDD - 0.4V 0.2 µA
DQ, PIO Pulldown Current IPD Active mode, VPIN = 0.4V 0.2 µA
DQ Input Capacitance CDQ 50 pF
DQ Sleep Timeout tSLEEP VDQ < VIL 2 9 s
PIO, DQ Wake Debounce tWDB Sleep mode 100 ms
SHA-1 COMPUTATION TIMING
Computation Time tSHA 30 ms
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Overvoltage Detect VOV
VOV = 11000b 4.457 4.482 4.507 V
VOV = 00011b 4.252 4.277 4.302
Charge-Enable Voltage VCE Relative to VOV -75 -100 -125 mV
Undervoltage Detect VUV 2.40 2.45 2.50 V
Overcurrent Detect: Charge VCOC
OC = 11b -57 -72 -87 mV
OC = 00b -15.5 -23.5 -31.5
Overcurrent Detect:
Discharge VDOC
OC = 11b 76 96 116 mV
OC = 00b 23.5 35.5 47.5
Short-Circuit Current Detect VSC
SC = 1b 240 300 360 mV
SC = 0b 120 150 180
Overvoltage Delay tOVD (Note 6) 425 1150 ms
Undervoltage Delay tUVD (Notes 6, 7) 84 680 ms
Overcurrent Delay tOCD 8 10 12 ms
Short-Circuit Delay tSCD 80 120 160 µs
Test Threshold VTP COC, DOC conditions 0.3 0.8 1.5 V
Test Current ITST SC, COC, DOC condition 10 20 40 µA
PLS Pulldown Current IPPD Sleep mode 30 200 600 µA
Recovery Current IRC VUV condition, max: VPLS = 15V,
VDD = 1V min: VPLS = 4.2V, VDD = 2V 2.5 5.0 10.00 mA
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Electrical Characteristics: Protection Circuit
Electrical Characteristics (continued)
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted.)
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted.)
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C.)
Note 1: All voltages are referenced to VSS.
Note 2: Factory-calibrated accuracy. Higher accuracy can be achieved by in-system calibration by the user.
Note 3: Accumulation bias and offset bias registers set to 00h. NBEN bit set to 0.
Note 4: Parameters guaranteed by design.
Note 5: CP pin externally driven to 10V.
Note 6: Overvoltage and undervoltage delays (tOVD, tUVD) are reduced to 0s if the OV or UV condition is detected within 100ms of
entering Active mode.
Note 7: tUVD MIN determined by stepping the voltage on VIN from VUV + 250mV to VUV - 250mV.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
EEPROM Copy Time tEEC 10 ms
EEPROM Copy Endurance NEEC TA = +50°C 50,000 cycles
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Time Slot tSLOT 60 120 µs
Recovery Time tREC 1 µs
Write-0 Low Time tLOW0 60 120 µs
Write-1 Low Time tLOW1 1 15 µs
Read-Data Valid tRDV 15 µs
Reset-Time High tRSTH 480 µs
Reset-Time Low tRSTL 480 960 µs
Presence-Detect High tPDH 15 60 µs
Presence-Detect Low tPDL 60 240 µs
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Time Slot tSLOT 6 16 µs
Recovery Time tREC 1 µs
Write-0 Low Time tLOW0 6 16 µs
Write-1 Low Time tLOW1 1 2 µs
Read-Data Valid tRDV 2 µs
Reset-Time High tRSTH 48 µs
Reset-Time Low tRSTL 48 80 µs
Presence-Detect High tPDH 2 6 µs
Presence-Detect Low tPDL 8 24 µs
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EEPROM Reliability Specication
Electrical Characteristics: 1-Wire Interface, Standard
Electrical Characteristics: 1-Wire Interface, Overdrive
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DS2784 1-Cell Fuel Gauge with FuelPack,
Protector, and SHA-1 Authentication
Typical Operating Characteristics
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DS2784 1-Cell Fuel Gauge with FuelPack,
Protector, and SHA-1 Authentication
Typical Operating Characteristics (continued)
PIN NAME FUNCTION
1 V
DD
Power-Supply Input. Chip supply input. Bypass with 0.1µF to VSS.
2CTG Connect to Ground
3 V
SS
Device Ground. Chip ground and battery-side sense resistor input.
4V
IN
Battery Voltage-Sense Input. Connect to positive cell terminal through decoupling network.
5, 9, 10 N.C. No Connection
6PLS Pack Plus Terminal-Sense Input. Used to detect the removal of short-circuit, discharge overcurrent, and
charge overcurrent conditions.
7CC Charge Control. Charge FET control output.
8DC Discharge Control. Discharge FET control output.
11 DQ Data Input/Output. Serial data I/O, includes weak pulldown to detect battery disconnect and can be
configured as wake input.
12 SNS Sense Resistor Connection. Pack minus terminal and pack-side sense resistor sense input.
13 CP Charge Pump Output. Bypass with 0.1µF to VSS.
14 PIO Programmable I/O Pin. Can be congured as wake input.
— EP Exposed Pad. Connect to VSS or leave unconnected.
VDD
CTG
VSS
VIN
NC
PLS
CC
PIO
CP
SNS
DQ
NC
NC
DC
TDFN – 14
(3mm x 5mm)
PAD
TOP VIEW
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Pin Description
Pin conguration
Detailed Description
The The DS2784 functions as an accurate fuel gauge,
Li+ protector, and SHA-1-based authentication token.
The fuel gauge provides accurate estimates of remain-
ing capacity and reports timely voltage, temperature,
and current measurement data. Capacity estimates are
calculated from a piecewise-linear model of the battery
performance over load and temperature, and system
parameters for full and empty conditions. The algorithm
parameters are user programmable and can be modified
in pack. Critical capacity and aging data are periodically
saved to EEPROM in case of loss of power due to a short
circuit or deep depletion.
The Li+ protection function ensures safe, high-perfor-
mance operation. nFET protection switches are driven
with a 9V charge pump that increase gate drive as the cell
voltage decreases. The high-side topology preserves the
ground path for serial communication while eliminating
the parasitic charge path formed when the fuel gauge IC
is located inside the protection FETs in a low-side con-
figuration. The thresholds for overvoltage, overcurrent,
and short-circuit current are user programmable for easy
customization to each cell and application.
The 32-bit wide SHA-1 engine with 64-bit secret and 64-bit
challenge words resists brute force and other attacks with
financial-level HMAC security. The challenge of managing
secrets in the supply chain is addressed with the compute
next secret feature. The unique serial number or ROM ID
can be used to assign a unique secret to each battery.
FuelPack™
Algorithm
POWER MODE
CONTROL
PRECISION
ANALOG
OSCILLATOR
16 BYTE USER
EEPROM
1-WIRE INTERFACE
CHARGE
PUMP
VDD
VDD_INT
CP
CURRENT
(VSS - SNS)
TEMPERATURE
VOLTAGE
(VIN - VSSA)
VIN
VREF
DS2784
10-BIT + SIGN
ADC/MUX
SNS
VSS
PIO
DQ
WKP, WKD
LITHIUM ION
PROTECTOR
PLS
FET DRIVERS
CC
DC
UV, CD
32 BYTE
PARAMETER
EEPROM
PIN DRIVERS
AND PWR
SWITCH
CONTROL
PIO LOGIC
15-BIT + SIGN
ADC
CONTROL AND
STATUS REGISTERS
FUELPACK™
ALGORITHM
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Block Diagram
Power Modes
The DS2784 has two power modes: Active and Sleep.
On initial power-up, the DS2784 defaults to Active mode.
In Active mode, the DS2784 is fully functional with mea-
surements and capacity estimation registers continu-
ously updated. The protector circuit monitors the battery
voltages and current for unsafe conditions. The protec-
tion FET gate drivers are enabled when conditions are
deemed safe. Also, the SHA-1 authentication function is
available in Active mode. When a SHA-1 computation is
performed, the supply current increases to IDD3 for tSHA.
In Sleep mode, the DS2784 conserves power by disabling
measurement and capacity estimation functions, but
preserves register contents. Gate drive to the protection
FETs is disabled in Sleep. And the SHA-1 authentication
feature is not operational.
Sleep mode is entered under two different conditions: bus
low and undervoltage. An enable bit makes entry into Sleep
optional for each condition. Sleep mode is not entered if a
charger is connected (VPLS > VDD + 50mV) or if a charge
current of 1.6mV / R
SNS
is measured from SNS to VSS.
The DS2784 exits Sleep mode upon charger connection
and VIN ≥ VUV or a low to high transition on DQ.
The bus-low condition, where the DQ pin is low for
tSLEEP, indicates pack removal or system shutdown in
which the 1-Wire bus pullup voltage, VPULLUP, is not
present. The Power mode (PMOD) bit must be set to
enter Sleep when a bus-low condition occurs. After the
DS2784 enters Sleep due to a bus-low condition, it is
assumed that no charge or discharge current will flow and
that coulomb counting is unnecessary.
The second condition to enter Sleep is an undervoltage
condition, which reduces battery drain due to the DS2784
supply current and prevents over discharging the cell. The
DS2784 transitions to Sleep if the VIN voltage is less than
VUV (2.45V typical) and the undervoltage enable (UVEN)
bit is set. The 1-Wire bus must be in a static state, that
is, with DQ either high or low for tSLEEP. The DS2784
transitions from UVEN Sleep to Active mode when DQ
changes logic state.
The DS2784 has the “power switch” capability for waking
the device and enabling the protection FETs when the
host system is powered down. A simple dry-contact switch
on the PIO pin or DQ pin can be used to wake up the bat-
tery pack. The power switch function is enabled using the
PSPIO and PSDQ configuration bits in the control regis-
ter. When PSPIO or PSDQ is set and a Sleep condition
is satisfied, the PIO and DQ pins pull high weakly, then
become armed to detect a low-going transition. A 100ms
debounce period filters out glitches that can be caused
when a sleeping battery is inserted into a system.
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Figure 1. Sleep Mode State Diagram
ACTIVE
PMOD = 0
UVEN = 0
ACTIVE
PMOD = 1
UVEN = 1
ACTIVE
PMOD = 1
UVEN = 0
ACTIVE
PMOD = 0
UVEN = 1
SLEEP
PSIO = 1
PSDQ = 1
SLEEP
PSIO = 1
PSDQ = 0
SLEEP
PSIO = 0
PSDQ = 1
SLEEP
PSIO = 0
PSDQ = 0
Vin < V
UV
Vin < V
UV
DQ LOW FOR t
SLEEP
DQ LOW FOR t
SLEEP
I/O COMMUNICATION OR
CHARGER CONNECTION
I/O COMMUNICATION OR
CHARGER CONNECTION
PULL DQ LOW
PULL PIO LOW
PULL PIO LOW
PULL DQ LOW
I/O COMMUNICATION OR
CHARGER CONNECTION
I/O COMMUNICATION OR
CHARGER CONNECTION
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Control Register Format
All control register bits are read and write accessible. The control register is recalled from parameter EEPROM memory
at power-up. Register bit values can be modified in shadow RAM after power-up. Power-up default values are saved
using the Copy Data command.
ADDRESS 60h
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NBEN UVEN PMOD RNAOP 0 PSPIO PSDQ X
NBEN—Negative Blanking Enable. A value of 1 enables blanking of negative current values up to 25μV. A value of 0
disables blanking of negative currents. The power-up default of NBEN = 0.
UVEN—Undervoltage Enable. A value of 1 allows the DS2784 to enter Sleep mode when the voltage register value is
less than VUV and DQ is stable at either logic level for tSLEEP. A value of 0 disables transitions to Sleep mode in an
undervoltage condition.
PMOD—Power Mode Enable. A value of 1 allows the DS2784 to enter Sleep mode when DQ is low for tSLEEP. A value
of 0 disables DQ related transitions to Sleep mode.
RNAOP—Read Net Address Op Code. A value of 0 selects 33h as the op code value for the Read Net Address com-
mand. A value of 1 selects 39h as the Read Net Address opcode value.
0—Reserved bit, must be programmed to 0 for proper operation.
PSPIO—Power-Switch PIO Enable. A value of 1 enables the PIO pin as a power-switch input. A value of 0 disables the
power-switch input function on PIO pin. This control is independent of the PSDQ state.
PSDQ—Power-Switch DQ Enable. A value of 1 enables the DQ pin as a power-switch input. A value of 0 disables the
power-switch input function on DQ pin. This control is independent of the PSPIO state.
X—Reserved Bit.
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Note 1: All voltages are with respect to VSS.
Note 2: CC pin driven to VOLCC (VDD) for CC off response. DC pin driven to VOLDC (VSS) for DC off response.
Note 3: If VIN < VUV when charger connection is detected, release is delayed until VIN ≥ VUV. The recovery charge path provides
an internal current limit (IRC) to safely charge the battery. If the device does not enter sleep mode for an UV condition
(UVEN=0) then the FETs will turn on once VIN > VUV.
Note 4: With test current ITST flowing from PLS to VSS (pulldown on PLS) enabled.
Note 5: With test current ITST flowing from VDD to PLS (pullup on PLS).
Li+ Protection Circuitry
During Active mode, the DS2784 constantly monitors
SNS, VIN, and VPLS to protect the battery from overvolt-
age (overcharge), undervoltage (overdischarge), and
excessive charge and discharge currents (overcurrent,
short circuit). Table 1 summarizes the conditions that acti-
vate the protection circuit, the response of the DS2784,
and the thresholds that release the DS2784 from a pro-
tection state.
Overvoltage. If the voltage on VIN exceeds the overvolt-
age threshold (VOV) for a period longer than overvoltage
delay (tOVD), the CC pin is driven low to shut off the exter-
nal-charge FET, and the OV flag in the protection register
is set. The DC output remains high during overvoltage
to allow discharging. When VIN falls below the charge
enable threshold, VCE, the DS2784 turns the charge FET
on by driving CC high. The DS2784 drives CC high before
VIN < VCE if a discharge condition persists with VSNS ≥
1.2mV and VIN < VOV.
Undervoltage. If VIN drops below the undervoltage thresh-
old (VUV) for a period longer than undervoltage delay
(tUVD), the DS2784 shuts off the charge and discharge
FETs and sets the UV flag in the protection register. If
UVEN is set, the DS2784 also enters Sleep mode. The
DS2784 provides a current-limited recovery charge path
(IRC) from PLS to VDD to gently charge severely depleted
cells. The recovery charge path is enabled when 0 ≤ VIN <
(VOV - 100mV). Once VIN reaches 2.45V (typ), the DS2784
returns to normal operation. The DS2784 transitions from
Sleep to Active mode and the CC and DC outputs are
driven high to turn on the charge and discharge FETs. If
the device does not enter sleep mode for an UV condition
(UVEN=0) then the FETs will turn on once VIN > VUV.
Overcurrent, Charge Direction (COC). Charge current
develops a negative voltage on VSNS with respect to VSS.
If VSNS is less than the charge overcurrent threshold
(VCOC) for a period longer than overcurrent delay (tOCD),
the DS2784 shuts off both external FETs and sets the
COC flag in the protection register. The charge current
path is not re-established until the voltage on the PLS pin
drops below VDD - VTP. The DS2784 provides a pulldown
current (ITST) from PLS to VSS to pull PLS down in order
to detect the removal of the offending charge current
source.
Table 1. Li+ Protection Conditions and DS2784 Responses
CONDITION ACTIVATION RELEASE THRESHOLD
THRESHOLD DELAY RESPONSE(2)
Overvoltage VIN > VOV tOVD CC Off VIN < VCE or (VSNS > 1.2mV
and VIN < VOV)
Undervoltage VIN < VUV tUVD CC Off, DC Off,
Sleep Mode
VPLS > VIN(3)
(charger connected)
Overcurrent, Charge VSNS < VCOC tOCD CC Off, DC Off VPLS < VDD - VTP (4)
(charger removed)
Overcurrent, Discharge VSNS > VDOC tOCD DC Off VPLS > VDD - VTP (5)
(load removed)
Short Circuit VSNS > VSC tSCD DC Off VPLS > VDD - VTP (5)
(load removed)
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Overcurrent, Discharge Direction (DOC). Discharge current develops a positive voltage on VSNS with respect to VSS.
If VSNS exceeds the discharge overcurrent threshold (VDOC) for a period longer than tOCD, the DS2784 shuts off the
external discharge FET and sets the DOC flag in the protection register. The discharge current path is not re-established
until the voltage on PLS rises above VDD - VTP. The DS2784 provides a test current (ITST) from VDD to PLS to pull PLS
up in order to detect the removal of the offending low-impedance load.
Short Circuit. If VSNS exceeds short-circuit threshold VSC for a period longer than short-circuit delay (tSCD), the DS2784
shuts off the external discharge FET and sets the DOC flag in the protection register. The discharge current path is not
re-established until the voltage on PLS rises above VDD - VTP. The DS2784 provides a test current of value (ITST) from
VDD to PLS to pull PLS up in order to detect the removal of the short circuit.
Summary. All the protection conditions previously described are logic ANDed to affect the CC and DC outputs.
CC = (Overvoltage) AND (Undervoltage) AND (Overcurrent, Charge Direction) AND (Protection Register Bit CE)
DC =
(
Undervoltage
) AND (
Overcurrent
, Either Direction) AND (
Short Circuit
) AND (Protection Register Bit DE)
Protection Register Format
The protection register reports events detected by the Li+ safety circuit on bits 2 to 7. Bits 0 and 1 are used to disable
the charge and discharge FET gate drivers. Bits 2 to 7 are set by internal hardware only. Bits 2 and 3 are cleared by
hardware only. Bits 4 to 7 are cleared by writing the register with a 0 in the bit position of interest. Writing a 1 to bits 4 to
7 has no effect on the register. Bits 0 and 1 are set on power-up and a transition from Sleep to Active modes. While in
Active mode, these bits can be cleared to disable the FET gate drive of either or both FETs. Setting these bits only turns
on the FETs if there are no protection faults.
ADDRESS 00h
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
OV UV COC DOC CC DC CE DE
Figure 2. Li+ Protection Circuitry Example Waveforms
tOVD tOCD
tSCD
VOV
VCE
VUV
VIN
VSNS
VSC
VDOC
-VCOC
0
tOVD tUVD
CHARGE
DISCHARGE
POWER
MODE
ACTIVE
SLEEP
tUVD
tOCD
CC
DC
VCP
VDD
VPLS
VCP
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OV—Overvoltage Flag. OV is set to indicate that an overvoltage condition has been detected. The voltage on VIN has
persisted above the VOV threshold for tOV. OV remains set until written to a 0 or cleared by a power-on reset or transi-
tion to Sleep mode.
UV—Undervoltage Flag. UV is a read-only mirror of the UVF flag located in the status register. UVF is set to indicate that
VIN < VUV. The UVF bit must be written to 0 to clear UV and UVF.
COC—Charge Overcurrent Flag. COC is set to indicate that an overcurrent condition has occurred during a charge. The
sense-resistor voltage has persisted above the VCOC threshold for tOC. COC remains set until written to a 0, cleared by
a power-on reset, or transition to Sleep mode.
DOC—Discharge Overcurrent Flag. DOC is set to indicate that an overcurrent condition has occurred during a discharge.
The sense-resistor voltage has persisted above the VDOC threshold for tOC. DOC remains set until written to a 0, cleared
by a power-on reset, or transition to Sleep mode.
CC—Charge Control Flag. CC indicates the logic state of the CC pin driver. CC flag is set to indicate CC high. CC flag
is cleared to indicate CC low. CC flag is read only.
DC—Discharge Control Flag. DC indicates the logic state of the DC pin driver. DC flag is set to indicate DC high. DC flag
is cleared to indicate DC low. DC flag is read only.
CE—Charge Enable Bit. CE must be set to allow the CC pin to drive the charge FET to the on state. CE acts as an enable
input to the safety circuit. If all safety conditions are met AND CE is set, the CC pin drives to VCP. If CE is cleared, the CC
pin is driven low to disable the charge FET.
DE—Discharge Enable Bit. DE must be set to allow the DC pin to drive the discharge FET to the on state. DE acts as
an enable input to the safety circuit. If all safety conditions are met AND DE is set, the DC pin drives to VCP. If DE is
cleared, the DC pin is driven low to disable the charge FET.
Protector Threshold Register Format
The 8-bit threshold register consists of bit fields for setting the overvoltage threshold, charge overcurrent threshold,
discharge overcurrent threshold, and short-circuit threshold for the protection circuit.
ADDRESS 7Fh
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
VOV4 VOV3 VOV2 VOV1 VOV0 SC0 OC1 OC0
Table 2. VOV Threshold Table 2. VOV Threshold (continued)
VOV BIT FIELD VOV VOV BIT FIELD VOV
0 0 0 0 0 4.248 1 0 0 0 0 4.404
0 0 0 0 1 4.258 1 0 0 0 1 4.414
0 0 0 1 0 4.268 1 0 0 1 0 4.424
0 0 0 1 1 4.277 1 0 0 1 1 4.434
0 0 1 0 0 4.287 1 0 1 0 0 4.443
0 0 1 0 1 4.297 1 0 1 0 1 4.453
0 0 1 1 0 4.307 1 0 1 1 0 4.463
0 0 1 1 1 4.316 1 0 1 1 1 4.473
VOV BIT FIELD VOV VOV BIT FIELD VOV
0 1 0 0 0 4.326 1 1 0 0 0 4.482
0 1 0 0 1 4.336 1 1 0 0 1 4.492
0 1 0 1 0 4.346 1 1 0 1 0 4.502
0 1 0 1 1 4.356 1 1 0 1 1 4.512
0 1 1 0 0 4.365 1 1 1 0 0 4.522
0 1 1 0 1 4.375 1 1 1 0 1 4.531
0 1 1 1 0 4.385 1 1 1 1 0 4.541
0 1 1 1 1 4.395 1 1 1 1 1 4.551
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Voltage Measurement
Battery voltage is measured every 440ms on the VIN pin with respect to VSS. Measurements have a 0 to 4.6V range and
a 4.88mV resolution. The value is stored in the voltage register in two’s complement form and is updated every 440ms.
Voltages above the maximum register value are reported at the maximum value; voltages below the minimum register
value are reported at the minimum value.
Voltage Register Format
MSB—ADDRESS 0Ch LSB—ADDRESS 0Dh
S 29282726252423222120X X X X X
MSb LSb MSb LSb
“S”: Sign Bit(s), “X”: Reserved Units:
4.
886m
V
Temperature Measurement
The DS2784 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C.
Temperature measurements are updated every 440ms and placed in the temperature register in two’s complement form.
Temperature Register Format
MSB—ADDRESS 0Ah LSB—ADDRESS 0Bh
S 29282726252423222120X X X X X
MSb LSb MSb LSb
“S”: Sign Bit(s), “X”: Reserved Units:
0.
125°C
Note: Temperature and battery voltage (VIN) are measured using the same ADC. Therefore, measurements are a 220ms average
updated every 440ms.
Table 3. COC, DOC Threshold
Table 4. SC Threshold
OC[1:0] BIT FIELD VCOC (mV) VDOC (mV)
0 0 -23.5 35.5
0 1 -36 48
1 0 -48 72
1 1 -72 96
SC0 BIT FIELD VSC (mV)
0150
1300
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Current Measurement
The DS2784 continually measures the current flow into and out of the battery by measuring the voltage drop across a
low-value current-sense resistor, RSNS. The voltage-sense range between SNS and VSS is ±51.2mV. The input linearly
converts peak-signal amplitudes up to 102.4mV as long as the continuous signal level (average over the conversion cycle
period) does not exceed ±51.2mV. The ADC samples the input differentially at 18.6kHz and updates the current register
at the completion of each conversion cycle (3.52s). Charge currents above the maximum register value are reported as
7FFFh. Discharge currents below the minimum register value are reported as 8000h.
Current Register Format
MSB—ADDRESS 0Eh LSB—ADDRESS 0Fh
S 214 213 212 211 210 29282726252423222120
MSb LSb MSb LSb
“S”: Sign Bit(s) Units: 1.5625µV/RSNS
The average current register reports an average current level over the preceding 28s. The register value is updated every
28s in two’s complement form, and represents an average of the eight preceding current register values.
Average Current Register Format
MSB—ADDRESS 08h LSB—ADDRESS 09h
S 214 213 212 211 210 29282726252423222120
MSb LSb MSb LSb
“S”: Sign Bit(s) Units: 1.5625µV/RSNS
Current Offset Correction
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs
approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements. During
the offset correction conversion, the ADC does not measure the sense-resistor signal. A maximum error of 1/1024 in the
accumulated current register (ACR) is possible; however, to reduce the error, the current measurement made just
prior to the offset conversion is retained in the current register and is substituted for the dropped current measurement
in the current accumulation process. Therefore, the accumulated current error due to offset correction is typically much
less than 1/1024.
Current Offset Bias
The current offset bias (COB) value allows a programmable offset value to be added to raw current measurements. The
result of the raw current measurement plus COB is displayed as the current measurement result in the current register,
and is used for current accumulation. COB can be used to correct for a static offset error, or can be used to intentionally
skew the current results and, therefore, the current accumulation.
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Read and write access is allowed to COB. Whenever the COB is written, the new value is applied to all subsequent cur-
rent measurements. COB can be programmed in 1.56µV steps to any value between +198.1µV and -199.7µV. The COB
value is stored as a two’s complement value in EEPROM. The COB is loaded on power-up from EEPROM memory. The
factory default value is 00h.
The difference between the CAB and COB is that the CAB is not subject to current blanking. Offset currents between
100µV and -25µV are not accumulated if the offset is made by the COB. Offset currents between 100µV and -25µV are
accumulated if they are made by the CAB.
Current Offset Bias Register Format
ADDRESS 7Bh
S 26252423222120
MSb LSb
“S”: Sign Bit(s) Units: 1.56µV/RSNS
Current Blanking
The current blanking feature modifies current measurement result prior to being accumulated in the ACR. Current blank-
ing occurs conditionally when a current measurement (raw current + COBR) falls in one of two defined ranges. The
first range prevents charge currents less than 100µV from being accumulated. The second range prevents discharge
currents less than 25µV in magnitude from being accumulated. Charge current blanking is always performed; however,
discharge current blanking must be enabled by setting the NBEN bit in the control register. See the register description
for additional information.
Current Measurement Calibration
The DS2784’s current measurement gain can be adjusted through the RSGAIN register, which is factory calibrated to
meet the data sheet-specified accuracy. RSGAIN is user accessible and can be reprogrammed after module or pack
manufacture to improve the current measurement accuracy. Adjusting RSGAIN can correct for variation in an external
sense resistor’s nominal value, and allows the use of low-cost, nonprecision, current-sense resistors. RSGAIN is an
11-bit value stored in 2 bytes of the parameter EEPROM memory block. The RSGAIN value adjusts the gain from 0 to
1.999 in steps of 0.001 (precisely 2-10). The user must program RSGAIN cautiously to ensure accurate current mea-
surement. When shipped from the factory, the gain calibration value is stored in two separate locations in the parameter
EEPROM block: RSGAIN, which is reprogrammable, and FRSGAIN, which is read only. RSGAIN determines the gain
used in the current measurement. The FRSGAIN value is provided to preserve the factory calibration value only and is
not used to calibrate the current measurement. The 16-bit FRSGAIN value is readable from addresses B0h and B1h.
Current Measurement Gain Register Format
MSB—ADDRESS 78h LSB—ADDRESS 79h
X X X X X 210 29282726252423222120
MSb LSb MSb LSb
Units: 2-10
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Sense Resistor Temperature Compensation
The DS2784 can temperature compensate the current-sense resistor to correct for variation in a sense resistor’s value
overtemperature. The DS2784 is factory programmed with the sense-resistor temperature coefficient, RSTC, set to
zero, which turns off the temperature compensation function. RSTC is user accessible and can be reprogrammed after
module or pack manufacture to improve the current accuracy when using a high-temperature coefficient current-sense
resistor. RSTC is an 8-bit value stored in the parameter EEPROM memory block. The RSTC value sets the temperature
coefficient from 0 to +7782ppm/ºC in steps of 30.5ppm/ºC. The user must program RSTC cautiously to ensure accurate
current measurement.
Temperature compensation adjustments are made when the temperature register crosses 0.5°C boundaries. The tem-
perature compensation is most effective with the resistor placed as close as possible to the VSS terminal. This optimizes
thermal coupling of the resistor to the on-chip temperature sensor.
Sense Resistor Temperature Compensation Register Format
ADDRESS 7Ah
2726252423222120
MSb LSb
Units: 30.5ppm/°C
Current Accumulation
Current measurements are internally summed, or accumulated, at the completion of each conversion period and the
results are stored in the ACR. The accuracy of the ACR is dependent on both the current measurement and the conver-
sion time base. The ACR has a range of 0 to 409.6mVh with an LSb of 6.25µVh. Additional registers hold fractional results
of each accumulation to avoid truncation errors. The fractional result bits are not user accessible. Accumulation of charge
current above the maximum register value is reported at the maximum value; conversely, accumulation of discharge cur-
rent below the minimum register value is reported at the minimum value.
Charge currents (positive current register values) less than 100µV are not accumulated in order to mask the effect of
accumulating small positive offset errors over long periods. This limits the minimum charge current, for coulomb-counting
purposes, to 5mA for RSNS = 0.020Ω and 20mA for RSNS = 0.005Ω.
Read and write access is allowed to the ACR. The ACR must be written MSB first then LSB. Whenever the ACR is written,
the fractional accumulation result bits are cleared. The write must be completed in 3.5s (one ACR update period). A write
to the ACR forces the ADC to perform an offset correction conversion and update the internal offset correction factor. The
current measurement and accumulation begin with the second conversion following a write to the ACR.
The ACR value is backed up to EEPROM in case of power loss. The ACR value is recovered from EEPROM on power-
up. See Table 8 for specific address location and backup frequency.
Accumulated Current Register Format
MSB—ADDRESS 10h LSB—ADDRESS 11h
215 214 213 212 211 210 29282726252423222120
MSb LSb MSb LSb
Units: 6.25µVh/RSNS
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Accumulation Bias
In some designs a systematic error or an application preference requires the application of an arbitrary bias to the cur-
rent accumulation process. The current accumulation bias register (CAB) allows a user-programmed constant positive
or negative polarity bias to be included in the current accumulation process. The value in CAB can be used to estimate
battery currents that do not flow through the sense resistor, estimate battery self-discharge or estimate current levels
below the current measurement resolution. The user programmed two’s complement value, with bit weighting the same
as the current register, is added to the ACR once per current conversion cycle. The CAB is loaded on power-up from
EEPROM memory.
The difference between the CAB and COB is that the CAB is not subject to current blanking. Offset currents between
100µV and -25µV are not accumulated if the offset is made by the COB. Offset currents between 100µV and -25µV are
accumulated if they are made by the CAB.
Current Accumulation Bias Register Format
ADDRESS 61h
S 26252423222120
MSb LSb
“S”: Sign Bit Units: 1.5625µV/RSNS
Capacity Estimation Algorithm
Remaining capacity estimation uses real-time measured values, stored parameters describing the cell characteristics,
and application operating limits. Figure 3 describes the algorithm inputs and outputs.
Table 5. Resolution and Range vs. Sense Resistor
VSS - VSNS
RSNS
20mΩ 15mΩ 10mΩ 5mΩ
Current Resolution 1.5625µV 78.13µA 104.2µA 156.3µA 312.5µA
Current Range ±51.2mV ±2.56A ±3.41A ±5.12A ±10.24A
ACR Resolution 6.25µVh 312.5µAh 416.7µAh 625µAh 1.250mAh
ACR Range 409.6mVh 20.48Ah 27.31Ah 40.96Ah 81.92Ah
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Figure 3. Top-Level Algorithm Diagram
CAPACITY LOOK-UP
AVAILABLE CAPACITY CALCULATION
ACR HOUSEKEEPING
AGE ESTIMATOR
LEARN FUNCTION
CELL
MODEL
PARAMETERS
(EEPROM)
FULL(T) (R)
ACTIVE EMPTY (T) (R)
STANDBY EMPTY (T) (R)
REMAINING ACTIVE ABSOLUTE
CAPACITY (RAAC) MAH (R)
SENSE RESISTOR’
(RSNSP) (1BYTE EE)
USER MEMORY (EEPROM)
16 BYTES
AGING CAP (AC)
(2 BYTES EE)
CHARGE VOLTAGE
(VCHG) (1 BYTE EE)
REMAINING STANDBY ABSOLUTE
CAPACITY (RSAC) MAH (R)
REMAINING ACTIVE RELATIVE
CAPACITY (RARC) % (R)
REMAINING STANDBY RELATIVE
CAPACITY (RSRC) % (R)
AGE SCALAR (AS)
(1 BYTES EE)
MIN CHG CURRENT
(IMIN) (1 BYTE EE)
EMPTY VOLTAGE
(VAE) (1 BYTE EE)
EMPTY CURRENT (IAE)
(1 BYTE EE)
VOLTAGE (R)
AVERAGE CURRENT (R)
CURRENT (R)
ACCUMULATED
CURRENT (ACR) (R/W)
TEMPERATURE (R)
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Modeling Cell Characteristics
To achieve reasonable accuracy in estimating remaining
capacity, the cell performance characteristics overtem-
perature, load current, and charge-termination point must
be considered. Since the behavior of Li+ cells is nonlinear,
these characteristics must be included in the capacity esti-
mation to achieve an acceptable level of accuracy in the
capacity estimation. The FuelPack™ method used in the
DS2784 is described in general in Application Note 131:
Lithium-Ion Cell Fuel Gauging with Maxim Battery Monitor
ICs. To facilitate efficient implementation in hardware, a
modified version of the method outlined in AN131 is used
to store cell characteristics in the DS2784. Full and empty
points are retrieved in a lookup process which retraces a
piece-wise linear model consisting of three model curves
named full, active empty, and standby empty. Each model
curve is constructed with 5-line segments, numbered
1 through 5. Above 40°C, the segment 5 model curves
extend infinitely with zero slope, approximating the nearly
flat change in capacity of Li+ cells at temperatures above
40°C. Segment 4 of each model curves originates at +40°C
on its upper end and extends downward in temperature to
the junction with segment 3. Segment 3 joins with seg-
ment 2, which in turn joins with segment 1. Segment 1 of
each model curve extends from the junction with segment
2 to infinitely colder temperatures. The three junctions
or breakpoints that join the segments (labeled TBP12,
TBP23, and TBP34 in Figure 4) are programmable in 1°C
increments from -128°C to +40°C. The slope or derivative
for segments 1, 2, 3, and 4 are also programmable over a
range of 0 to 15,555ppm, in steps of 61ppm.
Full—The full curve defines how the full point of a given
cell varies over temperature for a given charge termina-
tion. The application’s charge termination method
should be used to determine the table values. The
DS2784 reconstructs the full line from the cell character-
istic table to determine the full capacity of the battery at
each temperature. Reconstruction occurs in one-degree
temperature increments.
Active Empty—The active-empty curve defines the
variation of the active-empty point over temperature. The
active-empty point is defined as the minimum voltage
required for system operation at a discharge rate based
on a high-level load current (one that is sustained
during a high-power operating mode). This load cur-
rent is programmed as the active-empty current (IAE),
and should be a 3.5s average value to correspond to
values read from the current register. The specified mini-
mum voltage, or active empty voltage (VAE), should be
a 220ms average value to correspond to the values read
from the voltage register. The DS2784 reconstructs the
active empty line from the cell characteristic table to
determine the active empty capacity of the battery at
each temperature. Reconstruction occurs in one-degree
temperature increments.
Figure 4. Cell Model Example Diagram
FuelPack is a trademark of Maxim Integrated Products, Inc.
TBP12 TBP23 TBP34 40°C
100%
SEGMENT 1
DERIVATIVE
[PPM/°C]
ACTIVE
EMPTY
STANDBY
EMPTY
FULL
CELL
CHARACTERIZATION
DATA POINTS
SEG. 2SEG. 3 SEG. 4SEG. 5
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Standby Empty—The standby-empty curve defines the
variation of the standby-empty point over temperature.
The standby-empty point is defined as the minimum volt-
age required for standby operation at a discharge rate dic-
tated by the application standby current. In typical hand-
held applications, standby empty represents the point that
the battery can no longer support DRAM refresh and thus
the standby voltage is set by the minimum DRAM voltage-
supply requirements. In other applications, standby empty
can represent the point that the battery can no longer
support a subset of the full application operation, such as
games or organizer functions. The standby load current
and voltage are used for determining the cell characteris-
tics but are not programmed into the DS2784. The DS2784
reconstructs the standby-empty line from the cell charac-
teristic table to determine the standby-empty capacity of
the battery at each temperature. Reconstruction occurs in
one-degree temperature increments.
Cell Model Construction
The model is constructed with all points normalized to
the fully charged state at +40°C. All values are stored in
the cell parameter EEPROM block. The +40°C full value
is stored in µVhr with an LSB of 6.25µVhr. The +40°C
active empty value is stored as a percentage of +40°C
full with a resolution of 2-10. Standby empty at +40°C is,
by definition, zero and, therefore, no storage is required.
The slopes (derivatives) of the 4 segments for each model
curve are stored in the cell parameter EEPROM block as
ppm/°C. The breakpoint temperatures of each segment
are stored there also (see Application Note 3584: Storing
Battery Fuel Gauge Parameters in DS2780 for more
details on how values are stored). An example of data
stored in this manner is shown in Table 6.
Table 6. Example Cell Characterization Table (Normalized to +40°C)
Figure 5. Lookup Function Diagram
Manufacturer’s Rated Cell Capacity: 1000mAh
Charge Voltage: 4.2V Termination Current: 50mA
Active Empty (V): 3.0V Active Empty (I): 300mA
Sense Resistor: 0.020Ω
TBP12 TBP23 TBP34
Segment Breakpoints -12°C 0°C 18°C
+40°C Nominal
(mAh) Seg. 1 ppm/°C Seg. 2 ppm/°C Seg. 3 ppm/°C Seg. 4 ppm/°C
Full 1051 3601 3113 1163 854
Active Empty 2380 1099 671 305
Standby Empty 1404 427 244 183
*SEE RESULT REGISTERS SECTION FOR A DESCRIPTION OF THESE REGISTERS.
CELL MODEL
PARAMETERS
(EEPROM)
TEMPERATURE
LOOKUP
FUNCTION
FULL(T)*
AE(T)*
SE(T)*
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Application Parameters
In addition to cell model characteristics, several applica-
tion parameters are needed to detect the full and empty
points, as well as calculate results in mAh units.
Sense Resistor Prime (RSNSP[1/Ω])—RSNSP stores the
value of the sense resistor for use in computing the abso-
lute capacity results. The resistance is stored as a 1-byte
conductance value with units of mhos (1/Ω). RSNSP sup-
ports resistor values of 1Ω to 3.922mΩ. RSNS is located
in the parameter EEPROM block.
RSNSP = 1/RSNS (units of mhos; 1/Ω)
Charge Voltage (VCHG)—VCHG stores the charge volt-
age threshold used to detect a fully charged state. The
voltage is stored as a 1-byte value with units of 19.5mV
and can range from 0V to 4.978V. VCHG should be set
marginally less than the cell voltage at the end of the
charge cycle to ensure reliable charge termination detec-
tion. VCHG is located in the parameter EEPROM block.
Minimum Charge Current (IMIN)—IMIN stores the
charge current threshold used to detect a fully charged
state. It is stored as a 1-byte value with units of 50µV
(IMIN x RSNS) and can range from 0 to 12.75mV.
Assuming RSNS = 20mΩ, IMIN can be programmed from
0mA to 637.5mA in 2.5mA steps. IMIN should be set mar-
ginally greater than the charge current at the end of the
charge cycle to ensure reliable charge termination detec-
tion. IMIN is located in the parameter EEPROM block.
Active Empty Voltage (VAE)—VAE stores the voltage
threshold used to detect the active empty point. The
value is stored in 1-byte with units of 19.5mV and can
range from 0V to 4.978V. VAE is located in the parameter
EEPROM block. See the Modeling Cell Characteristics
section for more information.
Active Empty Current (IAE)—IAE stores the discharge
current threshold used to detect the active empty point.
The unsigned value represents the magnitude of the
discharge current and is stored in 1-byte with units of
200µV and can range from 0 to 51.2mV. Assuming RSNS
= 20mΩ, IAE can be programmed from 0mA to 2550mA in
10mA steps. IAE is located in the Parameter EEPROM
block. See the Cell Model Construction section for more
information.
Aging Capacity (AC)—AC stores the rated cell capacity,
which is used to estimate the decrease in battery capac-
ity that occurs during normal use. The value is stored in
2 bytes in the same units as the ACR (6.25µVh). When
set to the manufacturer’s rated cell capacity the aging
estimation rate is approximately 2.4% per 100 cycles of
equivalent full capacity discharges. Partial discharge
cycles are added to form equivalent full capacity
discharges. The default aging estimation results in 88%
capacity after 500 equivalent cycles. The aging estimation
rate can be adjusted by setting the AC to a value other
than the cell manufacturer’s rating. Setting AC to a lower
value, accelerates the aging estimation rate. Setting AC to
a higher value, retards the aging estimation rate. The AC
is located in the parameter EEPROM block.
Age Scalar (AS)—AS adjusts the cell capacity estimation
results downward to compensate for aging. The AS is a
1-byte value that has a range of 49.2% to 100%. The LSb
is weighted at 0.78% (precisely 2-7). A value of 100% (128
decimal or 80h) represents an unaged battery. A value
of 95% is recommended as the starting AS value at the
time of pack manufacture to allow the learning of a larger
capacity on batteries that have an initial capacity greater
than the rated cell capacity programmed in the cell char-
acteristic table. The AS is modified by aging estimation
introduced under aging capacity and by the capacity-learn
function. The host system has read and write access to
the AS, however caution should exercised when writing
it to ensure that the cumulative aging estimate is not
overwritten with an incorrect value. The AS is automati-
cally saved to EEPROM (see Table 7 for details). The
EEPROM value is recalled on power-up.
Full capacity estimation based on the learn function is
more accurate than the cycle-count-based estimation.
The learn function reflects the current performance of the
cell. Cycle count based estimation is an approximation
derived from the manufacturer’s recommendation for a
typical cell. Batteries are typically considered worn-out
when the full capacity reaches 80% of the rated capacity,
therefore, the AS value is not required to range to 0%. It
is clamped to 50% (64d or 40h). If a value of 50% is read
from the AS, the host should prompt the user to initiate a
learning cycle.
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Capacity Estimation Operation
Aging Estimation
As discussed above, the AS register value is adjusted
occasionally based on cumulative discharge. As the ACR
register decrements during each discharge cycle, an
internal counter is incremented until equal to 32 times
the AC. The AS is then decremented by one, resulting in
a decrease of the scaled full battery capacity by 0.78%
(approximately 2.4% per 100 cycles). See the AC register
description above for recommendations on customizing
the age-estimation rate.
Learn Function
Since Li+ cells exhibit charge efficiencies near unity, the
charge delivered to a Li+ cell from a known empty point
to a known full point is a dependable measure of the cell
capacity. A continuous charge from empty to full results in
a learn cycle. First, the active empty point must be detect-
ed. The learn flag (LEARNF) is set at this point. Then,
once charging starts, the charge must continue uninter-
rupted until the battery is charged to full. Upon detecting
full, LEARNF is cleared, the charge to full (CHGTF) flag is
set, and the age scalar (AS) is adjusted according to the
learned capacity of the cell.
ACR Housekeeping
The ACR value is adjusted occasionally to maintain the
coulomb count within the model curve boundaries. When
the battery is charged to full (CHGTF set), the ACR is set
equal to the age scaled full lookup value at the present
temperature. If a learn cycle is in progress, correction
of the ACR value occurs after the age scalar (AS) is
updated.
When an empty condition is detected (LEARNF and/or
AEF set), the ACR adjustment is conditional:
• If the AEF is set and the LEARNF is not set, then the
active-empty point was not detected. The battery is
likely below the active-empty capacity of the model.
The ACR is set to the active-empty model value at
present temp only if it is greater than the active-empty
model value at present temp.
• If the AEF is set, the LEARNF is not set, and the ACR
is below the active-empty model value at present temp
the ACR is NOT updated.
• If the LEARNF is set, then the battery is at the active-
empty point and the ACR is set to the active-empty
model value.
Full Detect
Full detection occurs when the voltage (V) readings
remain continuously above the charge voltage (VCHG)
threshold for the duration of two average current (IAVG)
readings, and both IAVG readings are below terminating
current (IMIN). The two consecutive IAVG readings must
also be positive and nonzero (> 16 LSB). This ensures
that removing the battery from the charger does not result
in a false detection of full. Full detect sets the charge to
full (CHGTF) bit in the status register.
Active-Empty Point Detect
Active-empty point detection occurs when the voltage reg-
ister drops below the VAE threshold AND the two previous
current readings are above IAE. This captures the event
of the battery reaching the active-empty point. Note that
the two previous current readings must be negative and
greater in magnitude than IAE, that is, a larger discharge
current than specified by the IAE threshold. Qualifying
the voltage level with the discharge rate ensures that the
active-empty point is not detected at loads much lighter
than those used to construct the model. Also, the active-
empty point must not be detected when a deep discharge
at a very light load is followed by a load greater than
IAE. Either case would cause a learn cycle on the follow-
ing charge to include part of the standby capacity in the
measurement of the active capacity. Active-empty point
detection sets the learn flag (LEARNF) bit in the status
register. Do not confuse the active-empty point with the
active-empty flag. The active-empty flag is set only when
the VAE threshold is passed.
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24
Status Register Format
The status register contains bits that report the device status. All bits are set internally. The CHGTF, AEF, SEF, and
LEARNF bits are read only. The UVF and PORF bits can be cleared by writing a zero to the bit locations.
ADDRESS 01h
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
CHGTF AEF SEF LEARNF X UVF PORF X
CHGTF—Charge-Termination Flag. CHGTF is set to indicate that the voltage and average current register values have
persisted above the VCHG and below the IMIN thresholds sufficiently long to detect a fully charged condition. CHGTF is
cleared when RARC is less than 90%. CHGTF is read only.
AEF—Active-Empty Flag. AEF is set to indicate that the battery is at or below the active-empty point. AEF is set when the
voltage register value is less than the VAE threshold. AEF is cleared when RARC is greater than 5%. AEF is read only.
SEF—Standby-Empty Flag. SEF is set to indicate RSRC is less than 10%. SEF is cleared when RSRC is greater than
15%. SEF is read only.
LEARNF—Learn Flag. LEARNF indicates that the current charge cycle can be used to learn the battery capacity.
LEARNF is set when the active-empty point is detected. This occurs when the voltage register value drops below the VAE
threshold AND the two previous current register values were negative and greater in magnitude than the IAE threshold.
See the Active-Empty Point Detect section for additional information. LEARNF is cleared when any of the following occur:
1) Learn cycle completes (CHGTF set).
2) Current register value becomes negative indicating discharge current flow.
3) ACR = 0
4) ACR value is written or recalled from EEPROM.
5) Sleep mode is entered.
LEARNF is read only.
UVF—Undervoltage Flag. UVF is set to indicate that the voltage measurement of the VIN pin is less than VUV, and must
be written to a 0 to allow subsequent undervoltage events to be reported. UVF is not cleared internally. Writing UVF to
0 is effective only when VIN is greater or equal to VUV, otherwise, UV remains set due to the persistent undervoltage
condition. UVF is set on power-up.
PORF—Power-On Reset Flag. PORF is set to indicate initial power-up. PORF is not cleared internally. The user must
write this flag value to a 0 to use it to indicate subsequent power-up events. If PORF indicates a power-on reset, the ACR
could be misaligned with the actual battery state of charge. The system can request a charge to full to synchronize the
ACR with the battery charge state. PORF is read/write-to-zero.
X—Reserved Bits.
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Result Registers
The DS2784 processes measurement and cell characteristics on a 3.5s interval and yields seven result registers. The
result registers are sufficient for direct display to the user in most applications. The host system can produce customized
values for system use or user display by combining measurement, result and user EEPROM values.
FULL(T) [ ]—The full capacity of the battery at the present temperature is reported normalized to the 40°C full value.
This 15-bit value reflects the cell model Full value at the given temperature. FULL(T) reports values between 100% and
50% with a resolution of 61ppm (precisely 2-14). The register is clamped to a maximum value of 100% even though the
register format permits values greater than 100%.
Active Empty, AE(T) [ ]—The active-empty capacity of the battery at the present temperature is reported normal-
ized to the 40°C full value. This 13-bit value reflects the cell model active-empty value at the given temperature. AE(T)
reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2-14).
Standby Empty, SE(T) [ ]—The standby-empty capacity of the battery at the present temperature is reported normalized
to the 40°C full value. This 13-bit value reflects the cell model standby-empty value at the current temperature. SE(T)
reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2-14).
Remaining Active Absolute Capacity (RAAC) [mAh]—RAAC reports the remaining battery capacity available under
the current temperature conditions to the active-empty point in absolute units of milliamp-hours (mAhr). RAAC is 16 bits.
MSB—ADDRESS 02h LSB—ADDRESS 03h
215 214 213 212 211 210 29282726252423222120
MSb LSb MSb LSb
Units: 1.6mAhr
Remaining Standby Absolute Capacity (RSAC) [mAh]—RSAC reports the remaining battery capacity available under
the current temperature conditions to the standby-empty point capacity in absolute units of milliamp-hours (mAhr). RSAC
is 16 bits.
MSB—ADDRESS 04h LSB—ADDRESS 05h
215 214 213 212 211 210 29282726252423222120
MSb LSb MSb LSb
Units: 1.6mAhr
Remaining Active Relative Capacity (RARC) [%]—RARC reports the remaining battery capacity available under the
current temperature conditions to the active-empty point in relative units of percent. RARC is 8 bits.
ADDRESS 06h
2726252423222120
MSb LSb
Units: 1%
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Remaining Standby Relative Capacity (RSRC) [%]—RSRC reports the remaining battery capacity available under
the current temperature conditions to the standby-empty point capacity in relative units of percent. RSRC is 8 bits.
ADDRESS 07h
2726252423222120
MSb LSb
Units: 1%
Calculation of Results
RAAC [mAh] = (ACR[mVh] - AE(T) x FULL40[mVh]) x RSNSP [mhos]
Note: RSNSP = 1/RSNS
RSAC [mAh] = (ACR[mVh] - SE(T) x FULL40[mVh]) x RSNSP [mhos]
Note: RSNSP = 1/RSNS
RARC [%] = 100% x (ACR[mVh] - AE(T) x FULL40[mVh]) / {(AS x FULL(T) - AE(T)) x FULL40[mVh]}
RSRC [%] = 100% x (ACR[mVh] - SE(T) x FULL40[mVh]) / {(AS x FULL(T) - SE(T)) x FULL40[mVh]}
Special Feature Register Format
All register bits are read and write accessible, with default values specified in each bit definition.
ADDRESS 15H
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
XXXXXXXPIOB
PIOB—PIO Pin Sense and Control Bit. Writing a 0 to the PIOB bit activates the PIO pin open-drain output driver, forcing
the PIO pin low. Writing a 1 to PIOB disables the output driver, allowing the PIO pin to be pulled high or used as an input.
Reading PIOB returns the logic level forced on the PIO pin. Note that if the PIO pin is high impedance/unconnected with
PIOB set, a weak pulldown current source pulls the PIO pin to VSS. PIOB is set to a 1 on power-up. PIOB is also set in
Sleep mode to ensure the PIO pin is high-impedance in sleep mode.
Note: Do not write PIOB to 0 if PSPIO is enabled.
X—Reserved Bits.
EEPROM Register
The EEPROM register provides access control of the EEPROM blocks. EEPROM blocks can be locked to prevent altera-
tion of data within the block. Locking a block disables write access to the block. Once a block is locked, it cannot be
unlocked. Read access to EEPROM blocks is unaffected by the lock/unlock status.
EEPROM Register Format
ADDRESS 1Fh
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
EEC LOCK X X X X BL1 BL0
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EEC—EEPROM Copy Flag. A 1 in this read-only bit indi-
cates that a Copy Data Function command is in progress.
While this bit is high, writes to EEPROM addresses are
ignored. A 0 value in this bit indicates that data can be
written to unlocked EEPROM.
LOCK—EEPROM Lock Enable. When the lock bit is 0,
the Lock Function command is ignored. Writing a 1 to this
bit enables the Lock Function command. After setting the
lock bit the Lock Function command must be issued as
the next command, or else the lock bit is reset to 0. After
the lock operation is completed, the lock bit is reset to 0.
The lock bit is a volatile R/W bit, initialized to 0 upon POR.
BL1—Parameter EEPROM Block 1 Lock Flag. A 1 in this
read-only bit indicates that EEPROM block 1 (addresses
60h to 7Fh) is locked (read only) while a 0 indicates block
1 is unlocked (read/write).
BL0—User EEPROM Block 0 Lock Flag. A 1 in this read-
only bit indicates that EEPROM block 0 (addresses 20h
to 2Fh is locked (read only) while a 0 indicates block 0 is
unlocked (read/write).
X – Reserved Bits.
Memory
The DS2784 has a 256-byte linear memory space with
registers for instrumentation, status, and control, as
well as EEPROM memory blocks to store parameters
and user information. Byte addresses designated as
“Reserved” typically return FFh when read. These bytes
should not be written. Several byte registers are paired
into two-byte registers in order to store 16-bit values. The
most significant byte (MSB) of the 16-bit value is located
at the even address and the least significant byte (LSB)
is located at the next address (odd) byte. When the MSB
of a two-byte register is read, the MSB and LSB are
latched simultaneously and held for the duration of the
Read Data command. This prevents updates to the LSB
during the read ensuring synchronization between the
two register bytes. For consistent results, always read the
MSB and the LSB of a two-byte register during the same
read data sequence.
EEPROM memory consists of nonvolatile (NV) EEPROM
cells overlaying volatile shadow RAM. The read data and
write data protocols allow the 1-Wire interface to directly
accesses the shadow RAM only. The Copy Data and
Recall Data Function commands transfer data between
the EEPROM cells and the shadow RAM. In order to
modify the data stored in the EEPROM cells, data must
be written to the shadow RAM and then copied to the
EERPOM. To verify the data stored in the EEPROM
cells, the EEPROM data must be recalled to the shadow
RAM and then read from the shadow. After issuing the
Copy Data Function command, access to the EEPROM
block is not available until the EEPROM copy completes,
which takes 2ms typically (see tEEC in the Electrical
Characteristics table).
User EEPROM—Block 0
A 16-byte user EEPROM memory (block 0, addresses
20h–2Fh) provides NV memory that is uncommitted to
other DS2784 functions. Accessing the user EEPROM
block does not affect the operation of the DS2784. User
EEPROM is lockable; once locked, write access is not
allowed. The battery pack or host system manufacturer
can program lot codes, date codes, and other manufac-
turing or warranty or diagnostic information and then lock
it to safeguard the data. User EEPROM can also store
parameters for charging to support different size batteries
in a host device as well as auxiliary model data such as
time to full charge estimation parameters.
Figure 6. EEPROM Access via Shadow RAM
SERIAL
INTERFACE
WRITE
READ SHADOW RAM
EEPROM
COPY
RECALL
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Parameter EEPROM—BLOCK 1
Model data for the cells, as well as application operating
parameters, are stored in the parameter EEPROM (block
1, addresses 60h–7Fh). The ACR (MSB and LSB) and
AS registers are automatically saved to EEPROM when
the RARC result crosses 4% boundaries. This allows the
DS2784 to be located outside the protection FETs.
Table 7. Parameter EEPROM Memory Block
ADDRESS
(HEX) DESCRIPTION ADDRESS
(HEX) DESCRIPTION
60 CONTROL—Control Register 70 AE Segment 4 Slope
61 AB— Accumulation Bias 71 AE Segment 3 Slope
62 AC—Aging Capacity MSB 72 AE Segment 2 Slope
63 AC—Aging Capacity LSB 73 AE Segment 1 Slope
64 VCHG—Charge Voltage 74 SE Segment 4 Slope
65 IMIN—Minimum Charge Current 75 SE Segment 3 Slope
66 VAE—Active-Empty Voltage 76 SE Segment 2 Slope
67 IAE—Active-Empty Current 77 SE Segment 1 Slope
68 Active Empty 40 78 RSGAIN—Sense Resistor Gain MSB
69 RSNSP—Sense Resistor Prime 79 RSGAIN—Sense Resistor Gain LSB
6A Full 40 MSB 7A RSTC—Sense Resistor Temp Coefcient
6B Full 40 LSB 7B COB—Current Offset Bias
6C Full Segment 4 Slope 7C TBP34
6D Full Segment 3 Slope 7D TBP23
6E Full Segment 2 Slope 7E TBP12
6F Full Segment 1 Slope 7F Protector Threshold Register
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Table 8. Memory Map
* Register value is automatically saved to EEPROM during Active mode operation and recalled from EEPROM on power-up.
ADDRESS (HEX) DESCRIPTION READ/WRITE
00 Protection Register R/W
01 Status Register R/W
02 RAAC MSB R
03 RAAC LSB R
04 RSAC MSB R
05 RSAC LSB R
06 RARC R
07 RSRC R
08 Average Current Register MSB R
09 Average Current Register LSB R
0A Temperature Register MSB R
0B Temperature Register LSB R
0C Voltage Register MSB R
0D Voltage Register LSB R
0E Current Register MSB R
0F Current Register LSB R
10 Accumulated Current Register MSB R/W *
11 Accumulated Current Register LSB R/W *
12 Accumulated Current Register LSB-1 R
13 Accumulated Current Register LSB-2 R
14 Age Scalar R/W *
15 Special Feature Register R/W
16 Full MSB R
17 Full LSB R
18 Active-Empty MSB R
19 Active-Empty LSB R
1A Standby-Empty MSB R
1B Standby-Empty LSB R
1C to 1E Reserved —
1F EEPROM Register R/W
20 to 2F User EEPROM, Lockable, Block 0 R/W
38 to 5F Reserved —
60 to 7F Parameter EEPROM, Lockable, Block 1 R/W
80 to AF Reserved —
B0 Factory Gain RSGAIN MSB R
B1 Factory Gain RSGAIN LSB R
B2 to FF Reserved —
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Authentication
Authentication is performed using a FIPS-180-compliant
SHA-1 one-way hash algorithm on a 512-bit message
block. The message block consists of a 64-bit secret, a
64-bit challenge and 384 bits of constant data. Optionally,
the 64-bit net address replaces 64 of the 384 bits of con-
stant data used in the hash operation. Contact Maxim for
details of the message block organization.
The host and the DS2784 both calculate the result based
on the mutually known secret. The result of the hash
operation is known as the message authentication code
(MAC) or message digest. The MAC is returned by the
DS2784 for comparison to the host’s MAC. Note that the
secret is never transmitted on the bus and thus cannot
be captured by observing bus traffic. Each authentication
attempt is initiated by the host system by providing a 64-bit
random challenge by the Write Challenge command. The
host then issues the compute MAC or compute MAC with
ROM ID command. The MAC is computed per FIPS 180,
and then returned as a 160-bit serial stream, beginning
with the least significant bit.
DS2784 Authentication Commands
Write Challenge [0Ch]. This command writes the 64-bit
challenge to the DS2784. The LSB of the 64-bit data
argument can begin immediately after the MSB of the
command has been completed. If more than 64-bits are
written, the final value in the challenge register will be
indeterminate. The Write Challenge command must be
issued prior to every Compute MAC or Compute Next
Secret command for reliable results.
Compute MAC Without ROM ID [36h]. This command
initiates a SHA-1 computation without including the ROM
ID in the message block. Since the ROM ID is not used,
this command allows the use of a master secret and MAC
response independent of the ROM ID. The DS2784 com-
putes the MAC in tSHA after receiving the last bit of this
command. After the MAC computation is complete, the
host must write 8 write-zero time slots and then issue 160
read-time slots to receive the 20-byte MAC. See Figure 10
for command timing.
Compute MAC With ROM ID [35h]. This command is
structured the same as the compute MAC without ROM
ID, except that the ROM ID is included in the message
block. With the ROM ID unique to each DS2784 included
in the MAC computation, the MAC is unique to each
token. See White Paper 4: Glossary of 1-Wire SHA-1
Terms, for more information. See Figure 10 for command
timing.
SHA-1-related commands used while authenticating a
battery or peripheral device are summarized in Table 9
for convenience. Four additional commands for clearing,
computing, and locking of the secret are described in
detail in the following section.
Secret Management Function
Commands
Clear Secret [5Ah]. This command sets the 64-bit secret
to all 0s (0000 0000 0000 0000h). The host must wait
tEEC for the DS2784 to write the new secret value to
EEPROM. See Figure 13 for command timing.
Compute Next Secret Without ROM ID [30h]. This
command initiates a SHA-1 computation of the MAC and
uses a portion of the resulting MAC as the next or new
secret. The hash operation is performed with the current
64-bit secret and the 64-bit challenge. Logical 1s are
loaded in place of the ROM ID. 64 bits of the output MAC
are used as the new secret value. The host must allow
tSHA after issuing this command for the SHA calculation
to complete, then wait tEEC for the DS2784 to write the
new secret value to EEPROM. See Figure 11 for com-
mand timing.
Table 9. Authentication Function Commands
COMMAND HEX FUNCTION
Write Challenge 0C Writes 64-bit challenge for SHA-1 processing. Required prior to issuing
Compute MAC and Compute Next Secret commands.
Compute MAC Without ROM ID
and Return MAC 36 Computes hash operation of the message block with logical 1s in place of the
ROM ID. Returns the 160-bit MAC.
Compute MAC With ROM ID and
Return MAC 35 Computes hash operation of the message block including the
ROM ID. Returns the 160-bit MAC.
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Compute Next Secret With ROM ID [33h]. This com-
mand initiates a SHA-1 computation of the MAC and uses
a portion of the resulting MAC as the next or new secret.
The hash operation is performed with the current 64- bit
secret, the 64-bit ROM ID and the 64-bit challenge. 64
bits of the output MAC are used as the new secret value.
The host must allow tSHA after issuing this command for
the SHA calculation to complete, then wait tEEC for the
DS2784 to write the new secret value to EEPROM. See
Figure 11 for command timing.
Lock Secret [60h]. This command write protects the
64-bit secret to prevent accidental or malicious overwrite
of the secret value. The secret value stored in EEPROM
becomes “final”. The host must wait tEEC for the DS2784
to write the lock secret bit to EEPROM. See Figure 13 for
command timing.
1-Wire Bus System
The 1-Wire bus is a system that has a single bus master
and one or more slaves. A multidrop bus is a 1-Wire bus
with multiple slaves, while a single-drop bus has only
one slave device. In all instances, the DS2784 is a slave
device. The bus master is typically a microprocessor
in the host system. The discussion of this bus system
consists of five topics: 64-bit net address, CRC genera-
tion, hardware configuration, transaction sequence, and
1-Wire signaling.
64-BIT Net Address (ROM ID)
Each DS2784 has a unique, factory-programmed 1-Wire
net address that is 64 bits in length. The term net address
is synonymous with the ROM ID or ROM code terms used
in the DS2502 and other 1-Wire documentation. The first
eight bits of the net address are the 1-Wire family code
(32h). The next 48 bits are a unique serial number. The
last eight bits are a cyclic redundancy check (CRC) of
the first 56 bits (see Figure 7). The 64-bit net address
and the 1-Wire I/O circuitry built into the device enable
the DS2784 to communicate through the 1-Wire protocol
detailed in this data sheet.
CRC Generation
The DS2784 has an 8-bit CRC stored in the most signifi-
cant byte of its 1-Wire net address. To ensure error-free
transmission of the address, the host system can com-
pute a CRC value from the first 56 bits of the address and
compare it to the CRC from the DS2784.
The host system is responsible for verifying the CRC
value and taking action as a result. The DS2784 does
not compare CRC values and does not prevent a com-
mand sequence from proceeding as a result of a CRC
mismatch. Proper use of the CRC can result in a commu-
nication channel with a very high level of integrity.
Table 10. Secret Loading Function Commands
Figure 7. 1-Wire Net Address Format
COMMAND HEX FUNCTION
Clear Secret 5A Clears the 64-bit Secret to 0000 0000 0000 0000h.
Compute Next Secret Without
ROM ID 30 Generates new global secret.
Compute Next Secret With
ROM ID 33 Generates new unique secret.
Lock Secret 60 Sets lock bit to prevent changes to the secret.
8-BIT CRC 48-BIT SERIAL NUMBER 8-BIT FAMILY
CODE (32H)
LSbMSb
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The CRC can be generated by the host using a circuit
consisting of a shift register and XOR gates as shown
in Figure 8, or it can be generated in software using the
polynomial X8 + X5 + X4 + 1. Additional information about
the Maxim 1-Wire CRC is available in Application Note
27: Understanding and Using Cyclic Redundancy Checks
with Maxim iButton Products.
In the circuit in Figure 8, the shift register bits are initial-
ized to 0. Then, starting with the least significant bit of the
family code, one bit at a time is shifted in. After the 8th bit
of the family code has been entered, then the serial num-
ber is entered. After the 48th bit of the serial number has
been entered, the shift register contains the CRC value.
Hardware Conguration
Because the 1-Wire bus has only a single line, it is impor-
tant that each device on the bus be able to drive it at the
appropriate time. To facilitate this, each device attached to
the 1-Wire bus must connect to the bus with open-drain or
tri-state output drivers. The DS2784 uses an open-drain
output driver as part of the bidirectional interface circuitry
shown in Figure 9. If a bidirectional pin is not available on
the bus master, separate output, and input pins can be
connected together.
The 1-Wire bus must have a pullup resistor at the bus-
master end of the bus. A value of between 2kΩ and 5kΩ is
recommended. The idle state for the 1-Wire bus is high. If,
for any reason, a bus transaction must be suspended, the
bus must be left in the idle state to properly resume the
transaction later. Note that if the bus is left low for more
than tLOW0, slave devices on the bus begin to interpret
the low period as a reset pulse, effectively terminating the
transaction.
Transaction Sequence
The protocol for accessing the DS2784 through the
1-Wire port is as follows:
• Initialization
• Net Address Command
• Function Command(s)
• Data Transfer (not all commands have data transfer)
All transactions of the 1-Wire bus begin with an initializa-
tion sequence consisting of a reset pulse transmitted by
the bus master, followed by a presence pulse simultane-
ously transmitted by the DS2784 and any other slaves on
the bus. The presence pulse tells the bus master that one
or more devices are on the bus and ready to operate. For
more details, see the NET Address Commands section.
Figure 8. 1-Wire CRC Generation Block Diagram
Figure 9. 1-Wire Bus Interface Circuitry
MSb XOR XOR LSb
XOR
INPUT
VPULLUP
(2.0 TO 5.5V)
4.7kΩ
Rx
Tx
Rx
Tx
Rx = RECEIVE
Tx = TRANSMIT
100Ω
MOSFET
0.2μA
(TYP)
BUS MASTER DEVICE 1-WIRE PORT (DQ)
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NET Address Commands
Once the bus master has detected the presence of one
or more slaves, it can issue one of the net address com-
mands described in the following paragraphs. The name
of each net address command (ROM command) is fol-
lowed by the 8-bit op code for that command in square
brackets.
Read Net Address [33h]. This command allows the bus
master to read the DS2784’s 1-Wire net address. This
command can only be used if there is a single slave on
the bus. If more than one slave is present, a data collision
occurs when all slaves try to transmit at the same time
(open drain produces a wired-AND result).
Match Net Address [55h]. This command allows the bus
master to specifically address one DS2784 on the 1-Wire
bus. Only the addressed DS2784 responds to any subse-
quent function command. All other slave devices ignore
the function command and wait for a reset pulse. This
command can be used with one or more slave devices
on the bus.
Skip Net Address [CCh]. This command saves time
when there is only one DS2784 on the bus by allowing the
bus master to issue a function command without specify-
ing the address of the slave. If more than one slave
device
is present on the bus, a subsequent function command
can cause a data collision when all slaves transmit
data
at the same time.
Search Net Address [F0h]. This command allows the
bus master to use a process of elimination to identify the
1-Wire net addresses of all slave devices on the bus.
The search process involves the repetition of a simple
three- step routine: read a bit, read the complement of
the bit, then write the desired value of that bit. The bus
master performs this simple three-step routine on each
bit location of the net address. After one complete pass
through all 64 bits, the bus master knows the address of
one device. The remaining devices can then be identified
on additional iterations of the process. See Chapter 5
of the Book of iButton® Standards for a comprehensive
discussion of a net address search, including an actual
example (www.maximintegrated.com/iButtonBook).
Function Commands
After successfully completing one of the net address com-
mands, the bus master can access the features of the
DS2784 with any of the function commands described in
the following paragraphs. The name of each function is
followed by the 8-bit op code for that command in square
brackets. The function commands are summarized below
in Table 11.
Table 11. All Function Commands
iButton is a registered trademark of Maxim Integrated Products, Inc.
COMMAND HEX DESCRIPTION
Write Challenge 0C Writes 64-bit challenge for SHA-1 processing. Required immediately prior
to all Compute MAC and Compute Next Secret commands.
Compute MAC Without ROM ID and
Return MAC 36 Computes hash operation of message block with logical 1s in place
of the ROM ID.
Compute MAC With ROM ID and
Return MAC 35 Computes hash operation of message block using the ROM ID.
Clear Secret 5A Clears the 64-bit secret to 0000 0000 0000 0000h.
Compute Next Secret Without ROM ID 30 Generates new global secret.
Compute Next Secret With ROM ID 33 Generates new unique secret.
Lock Secret 60 Sets lock bit to prevent changes to the secret.
Read Data 69, XX Reads data from memory starting at address XX.
Write Data 6C, XX Writes data to memory starting at address XX.
Copy Data 48, XX Copies shadow RAM data to EEPROM block containing address XX.
Recall Data B8, XX Recalls EEPROM block containing address XX to RAM.
Lock 6A, XX Permanently locks the block of EEPROM containing address XX.
Set Overdrive 8B Sets 1-Wire interface timings to overdrive.
Clear Overdrive 8D Sets 1-Wire interface timings to standard (factory default).
Reset C4 Resets DS2784 (software POR).
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Read Data [69h, XX]. This command reads data from the
DS2784 starting at memory address XX. The LSb of the
data in address XX is available to be read immediately
after the MSb of the address has been entered. Because
the address is automatically incremented after the MSb of
each byte is received, the LSb of the data at address XX +
1 is available to be read immediately after the MSb of the
data at address XX. If the bus master continues to read
beyond address FFh, data is read starting at memory
address 00 and the address is automatically incremented
until a reset pulse occurs. Addresses labeled “Reserved” in
the memory map contain undefined data values. The Read
Data command can be terminated by the bus master with
a reset pulse at any bit boundary. Reads from EEPROM
block addresses return the data in the shadow RAM. A
Recall Data command is required to transfer data from the
EEPROM to the shadow. See Table 7 for more details.
Write Data [6Ch, XX]. This command writes data to the
DS2784 starting at memory address XX. The LSb of the
data to be stored at address XX can be written immediate-
ly after the MSb of address has been entered. Because
the address is automatically incremented after the MSb of
each byte is written, the LSb to be stored at address XX +
1 can be written immediately after the MSb to be stored at
address XX. If the bus master continues to write beyond
address FFh, the data starting at address 00 is overwrit-
ten. Writes to read-only addresses, reserved addresses
and locked EEPROM blocks are ignored. Incomplete
bytes are not written. Writes to unlocked EEPROM block
addresses modify the shadow RAM. A Copy Data com-
mand is required to transfer data from the shadow to the
EEPROM. See Table 7 for more details.
Copy Data [48h, XX]. This command copies the con-
tents of the EEPROM shadow RAM to EEPROM cells
for the EEPROM block containing address XX. Copy
Data commands that address locked blocks are ignored.
While the copy data command is executing, the EEC
bit in the EEPROM register is set to 1 and writes to
EEPROM addresses are ignored. Reads and writes to
non-EEPROM addresses can still occur while the copy
is in progress. The Copy Data command takes tEEC time
to execute, starting on the next falling edge after the
address is transmitted.
Recall Data [B8h, XX]. This command recalls the con-
tents of the EEPROM cells to the EEPROM shadow
memory for the EEPROM block containing address XX.
Lock [6Ah, XX]. This command locks (write protects)
the block of EEPROM containing address XX. The lock
bit in the EEPROM register must be set to 1 before the
Lock command is executed. To help prevent unintentional
locks, one must issue the Lock command immediately
after setting the lock bit (EEPROM register, address 1Fh,
bit 06) to a 1. If the lock bit is 0 or if setting the lock bit
to 1 does not immediately precede the Lock command,
the Lock command has no effect. The Lock command is
permanent; a locked block can never be written again.
Table 12. Guide to Function Command Requirements
COMMAND ISSUE MEMORY
ADDRESS
ISSUE 00h
BEFORE READ
READ/WRITE
TIME SLOTS
Write Challenge — — Write: 64
Compute MAC —Yes Read: up to 160
Compute Next Secret ———
Clear/Lock Secret, Set/Clear Overdrive ———
Read Data 8 bits —Read: up to 2048
Write Data 8 bits —Write: up to 2048
Copy Data 8 bits — —
Recall Data 8 bits — —
Lock 8 bits — —
Reset ———
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Figure 10. Compute MAC Function Command
Figure 11. Compute Next Secret Function Command
Figure 12. Copy Function Command
8 WRITE 0
TIME SLOTS
UP TO 160 READ TIME SLOTS
(READ 20-BYTE MAC)
SKIP ROM
CMD
COMPUTE
MAC
CMD
1-WIRE
RESET
PRESENCE
PULSE
tSHA
WAIT FOR MAC
COMPUTATION
SKIP ROM
CMD
COMPUTE
NEXT SECRET
CMD
1-WIRE
RESET
PRESENCE
PULSE
tSHA
WAIT FOR MAC
COMPUTATION
WAIT FOR EEPROM
PROGRAMMING
tEEC
SKIP ROM
CMD
COPY
CMD
1-WIRE
RESET
PRESENCE
PULSE
WAIT FOR EEPROM
PROGRAMMING
t
EEC
8 WRITE
TIME SLOTS
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I/O Signaling
The 1-Wire bus requires strict signaling protocols to
ensure data integrity. The four protocols used by the
DS2784 are as follows: the initialization sequence (reset
pulse followed by presence pulse), write 0, write 1, and
read data. The bus master initiates all these types of sig-
naling except the presence pulse.
The initialization sequence required to begin any com-
munication with the DS2784 is shown in Figure 14. A
presence pulse following a reset pulse indicates that the
DS2784 is ready to accept a net address command. The
bus master transmits (Tx) a reset pulse for tRSTL. The
bus master then releases the line and goes into Receive
mode (Rx). The 1-Wire bus line is then pulled high by the
pullup resistor. After detecting the rising edge on the DQ
pin, the DS2784 waits for tPDH and then transmits the
presence pulse for tPDL.
Write-Time Slots
A write-time slot is initiated when the bus master pulls the
1-Wire bus from a logic-high (inactive) level to a logic-
low level. There are two types of write-time slots: write
1 and write 0. All write-time slots must be tSLOT in dura-
tion with a 1µs minimum recovery time, tREC, between
cycles. The DS2784 samples the 1-Wire bus line between
tLOW1_MAX and tLOW0_MIN after the line falls. If the line
is high when sampled, a write 1 occurs. If the line is low
when sampled, a write 0 occurs. The sample window is
illustrated in Figure 15. For the bus master to generate
a write-1 time slot, the bus line must be pulled low and
then released, allowing the line to be pulled high less than
tRDV after the start of the write time slot. For the host to
generate a write 0 time slot, the bus line must be pulled
low and held low for the duration of the write-time slot.
Figure 13. Clear/Lock Secret, Set/Clear Overdrive Function Commands
Figure 14. 1-Wire Initialization Sequence
t
EEC
SKIP ROM
CMD
CLEAR/LOCK
SECRET CMD
OR
SET/CLEAR
OVERDRIVE CMD
1-WIRE
RESET
PRESENCE
PULSE
WAIT FOR EEPROM
COPY TIME
tRSTL
tPDL
tRSTH
tPDH
PACK+
PACK-
LINE TYPE LEGEND:
BUS MASTER ACTIVE LOW DS2784ACTIVE LOW
RESISTOR PULLUPBOTH BUS MASTER AND
DS2784 ACTIVE LOW
DQ
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Read-Time Slots
A read-time slot is initiated when the bus master pulls the
1-Wire bus line from a logic-high level to a logic-low level.
The bus master must keep the bus line low for at least 1µs
and then release it to allow the DS2784 to present valid
data. The bus master can then sample the data tRDV from
the start of the read-time slot. By the end of the read-time
slot, the DS2784 releases the bus line and allows it to
be pulled high by the external pullup resistor. All read-
time slots must be tSLOT in duration with a 1µs minimum
recovery time, tREC, between cycles. See Figure 15 and
the timing specifications in the Electrical Characteristics
table for more information.
Figure 15. 1-Wire Write and Read-Time Slots
WRITE 0 SLOT WRITE 1 SLOT
tSLOT
tLOW0
tSLOT
tREC
tLOW1
VPULLUP
GND
DEVICE SAMPLE WINDOW
MIN TYP MAX
15µS
2µS
15µS 30µS
1µS 3µS
DEVICE SAMPLE WINDOW
MIN TYP MAX
15µS
2µS
15µS 30µS
1µS 3µS
OVERDRIVE
STANDARD
MODE
>1µS
READ DATA SLOT
DATA = 0
tSLOT
15µS
tSLOT
tREC
VPULLUP
GND
MASTER SAMPLE WINDOW
tRDV
15µS
MASTER SAMPLE WINDOW
>1µS
DATA = 1
OVERDRIVE
STANDARD
MODE
2µS 2µS
LINE TYPE LEGEND:
BUS MASTER ACTIVE LOW DEVICE ACTIVE LOW
BOTH BUS MASTER AND DEVICE
ACTIVE LOW
RESISTOR PULLUP
tRDV
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+Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
*EP = Exposed pad.
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
14 TDFN-EP (3mm x 5mm) T1435N+1 21-0253 90-0246
PART TEMP RANGE TOP MARK PIN PACKAGE
DS2784G+ -40°C to +85°C D2784 14 TDFN-EP*
DS2784G+T&R -40°C to +85°C D2784 14 TDFN-EP*
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Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
Ordering Information
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/07 Initial release —
1 5/09
Changed the VDD maximum operating range in the Electrical Characteristics table to
4.6V. 2–4
Added text in Note 3 of Table 1 for UV case where UVEN = 0 and to the Undervoltage
section. 9
Changed VDD to VIN for pin monitored for UV release condition. 9
Added “VIN pin is limited to VDD voltage” text in the Voltage Measurement section. 13
Added CC FET Turn Off, DC FET Turn Off, COC Delay, DOC Delay, SC Delay, OV
Delay, UV Delay TOCs. 5–8
2 8/09 Added the CTG pin and connection to GND in the Typical Operating Circuit. 9
Changed the DOCUMENT NO. to 21-0253 in the Package Information table. 41
3 4/10 Corrected the “Top Mark” in the Ordering Information table. 1
4 3/12 Deleted all references to CRC generation during any command sequences unrelated
to 64-bit ID in the CRC Generation section 34
5 1/17
Updated front page title and Applications section; moved Simple Fuel Gauge Circuit
Diagram to front page; moved Pin Conguration above Pin Description table; moved
Ordering Information table to end of data sheet
1, 7, 39
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2017 Maxim Integrated Products, Inc.
│
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DS2784 1-Cell Fuel Gauge with FuelPack,
Protector, and SHA-1 Authentication
Revision History
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