General Description
The MAX1617A is a precise digital thermometer that
reports the temperature of both a remote sensor and its
own package. The remote sensor is a diode-connected
transistor—typically a low-cost, easily mounted 2N3904
NPN type—that replaces conventional thermistors or
thermocouples. Remote accuracy is ±3°C for multiple
transistor manufacturers, with no calibration needed. The
remote channel can also measure the die temperature of
other ICs, such as microprocessors, that contain an on-
chip, diode-connected transistor.
The 2-wire serial interface accepts standard System
Management Bus (SMBus) Write Byte, Read Byte, Send
Byte, and Receive Byte commands to program the alarm
thresholds and to read temperature data. The data format
is 7 bits plus sign, with each bit corresponding to 1°C, in
two’s complement format. Measurements can be done
automatically and autonomously, with the conversion rate
programmed by the user or programmed to operate in a
single-shot mode. The adjustable rate allows the user to
control the supply-current drain.
The MAX1617A is nearly identical to the popular
MAX1617, but has improved SMBus timing specifications,
improved bus collision immunity, software manufacturer
and device identification available via the serial interface,
and a power-on reset function that can force a reset of the
slave address via the serial interface.
Features
●Two Channels: Measures Both Remote and Local
Temperatures
●No Calibration Required
●SMBus 2-Wire Serial Interface
●Programmable Under/Overtemperature Alarms
●Supports SMBus Alert Response
●Supports Manufacturer and Device ID Codes
●Accuracy
• ±2°C (+60°C to +100°C, local)
• ±3°C (-40°C to +125°C, local)
• ±3°C (+60°C to +100°C, remote)
● 3μA (typ) Standby Supply Current
● 70μA (max) Supply Current in Auto-Convert Mode
●+3V to +5.5V Supply Range
●Small 16-Pin QSOP Package
●Desktop and Notebook
Computers
●Smart Battery Packs
●LAN Servers
●Industrial Controls
●Central Office
Telecom Equipment
●Test and Measurement
●Multichip Modules
19-4508; Rev 2; 11/16
Applications
+Denotes a lead(Pb)-free/RoHS-compliant package.
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
Ordering Information
Pin Conguration
Typical Operating Circuit
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
N.C. N.C.
STBY
SMBCLK
N.C.
SMBDATA
ALERT
ADD0
N.C.
TOP VIEW
MAX1617A
QSOP
VCC
DXP
ADD1
DXN
N.C.
GND
GND
+MAX1617A
SMBCLK
ADD0 ADD1
VCC STBY
GND
ALERT
SMBDATA
DXP
DXN INTERRUPT
TO µC
3V TO 5.5V
0.1µF
CLOCK
10k EACH
DATA
2N3904 2200pF
PART PIN-PACKAGE PIN-PACKAGE
MAX1617AMEE+ -55°C to +125°C 16 QSOP
EVALUATION KIT AVAILABLE
VCC to GND ............................................................-0.3V to +6V
DXP, ADD_ to GND .................................. -0.3V to (VCC + 0.3V)
DXN to GND ......................................................... -0.3V to +0.8V
SMBCLK, SMBDATA, ALERT, STBY to GND ........-0.3V to +6V
SMBDATA, ALERT Current ................................ -1mA to +50mA
DXN Current ....................................................................... ±1mA
ESD Protection (SMBCLK, SMBDATA,
ALERT, Human Body Model) ........................................4000V
ESD Protection (other pins, Human Body Model).............2000V
Continuous Power Dissipation (TA = +70°C)
QSOP (derate 8.30mW/°C above +70°C) ...................667mW
Operating Temperature Range ......................... -55°C to +125°C
Junction Temperature ...................................................... +150°C
Storage Temperature Range ............................ -65°C to +165°C
Lead Temperature (soldering, 10sec) .............................+300°C
Soldering Temperature (reflow) ....................................... +260°C
(VCC = +3.3V, TA = 0°C to +85°C, unless otherwise noted.) (Note 1)
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Electrical Characteristics
PARAMETER CONDITIONS MIN TYP MAX UNITS
ADC AND POWER SUPPLY
Temperature Resolution (Note 2) Monotonicity guaranteed 8 Bits
Initial Temperature Error,
Local Diode (Note 3)
TA = +60°C to +100°C -2 2 °C
TA = 0°C to +85°C -3 3
Temperature Error, Remote Diode
(Notes 3 and 4)
TR = +60°C to +100°C -3 3 °C
TR = -55°C to +125°C -5 5
Temperature Error, Local Diode
(Notes 2 and 3) Including long-term drift TA = +60°C to +100°C -2.5 2.5 °C
TA = 0°C to +85°C -3.5 3.5
Supply-Voltage Range 3.0 5.5 V
Undervoltage Lockout Threshold VCC input, disables A/D conversion, rising edge 2.60 2.80 2.95 V
Undervoltage Lockout Hysteresis 50 mV
Power-On Reset Threshold VCC, falling edge 1.0 1.7 2.5 V
POR Threshold Hysteresis 50 mV
Standby Supply Current Logic inputs forced to
VCC or GND
SMBus static 3 10
μA
Hardware or software
standby, SMBCLK at
10kHz
4
Average Operating Supply Current
Auto-convert mode,
average measured over
4sec. Logic inputs forced
to VCC or GND.
0.25 conv/sec 35 70
μA
2.0 conv/sec 120 180
Conversion Time From stop bit to conversion complete
(both channels) 94 125 156 ms
Conversion Rate Timing Error Auto-convert mode -25 25 %
Remote-Diode Source Current DXP forced to 1.5V High level 80 100 120 μA
Low level 8 10 12
DXN Source Voltage 0.7 V
Address Pin Bias Current ADD0, ADD1; momentary upon power-on reset 160 μA
(VCC = +3.3V, TA = -55°C to +125°C, unless otherwise noted.) (Note 1)
(VCC = +3.3V, TA = 0°C to +85°C, unless otherwise noted.) (Note 1)
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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Electrical Characteristics
Electrical Characteristics (continued)
PARAMETER CONDITIONS MIN TYP MAX UNITS
SMBus INTERFACE
Logic Input High Voltage STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V 2.2 V
Logic Input Low Voltage STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V 0.8 V
Logic Output Low Sink Current ALERT, SMBDATA forced to 0.4V 6 mA
ALERT Output High Leakage
Current ALERT forced to 5.5V 1 µA
Logic Input Current Logic inputs forced to VCC or GND -1 1 µA
SMBus Input Capacitance SMBCLK, SMBDATA 5 pF
SMBus Clock Frequency (Note 5) DC 100 kHz
SMBCLK Clock Low Time tLOW, 10% to 10% points 4.7 μs
SMBCLK Clock High Time tHIGH, 90% to 90% points 4 μs
SMBus Start-Condition Setup Time 4.7 µs
SMBus Repeated Start-Condition
Setup Time tSU:STA, 90% to 90% points 500 ns
SMBus Start-Condition Hold Time tHD:STA, 10% of SMBDATA to 90% of SMBCLK 4 µs
SMBus Stop-Condition Setup Time tSU:STO, 90% of SMBCLK to 10% of SMBDATA 4 µs
SMBus Data Valid to SMBCLK
Rising-Edge Time
tSU:DAT, 10% or 90% of SMBDATA to 10% of
SMBCLK 250 ns
SMBus Data-Hold Time tHD:DAT (Note 6) 0 μs
SMBCLK Falling Edge to SMBus
Data-Valid Time Master clocking in data 1 µs
PARAMETER CONDITIONS MIN TYP MAX UNITS
ADC AND POWER SUPPLY
Temperature Resolution (Note 2) Monotonicity guaranteed 8 Bits
Initial Temperature Error,
Local Diode (Note 3)
TA = +60°C to +100°C -2 2 °C
TA = -55°C to +125°C -3 3
Temperature Error, Remote Diode
(Notes 3 and 4)
TR = +60°C to +100°C -3 3 °C
TR = -55°C to +125°C -5 5
Supply-Voltage Range 3.0 5.5 V
Conversion Time From stop bit to conversion complete
(both channels) 94 125 156 ms
Conversion Rate Timing Error Auto-convert mode -25 25 %
(VCC = +3.3V, TA = -55°C to +125°C, unless otherwise noted.) (Note 1)
Note 1: All devices 100% production tested at TA = +85°C. Limits over temperature are guaranteed by design.
Note 2: Guaranteed but not 100% tested.
Note 3: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1617A device tempera-
ture is exactly +66.7°C, the ADC may report +66°C, +67°C, or +68°C (due to the quantization error plus the +1/2°C offset used
for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to +100°C temperature range (Table 2).
Note 4: A remote diode is any diode-connected transistor from Table 1. TR is the junction temperature of the remote diode. See
Remote-Diode Selection for remote diode forward voltage requirements.
Note 5: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it
violates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus.
Note 6: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of
SMBCLK’s falling edge.
(TA = +25°C, unless otherwise noted.)
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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│
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Electrical Characteristics (continued)
PARAMETER CONDITIONS MIN TYP MAX UNITS
SMBus INTERFACE
Logic Input High Voltage STBY, SMBCLK, SMBDATA VCC = 3V 2.2 V
VCC = 5.5V 2.4
Logic Input Low Voltage STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V 0.8 V
Logic Output Low Sink Current ALERT, SMBDATA forced to 0.4V 6 mA
ALERT Output High Leakage
Current ALERT forced to 5.5V 1 µA
Logic Input Current Logic inputs forced to VCC or GND -2 2 µA
Typical Operating Characteristics
-20
-10
0
10
20
1 10 303 100
TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
MAX1617ATOC01
LEAKAGE RESISTANCE (MΩ)
TEMPERATURE ERROR (°C)
PATH = DXP TO VCC (5V)
PATH = DXP TO GND
0
6
3
9
12
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
POWER-SUPPLY NOISE FREQUENCY
MAX1617ATOC04
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE APPLIED TO
VCC WITH NO 0.1µF VCC CAPACITOR
VIN = 250mVp-p
REMOTE DIODE
VIN = 250mVp-p
LOCAL DIODE
VIN = 100mVp-p
REMOTE DIODE
-2
-1
0
1
2
-50 50 1000 150
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX1617ATOC02
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
SAMSUNG KST3904
MOTOROLA MMBT3904
ZETEX FMMT3904
RANDOM
SAMPLES
(TA = +25°C, unless otherwise noted.)
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
Maxim Integrated
│
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www.maximintegrated.com
Typical Operating Characteristics (continued)
0
10
20
30
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
COMMON-MODE NOISE FREQUENCY
MAX1617ATOC05
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE
AC COUPLED TO DXN
VIN = 100mVp-p
VIN = 50mVp-p
VIN = 25mVp-p
0
10
20
0 40 60 80
20 100
TEMPERATURE ERROR vs.
DXP–DXN CAPACITANCE
MAX1617ATOC07
DXP–DXN CAPACITANCE (nF)
TEMPERATURE ERROR (°C)
VCC = 5V
0
100
400
200
300
500
0 10.0625 40.25 20.125 0.5 8
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
MAX1617ATOC10
CONVERSION RATE (Hz)
SUPPLY CURRENT (µA)
VCC = 5V
AVERAGED MEASUREMENTS
0
25
100
50
75
125
-2 8 0 42 6 10
RESPONSE TO THERMAL SHOCK
MAX1617ATOC11
TIME (sec)
TEMPERATURE (°C)
16-QSOP IMMERSED
IN +115°C FLUORINERT BATH
-5
5
0
10
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCY
MAX1617ATOC06
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = 10mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
0
3
60
6
20
100
0 31 42 5
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1617ATOC09
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
ADD0, ADD1
= GND
ADD0, ADD1
= HIGH-Z
-5
0
5
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCY
MAX1617ATOC03
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = 3mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
0
5
15
25
10
20
30
35
1k 100k10k 1000k
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
MAX1617ATOC08
SMBCLK FREQUENCY (Hz)
SUPPLY CURRENT (µA)
VCC = 5V
VCC = 3.3V
SMBCLK IS
DRIVEN RAIL-TO-RAIL
General Description
The MAX1617A is a temperature sensor designed to
work in conjunction with an external microcontroller (μC)
or other intelligence in thermostatic, process-control, or
monitoring applications. The μC is typically a power-man-
agement or keyboard controller, generating SMBus serial
commands by “bit-banging” general-purpose input/output
(GPIO) pins or via a dedicated SMBus interface block.
Essentially an 8-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the MAX1617A
contains a switched current source, a multiplexer, an
ADC, an SMBus interface, and associated control logic
(Figure 1). Temperature data from the ADC is loaded into
two data registers, where it is automatically compared
with data previously stored in four over/under-tempera-
ture alarm registers.
ADC and Multiplexer
The ADC is an averaging type that integrates over a
60ms period (each channel, typical) with excellent noise
rejection.
The multiplexer automatically steers bias currents through
the remote and local diodes, measures their forward
voltages, and computes their temperatures. Both chan-
nels are automatically converted once the conversion
process has started, either in free-running or single-shot
mode. If one of the two channels is not used, the device
still performs both measurements, and the user can
simply ignore the results of the unused channel. If the
remote diode channel is unused, tie DXP to DXN rather
than leaving the pins open.
The DXN input is biased at 0.65V(typ) above ground by
an internal diode to set up the analog-to-digital (A/D)
inputs for a differential measurement. The typical DXP–
DXN differential input voltage range is 0.25V to 0.95V.
To ensure proper operation over full temperature range,
ensure VDXP ≤ (0.78 x VCC - 1.1) volts.
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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Pin Description
PIN NAME FUNCTION
1, 5, 9,
13, 16 N.C. No Connection. Not internally connected. May be used for PC board trace routing.
2 VCC Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1μF capacitor.
3 DXP
Combined Current Source and A/D Positive Input for Remote-Diode Channel. Do not leave DXP
unconnected; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and
DXN for noise ltering.
4 DXN Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above ground.
6 ADD1 SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance
(>50pF) at the address pins when unconnected may cause address-recognition problems.
7, 8 GND Ground
10 ADD0 SMBus Slave Address Select Pin
11 ALERT SMBus Alert (interrupt) Output, Open Drain
12 SMBDATA SMBus Serial-Data Input/Output, Open Drain
14 SMBCLK SMBus Serial-Clock Input
15 STBY Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.
Low = standby mode, high = operate mode.
Figure 1. Functional Diagram
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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REMOTE
MUX
LOCAL
REMOTE TEMPERATURE
DATA REGISTER
HIGH-TEMPERATURE THRESHOLD
(REMOTE T
HIGH
)
LOW-TEMPERATURE THRESHOLD
(REMOTE T
LOW
)
DIGITAL COMPARATOR
(REMOTE)
LOCAL TEMPERATURE
DATA REGISTER
HIGH-TEMPERATURE THRESHOLD
(LOCAL T
HIGH)
LOW-TEMPERATURE THRESHOLD
(LOCAL T
LOW
)
DIGITAL COMPARATOR
(LOCAL)
COMMAND BYTE
(INDEX) REGISTER
SMBDATA
SMBCLK
ADDRESS
DECODER
READ WRITE
CONTROL
LOGIC
SMBus
ADD1ADD0STBY
STATUS BYTE REGISTER
CONFIGURATION
BYTE REGISTER
CONVERSION RATE
REGISTER
ALERT RESPONSE
ADDRESS REGISTER
SELECTED VIA
SLAVE ADD = 0001 100
ADC
+
DIODE
FAULT
DXP
DXN
GND
V
CC
-
+
+
-
8
8
8
8
8
8
8 8
27
ALERT
Q S
R
MAX1617A
Excess resistance in series with the remote diode causes
about +1/2°C error per ohm. Likewise, 200μV of offset
voltage forced on DXP–DXN causes about 1°C error.
A/D Conversion Sequence
If a Start command is written (or generated automatically
in the free-running auto-convert mode), both channels
are converted, and the results of both measurements are
available after the end of conversion. A BUSY status bit in
the status byte shows that the device is actually performing
a new conversion; however, even if the ADC is busy, the
results of the previous conversion are always available.
Remote-Diode Selection
Temperature accuracy depends on having a good-quality,
diode-connected small-signal transistor. See Table 1 for a
recommended list of diode-connected small-signal tran-
sistors. The MAX1617A can also directly measure the die
temperature of CPUs and other integrated circuits having
on-board temperature-sensing diodes.
The transistor must be a small-signal type with a rela-
tively high forward voltage; otherwise, the A/D input volt-
age range can be violated. The forward voltage must be
greater than 0.25V at 10μA; check to ensure this is true
at the highest expected temperature. The forward voltage
(VDXP - VDXN) must be less than 0.95V at 100μA; addi-
tionally, ensure the maximum VDXP (DXP voltage) ≤ (0.78
x VCC - 1.1) volts over your expected range of tempera-
ture. Large power transistors don’t work at all. Also ensure
that the base resistance is less than 100Ω. Tight specifica-
tions for forward-current gain (+50 to +150, for example)
indicate that the manufacturer has good process controls
and that the devices have consistent VBE characteristics.
For heatsink mounting, the 500-32BT02-000 thermal sen-
sor from Fenwal Electronics is a good choice. This device
consists of a diode-connected transistor, an aluminum
plate with screw hole, and twisted-pair cable (Fenwal Inc.,
Milford, MA, 508-478-6000).
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the MAX1617A’s
effective accuracy. The thermal time constant of the
QSOP-16 package is about 140sec in still air. For the
MAX1617A junction temperature to settle to within +1°C
after a sudden +100°C change requires about five time
constants or 12 minutes. The use of smaller packages
for remote sensors, such as SOT23s, improves the situa-
tion. Take care to account for thermal gradients between
the heat source and the sensor, and ensure that stray air
currents across the sensor package do not interfere with
measurement accuracy.
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For the local diode, the
worst-case error occurs when auto-converting at the fast-
est rate and simultaneously sinking maximum current at
the ALERT output. For example, at an 8Hz rate and with
ALERT sinking 1mA, the typical power dissipation is VCC
x 450μA plus 0.4V x 1mA. Package theta J-A is about
150°C/W, so with VCC = 5V and no copper PC board
heatsinking, the resulting temperature rise is:
dT = 2.7mW x 150°C/W = 0.4°C
Even with these contrived circumstances, it is difficult to
introduce significant self-heating errors.
ADC Noise Filtering
The ADC is an integrating type with inherently good noise
rejection, especially of low-frequency signals such as
60Hz/120Hz power-supply hum. Micropower operation
places constraints on high-frequency noise rejection;
therefore, careful PC board layout and proper external
noise filtering are required for high-accuracy remote mea-
surements in electrically noisy environments.
High-frequency EMI is best filtered at DXP and DXN
with an external 2200pF capacitor. This value can be
increased to about 3300pF (max), including cable capaci-
tance. Higher capacitance than 3300pF introduces errors
due to the rise time of the switched current source.
Nearly all noise sources tested cause the ADC measure-
ments to be higher than the actual temperature, typically
by +1°C to +10°C, depending on the frequency and ampli-
tude (see Typical Operating Characteristics).
Table 1. Remote-Sensor Transistor
Manufacturers
Note: Transistors must be diode-connected (base shorted to
collector).
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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MANUFACTURER MODEL NUMBER
Central Semiconductor (USA) CMPT3904
Motorola (USA) MMBT3904
National Semiconductor (USA) MMBT3904
Rohm Semiconductor (Japan) SST3904
Samsung (Korea) KST3904-TF
Siemens (Germany) SMBT3904
Zetex (England) FMMT3904CT-ND
PC Board Layout
1) Place the MAX1617A as close as practical to the
remote diode. In a noisy environment, such as a
computer motherboard, this distance can be 4 in. to 8
in. (typical) or more as long as the worst noise sourc-
es (such as CRTs, clock generators, memory buses,
and ISA/PCI buses) are avoided.
2) Do not route the DXP–DXN lines next to the deection
coils of a CRT. Also, do not route the traces across a
fast memory bus, which can easily introduce +30°C
error, even with good ltering. Otherwise, most noise
sources are fairly benign.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any high-
voltage traces such as +12VDC. Leakage currents
from PC board contamination must be dealt with care-
fully, since a 20MΩ leakage path from DXP to ground
causes about +1°C error.
4) Connect guard traces to GND on either side of the
DXP–DXN traces (Figure 2). With guard traces in
place, routing near high-voltage traces is no longer
an issue.
5) Route through as few vias and crossunders as pos-
sible to minimize copper/solder thermocouple effects.
6) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching ther-
mocouples. In general, PC board-induced thermo-
couples are not a serious problem. A copper-solder
thermocouple exhibits 3μV/°C, and it takes about
200μV of voltage error at DXP–DXN to cause a +1°C
measurement error. So, most parasitic thermocouple
errors are swamped out.
7) Use wide traces. Narrow ones are more inductive
and tend to pick up radiated noise. The 10 mil widths
and spacings recommended in Figure 2 aren’t ab-
solutely necessary (as they offer only a minor im-
provement in leakage and noise), but try to use them
where practical.
8) Keep in mind that copper can’t be used as an EMI
shield, and only ferrous materials, such as steel, work
well. Placing a copper ground plane between the
DXP-DXN traces and traces carrying high-frequency
noise signals does not help reduce EMI.
PC Board Layout Checklist
●Place the MAX1617A close to a remote diode.
●Keep traces away from high voltages (+12V bus).
●Keep traces away from fast data buses and CRTs.
●Use recommended trace widths and spacings.
●Place a ground plane under the traces.
●Use guard traces flanking DXP and DXN and connect-
ing to GND.
● Place the noise filter and the 0.1μF VCC bypass
capacitors close to the MAX1617A.
Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8 in., or in partic-
ularly noisy environments, a twisted pair is recommended.
Its practical length is 6 feet to 12 feet (typical) before
noise becomes a problem, as tested in a noisy electron-
ics laboratory. For longer distances, the best solution is a
shielded twisted pair like that used for audio microphones.
For example, the Belden 8451 works well for distances up
to 100 feet in a noisy environment. Connect the twisted
pair to DXP and DXN and the shield to GND, and leave
the shield’s remote end unterminated.
Excess capacitance at DX_ limits practical remote sensor
distances (see Typical Operating Characteristics). For
very long cable runs, the cable’s parasitic capacitance
often provides noise filtering, so the 2200pF capacitor can
often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy;
1Ω series resistance introduces about +1/2°C error.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the sup-
ply- current drain to less than 10μA. Enter standby mode
by forcing the STBY pin low or via the RUN/STOP bit in
the configuration byte register. Hardware and software
standby modes behave almost identically: all data is
retained in memory, and the SMB interface is alive and
listening for reads and writes. The only difference is that
in hardware standby mode, the one-shot command does
not initiate a conversion.
Standby mode is not a shutdown mode. With activity on
the SMBus, extra supply current is drawn (see Typical
Operating Characteristics). In software standby mode,
the MAX1617A can be forced to perform A/D conversions
Figure 2. Recommended DXP/DXN PC Traces
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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9
MINIMUM
10 MILS
10 MILS
10 MILS
10 MILS
GND
DXN
DXP
GND
through the one-shot command, despite the RUN/STOP
bit being high.
Activate hardware standby mode by forcing the STBY pin
low. In a notebook computer, this line may be connected
to the system SUSTAT# suspend-state signal.
The STBY pin low state overrides any software conversion
command. If a hardware or software standby command is
received while a conversion is in progress, the conversion
cycle is truncated, and the data from that conversion is not
latched into either temperature reading register. The previ-
ous data is not changed and remains available.
Supply-current drain during the 125ms conversion period
is always about 450μA. Slowing down the conversion rate
reduces the average supply current (see
Typical Operating
Characteristics
). Between conversions, the instantaneous
supply current is about 25μA due to the current consumed
by the conversion rate timer. In standby mode, supply
current drops to about 3μA. At very low supply voltages
(under the power-on-reset threshold), the supply current is
higher due to the address pin bias currents. It can be as
high as 100μA, depending on ADD0 and ADD1 settings.
SMBus Digital Interface
From a software perspective, the MAX1617A appears as
a set of byte-wide registers that contain temperature data,
alarm threshold values, or control bits. A standard SMBus
2-wire serial interface is used to read temperature data
and write control bits and alarm threshold data. Each A/D
channel within the device responds to the same SMBus
slave address for normal reads and writes.
The MAX1617A employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figure 3). The shorter Receive Byte protocol allows
quicker transfers, provided that the correct data regis-
ter was previously selected by a Read Byte instruction.
Use caution with the shorter protocols in multi-master
systems, since a second master could overwrite the
command byte without informing the first master.
The temperature data format is 7 bits plus sign in two’s
complement form for each channel, with each data bit repre-
senting 1°C (Table 2), transmitted MSB first. Measurements
are offset by +1/2°C to minimize internal rounding errors;
for example, +99.6°C is reported as +100°C.
Figure 3. SMBus Protocols
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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Write Byte Format
S ADDRESS WR ACK COMMAND ACK DATA ACK P
7 bits 8 bits 8 bits 1
Slave Address: equivalent
to chip-select line of a
3-wire interface
Command Byte: selects which
register you are writing to
Data Byte: data goes into the register set
by the command byte (to set thresholds,
conguration masks, and sampling rate)
Read Byte Format
S ADDRESS WR ACK COMMAND ACK S ADDRESS RD ACK DATA /// P
7 bits 8 bits 7 bits 8 bits
Slave Address:
equivalent to
chip-select line
Command Byte:
selects which
register you are
reading from
Slave Address:
repeated due to change
in data-ow direction
Data Byte: reads from
the register set by the
command byte
Send Byte Format Receive Byte Format
S ADDRESS WR ACK COMMAND ACK P S ADDRESS RD ACK DATA /// P
7 bits 8 bits 7 bits 8 bits
Command Byte: sends
command with no data,
usually used for
one-shot command
Data Byte: reads data from
the register commanded by
the last Read Byte or Write
Byte transmission; also used
for SMBus Alert Response
return address
S = Start condition
P = Stop condition
Shaded = Slave transmission
/// = Not acknowledged
Alarm Threshold Registers
Four registers store alarm threshold data, with high-
temperature (THIGH) and low-temperature (TLOW) regis-
ters for each A/D channel. If either measured temperature
equals or exceeds the corresponding alarm threshold
value, an ALERT interrupt is asserted.
The power-on-reset (POR) state of both THIGH registers
is full scale (0111 1111, or +127°C). The POR state of both
TLOW registers is 1100 1001 or -55°C.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
whether the remote diode has an open-circuit condition.
At the beginning of each conversion, the diode fault is
checked, and the status byte is updated. This fault detec-
tor is a simple voltage detector; if DXP rises above VCC
- 1V (typical) due to the diode current source, a fault is
detected. Note that the diode fault isn’t checked until a
conversion is initiated, so immediately after power-on
reset the status byte indicates no fault is present, even if
the diode path is broken.
If the remote channel is shorted (DXP to DXN or DXP
to GND), the ADC reads 0000 0000 so as not to trip
either the THIGH or TLOW alarms at their POR settings.
In applications that are never subjected to 0°C in normal
operation, a 0000 0000 result can be checked to indicate
a fault condition in which DXP is accidentally short cir-
cuited. Similarly, if DXP is short circuited to VCC, the ADC
reads +127°C for both remote and local channels, and the
device alarms.
ALERT Interrupts
The ALERT interrupt output signal is latched and can
only be cleared by reading the Alert Response address.
Interrupts are generated in response to THIGH and TLOW
comparisons and when the remote diode is disconnected
(for continuity fault detection). The interrupt does not halt
automatic conversions; new temperature data continues
to be available over the SMBus interface after ALERT is
asserted. The interrupt output pin is open-drain so that
devices can share a common interrupt line. The interrupt
rate can never exceed the conversion rate.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature (see
Alert Response Address section). Prior to taking correc-
tive action, always check to ensure that an interrupt is
valid by reading the current temperature.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that lack
the complex, expensive logic needed to be a bus mas-
ter. Upon receiving an ALERT interrupt signal, the host
master can broadcast a Receive Byte transmission to the
Alert Response slave address (0001 100). Then any slave
device that generated an interrupt attempts to identify
itself by putting its own address on the bus (Table 3).
Table 3. Read Format for Alert Response
Address (0001100)
Table 2. Data Format (Two’s Complement)
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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TEMP.
(°C)
ROUNDED
TEMP.
(°C)
DIGITAL OUTPUT
DATA BITS
SIGN MSB LSB
+130.00 +127 0 111 1111
+127.00 +127 0 111 1111
+126.50 +127 0 111 1111
+126.00 +126 0 111 1110
+25.25 +25 0 001 1001
+0.50 +1 0 000 0001
+0.25 0 0 000 0000
0.00 0 0 000 0000
-0.25 0 0 000 0000
-0.50 0 0 000 0000
-0.75 -1 1 111 1111
-1.00 -1 1 111 1111
-25.00 -25 1 110 0111
-25.50 -26 1 110 0110
-54.75 -55 1 100 1001
-55.00 -55 1 100 1001
-65.00 -65 1 011 1111
-70.00 -65 1 011 1111
BIT NAME FUNCTION
7
(MSB) ADD7
Provide the current MAX1617A
slave address that was latched at
POR (Table 8)
6 ADD6
5 ADD5
4 ADD4
3 ADD3
2 ADD2
1 ADD1
0
(LSB) 1Logic 1
The Alert Response can activate several different slave
devices simultaneously, similar to the I2C general call. If
more than one slave attempts to respond, bus arbitration
rules apply, and the device with the lower address code
wins. The losing device does not generate an acknowl-
edge and continues to hold the ALERT line low until
serviced (implies that the host interrupt input is level-sen-
sitive). Successful reading of the alert response address
clears the interrupt latch.
Command Byte Functions
The 8-bit command byte register (Table 4) is the master
index that points to the various other registers within the
MAX1617A. The register’s POR state is 0000 0000, so
that a Receive Byte transmission (a protocol that lacks
the command byte) that occurs immediately after POR
returns the current local temperature data.
The one-shot command immediately forces a new con-
version cycle to begin. In software standby mode (RUN/
STOP bit = high), a new conversion is begun, after which
the device returns to standby mode. If a conversion is
in progress when a one-shot command is received, the
command is ignored. If a one-shot command is received
in auto-convert mode (RUN/STOP bit = low) between
conversions, a new conversion begins, the conversion
rate timer is reset, and the next automatic conversion
takes place after a full delay elapses.
Conguration Byte Functions
The configuration byte register (Table 5) is used to mask
(disable) interrupts and to put the device in software
standby mode. The lower six bits are internally set to
(XX1111), making them “don’t care” bits. Write zeros to
these bits. This register’s contents can be read back over
the serial interface.
Status Byte Functions
The status byte register (Table 6) indicates which (if
any) temperature thresholds have been exceeded. This
byte also indicates whether or not the ADC is convert-
ing and whether there is an open circuit in the remote
diode DXP–DXN path. After POR, the normal state of all
the flag bits is zero, assuming none of the alarm condi-
tions are present. The status byte is cleared by any suc-
cessful read of the status byte, unless the fault persists.
Table 4. Command-Byte Bit Assignments
*If the device is in hardware standby mode at POR, both temperature registers read 0°C.
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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REGISTER COMMAND POR STATE FUNCTION
RLTS 00h 0000 0000* Read local temperature: returns latest temperature
RRTE 01h 0000 0000* Read remote temperature: returns latest temperature
RSL 02h N/A Read status byte (ags, busy signal)
RCL 03h 0000 0000 Read conguration byte
RCRA 04h 0000 0000 Read conversion rate byte
RLHN 05h 0111 1111 Read local THIGH limit
RLLI 06h 1100 1001 Read local TLOW limit
RRHI 07h 0111 1111 Read remote THIGH limit
RRLS 08h 1100 1001 Read remote TLOW limit
WCA 09h N/A Write conguration byte
WCRW 0Ah N/A Write conversion rate byte
WLHO 0Bh N/A Write local THIGH limit
WLLM 0Ch N/A Write local TLOW limit
WRHA 0Dh N/A Write remote THIGH limit
WRLN 0Eh N/A Write remote TLOW limit
OSHT 0Fh N/A One-shot command (use send-byte format)
SPOR FCh N/A Write software POR
MFGID FEh 0100 1101 Read manufacturer ID code
DEVID FFh 00000001 Read device ID code
Note that the ALERT interrupt latch is not automatically
cleared when the status flag bit is cleared.
When auto-converting, if the THIGH and TLOW limits are
close together, it’s possible for both high-temp and low-
temp status bits to be set, depending on the amount of
time between status read operations (especially when
converting at the fastest rate). In these circumstances, it’s
best not to rely on the status bits to indicate reversals in
long-term temperature changes and instead use a current
temperature reading to establish the trend direction.
Conversion Rate Byte
The conversion rate register (
Table 7
) programs the time
interval between conversions in free-running auto-convert
mode. This variable rate control reduces the supply
current in portable-equipment applications. The conversion
rate byte’s POR state is 02h (0.25Hz). The MAX1617A
looks only at the 3 LSB bits of this register, so the upper 5
bits are “don’t care” bits, which should be set to zero. The
conversion rate tolerance is ±25% at any rate setting.
Valid A/D conversion results for both channels are avail-
able one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conver-
sion is initiated via the RUN/STOP bit, hardware STBY
pin, one-shot command, or initial power-up. Changing the
conversion rate can also affect the delay until new results
are available (Table 8).
Manufacturer and Device ID Codes
Two ROM registers provide manufacturer and device ID
codes (Table 4). Reading the manufacturer ID returns
4Dh, which is the ASCII code “M” (for Maxim). Reading
the device ID returns 01h, indicating a MAX1617A device.
If READ WORD 16-bit SMBus protocol is employed (rath-
er than the 8-bit READ BYTE), the least significant byte
contains the data and the most significant byte contains
00h in both cases.
Slave Addresses
The MAX1617A appears to the SMBus as one device
having a common address for both ADC channels. The
device address can be set to one of nine different values
by pin-strapping ADD0 and ADD1 so that more than one
MAX1617A can reside on the same bus without address
conflicts (Table 9).
Table 6. Status-Byte Bit Assignments
Table 7. Conversion-Rate Control Byte
*These flags stay high until cleared by POR, or until the status
byte register is read.
Table 5. Configuration-Byte Bit
Assignments
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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BIT NAME POR
STATE FUNCTION
7 (MSB) MASK 0 Masks all ALERT interrupts
when high.
6RUN/
STOP 0
Standby mode control bit.
If high, the device
immediately stops
converting and enters
standby mode. If low, the
device converts in either
one-shot or timer mode.
5–0 RFU 0 Reserved for future use
BIT NAME FUNCTION
7
(MSB) BUSY A high indicates that the ADC is busy
converting.
6 LHIGH* A high indicates that the local high-
temperature alarm has activated.
5 LLOW* A high indicates that the local low-
temperature alarm has activated.
4 RHIGH* A high indicates that the remote high-
temperature alarm has activated.
3 RLOW* A high indicates that the remote low-
temperature alarm has activated.
2 OPEN* A high indicates a remote-diode
continuity (open-circuit) fault.
1 RFU Reserved for future use (returns 0)
0
(LSB) RFU Reserved for future use (returns 0)
DATA
CONVERSION
RATE
(Hz)
AVERAGE SUPPLY
CURRENT
(μA typ, at VCC = 3.3V)
00h 0.0625 30
01h 0.125 33
02h 0.25 35
03h 0.5 48
04h 1 70
05h 2 128
06h 4 225
07h 8 425
08h to
FFh RFU —
The address pin states are checked at POR and SPOR
only, and the address data stays latched to reduce qui-
escent supply current due to the bias current needed for
high-Z state detection.
The MAX1617A also responds to the SMBus Alert Response
slave address (see the
Alert Response Address
section).
POR and UVLO
The MAX1617A has a volatile memory. To prevent ambig-
uous power-supply conditions from corrupting the data
in memory and causing erratic behavior, a POR voltage
detector monitors VCC and clears the memory if VCC falls
below 1.7V (typical, see Electrical Characteristics table).
When power is first applied and VCC rises above 1.75V
(typical), the logic blocks begin operating, although reads
and writes at VCC levels below 3V are not recommended.
A second VCC comparator, the ADC UVLO comparator,
prevents the ADC from converting until there is sufficient
headroom (VCC = 2.8V typical).
The SPOR software POR command can force a power-on
reset of the MAX1617A registers via the serial interface.
Use the SEND BYTE protocol with COMMAND = FCh. This
is most commonly used to reconfigure the slave address of
the MAX1617A “on the fly,” where external hardware has
forced new states at the ADD0 and ADD1 address pins prior
to the software POR. The new address takes effect less
than 100μs after the SPOR transmission stop condition.
Power-Up Defaults:
●Interrupt latch is cleared.
●Address select pins are sampled.
●ADC begins auto-converting at a 0.25Hz rate.
●Command byte is set to 00h to facilitate quick remote
Receive Byte queries.
●THIGH and TLOW registers are set to max and min
limits, respectively.
Table 8. RLTS and RRTE Temp Register Update Timing Chart
Table 9. Slave Address Decoding
(ADD0 and ADD1)
Note: High-Z means that the pin is left unconnected.
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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OPERATING MODE CONVERSION INITIATED BY:
NEW CONVERSION RATE
(CHANGED VIA WRITE TO
WCRW)
TIME UNTIL RLTS AND RRTE
ARE UPDATED
Auto-Convert Power-on reset n/a (0.25Hz) 156ms max
Auto-Convert 1-shot command, while idling
between automatic conversions n/a 156ms max
Auto-Convert 1-shot command that occurs
during a conversion n/a When current conversion is
complete (1-shot is ignored)
Auto-Convert Rate timer 0.0625Hz 20sec
Auto-Convert Rate timer 0.125Hz 10sec
Auto-Convert Rate timer 0.25Hz 5sec
Auto-Convert Rate timer 0.5Hz 2.5sec
Auto-Convert Rate timer 1Hz 1.25sec
Auto-Convert Rate timer 2Hz 625ms
Auto-Convert Rate timer 4Hz 312.5ms
Auto-Convert Rate timer 8Hz 237.5ms
Hardware Standby STBY pin n/a 156ms
Software Standby RUN/STOP bit n/a 156ms
Software Standby 1-shot command n/a 156ms
ADD0 ADD1 ADDRESS
GND GND 0011 000
GND High-Z 0011 001
GND VCC 0011 010
High-Z GND 0101 001
High-Z High-Z 0101 010
High-Z VCC 0101 011
VCC GND 1001 100
VCC High-Z 1001 101
VCC VCC 1001 110
Figure 4. SMBus Write Timing Diagram
Figure 5. SMBus Read Timing Diagram
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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SMBCLK
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
A B C D EF G H IJ
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tSU:STO tBUF
K
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
SMBCLK
A B C D EF G H IJK
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tHD:DAT tSU:STO tBUF
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
LM
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
Listing 1. Pseudocode Example
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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Programming Example:
Clock-Throttling Control for CPUs
Listing 1 gives an untested example of pseudocode for
proportional temperature control of Intel mobile CPUs
via a power-management microcontroller. This program
consists of two main parts: an initialization routine and
an interrupt handler. The initialization routine checks
for SMBus communications problems and sets up the
MAX1617A configuration and conversion rate. The inter-
rupt handler responds to ALERT signals by reading
the current temperature and setting a CPU clock duty
factor proportional to that temperature. The relationship
between clock duty and temperature is fixed in a look-
up table contained in the microcontroller code.
Note: Thermal management decisions should be made
based on the latest temperature obtained from the
MAX1617A rather than the value of the Status Byte. The
MAX1617A responds very quickly to changes in its envi-
ronment due to its sensitivity and its small thermal mass.
High and low alarm conditions can exist in the Status Byte
due to the MAX1617A correctly reporting environmental
changes around it.
Listing 1. Pseudocode Example (continued)
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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Listing 1. Pseudocode Example (continued)
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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│
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MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
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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.
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
16 QSOP E116+1 21-0055 90-0167
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 specications 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.
MAX1617A Remote/Local Temperature Sensor
with SMBus Serial Interface
© 2016 Maxim Integrated Products, Inc.
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Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 1/99 Initial release —
1 10/12 Updated Electrical Characteristics tables (added new Note 1); updated ADC and
Multiplexer and Remote-Diode Selection sections 2–4, 6, 8
2 11/16 Removed 200Ω resistor from Typical Operating Circuit and references to the same
throughout document 1, 6, 9
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
