IN OUT
TEMP
SW
ENABLE
TORCH
TX
SDA
SCL GND
1 PH
10 PF10 PF
STROBE
LED
Flash
LED
2.5 V to 5.5 V
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LM3556
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LM3556 1.5-A Synchronous Boost LED Flash Driver With High-Side Current Source
1 Features 3 Description
The LM3556 is a 4-MHz fixed-frequency synchronous
1• Grounded Cathode LED Operation for Improved boost converter plus 1.5-A constant current driver for
Thermal Management a high-current white LED. The high-side current
• 1.5-A High-Side Current Source for Single LED source allows for grounded cathode LED operation
• Accurate and Programmable LED Current from providing flash current up to 1.5 A. An adaptive
regulation method ensures the current source
46.9 mA to 1.5 A remains in regulation and maximizes efficiency.
• > 85% Efficiency in Torch Mode (at 100 mA) and
Flash Mode (at 1 A to 1.5 A) The LM3556 is controlled via an I2C-compatible
interface. Features include: a hardware flash enable
• Small Solution Size: < 20 mm2(STROBE) allowing a logic input to trigger the flash
• LED Thermal Sensing and Current Scale-Back pulse, a hardware torch enable (TORCH) for Movie
• Soft-Start Operation for Battery Protection Mode or flashlight functions, a TX input which forces
the flash pulse into a low-current Torch Mode
• Hardware Enable Pin allowing for synchronization to RF power amplifier
• Hardware Torch Enable events or other high-current conditions, and an
• Hardware Strobe Enable integrated comparator designed to monitor an NTC
• Synchronization Input for RF Power Amplifier thermistor and provide an interrupt to the LED
current. With a fast 1-μs transition from 0 mA to
Pulse Events 46.9 mA, the TORCH input pin can be used to
• VIN Flash Monitor Optimization develop custom LED current waveforms.
• 400-kHz I2C-Compatible Interface The 4-MHz switching frequency, overvoltage
• I2C-Compatible Programmable NTC Trip Point protection and adjustable current limit allow for the
• 0.4-mm Pitch, 16-Pin DSBGA Package use of tiny, low-profile inductors and 10-µF ceramic
capacitors. The device is operates over a −40°C to
2 Applications +85°C temperature range.
Camera Phone LED Flash Device Information(1)
PART NUMBER PACKAGE BODY SIZE (MAX)
LM3556 DSBGA (16) 1.69 mm × 1.64 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application Circuit
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM3556
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Table of Contents
7.5 Programming........................................................... 17
1 Features.................................................................. 17.6 Register Maps......................................................... 19
2 Applications ........................................................... 18 Application and Implementation ........................ 27
3 Description............................................................. 18.1 Application Information............................................ 27
4 Revision History..................................................... 28.2 Typical Application ................................................. 27
5 Pin Configuration And Functions ........................ 39 Power Supply Recommendations...................... 29
6 Specifications......................................................... 410 Layout................................................................... 30
6.1 Absolute Maximum Ratings ...................................... 410.1 Layout Guidelines ................................................. 30
6.2 ESD Ratings.............................................................. 410.2 Layout Example .................................................... 31
6.3 Recommended Operating Conditions....................... 411 Device And Documentation Support................. 32
6.4 Thermal Information.................................................. 411.1 Device Support .................................................... 32
6.5 Electrical Characteristics .......................................... 511.2 Documentation Support ........................................ 32
6.6 Timing Requirements................................................ 611.3 Community Resources.......................................... 32
6.7 Typical Characteristics.............................................. 711.4 Trademarks........................................................... 32
7 Detailed Description............................................ 12 11.5 Electrostatic Discharge Caution............................ 32
7.1 Overview................................................................. 12 11.6 Glossary................................................................ 32
7.2 Functional Block Diagram....................................... 13 12 Mechanical, Packaging, And Orderable
7.3 Feature Description................................................. 13 Information........................................................... 33
7.4 Device Functional Modes........................................ 15
4 Revision History
Changes from Revision C (April 2013) to Revision D Page
• Added Device Information and Pin Configuration and Functions sections, ESD Rating table, Feature Description,
Device Functional Modes,Application and Implementation,Power Supply Recommendations,Layout,Device and
Documentation Support, and Mechanical, Packaging, and Orderable Information sections................................................. 1
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A1 A2
B1 B2 B3
A3
C2
C1 C3
D2 D3
A4
B4
C4
D4
D1
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SNVS796D –AUGUST 2011–REVISED OCTOBER 2015
5 Pin Configuration And Functions
YFQ Package
16-Pin DSBGA
Top View
Pin Functions
PIN TYPE DESCRIPTION
NUMBER NAME
High-side current source output for flash LED. Both pins must be connected for proper
A1, B1 LED Power operation.
Step-up DC-DC converter output. Connect a 10-µF ceramic capacitor between this pin
B2, A2 OUT Power and GND.
B3, A3 SW Power Drain connection for internal NMOS and synchronous PMOS switches.
A4, B4 GND Ground Ground
C1 TEMP Power Threshold detector for LED temperature sensing and current scale back.
Active high hardware torch enable. Drive TORCH high to turn on Torch or Movie mode.
C2 TORCH Power Used for external PWM Mode. Has an internal pulldown resistor of 300 kΩbetween
TORCH and GND.
Active high hardware flash enable. Drive STROBE high to turn on flash pulse. STROBE
C3 STROBE I/O overrides TORCH. Has an internal pulldown resistor of 300 kΩbetween STROBE and
GND.
Input voltage connection. Connect IN to the input supply, and bypass to GND with a 10-
C4 IN Input µF or larger ceramic capacitor.
Configurable dual polarity power amplifier synchronization input. Has an internal pulldown
D1 TX I/O resistor of 300 kΩbetween TX and GND.
D2 SDA I/O Serial data input/output.
D3 SCL Input Serial clock input.
Active high enable pin. High = standby, low = shutdown/reset. There is no internal
D4 ENABLE Power pulldown resistor on this pin.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1) (2)
MIN MAX UNIT
VIN, VSW ,VOUT –0.3 6 V
VSCL, VSDA, VENABLE, VSTROBE, VTX, VTORCH, VLED, VTEMP −0.3 V to the lesser of (VIN + 0.3 V)
w/ 6 V maximum
Continuous power dissipation(3) Internally limited
Junction temperature, TJ-MAX 150 °C
Maximum lead temperature (soldering) See(4) °C
Storage temperature, Tstg –65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) All voltages are with respect to the potential at the GND pin.
(3) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ= 150°C (typical) and
disengages at TJ= 135°C (typical). Thermal shutdown is ensured by design.
(4) For detailed soldering specifications and information, refer to Texas Instruments Application Note 1112: DSBGA Wafer Level chip Scale
Package (SNVA009).
6.2 ESD Ratings VALUE UNIT
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±1000
V(ESD) Electrostatic discharge V
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) ±250
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN NOM MAX UNIT
VIN 2.5 5.5 V
Junction temperature, TJ−40 125 °C
Ambient temperature, TA(2) −40 85 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP =
125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the
part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).
6.4 Thermal Information LM3556
THERMAL METRIC(1) YFQ (DSBGA) UNIT
16 PINS
RθJA(2) Junction-to-ambient thermal resistance 60 °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2) Junction-to-ambient thermal resistance (RθJA) is taken from a thermal modeling result, performed under the conditions and guidelines
set forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102 mm × 76 mm × 1.6 mm with a 2 × 1
array of thermal vias. The ground plane on the board is 50 mm × 50 mm. Thickness of copper layers are 36 µm/18 µm/18 µm/36 µm
(1.5 oz/1 oz/1 oz/1.5 oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1 W.
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6.5 Electrical Characteristics
Unless otherwise specified, VIN = 3.6 V, typical limits apply for TA= 25°C, and minimum (MIN) and maximum (MAX) limits
apply over the full operating ambient temperature range (−40°C ≤TA≤+85°C).(1)(2)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
CURRENT SOURCE SPECIFICATIONS
1.425 1.575
1.5-A Flash, VOUT = 4 V 1.5 A
(–5%) (+5%)
ILED Current source accuracy 46.88-mA Torch, VOUT = 3.6 V 42.3 (−10%) 47 51.7 (+10%) mA
ILED = 1.5 A Flash 250 280 (+12%)
Current source regulation
VHR mV
voltage ILED = 46.88 mA Torch 150 172.5 (+15%)
ON Threshold 4.86 5 5.1
Output overvoltage protection
VOVP V
trip point OFF Threshold 4.75 4.88 4.99
STEP-UP DC-DC CONVERTER SPECIFICATIONS
RPMOS PMOS switch on-resistance IPMOS = 1 A 85 mΩ
RNMOS NMOS switch on-resistance INMOS = 1 A 65
−12% 1.7 12%
−12% 1.9 12%
ICL Switch current limit A
−10% 2.5 10%
−12% 3.1 12%
NTC comparator trip
VTRIP Configuration Register, bit [1] = 1 −6% 600 6% mV
threshold
Undervoltage lockout
UVLO Falling VIN 2.74 2.8 2.85 V
threshold
INTC NTC current −6% 75 6% µA
Input voltage flash monitor
VIVFM –3.2% 2.9 3.2% V
trip threshold
ƒSW Switching frequency 2.5 V ≤VIN ≤5.5 V 3.72 4 4.28 MHz
IQQuiescent supply current Device not switching Pass Mode 0.6 0.75 mA
Device disabled, EN = 0V
ISD Shutdown supply current 0.1 1.3 µA
2.5 V ≤VIN ≤5.5 V
Device disabled, EN = 2 V
ISB Standby supply current 2.5 4 µA
2.5 V ≤VIN ≤5.5 V
Flash-to-torch LED current TX low to high,
tTX 4 µs
settling time ILED = 1.5 A to 46.88 mA
ILED overshoot in external
IOS 0 mA to ITORCH 8%
indicator mode
ENABLE, STROBE, TORCH, TX VOLTAGE SPECIFICATIONS
VIL Input logic low 0 0.4
2.5 V ≤VIN ≤5.5 V V
VIH Input logic high 1.2 VIN
I2C-COMPATIBLE INTERFACE SPECIFICATIONS (SCL, SDA)
VIL Input logic low 0 0.4
2.5 V ≤VIN ≤4.2 V V
VIH Input logic high 1.2 VIN
VOL Output logic low ILOAD = 3 mA 400 mV
(1) Minimum and maximum limits are specified by design, test, or statistical analysis. Typical numbers are not verified, but do represent the
most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6 V and TA= 25°C.
(2) All voltages are with respect to the potential at the GND pin.
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SCL
SDA_IN
SDA_OUT
t5
t1
t4
t3
t2
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6.6 Timing Requirements MIN NOM MAX UNIT
t1SCL clock frequency 2.4 µs
t2Data in setup time to SCL high 100 ns
t3Data out stable after SCL low 0 ns
t4SDA low setup time to SCL low (start) 100 ns
t5SDA high hold time after SCL high (stop) 100 ns
Figure 1. I2C-Compatible Timing Diagram
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2.7 3.1 3.4 3.8 4.1 4.5 4.8 5.2 5.5
50
55
60
65
70
75
80
85
90
95
100
LED EFFICIENCY (%)
VIN (V)
TA=25°C
TA=85°C
TA=-40°C
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
IQ STANDBY (A)
VIN (V)
25°C
85°C
- 40°C
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5
60
64
68
72
76
80
84
88
92
96
100
EFFLED(%)
ILED(A)
VIN =4.2V
VIN =3.9V
VIN =3.6V
VIN =3.3V
VIN =3.0V
VIN =2.7V
2.7 3.1 3.4 3.8 4.1 4.5 4.8 5.2 5.5
0.340
0.348
0.355
0.363
0.370
0.378
0.385
0.393
0.400
ILED(A)
VIN (V)
TA=25°C
TA=85°C
TA=-40°C
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
1.40
1.45
1.50
1.55
1.60
ILED(A)
VIN(V)
TA = -40°C
TA = +25°C
TA = -+85°C
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
50
60
70
80
90
100
EFFLED(%)
VIN(V)
TA = -40°C
TA = +25°C
TA = +85°C
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6.7 Typical Characteristics
VLED = 3.6 V ILED = 1.5 A VLED = 3.6 V ILED = 1.5 A
Figure 2. Flash LED Current vs VIN Figure 3. Flash LED Efficiency vs VIN
VLED = 3 V ILED = 375 mA
VLED = 3.8 V
Figure 5. Torch LED Current vs VIN
Figure 4. Flash LED Efficiency vs Flash LED Current
VLED = 3 V EN = 1.8 V
Figure 6. Torch LED Efficiency vs VIN Figure 7. IQStandby vs VIN
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2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2
1.95
2.00
2.05
2.10
2.15
2.20
2.25
2.30
PEAK INPUT CURRENT (A)
VIN (V)
25°C
- 40°C
85°C
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
PEAK INPUT CURRENT (A)
VIN (V)
25°C
- 40°C
85°C
2.7 3.0 3.3 3.6 3.9 4.2 4.5
3.980
3.997
4.015
4.031
4.048
4.066
4.082
4.099
4.116
4.133
4.150
SWITCHING FREQUENCY (MHz)
VIN (V)
25°C
85°C
- 40°C
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2
1.64
1.68
1.72
1.76
1.80
1.84
1.88
1.92
PEAK INPUT CURRENT (A)
VIN (V)
25°C
- 40°C
85°C
VIN (V)
Iq SHUTDOWN (A)
1.000
0.1
0.01
0.001
2.7 3.1 3.5 3.9 4.3 4.7 5.1
85°C
25°C
-40°C
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
5.10
5.12
5.14
5.16
5.18
5.20
5.22
5.24
OVP (V)
VIN (V)
25°C
85°C
- 40°C
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Typical Characteristics (continued)
EN = 0 V
Figure 9. Variation of OVP With VIN
Figure 8. IQShutdown vs VIN
Current Limit = 1.7 A
Figure 10. Frequency With VIN and Over Temperature Figure 11. Input Current Limit Over Temperature and VIN
Current Limit = 1.9 A Current Limit = 2.5 A
Figure 12. Input Current Limit Over Temperature and VIN Figure 13. Input Current Limit Over Temperature and VIN
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40 ms/DIV
100 mV/
DIV
VOUT
200 mA/
DIV
IIN
ILED 200 mA/
DIV
400 s/DIV
1A/DIV
VIN 200 mV/
DIV
ILED
IIN
1A/DIV
100ms/DIV
2V/DIV
VOUT
500mA/
DIV
IIN
STROBE
ILED
2V/DIV
1A/DIV
100 ms/DIV
2V/DIV
VOUT
500 mA/
DIV
IIN
STROBE
ILED
2V/DIV
1A/DIV
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2
3.34
3.36
3.38
3.40
3.42
3.44
3.46
3.48
3.50
3.52
PEAK INPUT CURRENT (A)
VIN (V)
25°C
- 40°C
85°C
1 ms/DIV
1V/DIV
VOUT 1A/DIV
IIN
VIN
ILED
2V/DIV
1A/DIV
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Typical Characteristics (continued)
Current Limit = 1.7 A
Current Limit = 3.1 A
Figure 15. Start-Up Plot With Part In Boost Mode Current
Figure 14. Input Current Limit Over Temperature and VIN Limit
400 ms
400 ms
Figure 17. Strobe With Level-Triggered Signal
Figure 16. Strobe With Edge-Triggered Signal
Figure 18. Internal Indicator Operation Figure 19. Input Voltage Flash Monitor Report Mode With
Default Settings
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400 s/DIV
1A/DIV
VIN 200 mV/
DIV
ILED
IIN
1A/DIV
400 s/DIV
1A/DIV
VIN 200 mV/
DIV
ILED
IIN
1A/DIV
400 s/DIV
1A/DIV
VIN 200 mV/
DIV
ILED
IIN
1A/DIV
400 s/DIV
1A/DIV
VIN 200 mV/
DIV
ILED
IIN
1A/DIV
400 s/DIV
1A/DIV
VIN 200 mV/
DIV
ILED
IIN
1A/DIV
400 s/DIV
1A/DIV
VIN 200 mV/
DIV
ILED
IIN
1A/DIV
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Typical Characteristics (continued)
Figure 20. Input Voltage Flash Monitor Stop and Hold Mode Figure 21. Input Voltage Flash Monitor Down Mode With
With Default Settings Default Settings
0-mV Hysteresis 1/2 Step Filter Time
Figure 22. Input Voltage Flash Monitor Up and Down Mode Figure 23. Input Voltage Flash Monitor, Up and Down Mode
With Default Settings
256-µs Flash Ramp 1/2 Step Filter Time
0-mV Hysteresis 512-ms Filter Time
Figure 25. Input Voltage Flash Monitor, Up and Down Mode
Figure 24. Input Voltage Flash Monitor, Up and Down Mode
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40 s/DIV
VIN 200 mV/
DIV
ILED 200 mA/
DIV
400 s/DIV
500 mA/
DIV
VOUT
2V/DIV
TX
ILED
2V/DIV
1 s/DIV
500 mA/
DIV
VOUT 2V/DIV
TX
ILED
2V/DIV
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Typical Characteristics (continued)
Figure 27. Time Taken for LM3556 to Ramp from Torch to
Figure 26. Impact on LED Current With a TX Event Flash After TX Event
Figure 28. Transient Plot When VIN Stepped from 3 →2.9 V
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7 Detailed Description
7.1 Overview
The LM3556 is a high-power white LED flash driver capable of delivering up to 1.5 A into a single high-powered
LED. The device incorporates a 4-MHz constant-frequency synchronous current-mode PWM boost converter,
and a single high-side current source to regulate the LED current over the 2.5-V to 5.5-V input voltage range.
The LM3556 PWM converter switches and maintains at least VHR across the current source (LED). This
minimum headroom voltage ensures that the current source remains in regulation. If the input voltage is above
the LED voltage plus current source headroom voltage, the device does not switch, and turns the PFET on
continuously (Pass Mode). In Pass Mode the difference between (VIN −ILED × RPMOS) and the voltage across the
LED is dropped across the current source.
The LM3556 has three logic inputs including a hardware flash enable (STROBE), a hardware torch enable
(TORCH) used for external torch mode control and custom LED indication waveforms, and a flash interrupt input
(TX) designed to interrupt the flash pulse during high battery-current conditions. All three logic inputs have
internal 300-kΩ(typical) pulldown resistors to GND.
Additional features of the LM3556 include an internal comparator for LED thermal sensing via an external NTC
thermistor and an input voltage monitor that can reduce the Flash current (during low VIN conditions).
Control of the LM3556 is done via an I2C-compatible interface. This includes adjustment of the flash and torch
current levels, changing the flash time-out duration, changing the switch current limit, and enabling the NTC
block. Additionally, there are flag and status bits that indicate flash current time-out, LED overtemperature
condition, LED failure (open or short), device thermal shutdown, TX interrupt, and VIN undervoltage conditions.
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+
-
VOVP
PWM
Control
Thermal
Shutdown
+150°C
IN VREF
I2C
Interface
+
-
+
-
Error
Amplifier
Slope
Compensation
SDA
SCL
Control
Logic/
Registers
GND
OUT
LED
TEMP
TXSTROBETORCHENABLE
SW
65 m:
85 m:
Over Voltage
Comparator
+
-
NTC VTRIP
INTC
ILED
Soft-Start
+
-
4 MHz
Oscillator
+
-
UVLO Input Voltage
Flash Monitor
OUT-VHR
Current Sense/
Current Limit
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7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Power-Amplifier Synchronization (TX)
The TX pin is a power-amplifier synchronization input. It is designed to reduce the flash LED current and thus
limit the battery current during high battery-current conditions such as PA transmit events. When the LM3556 is
engaged in a flash event, and the TX pin is pulled high, the LED current is forced into Torch Mode at the
programmed torch current setting or shutdown. If the TX pin is then pulled low before the flash pulse terminates,
the LED current returns to the previous flash current level. At the end of the flash time-out, whether the TX pin is
high or low, the LED current turns off. The polarity of the TX input can be changed from active high to active low
through the Configuration Register (0x07) and can be disabled/enabled by setting the TX Enable bit in the
Enable Register (0x0A) to a '0'.
7.3.2 Input Voltage Flash Monitor (IVFM)
The LM3556 device can adjust the flash current based upon the voltage level present at the IN pin using an input
voltage flash monitor. Two adjustable thresholds (IVM-D and IVM-U) ranging from 2.9 V to 3.6 V in 100-mV
steps, and four different usage modes (Report Mode, Stop and Hold Mode, Adjust Down Only Mode, Adjust Up
and Down Mode), are provided. The Flags Register has the fault flag set when the input voltage crosses the
IVM-D value. In Report Mode, apart from the fault flag triggering, no action is taken on the LED current.
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Feature Description (continued)
Additionally, the IVM-D threshold sets the input voltage boundary that forces the LM3556 to either stop ramping
the flash current during start-up (Stop and Hold Mode) or to start decreasing the LED current during the flash
(Adjust Down Only Mode and Adjust Down and Up Mode). The IVM-U threshold sets the input voltage boundary
that forces the LM3556 to start ramping the flash current back up towards the target (Adjust Up and Down
Mode). The IVM-U threshold is equal to the IVM-D value plus the programmed hysteresis value also stored in the
Input Voltage Flash Monitor (IVFM) Mode Register (0x01).
To help prevent a premature current reduction, the LM3556 has four different filter timers that start once the input
voltage decreases below the IVM-D line. These filter times are set in the Silicon Revision and Filter Time
Register (0x00). For more information, refer to Input Voltage Flash Monitor (IVFM) Mode Register (0x01) and
Configuration Register (0x07).
7.3.3 Fault Protections
7.3.3.1 Fault Operation
Upon entering a fault condition, the LM3556 sets the appropriate flag in the Flags Register (0x0B), placing the
part into standby by clearing and locking the Torch Enable bit (TEN), Pre-Charge bit, and Mode bits (M1, M0) in
the Enable Register (0x0A), until the Flags Register (0x0B) is read back via I2C.
7.3.3.2 Flash Time-Out
The Flash time-out period sets the amount of time that the flash current is being sourced from the current source
(LED). The LM3556 has 8 time-out levels ranging 100 ms to 800 ms in 100-ms steps. The flash time-out period
is controlled in the Flash Features Register (0x08). Flash time-out only applies to the Flash Mode operation. The
mode bits are cleared upon a flash time-out.
7.3.3.3 Overvoltage Protection (OVP)
The output voltage is limited to typically 5 V (see VOVP in Electrical Characteristics . In situations such as an open
LED, the LM3556 device raises the output voltage in order to keep the LED current at its target value. When
VOUT reaches 5 V (typical), the overvoltage comparator trips and turns off the internal NFET. When VOUT falls
below the VOVP off threshold, the LM3556 begins switching again. The mode bits in the Enable Register (0x0A)
are not cleared upon an OVP.
7.3.3.4 Current Limit
The LM3556 features selectable inductor-current limits that are programmable through the Flash Features
Register (0x08) of the I2C-compatible interface. When the inductor-current limit is reached, the LM3556
terminates the charging phase of the switching cycle.
Because the current limit is sensed in the NMOS switch, there is no mechanism to limit the current when the
device operates in Pass Mode. In Boost Mode or Pass Mode, if VOUT falls below 2.3 V, the device stops
switching, and the PFET operates as a current source limiting the current to 200 mA. This prevents damage to
the LM3556 and excessive current draw from the battery during output short-circuit conditions. The mode bits in
the Enable Register (0x0A) are not cleared upon a current limit event.
Pulling additional current from the VOUT node during normal operation is not recommended.
7.3.3.5 NTC Thermistor Input (TEMP)
The TEMP pin serves as a threshold detector for negative temperature coefficient (NTC) thermistors. It interrupts
the LED current when the voltage at TEMP goes below the programmed threshold. The NTC threshold voltage is
adjustable from 200 mV to 900 mV in 100-mV steps. The NTC current is adjustable from 25 µA to 100 µA in 25-
µA steps. When an overtemperature event is detected, the LM3556 can be set to force the LED current from
Flash Mode into Torch Mode or into shutdown. These settings are adjusted via the NTC Settings Register (0x02),
and the NTC detection circuitry can be enabled or disabled via the Enable Register (0x0A). If enabled, the NTC
block turns on and off during the start and stop of a flash, torch, or indicator event. The NTC mode of operation is
set by adjusting the NTC Mode bit in the Configuration Register (0x07). See NTC Settings Register (0x02) for
more details. The mode bits in the Enable Register (0x0A) are cleared upon an NTC event.
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Feature Description (continued)
7.3.3.6 Undervoltage Lockout (UVLO)
The LM3556 has an internal comparator that monitors the voltage at IN and forces the LM3556 into shutdown if
the input voltage drops to 2.8 V. If the UVLO monitor threshold is tripped, the UVLO flag bit is set in the Flags
Register (0x0B). If the input voltage rises above 2.8 V, the device is available for operation until there is an I2C
read command initiated for the Flags Register (0x0B). Upon a read, the Flags Register is cleared, and normal
operation can resume. This feature can be disabled by writing a '0' to the UVLO EN bit in the Input Voltage Flash
Monitor (IVFM) Mode Register (0x01). The mode bits in the Enable Register (0x0A) are cleared upon a UVLO
event.
7.3.3.7 Thermal Shutdown (TSD)
When the LM3556 device’s die temperature reaches 150°C, the boost converter shuts down, and the NFET and
PFET turn off, as does the current source (LED). When the thermal shutdown threshold is tripped, a '1' gets
written to the corresponding bit of the Flags Register (0x0B) (TSD bit), and the device goes into standby. The
LM3556 can only restart after the Flags Register (0x0B) is read, clearing the fault flag. Upon restart, if the die
temperature is still above 150°C, the device resets the fault flag and re-enters standby. The mode bits in the
Enable Register (0x0A) are cleared upon a TSD.
7.3.3.8 LED and/or VOUT Fault
The LED fault flag in the Flags Register (0x0B) reads back a '1' if the part is active in Flash Mode or Torch Mode,
and the LED output or the VOUT node experiences a short condition. The LM3556 determines an LED open
condition if the OVP threshold is crossed at the OUT pin while the device is in Flash or Torch Mode. An LED
short condition is determined if the voltage at LED goes below 500 mV (typical) while the device is in either
Torch or Flash Mode. There is a delay of 256-μs deglitch time before the LED flag is valid, and 2.048 ms before
the VOUT flag is valid. This delay is the time between when the flash or torch current is triggered and when the
LED voltage and the output voltage are sampled. The LED flag can only be reset to '0' by removing power to the
LM3556, or by reading back the Flags Register (0x0B). The mode bits in the Enable Register (0x0A) are cleared
upon an LED and/or VOUT fault.
7.4 Device Functional Modes
7.4.1 Start-Up (Enabling The Device)
Turnon of the LM3556 Torch and Flash Modes can be done through the Enable Register (0x0A). On start-up,
when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers 200 mA
(typical) to the output capacitor. During this time the current source (LED) is off. When the voltage across the
output capacitor reaches 2.2 V (typical) the current source turns on. At turnon the current source steps through
each FLASH or TORCH level until the target LED current is reached. This gives the device a controlled turnon
and limits inrush current from the VIN supply.
7.4.2 Pass Mode
The LM3556 starts up in Pass Mode and stays there until Boost Mode is needed to maintain regulation. If the
voltage difference between VOUT and VLED falls below VHR, the device switches to Boost Mode. In Pass Mode the
boost converter does not switch, and the synchronous PFET fully turns on bringing VOUT up to (VIN −ILED ×
RPMOS). In Pass Mode the inductor current is not limited by the peak current limit. In this situation the output
current must be limited to 2 A.
7.4.3 Flash Mode
In Flash Mode, the LED current source (LED) provides 16 target current levels from 93.75 mA to 1500 mA. The
Flash currents are adjusted via the Current Control Register (0x09). Flash mode is activated by the Enable
Register (0x0A), or by pulling the STROBE pin HIGH. Once the Flash sequence is activated the current source
(LED) ramps up to the programmed Flash current by stepping through all current steps until the programmed
current is reached.
When the device is enabled in Flash Mode through the Enable Register, all mode bits in the Enable Register are
cleared after a flash time-out event.
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Device Functional Modes (continued)
Data can be written to the mode bits (bits[1:0]) in Enable Register (0x0A) only after the flash has ramped down to
the desired value, and VOUT has decayed.
Table 1 shows the I2C commands and the state of the mode bits, if the STROBE pin is used to enable the Flash
Mode.
Table 1. I2C Commands and the State of the Mode Bits
ENABLE AND CONFIGURATION STATUS OF MODE BITS IN THE ENABLE REGISTER AFTER
MODE CHANGE REQUIRED REGISTER SETTING (0x0A=Enable A FLASH
Register, 0x07=Configuration Register)
Using edge-triggered STROBE to Flash 0x0A = 0x23; 0x07 = 0x78 (default setting) Mode bits are cleared after a single flash. To reflash, 0x23 has to
be written to 0x0A.
Using level-triggered STROBE to Flash 0x0A = 0x23; 0x07 = 0xF8 Mode bits are cleared after a single flash. To reflash, 0x23 has to
be written to 0x0A.
Part is required to go from external TORCH 0x0A = 0x33; 0x07 = 0x78 (default setting) Mode bits are cleared after a single flash. To reflash, 0x33 has to
Mode to external STROBE mode using be written to 0x0A.
edge-triggered STROBE
Part is required to go from external TORCH 0x0A = 0x33; 0x0 7= 0xF8 Mode bits are cleared only if the part has an internal flash time-
Mode to external STROBE mode using out event happening before the STROBE level goes low. To re-
Level Triggered STROBE flash, 0x33 has to be written to 0x0A. If the STROBE level goes
low before an internal flash time-out event, then mode bits are not
cleared.
7.4.4 Torch Mode
In Torch Mode, the current source (LED) is programmed via the Current Control Register (0x09). Torch Mode is
activated by the Enable Register (0x0A) or by the hardware TORCH input. Once the Torch Mode is enabled the
current source ramps up to the programmed torch current level. The ramp-up and ramp-down times are
independently adjustable via the Torch Ramp Time Register (0x06). Torch Mode is not affected by flash timeout.
7.4.5 Indicator Mode
This mode has two options: the Internal Indicator Mode and the External Indicator mode. Both these modes are
activated by the Configuration Register (0x07) in addition to the Enable Register (0x0A).
In the Internal Indicator Mode, the current source (LED) can be programmed to 8 different intensity levels, with
current values being 1/8th the values in Current Control Register (0x09) bits [6:4]. The ramp-up, ramp-down, the
pulse time, number of blanks and periods of the desired output current can be independently controlled via the
Indicator Ramp Time Indicator (0x03),Indicator Blinking Register (0x04) and the Indicator Period Count Register
(0x05).
In the External Indicator Mode, the current source (LED) is controlled via the TORCH pin. An external PWM
signal can be input to the part via the TORCH pin to choose any one of the 8 available intensity settings (bits
[6:4] of the Current Control Register (0x09)) for the current source (LED).
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SDA
Start Condition Stop Condition
SCL S P
SCL
SDA
data
change
allowed
data
valid data
change
allowed
data
valid data
change
allowed
LM3556
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SNVS796D –AUGUST 2011–REVISED OCTOBER 2015
7.5 Programming
7.5.1 I2C-Compatible Interface
7.5.1.1 Data Validity
The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, state of
the data line can only be changed when SCL is LOW.
Figure 29. Data Validity Diagram
A pullup resistor between the controller's VIO line and SDA must be greater than [(VIO – VOL) / 3mA] to meet the
VOL requirement on SDA. Using a larger pullup resistor results in lower switching current with slower edges, while
using a smaller pullup results in higher switching currents with faster edges.
7.5.1.2 Start and Stop Conditions
START and STOP conditions classify the beginning and the end of the I2C session. A START condition is
defined as the SDA signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined
as the SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and
STOP conditions. The I2C bus is considered to be busy after a START condition and free after a STOP condition.
During data transmission, the I2C master can generate repeated START conditions. First START and repeated
START conditions are equivalent, function-wise.
Figure 30. Start and Stop Conditions
7.5.1.3 Transferring Data
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each
byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated by the
master. The master releases the SDA line (HIGH) during the acknowledge clock pulse. The LM3556 pulls down
the SDA line during the 9th clock pulse, signifying an acknowledge. The LM3556 generates an acknowledge
after each byte is received. There is no acknowledge created after data is read from the LM3556.
After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (R/W). The LM3556 7-bit address is 0x63. For the eighth bit, a '0' indicates
a WRITE and a '1' indicates a READ. The second byte selects the register to which the data will be written. The
third byte contains data to write to the selected register.
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R/W
Bit 0
1
Bit 1
1
Bit 2
0
Bit 3
0
Bit 4
0
Bit 5
1
Bit 7 1
Bit 6
MSB LSB
I2C Slave Address (chip address)
start msb Chip Address lsb w ack msb Register Add lsb ack msb DATA lsb ack stop
ack from slave ack from slave ack from slave
SCL
SDA
start Id = 63h w ack addr = 0Ah ack ackData = 03h stop
LM3556
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Programming (continued)
W = Write (SDA = '0')
R = Read (SDA = '1')
Ack = Acknowledge (SDA Pulled Down By Either Master Or Slave)
ID= Chip Address, 63h For LM3556
Figure 31. Write Cycle
7.5.1.4 I2C-Compatible Chip Address
The device address for the LM3556 is 1100011 (63). After the START condition, the I2C-compatible master
sends the 7-bit address followed by an eighth read or write bit (R/W). R/W = 0 indicates a WRITE and R/W = 1
indicates a READ. The second byte following the device address selects the register address to which the data
will be written. The third byte contains the data for the selected register.
Figure 32. I2C-Compatible Device Address
7.5.1.5 Transferring Data
Every byte on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte
of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is
generated by the master. The master releases SDA (HIGH) during the 9th clock pulse. The LM3556 pulls down
SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each byte has
been received.
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7.6 Register Maps
7.6.1 Register Descriptions
REGISTER NAME INTERNAL HEX ADDRESS POWER ON/RESET VALUE
Silicon Revision and Filter Time Register 0x00 0x04
IVFM Mode Register 0x01 0x80
NTC Settings Register 0x02 0x12
Indicator Ramp Time Register 0x03 0x00
Indicator Blinking Register 0x04 0x00
Indicator Period Count Register 0x05 0x00
Torch Ramp Time Register 0x06 0x00
Configuration Register 0x07 0x78
Flash Features Register 0x08 0xD2
Current Control Register 0x09 0x0F
Enable Register 0x0A 0x00
Flags Register 0x0B 0x00
7.6.1.1 Silicon Revision and Filter Time Register (0x00)
Table 2. Silicon Revision and Filter Time Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
RFU RFU RFU IVFM Filter Times Bits available for Silicon Revision
'00' = 1/2 of the Current Step Time Current Value = '100'
'01' = 256 µs
'10' =512 µs
'11' = 1024 µs
7.6.1.2 Input Voltage Flash Monitor (IVFM) Mode Register (0x01)
Table 3. Input Voltage Flash Monitor (IVFM) Mode Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
1 = UVLO EN Hysteresis Level IVM-D (Down) Threshold IVFM Adjust Mode
(default) 00 = 50 mV (default) 000 = 2.9 V (default) 00 = Report Mode (default)
01 = 100 mV 001 = 3 V 01 = Stop and Hold Mode
10 = 150 mV 010 = 3.1 V 10 = Down Mode
11 = Hysteresis Disabled 011 = 3.2 V 11 = Up and Down Mode
100 = 3.3 V
101 = 3.4 V
110 = 3.5 V
111 = 3.6 V
00 = Report Mode Sets IVFM flag in Flags Register upon crossing IVM-D line Only. Does not adjust current.
01 = Stop and Hold Mode Stops current ramp and holds the level for the remaining flash if VIN crosses IVM-D
Line. Sets IVFM flag in Flags Register upon crossing IVM-D line.
10 = Down Mode Adjusts current down if VIN crosses IVM-D Line and stops decreasing once VIN rises above the
IVM-D line plus the IVFM hystersis setting. The LM3556 decreases the current throughout the flash
pulse anytime the input voltage falls below the IVM-D line, and not just once. The flash current does
not increase again until the next flash. Sets IVFM flag in Flags Register upon crossing IVM-D Line.
11 = Up and Down Mode Adjusts current down if VIN crosses IVM-D Line and adjusts current up if VIN rises
above the IVM-D line plus the IVFM hystersis setting. In this mode, the current continually adjusts
with the rising and falling of the input voltage throughout the entire flash pulse. Sets IVFM flag in
Flags Register upon crossing IVM-D Line.
UVLO EN If enabled and VIN drops below 2.8 V, the LM3556 enters standby and sets the UVLO flag in the
Flags Register. Enabled = ‘1’, Disabled = ‘0’
IVM-U = IVM-D + IVFM Hysteresis
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IVM-D
IVM-U
tfilter
VIN
ILED
t
0 mA
IFLASH
tfilter tfilter
IVM-D
IVM-U
tfilter
VIN
ILED
t
0 mA
IFLASH
IVM-D
IVM-U
tfilter tfilter
VIN
ILED
t
0 mA
IFLASH
LM3556
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Figure 33. Stop and Hold Mode
Figure 34. Adjust Down-Only Mode
Figure 35. Adjust Up and Down Mode
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VIN
VTRIP Control
Logic
NTC Control Block
TEMP INTC
NTC +
-
LM3556
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7.6.1.3 NTC Settings Register (0x02)
Table 4. NTC Settings Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
RFU RFU NTC Event NTC Trip Thresholds NTC Bias Current Level
Level 000 = 200 mV 00 = 25 µA
0 = Go to 001 = 300 mV 01 = 50 µA
standby 010 = 400 mV 10 = 75 µA (default)
(default) 011 = 50 mV 11 = 100 µA
1 = Reduce 100 = 600 mV (default)
to minimum 101 = 700 mV
torch current 110 = 800 mV
111 = 900 mV
Figure 36. NTC Control Block
The TEMP node is connected to an NTC resistor as shown in Figure 36 above. A constant current source from
the input is connected to this node. Any change in the voltage because of a change in the resistance of the NTC
resistor is compared to a set VTRIP. The trip thresholds are selected by Bits[4:2] of the NTC Register. The output
of the Control Logic upon an NTC trip is selected through Bit[5].
7.6.1.4 Indicator Ramp Time Indicator (0x03)
Table 5. Indicator Ramp Time Indicator Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
RFU RFU Indicator Ramp-Up Time (tR) Indicator Ramp-Down Time (tF)
000 = 16 ms (default) 000 = 16 ms (default)
001 = 32 ms 001 = 32 ms
010 = 64 ms 010 = 64 ms
011 = 128 ms 011 = 128 ms
100 = 256 ms 100 = 256 ms
101 = 512 ms 101 = 512 ms
110 = 1.024 s 110 = 1.024 s
111 = 2.048 s 111 = 2.048 s
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tBLANK tPERIOD
tPERIOD
ITORCH
tBLANK
tRtF
tPULSE
tPULSE
tPERIOD
tRtF
tPULSE
tPULSE
tPERIOD
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7.6.1.5 Indicator Blinking Register (0x04)
Table 6. Indicator Blinking Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
NBLANK Pulse Time (tPULSE)
0000 = 0 (default) 0000 = 0 (default)
0001 = 1 0001 = 32 ms
0010 = 2 0010 = 64 ms
0011 = 3 0011 = 92 ms
0100 = 4 0100 = 128 ms
0101 = 5 0101 = 160 ms
0110 = 6 0110 = 196 ms
0111 = 7 0111 = 224 ms
1000 = 8 1000 = 256 ms
1001 = 9 1001 = 288 ms
1010 = 10 1010 = 320 ms
1011 = 11 1011 = 352 ms
1100 = 12 1100 = 384 ms
1101 = 13 1101 = 416 ms
1110 = 14 1110 = 448 ms
1111 = 15 1111 = 480 ms
7.6.1.6 Indicator Period Count Register (0x05)
Table 7. Indicator Period Count Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
RFU RFU RFU RFU RFU NPERIOD
000 = 0 (default)
001 = 1
010 = 2
011 = 3
100 = 4
101 = 5
110 = 6
111 = 7
Figure 37. Indicator Usage
1. Number of periods (tPERIOD = tR+ tF+ tPULSE × 2)
2. Active Time (tACTIVE = tPERIOD × NPERIOD)
3. Blank Time (tBLANK = tACTIVE × NBLANK)
Figure 38. Single Pulse With Dead Time
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tBLANK
tPERIOD tPERIOD tPERIOD
tACTIVE
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Figure 39. Multiple Pulse With Dead Time
7.6.1.7 Torch Ramp Time Register (0x06)
Table 8. Torch Ramp Time Register
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
RFU RFU Torch Ramp-Up Time Torch Ramp-Down Time
000 = 16 ms (default) 000 = 16 ms (default)
001 = 32 ms 001 = 32 ms
010 = 64 ms 010 = 64 ms
011 = 128 ms 011 = 128 ms
100 = 256 ms 100 = 256 ms
101 = 512 ms 101 = 512 ms
110 = 1.024 s 110 = 1.024 s
111 = 2.048 s 111 = 2.048 s
7.6.1.8 Configuration Register (0x07)
Table 9. Configuration Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Strobe Pin Torch Pin TX Pin TX Event Level IVFM Enable NTC Mode Indicator Mode
Strobe Usage Polarity Polarity Polarity 0 = Off 0 = Disabled 0 = Normal 0 = Internal
0 = Edge 0 = Active Low 0 = Active Low 0 = Active Low 1 = Torch Current (default) (default) (default)
(default) 1 = Active 1 = Active 1 = Active (default) 1 = Enabled 1 = Monitor 1 = External
1 = Level High (default) High (default) High (default)
Strobe Usage Level or edge. Flash follows strobe timing if Level and internal timing if edge.
Strobe Polarity Active high or active low select.
Torch Polarity Active high or active low select.
TX Polarity Active high or active low select.
TX Event Level Transition to torch current level or off setting if TX event occurs.
The TX Event Level off setting is designed to force a shutdown only during a flash event. When
Torch or Indicator Mode is enabled, and a TX event occurs with the TX event level set to Off , the
LM3556 does not shut down. The TX flag bit (bit7 in the Table 14) is set, and the mode bits (bit0
and bit1 in Table 12) get locked out until the fault register is cleared via an I2C read. Because a TX
event is periodic and frequently occurring, clearing the fault register becomes more difficult.
Depending on the I2C read/write speed and TX event frequency, it may be necessary to set the TX
enable bit (bit6 in the Table 12) to a '0' before clearing the fault register to prevent future flag sets.
IVFM Enable Enables input voltage flash monitoring.
NTC Mode Monitor Mode (report only) or Normal Mode (reduce current or shutdown).
Indicator Mode Externally generated via TORCH pin or internally generated PWM.
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7.6.1.9 Flash Features Register (0x08)
Table 10. Flash Features Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Inductor Current Limit Flash Ramp Time Flash Time-Out Time
00 =1.7 A 000 = 256 µs 000 = 100 ms
01 = 1.9 A 001 = 512 µs 001 = 200 ms
10 = 2.5 A 010 = 1.024 ms (default) 010 = 300 ms (default)
11 = 3.1 A (default) 011 = 2.048 ms 011 = 400 ms
100 = 4.096 ms 100 = 500 ms
101 = 8.192 ms 101 = 600 ms
110 = 16.384 ms 110 = 700 ms
111 = 32.768 ms 111 = 800 ms
7.6.1.10 Current Control Register (0x09)
Table 11. Current Control Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
RFU Torch Current Flash Current
000 = 46.88 mA (default) 0000 = 93.75 mA
001 =93.75 mA 0001 = 187.5 mA
010 =140.63 mA 0010 = 281.25 mA
011 = 187.5 mA 0011 = 375 mA
100 =234.38 mA 0100 = 468.75 mA
101 = 281.25 mA 0101 = 562.5mA
110 = 328.13 mA 0110 = 656.25 mA
111 =375 mA 0111 = 750 mA
1000 = 843.75 mA
1001 = 937.5 mA
1010 = 1031.25 mA
1011 = 1125 mA
1100 = 1218.75 mA
1101 = 1312.5 mA
1110 = 1406.25 mA
1111 = 1500 mA (default)
7.6.1.11 Enable Register (0x0A)
Table 12. Enable Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
TX Pin Enable STROBE Pin TORCH Pin PreCharge Mode Pass-Mode Mode Bits: M1, M0
NTC Enable 0 = Disabled Enable Enable Enable Only Enable 00 = Standby (default)
0 = Disabled (default) 0 = Disabled 0 = Disabled 0 = Normal 0 = Normal 01 = Indicator
(default) 1 = Enabled (default) (default) (default) (default) 10 = Torch
1 = Enabled 1 = Enabled 1 = Enabled 1 = PreCharge 1 = Pass Only 11 = Flash
NTC EN Enables NTC block.
TX EN Allows TX events to change the current.
Strobe EN Enables STROBE pin to start a flash event.
Torch EN Enables TORCH pin to start a torch event.
PreCharge Mode EN Enables Pass Mode to pre-charge the output cap.
Pass-Only Mode EN Only allows Pass Mode and disallows Boost Mode.
If Pass-Only Mode is enabled during any LED mode (Indicator, Torch or Flash), it remains enabled
until the LM3556 enters the standby state regardless of whether the Pass-Only Mode bit is reset or
not during the following command.
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I2C Flash I2C Stop STROBE
I2C
Bus
ILED ILED
TORCH
ILED
I2C Controlled Flash Start and Stop
Delay Times Strobe Controlled Flash Start and
Stop Delay Times
External Indicator Start and Stop
Delay Times
Using Torch Pin
ILED
Flash time-out
tatbtctd
tetf
tgth
TX event ± Start and Stop
Delay Times
TX
EDGE TRIG
STROBE
LM3556
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7.6.1.11.1 Enable Register Mode Bits
00–Standby Off
01–Indicator Sets Indicator Mode. Default Indicator Mode uses external pattern on TORCH pin.
10–Torch Sets Torch Mode with ramping. If Torch EN = 0, Torch starts after I2C-compatible command.
11–Flash Sets Flash Mode with ramping. If Strobe EN = 0, Flash starts after I2C-compatible command.
7.6.1.11.2 Control Logic Delays
Figure 40. Control Logic Delays
Table 13. Control Logic Delay Timing
DELAY EXPLANATION TIME
taTime for the LED current to start ramping up after an I2C Write command. 554 µs
tbTime for the LED current to start ramping down after an I2C Stop command. 32 µs
tcTime for the LED current to start ramping up after the STROBE pin is raised high. 400 µs
tdTime for the LED current to start ramping down after the STROBE pin is pulled low. 16 µs
teTime for the LED current to start ramping up after the TORCH pin is raised high. 300 µs
tfTime for the LED current to start ramping down after the TORCH pin is pulled low. 16 µs
tgTime for the LED current to start ramping down after the TX pin is pulled high. 3 µs
thTime for the LED current to start ramping up after the TX pin is pulled low, provide the part has 2 µs
not timed out in Flash Mode.
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7.6.1.12 Flags Register (0x0B)
Table 14. Flags Register Description
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
TX Event NTC Trip IVFM UVLO OVP LED or VOUT Thermal Flash Time-out
0 = Default 0 = Default 0 = Default 0 = Default 0 = Default Short Fault Shutdown 0 = Default
0 = Default 0 = Default
TX Event Flag TX event occurred.
NTC Trip Flag NTC threshold crossed.
IVFM Flag IVFM block reported and/or adjusted LED current.
UVLO Fault UVLO threshold crossed.
OVP Flag Overvoltage Protection tripped. Open output capacitor or open LED.
LED Short Fault LED short detected.
Thermal Shutdown Fault LM3556 die temperature reached thermal shutdown value.
Time-Out Flag Flash Timer tripped.
NOTE
Faults require a read-back of the Flags Register to resume operation. Flags report an
event occurred, but do not inhibit future functionality. A read-back of the Flags Register
updates again if the fault or flags are still present upon a restart.
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Product Folder Links: LM3556
IN OUT
TEMP
SW
ENABLE
TORCH
TX
SDA
SCL GND
1 PH
10 PF10 PF
STROBE
LED
Flash
LED
2.5 V to 5.5 V
LM3556
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SNVS796D –AUGUST 2011–REVISED OCTOBER 2015
8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM3556 can drive one flash LED at currents up to 1.5 A. The 4-MHz DC-DC boost regulator allows for the
use of small-value discrete external components.
8.2 Typical Application
Figure 41. LM3556 Typical Application
8.2.1 Design Requirements
Example requirements based on default register values are listed in Table 15:
Table 15. Design Parameters
DESIGN PARAMETER EXAMPLE VALUE
Input Voltage Range 2.5 V to 5.5 V
Brightness Control I2C Register
Output current 1.5 A
LED Configuration 1 Flash LED
Switching frequency 4 MHz (typical)
8.2.2 Detailed Design Procedure
8.2.2.1 Output Capacitor Selection
The LM3556 is designed to operate with a ceramic output capacitor of at least 10 µF. When the boost converter
is running, the output capacitor supplies the load current during the boost converter's on-time. When the NMOS
switch turns off, the inductor energy is discharged through the internal PMOS switch, supplying power to the load
and restoring charge to the output capacitor. This causes a sag in the output voltage during the on-time and a
rise in the output voltage during the off-time. The output capacitor is therefore chosen to limit the output ripple to
an acceptable level depending on load current and input/output voltage differentials and also to ensure the
converter remains stable.
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Product Folder Links: LM3556
PEAK
ILOAD
I
=KxL
I+'where L=I'IN xV ( )
INOUT - VV
OUTSW VxLxfx2
IN
OUT
V
V
where IN INOUT
( )
- VV
x
V
L=I'
OUTSW V
x
L
x
f
x
2
I+
xR=V L
ESRESR '
'VxI OUTLED VIN ¹
·
©
§
Q=V'( )
INOUTLED - VVxI
OUTOUTSW CxVxf
LM3556
SNVS796D –AUGUST 2011–REVISED OCTOBER 2015
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Larger capacitors (for example, a 22-µF capacitor) or capacitors in parallel may be used if lower output voltage
ripple is desired. To estimate the output voltage ripple, considering the ripple due to capacitor discharge (ΔVQ)
and the ripple due to the capacitors equivalent series resistance (ESR) (ΔVESR), use Equation 1 and Equation 2.
For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:
(1)
The output voltage ripple due to the ESR of the output capacitor is found by:
(2)
In ceramic capacitors the ESR is very low so the assumption is that 80% of the output voltage ripple is due to
capacitor discharge and 20% from ESR. Table 16 lists different manufacturers for various output capacitors and
their case sizes suitable for use with the LM3556.
8.2.2.2 Input Capacitor Selection
Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching
of the LM3556 device’s boost converter and reduces noise on the boost converter's input terminal that can feed
through and disrupt internal analog signals. In the Figure 41 a 10-µF ceramic input capacitor works well. It is
important to place the input capacitor as close as possible to the LM3556’s input (IN) pin. This reduces the series
resistance and inductance that can inject noise into the device due to the input switching currents. Table 16 lists
various input capacitors recommended for use with the LM3556.
Table 16. Recommended Input/Output Capacitors (X5R/X7R Dielectric)
MANUFACTURER PART NUMBER VALUE CASE SIZE VOLTAGE RATING
TDK Corporation C1608JB0J106M 10 µF 0603 (1.6 mm × 0.8 mm × 0.8 mm) 6.3 V
TDK Corporation C2012JB1A106M 10 µF 0805 (2 mm × 1.25 mm × 1.25 mm) 10 V
Murata GRM188R60J106M 10 µF 0603 (1.6 mm x 0.8 mm x 0.8 mm) 6.3 V
Murata GRM21BR61A106KE19 10 µF 0805 (2 mm × 1.25 mm × 1.25 mm) 10 V
8.2.2.3 Inductor Selection
The LM3556 is designed to use a 1-µH or 0.47-µH inductor. Table 17 lists various inductors and their
manufacturers that work well with the LM3556. When the device is boosting (VOUT > VIN) the inductor is typically
the largest area of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest possible series
resistance is important. Additionally, the saturation rating of the inductor must be greater than the maximum
operating peak current of the LM3556. This prevents excess efficiency loss that can occur with inductors that
operate in saturation. For proper inductor operation and circuit performance, ensure that the inductor saturation
and the peak current limit setting of the LM3556 are greater than IPEAK in Equation 3:
where
• ƒSW = 4 MHz
• Efficiency can be found in Typical Characteristics. (3)
Table 17. Recommended Inductors
MANUFACTURER L PART NUMBER DIMENSIONS (L × W × H) ISAT RDC
TOKO 1 µH FDSD0312 3 mm x 3 mm x 1.2 mm 4.5 A 43 mΩ
TOKO 1 µH DFE252010C 2.5 mm × 2 mm × 1 mm 3.4 A 60 mΩ
TOKO 1 µH DFE252012C 2.5 mm × 2 mm × 1.2 mm 3.8 A 45 mΩ
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2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
50
60
70
80
90
100
EFFLED(%)
VIN(V)
TA = -40°C
TA = +25°C
TA = +85°C
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5
60
64
68
72
76
80
84
88
92
96
100
EFFLED(%)
ILED(A)
VIN =4.2V
VIN =3.9V
VIN =3.6V
VIN =3.3V
VIN =3.0V
VIN =2.7V
ex
( ) C25
R=TR °298
1
273+C°T 1
E-¹
·
©
§
LM3556
www.ti.com
SNVS796D –AUGUST 2011–REVISED OCTOBER 2015
8.2.2.4 NTC Thermistor Selection
The TEMP pin is a comparator input for flash LED thermal sensing. NTC mode is intended to monitor an external
thermistor which monitors LED temperature and prevents LED overheating. An internal comparator checks the
voltage on the TEMP pin against the trip point programmed in the NTC Settings Register (0x02). The thermistor
is driven by an internally regulated current source, and the voltage on the TEMP pin is related to the source
current and the NTC resistance.
NTC thermistors have a temperature to resistance relationship of:
where
•βis given in the thermistor datasheet
• R25°C is the thermistor's value at 25°C. (4)
8.2.3 Application Curves
VLED = 3.6 V ILED = 1.5 A VLED = 3.8 V
Figure 42. Flash LED Efficiency vs VIN Figure 43. Flash LED Efficiency vs Flash LED Current
9 Power Supply Recommendations
The LM3556 is designed to operate from an input supply range of 2.5 V to 5.5 V. This input supply must be well
regulated and provide the peak current required by the LED configuration and inductor selected.
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10 Layout
10.1 Layout Guidelines
The high switching frequency and large switching currents of the LM3556 make the choice of layout important.
The following steps should be used as a reference to ensure the device is stable and maintains proper LED
current regulation across its intended operating voltage and current range.
1. Place CIN on the top layer (same layer as the device), as close as possible to the device. The input capacitor
conducts the driver currents during the low-side MOSFET turnon and turnoff and can see current spikes over
1 A in amplitude. Connecting the input capacitor through short, wide traces to both the IN and GND pins
reduces the inductive voltage spikes that occur during switching which can corrupt the VIN line.
2. Place COUT on the top layer (same layer as the device) and as close as possible to the OUT and GND pins.
The returns for both CIN and COUT must come together at one point, as close as possible to the GND pin.
Connecting COUT through short, wide traces reduces the series inductance on the OUT and GND pins that
can corrupt the VOUT and GND lines and cause excessive noise in the device and surrounding circuitry.
3. Connect the inductor on the top layer close to the SW pin. There must be a low-impedance connection from
the inductor to SW due to the large DC inductor current, and at the same time the area occupied by the SW
node must be small to reduce the capacitive coupling of the high dV/dt present at SW that can couple into
nearby traces.
4. Logic traces must not be routed near the SW node to avoid any capacitively coupled voltages from SW onto
any high-impedance logic lines such as TORCH, STROBE, HWEN, TEMP, SDA, and SCL. A good approach
is to insert an inner layer GND plane underneath the SW node and between any nearby routed traces. This
creates a shield from the electric field generated at SW.
5. Terminate the flash LED cathodes directly to the GND pin of the LM3556. If possible, route the LED returns
with a dedicated path to keep the high amplitude LED currents out of the GND plane. For flash LEDs that are
routed relatively far away from the device, sandwich the forward and return current paths over the top of
each other on two layers. This helps reduce the inductance of the LED current paths.
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11 Device And Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2 Documentation Support
11.2.1 Related Documentation
For additional information, see the following:
TI Application Note DSBGA Wafer Level Chip Scale Package (SNVA009)
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.6 Glossary
SLYZ022 —TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
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12 Mechanical, Packaging, And Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
Copyright © 2011–2015, Texas Instruments Incorporated Submit Documentation Feedback 33
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PACKAGE OPTION ADDENDUM
www.ti.com 10-Dec-2020
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead finish/
Ball material
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM3556TME/NOPB ACTIVE DSBGA YFQ 16 250 RoHS & Green SNAGCU Level-1-260C-UNLIM -40 to 85 D36
LM3556TMX/NOPB ACTIVE DSBGA YFQ 16 3000 RoHS & Green SNAGCU Level-1-260C-UNLIM -40 to 85 D36
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
PACKAGE OPTION ADDENDUM
www.ti.com 10-Dec-2020
Addendum-Page 2
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM3556TME/NOPB DSBGA YFQ 16 250 178.0 8.4 1.78 1.78 0.76 4.0 8.0 Q1
LM3556TMX/NOPB DSBGA YFQ 16 3000 178.0 8.4 1.78 1.78 0.76 4.0 8.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 28-Jun-2018
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM3556TME/NOPB DSBGA YFQ 16 250 210.0 185.0 35.0
LM3556TMX/NOPB DSBGA YFQ 16 3000 210.0 185.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 28-Jun-2018
Pack Materials-Page 2
MECHANICAL DATA
YFQ0016xxx
www.ti.com
TMD16XXX (Rev A)
E
0.600±0.075
D
A
. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
NOTES:
4215081/A 12/12
D: Max =
E: Max =
1.69 mm, Min =
1.64 mm, Min =
1.63 mm
1.58 mm
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