LM3554TMX/NOPB - Texas Instruments High-Performance Analog

HWEN

ENVM/TX2/GPIO2

4.5 mm

5.1 mm

/TORCH/GPIO1

HWEN

SCL

SDA

STROBE

TX1/TORCH/

GPIO1

IN OUT

GND

LED1

LED2

LEDI/NTC

SW 4.5V or 5V DC Power Rail

Flash

LEDs

Indicator

LED

ENVM/TX2

/GPIO

VBIAS

D1D2

LM3554

0.1 PF

RBIAS

4.7 PF4.7 PF

2.2 PH

2 k:

Thermistor

.5V ± 5.5V

LM3554

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SNVS549B –JUNE 2009–REVISED MAY 2013

LM3554 Synchronous Boost Converter with 1.2A Dual High Side LED Drivers and I

C-

Compatible Interface

Check for Samples: LM3554

1FEATURES

2• Dual High Side Current Sources • 400kHz I2C-Compatible Interface

• Grounded Cathode Allowing for Better Heat • 16-Bump (1.7mm × 1.7mm × 0.6mm) DSBGA

Sinking and LED Routing APPLICATIONS

• >90% Efficiency • Camera Phone LED Flash Controller

• Ultra-Small Solution Size: < 23mm2

• Class D Audio Amplifier Power

• Four Operating Modes: Torch, Flash, LED

Indicator and Voltage Output • LED Current Source Biasing

• Accurate and Programmable LED Current from DESCRIPTION

37.5mA to 1.2A The LM3554 is a 2MHz fixed frequency, current

• Programmable 4.5V or 5.0V Constant Output mode synchronous boost converter. The device is

Voltage designed to operate as a dual 600mA (1.2A total)

• Hardware Flash and Torch Enable constant-current driver for high-current white LEDs, or

• LED Thermal Sensing and Current Scaleback as a regulated 4.5V or 5V voltage source.

• Software Selectable Input Voltage Monitor The dual high-side current sources allow for

• Programmable Flash Timeout grounded cathode LED operation. An adaptive

regulation method ensures the current source for

• Dual Synchronization Inputs for RF Power each LED remains in regulation and maximizes

Amplifier Pulse Events efficiency.

• Open and Short LED Detection

• Active High Hardware Enable for Protection

Against System Faults

Typical Application Circuits

Figure 1. Typical Application Circuit Figure 2. Example Layout

1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2All trademarks are the property of their respective owners.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

A1 A2

B1 B2 B3

Top View

C1 C3

D2 D3

LM3554

SNVS549B –JUNE 2009–REVISED MAY 2013

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DESCRIPTION (CONTINUED)

The main features include: an I2C-compatible interface for controlling the LED current or the desired output

voltage, a hardware Flash enable input for direct triggering of the Flash pulse, and dual TX inputs which force the

Flash pulse into a low-current Torch mode allowing for synchronization to RF power amplifier events or other

high-current conditions. Additionally, an active high hardware enable (HWEN) input provides a hardware

shutdown during system software failures.

Five protection features are available within the LM3554 including a software selectable input voltage monitor, an

internal comparator for interfacing with an external temperature sensor, four selectable current limits to ensure

the battery current is kept below a predetermined peak level, an over-voltage protection feature to limit the output

voltage during LED open circuits, and an output short circuit protection which limits the output current during

shorts to GND. Additionally, the device provides various fault indicators including: a thermal fault flag indicating

the LED temperature has tripped the thermal threshold, a flag indicating a TX event has occurred, a flag

indicating the flash timeout counter has expired, a flag indicating the devices die temperature has reached the

thermal shutdown threshold, and a flag indicating an open or short LED.

Table 1. Application Circuit Component List

Component Manufacturer Value Part Number Size (mm) Rating

L TOKO 2.2µH FDSE0312-2R2M 3×3×1.2 2.3A(0.2Ω)

COUT Murata 4.7µF/10µF GRM188R60J475M, 1.6×0.8×0.8 (0603) 6.3V

GRM188R60J106M

CIN Murata 4.7µF GRM185R60J475M 1.6×0.8×0.8 (0603) 6.3V

LEDs Lumiled LXCL-PWF4 1.5A

Connection Diagram

PIN DESCRIPTIONS

Pin Name Function

A1 LED1 High-Side Current Source Output for Flash LED.

A2, B2 OUT Step-Up DC/DC Converter Output.

A3, B3 SW Drain Connection for Internal NMOS and Synchronous PMOS Switches.

A4, B4 GND Ground

B1 LED2 High-Side Current Source Output for Flash LED.

LEDI/NTC Configurable as a High-Side Current Source Output for Indicator LED or Threshold Detector for LED

C1 Temperature Sensing.

TX1/TORCH/GPIO Configurable as a RF Power Amplifier Synchronization Control Input (TX1), a Hardware Torch

C2 1 Enable (TORCH), or a programmable general-purpose logic Input/Output (GPIO1).

C3 STROBE Active High Hardware Flash Enable. Drive STROBE high to turn on Flash pulse.

C4 IN Input Voltage Connection. Connect IN to the input supply, and bypass to GND with a minimum

4.7µF ceramic capacitor.

D1 ENVM/TX2/GPIO2 Configurable as an Active High Voltage Mode Enable (ENVM), Dual Polarity Power Amplifier

/INT Synchronization Input (TX2), or Programmable General Purpose Logic Input/Output (GPIO2).

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PIN DESCRIPTIONS (continued)

Pin Name Function

D2 SDA Serial Data Input/Output.

D3 SCL Serial Clock Input.

D4 HWEN Active Low Hardware Reset.

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.

Absolute Maximum Ratings (1)(2)(3)

VIN, VSW, VOUT -0.3V to 6V

VSCL, VSDA, VHWEN, VSTROBE, VTX1/TORCH, VENVM/TX2, VLED1, VLED2, VLEDI/NTC -0.3V to to (VIN+0.3V) w/ 6.0V max

Continuous Power Dissipation(4) Internally Limited

Junction Temperature (TJ-MAX) +150°C

Storage Temperature Range -65°C to +150°C

Maximum Lead Temperature (Soldering) (5)

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under

which operation of the device is ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits

and associated test conditions, see Electrical Characteristics.

(2) All voltages are with respect to the potential at the GND pin.

(3) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and

specifications.

(4) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150°C (typ.) and

disengages at TJ=135°C (typ.).

(5) For detailed soldering specifications and information, please refer to Application Note AN-1112: DSBGA Wafer Level chip Scale

Package SNVA009

Operating Ratings (1) (2)

VIN 2.5V to 5.5V

Junction Temperature (TJ) -30°C to +125°C

Ambient Temperature (TA)(3) -30°C to +85°C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under

which operation of the device is ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits

and associated test conditions, see Electrical Characteristics.

(2) All voltages are with respect to the potential at the GND pin.

(3) 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 (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).

Thermal Properties

Junction-to-Ambient Thermal Resistance (θJA), YFQ0016 Package(1) 60°C/W

(1) Junction-to-ambient thermal resistance (θJA) 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 102mm x 76mm x 1.6mm with a 2x1 array of

thermal via's. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36µm/18µm/18µm/36µm

(1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W.

Electrical Characteristics

Limits in standard typeface are for TA= +25°C. Limits in boldface type apply over the full operating ambient temperature

range (-30°C ≤TA≤+85°C). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN.(1)(2)

Symbol Parameter Conditions Min Typ Max Units

Current Source Specifications

(1) All voltages are with respect to the potential at the GND pin.

(2) Min and Max limits are ensured by design, test, or statistical analysis. Typical (Typ) numbers are not ensured, but do represent the most

likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6V and TA= +25°C.

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Electrical Characteristics (continued)

Limits in standard typeface are for TA= +25°C. Limits in boldface type apply over the full operating ambient temperature

range (-30°C ≤TA≤+85°C). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN.(1)(2)

Symbol Parameter Conditions Min Typ Max Units

600mA Flash ILED1+ILED2 1128 1200 1284

LED Setting, ILED1 or ILED2 541 600 657

VOUT = VIN

Current Source

ILED mA

Accuracy 17mA Torch

Current Setting, ILED1+ILED2 30.4 33.8 37.2

VHR = 500mV

Current Source

Regulation

VHR 600mA setting, VOUT = 3.75V 300 mV

Voltage (VOUT -

VLED)

LED Current

IMATCH 600mA setting, VLED = 3.2V 0.35 %

Matching

Step-Up DC/DC Converter Specifications

Output Voltage 2.7V ≤VIN ≤4.2V, IOUT = 0mA,

VREG 4.8 55.2 V

Accuracy VENVM = VIN, OV bit = 0

Output Over- On Threshold, 2.7V ≤VIN ≤5.5V 5.4 5.6 5.7

Voltage

VOVP V

Protection Trip Off Threshold 5.3

Point(3)

PMOS Switch

RPMOS IPMOS = 1A 150 mΩ

On-Resistance

NMOS Switch

RNMOS INMOS = 1A 150 mΩ

On-Resistance CL bits = 00 0.711 1.05 1.373

CL bits = 01 1.295 1.51 1.8

Switch Current

ICL A

Limit(4) CL bits = 10 1.783 1.99 2.263

CL bits = 11 2.243 2.45 2.828

Output Short

IOUT_SC Circuit Current VOUT < 2.3V 550 mA

Limit IND1, IND0 bits 2.3

= 00

IND1, IND0 bits 4.6

= 01

Indicator LEDI/NTC bit =

ILED/NTC mA

Current 0 IND1, IND0 bits 6.9

= 10

IND1, IND0 bits 8.2

= 11

Comparator LEDI/NTC bit = 1, 2.7V ≤VIN ≤

VTRIP 0.947 1.052 1.157 V

Trip Threshold 5.5V

Switching

fSW 2.7V ≤VIN ≤5.5V 1.75 22.23 MHz

Frequency

Quiescent

IQDevice Not Switching 630 µA

Supply Current

(3) The typical curve for Over-Voltage Protection (OVP) is measured in closed loop using the typical application circuit . The OVP value is

found by forcing an open circuit in the LED1 and LED2 path and recording the peak value of VOUT. The value given in the Electrical

Table is found in an open loop configuration by ramping the voltage at OUT until the OVP comparator trips. The closed loop data can

appear higher due to the stored energy in the inductor being dumped into the output capacitor after the OVP comparator trips. At worst

case is an open circuit condition where the output voltage can continue to rise after the OVP comparator trips by approximately

IIN×sqrt(L/COUT).

(4) The typical curve for Current Limit is measured in closed loop using the typical application circuit by increasing IOUT until the peak

inductor current stops increasing. The value given in the Electrical Table is measured open loop and is found by forcing current into SW

until the current limit comparator threshold is reached. Closed loop data appears higher due to the delay between the comparator trip

point and the NFET turning off. This delay allows the closed loop inductor current to ramp higher after the trip point by approximately

20ns × VIN/L

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Electrical Characteristics (continued)

Limits in standard typeface are for TA= +25°C. Limits in boldface type apply over the full operating ambient temperature

range (-30°C ≤TA≤+85°C). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN.(1)(2)

Symbol Parameter Conditions Min Typ Max Units

Shutdown

ISHDN 2.7V ≤VIN ≤5.5V 3.5 6.6 µA

Supply Current

Flash-to-Torch TX_ Low to High, ILED1 + ILED2 =

tTX LED Current 20 µs

1.2A to 180mA

Settling Time VIN Falling, VIN Monitor Register

VIN Monitor

VIN_TH = 0x01 (Enabled with VIN_TH =2.95 3.09 3.23 V

Trip Threshold 3.1V)

TX1/TORCH/GPIO1, STROBE, HWEN, ENVM/TX2/GPIO2 Voltage Specifications

VIL Input Logic Low 2.7V ≤VIN ≤5.5V 0 0.4 V

Input Logic

VIH 2.7V ≤VIN ≤5.5V 1.2 VIN V

High

Output Logic

VOL ILOAD = 3mA, 2.7V ≤VIN ≤5.5V 400 mV

Low

Internal Pull-

down

RTX1/TORCH 300 kΩ

Resistance at

TX1/TORCH

Internal Pull-

Down

RSTROBE 300 kΩ

Resistance at

STROBE

I2C-Compatible Voltage Specifications (SCL, SDA)

VIL Input Logic Low 2.7V ≤VIN ≤5.5V 0 0.4 V

Input Logic

VIH 2.7V ≤VIN ≤5.5V 1.22 VIN V

High

Output Logic

VOL ILOAD = 3mA, 2.7V ≤VIN ≤5.5V 400 mV

Low (SCL)

I2C-Compatible Timing Specifications (SCL, SDA) — See Figure 3

SCL Clock

1/t1400 kHz

Frequency

Data In Setup

t2Time to SCL 100 ns

High

Data Out

t3Stable After 0ns

SCL Low

SDA Low Setup

t4Time to SCL 160 ns

Low (Start)

SDA High Hold

t5Time After SCL 160 ns

High (Stop)

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SCL

SDA_IN

SDA_OUT

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Figure 3. I2C Timing

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Typical Performance Characteristics

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified.

LED Efficiency vs VIN LED Efficiency vs VIN

(Single LED, L = TOKO FDSE0312-2R2) (Dual LEDs, L = TOKO FDSE0312-2R2)

Figure 4. Figure 5.

Input Current vs VIN LED Efficiency vs VIN

(Single LED, L = TOKO FDSE0312-2R2) (Single LED, L = Coilcraft LPS4018-222)

Figure 6. Figure 7.

LED Efficiency vs VIN Input Current vs VIN

(Dual LED's, L = Coilcraft LPS4018-222) (Single LED, L = Coilcraft LPS4018-222)

Figure 8. Figure 9.

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified. Efficiency vs IOUT Efficiency vs VIN

(Voltage Output Mode, VOUT = 5V) (Voltage Output Mode, VOUT = 5V)

Figure 10. Figure 11.

VOUT vs IOUT VOUT vs VIN

(Voltage Output Mode, VOUT = 5V) (Voltage Output Mode, VOUT = 5V)

Figure 12. Figure 13.

Torch Current Matching vs Code

(VIN= 3.6V, VLED1, VLED2 = 3.2V, Torch Current vs VIN

TA= -40°C to +85°C, (1) ) (VLED1, VLED2 = 3.2V, TA= +25°C, 75mA setting)

Figure 14. Figure 15.

(1) Current Matching = Absolute Value((ILED1 - ILED2)/(ILED1 + ILED2)) × 100

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified. Torch Current vs VIN Torch Current vs VIN

(VLED1, VLED2 = 3.2V, TA= +85°C, 75mA setting) (VLED1, VLED2 = 3.2V, TA=−40°C, 75mA setting)

Figure 16. Figure 17.

Flash Current Matching vs Code (VIN= 3.6V, VLED1, VLED2 =

3.2V, Flash Current vs VIN

TA= -40°C to +85°C, (2) (VLED1, VLED2 = 3.2V, TA= +25°C, 600mA setting)

Figure 18. Figure 19.

Flash Current vs VIN Flash Current vs VIN

(VLED1, VLED2 = 3.2V, TA= +85°C, 600mA setting) (VLED1, VLED2 = 3.2V, TA= -40°C, 600mA setting)

Figure 20. Figure 21.

(2) Current Matching = Absolute Value((ILED1 - ILED2)/(ILED1 + ILED2)) × 100

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified. Shutdown Current vs VIN

Switching Frequency vs VIN (VHWEN = 0V)

Figure 22. Figure 23.

Active (Non-Switching) Supply Current vs VIN Active (Switching) Supply Current vs VIN

(VLED = 1.5V) (VOUT = 5V, IOUT = 400mA)

Figure 24. Figure 25.

Closed Loop Current Limit vs VIN Closed Loop Current Limit vs VIN

(Flash Duration Register bits [6:5] = 00, (3)) (Flash Duration Register bits [6:5] = 01, (3) )

Figure 26. Figure 27.

(3) The typical curve for Current Limit is measured in closed loop using the typical application circuit by increasing IOUT until the peak

inductor current stops increasing. The value given in the Electrical Table is measured open loop and is found by forcing current into SW

until the current limit comparator threshold is reached. Closed loop data appears higher due to the delay between the comparator trip

point and the NFET turning off. This delay allows the closed loop inductor current to ramp higher after the trip point by approximately

20ns × VIN/L

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified.

Closed Loop Current Limit vs VIN Closed Loop Current Limit vs VIN

(Flash Duration Register bits [6:5] = 10, (3)) (Flash Duration Register bits [6:5] = 11, (3))

Figure 28. Figure 29.

VIN Monitor Thresholds vs Temperature OVP Thresholds vs VIN (4)

Figure 30. Figure 31.

Indicator Current vs VIN, VLEDI = 2V

Short Circuit Current Limit vs VIN (Torch Brightness Register bits[7:6] = 00)

Figure 32. Figure 33.

(4) The typical curve for Over-Voltage Protection (OVP) is measured in closed loop using the typical application circuit . The OVP value is

found by forcing an open circuit in the LED1 and LED2 path and recording the peak value of VOUT. The value given in the Electrical

Table is found in an open loop configuration by ramping the voltage at OUT until the OVP comparator trips. The closed loop data can

appear higher due to the stored energy in the inductor being dumped into the output capacitor after the OVP comparator trips. At worst

case is an open circuit condition where the output voltage can continue to rise after the OVP comparator trips by approximately

IIN×sqrt(L/COUT).

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified.

Indicator Current vs VIN, VLEDI = 2V Indicator Current vs VIN, VLEDI = 2V

(Torch Brightness Register bits[7:6] = 01) (Torch Brightness Register bits[7:6] = 10)

Figure 34. Figure 35.

Indicator Current vs VIN, VLEDI = 2V

(Torch Brightness Register bits[7:6] = 11) NTC Comparator Trip Threshold vs VIN

Figure 36. Figure 37.

Startup into Torch Mode Single LED, Hardware Torch Mode,

Startup into Flash Mode Single LED 90mA Torch Setting

IFLASH = 1.2A ITORCH = 180mA

Channel 1: VOUT (2V/div) Channel 1: VOUT (2V/div)

Channel 4: ILED (500mA/div) Channel 4: ILED (100mA/div)

Channel 2: IL(500mA/div) Channel 2: IL(500mA/div)

Channel 3: STROBE (5V/div) Channel 3: TX1 (5V/div)

Time Base: (100µs/div) Time Base: (100µs/div)

Figure 38. Figure 39.

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified.

Torch Mode to Flash Mode Transition Single LED TX1 Interrupt Operation, TX1 Rising Single LED

ITORCH = 295mA, IFLASH = 1.2A IFLASH = 1.2A, ITORCH = 180mA

Channel 1: VOUT (5V/div) Channel 1: VOUT (2V/div)

Channel 4: ILED (500mA/div) Channel 4: ILED (500mA/div)

Channel 2: IL(1A/div) Channel 2: IL(1A/div)

Channel 3: STROBE (5V/div) Channel 3: TX1 (5V/div)

Time Base: (100µs/div) Time Base: (20µs/div)

Figure 40. Figure 41.

TX1 Interrupt Operation, TX1 Falling Single LED Line Transient

IFLASH = 1.2A, ITORCH = 180mA (LED Mode, Single LED, IFLASH = 1.2A)

Channel 1: VOUT (2V/div) Channel 3: VIN (1V/div)

Channel 4: ILED (500mA/div) Channel 4: ILED (500mA/div)

Channel 2: IL(1A/div) Channel 2: IL(1A/div)

Channel 3: TX1 (5V/div) Time Base: (400µs/div)

Time Base: (20µs/div) Figure 42. Figure 43.

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified. Load Transient VIN = 3.6V Line Transient IOUT = 500mA

(Voltage Output Mode, VOUT = 5V) (Voltage Output Mode, VOUT = 5V)

Channel 1: VOUT (500mV/div, AC Coupled) Channel 3 (Top Trace): VIN (1V/div)

Channel 4: IOUT (200mA/div) Channel 1: VOUT (100mV/div, AC Coupled)

Channel 2: IL(500mA/div) Channel 2: IL+ IIN (500mA/div)

Time Base: (40µs/div) Time Base: (200µs/div)

Figure 44. Figure 45.

Flash Pulse to HWEN Low Flash Pulse to Flash Pulse + VOUT Mode

Single LED, ILED = 1.2A Single LED, ILED = 1.2A, VOUT = 5V

Channel 1: VOUT (2V/div) Channel 1: VOUT (2V/div)

Channel 4: ILED (500mA/div) Channel 4: ILED (500mA/div)

Channel 2: IL(1A/div) Channel 2: IL(1A/div)

Channel 3: HWEN (5V/div) Channel 3: ENVM (5V/div)

Time Base: (20µs/div) Time Base: (100µs/div)

Figure 46. Figure 47.

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Typical Performance Characteristics (continued)

VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10µF, CIN = 4.7µF, L = FDSE0312-2R2 (2.2µH, RL= 0.15Ω), TA= +25°C unless

otherwise specified.

Flash Pulse + VOUT to Flash Pulse NTC Mode Response Single LED, ILED = 1.2A

Single LED, ILED = 1.2A, VOUT = 5V Circuit of Figure 74 (R(T) = 100kΩ(@+25°C), R3 = 9kΩ)

Channel 3: NTC Pin Voltage (500mV/div)

Channel 1: VOUT (2V/div) Channel 4: ILED (500mA/div)

Channel 4: ILED (500mA/div) Time Base: (200ms/div)

Channel 2: IL (1A/div)

Channel 3: ENVM (5V/div)

Time Base: (100µs/div) Figure 48. Figure 49.

VIN Monitor Response

Single LED, ILED = 1.2A 3.1V UVLO Setting

Channel 3: VIN (1V/div)

Channel 4: ILED (500mA/div)

Time Base: (100ms/div) Figure 50.

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VREF

PWM

Control

2 MHz

Oscillator

Thermal

Shutdown

+150oC

VREF

I2C

Interface

Error

Amplifier

Current

Sense/Current

Limit

Slope

Compensation

SDA

SCL

Control

Logic/

Soft-Start

GND

OUT

LED1

LED2

LEDI/

NTC

ENVM/TX2/

GPIO2

STROBE

TX1/TORCH/

GPIO1

HWEN

Reference

Mode

Select

Feedback

Mode

Select

Max

VLED

ISET

VREF

150 mΩ

150 m:

Over Voltage

Comparator

VTRIP

ILEDI

ILED2 ILED1

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BLOCK DIAGRAM

Overview

The LM3554 is a high-power white LED flash driver capable of delivering up to 1.2A of LED current into a single

LED, or up to 600mA into two parallel LEDs. The device incorporates a 2MHz constant frequency, synchronous,

current mode PWM boost converter, and two high-side current sources to regulate the LED current over the 2.5V

to 5.5V input voltage range.

The LM3554 operates in two modes: LED mode or constant Voltage Output mode. In LED mode when the output

voltage is greater than VIN – 150mV, the PWM converter switches and maintains at least 300mV (VHR) across

both current sources (LED1 and LED2). This minimum headroom voltage ensures that the current sinks remain

in regulation. When the input voltage is above VLED + VHR, the device operates in Pass mode with the device not

switching and the PFET on continuously. In Pass mode the difference between (VIN - ILED×RON_P) and VLED is

dropped across the current sources. If the device is operating in Pass mode, and VIN drops to a point that forces

the device into switching, the LM3554 will make a one-time decision to jump into switching mode. The LM3554

remains in switching mode until the device is shutdown and re-enabled. This is true even if VIN were to rise back

above VLED + 300mV during the current Flash or Torch cycle. This prevents the LED current from oscillating

when VIN is operating close to VOUT.

In Voltage Output mode the LM3554 operates as a voltage output boost converter with selectable output

voltages of 4.5V and 5V. In this mode the LM3554 is able to deliver up to typically 5W of output power. At light

loads and in Voltage Output mode the PWM switching converter changes over to a pulsed frequency regulation

mode and only switches as necessary to ensure proper LED current or output voltage regulation. This allows for

improved light load efficiency compared to converters that operate in fixed-frequency PWM mode at all load

currents.

Product Folder Links: LM3554

LM3554

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SNVS549B –JUNE 2009–REVISED MAY 2013

Additional features of the LM3554 include 4 logic inputs, an internal comparator for LED thermal sensing, and a

low-power indicator LED current source. The STROBE input provides a hardware Flash mode enable. The

ENVM/TX2/GPIO2 input is configurable as a hardware Voltage Output mode enable (ENVM), an active high

Flash interrupt that forces the device from FLASH mode to a low-power TORCH mode (TX2), or as a

programmable logic input/output (GPIO2). The TX1 input is configurable as an active high Flash interrupt that

forces the device from FLASH mode to a low-power TORCH mode (TX1), as a hardware Torch mode enable

(TORCH), or as a programmable logic input/output (GPIO1) . The HWEN input provides for an active low

hardware shutdown of the device. Finally, the LEDI/NTC pin is configurable as a low-power indicator LED driver

(LEDI), or as a threshold detector for thermal sensing (NTC). In NTC mode when the threshold (VTRIP) at the

LEDI/NTC pin is crossed (VLEDI/NTC falling), the Flash pulse is forced to the Torch current setting, or into

shutdown depending on the NTC Shutdown bit setting .

Control of the LM3554 is done via an I2C-compatible interface. This includes switch-over from LED to Voltage

Output mode, adjustment of the LED current in TORCH mode, adjustment of the LED current in FLASH mode,

adjustment of the indicator LED currents, changing the flash LED current duration, changing the switch current

limit. Additionally, there are 5 flag bits that can be read back indicating flash current timeout, over-temperature

condition, LED failure (open or short), LED thermal failure, and an input voltage fault.

STARTUP

Turn on of the LM3554 is done through bits [2:0] of the Torch Brightness Register (0xA0), bits [2:0] of the Flash

Brightness Register (0xB0), the ENVM input, or the STROBE input. Bits [1:0] of the Torch Brightness Register or

Flash Brightness Register enables/disables the current sources (LED1, LED2, and LEDI). Bit [2] enables/disables

the voltage output mode. A logic high at STROBE enables Flash mode. A logic high on the ENVM input forces

the LM3554 into Voltage Output mode.

On startup, when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers

typically 350mA to the output capacitor. During this time all current sources (LED1, LED2, and LEDI) are off.

When the voltage across the output capacitor reaches 2.2V, the current sources can turn on. At turn-on the

current sources step through each FLASH or TORCH level until the target LED current is reached (16 µs/step).

This gives the device a controlled turn-on and limits inrush current from the VIN supply.

PASS MODE

Once the Output voltage charges up to VIN - 150mV the LM3554 will decide if the part operates in Pass Mode or

Boost mode. If the voltage difference between VOUT and VLED is less than 300mV, the device will transition in

Boost Mode. If the difference between VOUT and VLED is greater than 300mV, the device will operate in Pass

Mode. In Pass Mode the boost converter stops switching, and the synchronous PFET turns fully on bringing VOUT

up to VIN – IIN×RPMOS (RPMOS = 150mΩ). In Pass Mode the inductor current is not limited by the peak current

limit. In this situation the output current must be limited to 2.5A.

LIGHT LOAD DISABLE

Configuration Register 1 bit [0] = 1 disables the light load comparator. With this bit set to 0 (default) the light load

comparator is enabled. Light Load mode only applies when the LM3554 is active in Voltage Output mode. In LED

mode the Light Load Comparator is always disabled. When the light load comparator is disabled the LM3554 will

operate at a constant frequency down to ILOAD = 0. Disabling light load can be useful when a more predictable

switching frequency across the entire load current range is desired.

VOLTAGE OUTPUT MODE

Bit 2 (VM) of the Torch Brightness Register, bit 2 (VM) of the Flash Brightness Register, or the ENVM input

enables or disables the Voltage Output mode. In Voltage Output mode the device operates as a simple boost

converter with two selectable voltage levels (4.5V and 5V). Write a (1) to bit 1 (OV) of Configuration Register 1 to

set VOUT to 5V. Write a (0) to this bit to set VOUT to 4.5V. In Voltage Output mode the LED current sources can

continue to operate; however, the difference between VOUT and VLED will be dropped across the current sources.

(See Maximum Output Power section.) In Voltage Output mode when VIN is greater than VOUT the LM3554

operates in Pass Mode (see PASS MODE section).

At light loads the LM3554 switches over to a pulsed frequency mode operation (light load comparator enabled).

In this mode the device will only switch as necessary to maintain VOUT within regulation. This mode provides a

better efficiency due to the reduction in switching losses which become a larger portion of the total power loss at

light loads.

Product Folder Links: LM3554

Maximum Output Current vs Efficiency

0.6

0.7

0.8

0.9

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.1

2.2

2.3

0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

Maximum Output Current (A)

VIN = 3.6V, VOUT = 4V

VIN = 3V, VOUT = 4V

VIN = 3.6V, VOUT = 5V

VIN = 2.5V, VOUT = 4V

VIN = 3V, VOUT = 5V

VIN = 2.5V, VOUT = 5V

Efficiency (POUT/ PIN)

(IPEAK = 2.5A)

=IN x

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INOUT - VV

OUTSW V

( ) INLPEAK V

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LOAD =I OUT

LM3554

SNVS549B –JUNE 2009–REVISED MAY 2013

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OVER-VOLTAGE PROTECTION

The output voltage is limited to typically 5.6V (5.7V max). In situations such as the current source open, the

LM3554 will raise the output voltage in order to try and keep the LED current at its target value. When VOUT

reaches 5.6V the over-voltage comparator will trip and turn off both the internal NFET and PFET. When VOUT

falls below 5.4V (typical), the LM3554 will begin switching again.

CURRENT LIMIT

The LM3554 features 4 selectable current limits: 1A, 1.5A, 2A, and 2.5A. These are selectable through the I2C-

compatible interface via bits 5 (CL0) and 6 (CL1) of the Flash Duration Register. When the current limit is

reached, the LM3554 stops switching for the remainder of the switching cycle.

Since 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 situations where there could potentially be large load currents at OUT, and the

LM3554 is operating in Pass mode, the load current must be limited to 2.5A. In Boost mode or Pass mode if

VOUT falls below approximately 2.3V, the part stops switching, and the PFET operates as a current source

limiting the current to typically 350mA. This prevents damage to the LM3554 and excessive current draw from

the battery during output short circuit conditions.

MAXIMUM LOAD CURRENT (VOLTAGE MODE)

Assuming the power dissipation in the LM3554 and the ambient temperature are such that the device will not hit

thermal shutdown, the maximum load current as a function of IPEAK is:

(1)

Where ηis efficiency and is found in the efficiency curves in the Typical Performance Characteristics and

(2)

Figure 51 shows the theoretical maximum Output current vs theoretical Efficiency at different input and output

voltages using the previous two equations for ΔILand ILOAD with a peak current of 2.5A. This plot represents the

theoretical maximum output current (for the LM3554 in Voltage Output mode) that the device can deliver just

before hitting current limit.

Figure 51. LM3554 Maximum Output Current

Product Folder Links: LM3554

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LM3554

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SNVS549B –JUNE 2009–REVISED MAY 2013

Maximum Output Power

Output power is limited by three things: the peak current limit, the ambient temperature, and the maximum power

dissipation in the package. If the LM3554’s die temperature is below the absolute maximum rating of +125°C, the

maximum output power can be over 6W. However, any appreciable output current will cause the internal power

dissipation to increase and therefore increase the die temperature. This can be additionally compounded if the

LED current sources are operating while the device is in Voltage Output mode since the difference between VOUT

and VLED is dropped across the current sources. Any circuit configuration must ensure that the die temperature

remains below +125°C taking into account the ambient temperature derating.

Maximum Output Power (Voltage Output Mode)

In Voltage Output mode the total power dissipated in the LM3554 can be approximated as: (3)

PNis the power lost in the NFET, PPis the PFET power loss, PLED1, PLED2, and PIND are the losses across the

current sinks. An approximate calculation of these losses gives:

(4)

The above formulas consider the average current through the NFET and PFET. The actual power losses will be

higher due to the RMS currents and the quiescent power into IN. These, however, can give a decent

approximation.

Maximum Output Power (Led Boost Mode)

In LED mode with VOUT > VIN the LM3554’s boost converter will switch and make VOUT = VLED + 0.3V. In this

situation the total power dissipated in the LM3554 is approximated as:

(5)

Maximum Output Power (Led Pass Mode)

In LED mode with VIN – ILOAD × RPFET > VLED + 0.3V, the LM3554 operates in Pass Mode. In this case. the NFET

is off, and the PFET is fully on. The difference between VIN - ILOAD×RPMOS and VLED will be dropped across the

current sources. In this situation the total power dissipated in the LM3554 is approximated as:

(6)

Once the total power dissipated in the LM3554 is calculated the ambient temperature and the thermal resistance

of the 16-bump micro SMD (TMD16) are used to calculate the total die temperature (or junction temperature TJ).

Product Folder Links: LM3554

.C°8.80

C°25+

°60

W93.0=TJ

mW930=mW14+mW420+mW357+mW139=PDISS

LM3554

SNVS549B –JUNE 2009–REVISED MAY 2013

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As an example, assume the LM3554 is operating at VIN = 3.6V and configured for Voltage Output mode with

VOUT = 5V and IOUT = 0.7A. The LED currents are then programmed in Torch mode with 150mA each at VLED =

3.6V. Additionally, the indicator LED has 10mA at VIND = 3.6V. Using Equation 5 and Equation 6 above, the

approximate total power dissipated in the device is:

(7)

The die temperature approximation will be:

(8)

In this case the device can operate at these conditions. If then the ambient temperature is increased to +85°C,

the die temperature would be +140.8°C; thus, the die temperature would be above the absolute maximum

ratings, and the load current would need to be scaled back. This example demonstrates the steps required to

estimate the amount of current derating based upon operating mode, circuit parameters, and the device's

junction-to-ambient thermal resistance. In this example a thermal resistance of 60°C/W was used (JESD51-7

standard). Since thermal resistance from junction-to-ambient is largely PCB layout dependent, the actual number

used will likely be different and must be taken into account when performing these calculations.

Flash Mode

In Flash mode the LED current sources (LED1 and LED2) each provide 16 different current levels from typically

34mA to approximately 600mA. The Flash currents are set by writing to bits [6:3] of the Flash Brightness

Resister. Flash mode is activated by either writing a (1, 1) to bits [1:0] of the Torch Brightness Register, writing a

(1,1) to bit [1:0] of the Flash Brightness Register, or by pulling the STROBE pin high. Once the Flash sequence

is activated, both current sinks (LED1 and LED2) will ramp up to the programmed Flash current by stepping

through all Flash levels (16µs/step) until the programmed current is reached.

Flash Termination (Strobe-Initiated Flash)

Bit [7] of the Flash Brightness Register (STR bit) determines how the Flash pulse terminates with STROBE-

initated flash pulses. With the STR bit = 1 the Flash current pulse will only terminate by reaching the end of the

Flash Timeout period. With STR = 0, Flash mode can be terminated by pulling STROBE low, or by allowing the

Flash Timeout period to elapse. If STR = 0 and STROBE is toggled before the end of the Flash Timeout period,

the Timeout period resets on the rising edge of STROBE. See LM3554 TIMING DIAGRAMS regarding the Flash

pulse termination for the different STR bit settings.

After the Flash pulse terminates, either by a flash timeout, or pulling STROBE low, LED1 and LED2 turn

completely off. This happens even when Torch is enabled via the I2C-compatible interface, and the Flash pulse is

turned on by toggling STROBE. After a Flash event ends the EN1, EN0 bits (bits [1:0] of the Torch Brightness

Flash Termination (I2C-Initiated FLASH)

For I2C initated flash pulses, the flash LED current can be terminated by either waiting for the timeout duration to

expire or by writing a (0, 0) to bits [1:0] of the Torch Brightness Register, or Flash Brightness Register. If the

timeout duration is allowed to elapse, the flash enable bits of the Torch Brightness and Flash Brightness

Registers are automatically reset to 0.

Flash Timeout

The Flash Timeout period sets the duration of the flash current pulse. Bits [4:0] of the Flash Duration Register

programs the 32 different Flash Timeout levels in steps of 32ms giving a Flash Timeout range of 32ms to

1024ms (see Table 5).

Torch Mode

In Torch mode the current sources LED1 and LED2 each provide 8 different current levels (see Table 3). The

Torch currents are adjusted by writing to bits [5:3] of the Torch Brightness Register. Torch mode is activated by

setting Torch Brightness Register bits [1:0] to (1, 0) or Flash Brightness bits [1:0] to (1, 0). Once the Torch mode

is enabled the current sources will ramp up to the programmed Torch current level by stepping through all of the

Torch currents at 16µs/step until the programmed Torch current level is reached.

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TX1/Torch

The TX1/TORCH/GPIO1 input has a triple function. With Configuration Register 1 Bit [7] = 0 (default),

TX1/TORCH/GPIO1 is a Power Amplifier Synchronization input (TX1 mode). This is designed to reduce the

current pulled from the battery during an RF power amplifier transmit event. When the LM3554 is engaged in a

Flash event, and the TX1 pin is pulled high, both LED1 and LED2 are forced into Torch mode at the programmed

Torch current setting. If the TX1 pin is then pulled low before the Flash pulse terminates the LED current will

ramp back to the previous Flash current level. At the end of the Flash timeout whether the TX1 pin is high or low,

the LED current will turn off.

With the Configuration Register Bit [7] = 1, TX1/TORCH/GPIO1 is configured as a hardware Torch mode enable

(TORCH). In this mode a high at TORCH turns on the LED current sources in Torch mode. STROBE (or I2-

initiated flash) will take precedence over the TORCH mode input. Figure 61 details the functionality of the

hardware TORCH mode. Additionally, when a flash pulse is initiated during hardware TORCH mode, the

hardware torch mode bit is reset at the end of the flash pulse. In order to re-enter hardware Torch mode, bit [7] of

Configuration Register 1 would have to be re-written with a 1.

The TX1/TORCH/GPIO1 input can also be configured as a GPIO input/output. for details on this, refer to the

GPIO Register section of the datasheet.

ENVM/TX2/GPIO2

The ENVM/TX2/GPIO2/INT pin has four functions. In ENVM mode (Configuration Register 1 bit [5] = 0), the

ENVM/TX2/GPIO2/INT pin is an active high logic input that forces the LM3554 into Voltage Output Mode. In TX2

mode (Configuration Register 1 bit [5] = 1), the ENVM/TX2/GPIO2/INT pin is a Power Amplifier Synchronization

input that forces the LM3554 from Flash mode into Torch mode. In GPIO2 mode (GPIO Register Bit [3] = 1) the

ENVM/TX2/GPIO2/INT pin is configured as a general purpose logic input/output and controlled via bits[3:5] of the

GPIO Register. In INT mode the ENVM/TX2/GPIO2/INT pin is a hardware interrupt output which pulls low when

the LM3554 is in NTC mode, and the voltage at LEDI/NTC falls below VTRIP.

In TX2 mode, when Configuration Register 1 bit [6] = 0 the ENVM/TX2/GPIO2 pin is an active low transmit

interrupt input. Under this condition, when the LM3554 is engaged in a Flash event, and ENVM/TX2/GPIO2 is

pulled low, both LED1 and LED2 are forced into either Torch mode or LED shutdown depending on the logic

state of Configuration Register 2 bit [0]. In TX2 mode with Configuration Register 1 bit [6] = 1, the

ENVM/TX2/GPIO2 pin is an active high transmit interrupt. Under this condition when the LM3554 is engaged in a

Flash event, and the TX2 pin is driven high, both LED1 and LED2 are forced into Torch mode or LED shutdown,

depending on the logic state of Configuration Register 2 bit [0]. After a TX2 event, if the ENVM/TX2/GPIO2 pin is

disengaged, and the TX2 Shutdown bit is set to force Torch mode, the LED current will ramp back to the

previous Flash current level. If the TX2 shutdown bit is programmed to force LED shutdown upon a TX2 event

the Flags Register must be read to resume normal LED operation. Table 6,Figure 57, and Figure 58 detail the

Functionality of the ENVM/TX2 input.

ENVM/TX2/GPIO2/INT as an Interrupt Output

In GPIO2 mode the ENVM/TX2/GPIO2 pin can be made to reflect the inverse of the LED Thermal Fault flag

(bit[5] in the Flags Register). Configure the LM3554 for this feature by:

set GPIO Register Bit [6] = 1 (NTC External Flag)

set GPIO Register Bit [3] = 1 (GPIO2 mode)

set GPIO Register Bit [4] = 1 (GPIO2 is an output)

set Configuration Register 1 Bit [3] = 1 (NTC mode)

When the voltage at the LEDI/NTC pin falls below VTRIP (1.05V typical), the LED Thermal Fault Flag (bit [5] in the

Flags Register) is set, and the ENVM/TX2/GPIO2/INT pin is forced low. In this mode the interrupt can only be

reset to the open-drain state by reading back the Flags register.

INDICATOR LED/THERMISTOR (LEDI/NTC)

The LEDI/NTC pin serves a dual function, either as an LED indicator driver or as a threshold detector for a

negative temperature coefficient (NTC) thermistor.

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Led Indicator Mode (LEDI)

LEDI/NTC is configured as an LED indicator driver by setting Configuration Register 1 bit [3] = (0) and Torch

Brightness Register bits [1:0] = (0, 1), or Flash Brightness Register bits [1:0] = (0, 1). In Indicator mode there are

4 different current levels available (2.3mA, 4.6mA, 6.9mA, 8.2mA). Bits [7:6] of the Torch Brightness Register set

the 4 different indicator current levels. The LEDI current source has a 1V typical headroom voltage.

Thermal Comparator Mode (NTC)

Writing a (1) to Configuration Register 1 bit [3] disables the indicator current source and configures the LEDI/NTC

pin as a detector for an NTC thermistor. In this mode LEDI/NTC becomes the negative input of an internal

comparator with the positive input internally connected to a reference (VTRIP = 1.05V typical). Additionally,

Configuration Register 2 bit [1] determines the action the device takes if the voltage at LEDI/NTC falls below

VTRIP (while the device is in NTC mode). With Configuration register 2 bit [1] = 0, the LM3554 will be forced into

Torch mode when the voltage at LEDI/NTC falls below VTRIP. With Configuration Register 2 bit [1] = 1 the device

will shut down the current sources when VLEDI/NTC falls below VTRIP. When the LM3554 is forced from Flash into

Torch (by VLEDI/NTC falling below VTRIP), normal LED operation (during the same Flash pulse) can only be re-

started by reading from the Flags Register (0xD0) and ensuring the voltage at VLEDI/NTC is above VTRIP. When

VLEDI/NTC falls below VTRIP, and the Flags register is cleared, the LM3554 will go through a 250µs deglitch

time before the flash current falls to either torch mode or goes into shutdown.

Alternative External Torch (AET Mode)

Configuration Register 2 bit [2] programs the LM3554 for Alternative External Torch mode. With this bit set to (0)

(default) TX1/TORCH is a transmit interrupt that forces Torch mode only during a Flash event. For example, if

TX1/TORCH goes high during a Flash event then the LEDs will be forced into Torch mode only for the duration

of the timeout counter. At the end of the timeout counter the LEDs will turn off.

With Configuration Register 2 bit [2] set to (1) the operation of TX1/TORCH becomes dependent on its

occurrence relative to STROBE. In this mode if TX1/TORCH goes high first, then STROBE goes high, the LEDs

are forced into Torch mode with no timeout. In this mode if TX1/TORCH goes high after STROBE has gone high

then the TX1/TORCH pin operates as a normal TX interrupt, and the LEDs will turn off at the end of the timeout

duration. (See LM3554 TIMING DIAGRAMS,Figure 59, and Figure 60.)

INPUT VOLTAGE MONITOR

The LM3554 has an internal comparator that monitors the voltage at IN and can force the LED current into Torch

mode or into shutdown if VIN falls below the programmable VIN Monitor Threshold. Bit 0 in the VIN Monitor

of 3.1V, 3.2V, 3.3V, and 3.4V. Bit 3 in Configuration Register 2 (0xF0) selects whether an under-voltage event

forces Torch mode or forces the LEDs off. See Figure 70/Table 8 and Figure 72/Table 10 for additional

information.

There is a set 100mV hysteresis for the input voltage monitor. When the input voltage monitor is active, and VIN

falls below the programmed VIN Monitor Threshold, the LEDs will either turn off or their current will get reduced

to the programmed Torch current setting. To reset the LED current to its previous level, two things must occur.

First, VIN must go at least 100mV above the UVLO threshold and secondly, the Flags register must be read back.

Product Folder Links: LM3554

STROBE

TX1/TORCH

Default State

(TX1 event before and after STROBE event)

Timeout

Duration

ITORCH

ILED

STROBE

TX1/TORCH

Timeout

Duration

Default State

(TX event during a STROBE event)

IFLASH

ITORCH

ILED

STROBE

Timeout

Duration

I2C Torch

Command

Default State

Flash Brightness Register bit 7 (STR) = 0

Configuration Register 1 bit 7 (TX1/TORCH) = 0

Configuration Register 1 bit 6 (TX2 Polarity) = 1

Configuration Register bit 5 (ENVM/TX2) = 0

Configuration Register 2 bit 2 (AET) = 0

IFLASH

ITORCH

ILED

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LM3554 TIMING DIAGRAMS

Figure 52. Normal Torch to Flash Operation (Default, Power On or RESET state of LM3554)

Figure 53. TX1 Event During a Flash Event (Default State,TX1/TORCH is an Active High TX Input)

Figure 54. TX1 Event Before and After Flash Event (Default State, TX1/TORCH is an Active High TX

Input)

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STROBE

ENVM/TX2

Timeout

Duration

I2C Torch

Command

Configuration Register 1 bit 5 (ENVM/TX2) = 1

(ENVM/TX2 operates as a transmit interrupt)

ENVM/TX2 as a transmit interrupt

ILED

ITORCH

IFLASH

STROBE

Timeout

Duration

I2C Torch

Command

ILEDITORCH

IFLASH

Flash Brightness Register bit 7 (STR) = 1

STROBE goes high and the LEDs turn on into Flash

mode. LEDs will stay on for the timeout duration even

if STROBE goes low before.

STROBE

Timeout

Duration

I2C Torch

Command

Start of

Timeout

Counter

Timeout

Counter

Reset

Default State

STROBE goes high and the LEDs turn on into Flash

mode. LEDs will turn off at the end of timeout

duration or when STROBE goes low. Everytime

STROBE goes high the timeout resets.IFLASH

ITORCH

ILED

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Figure 55. STROBE Input is Level Sensitive (Default State, STR bit = 0)

Figure 56. STROBE Input is Edge Sensitive (STR bit = 1)

Figure 57. ENVM/TX2 Pin is Configured as an Active High TX Input

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STROBE

TX1/TORCH

Timeout

Duration

Configuration Register 2 bit [2] = 1 (AET)

(TX1/TORCH pin goes high first. When STROBE pin

goes high, LEDs will turn on into Torch. Timeout

counter and flash pulse will not start until TX1/TORCH

goes low)

ILED

IFLASH

ITORCH

STROBE

ENVM/TX2

Timeout

Duration

I2C Torch

Command

Configuration Register 1 bit 5 (ENVM/TX2) = 1

Configuration Register 1 bit 6 (ENVM/TX2) = 0

(ENVM/TX2 is configured as an active low transmit interrupt)

ILED

ITORCH

IFLASH

LM3554

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Figure 58. ENVM/TX2 Pin is Configured as an Active Low TX Input

Figure 59. Alternative External Torch Mode (TX1/TORCH Turns on Before STROBE)

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STROBE

TX1/TORCH

Timeout

Duration

Configuration Register 1 bit 7 (TX1/TORCH) = 1

(TX1/TORCH pin is a hardware torch input)

IFLASH

ITORCH

ILED

STROBE

TX1/TORCH

Timeout

Duration

Configuration Register 2 bit [2] = 1 (AET)

(STROBE goes high before TX1)

ITORCH

IFLASH

ILED

LM3554

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Figure 60. Alternative External Torch Mode (STROBE Goes High Before TX1/TORCH, Same as Default

with SEM = 0)

Figure 61. TX1/TORCH Configured as a Hardware Torch input

Flags Register And Fault Indicators

The Flags Register (0xD0) contains the Interrupt and Fault indicators. Five fault flags are available in the

LM3554. These include a Thermal Shutdown, an LED Failure Flag (LEDF) , a Timeout indicator Flag (TO), a

LED Thermal Flag (NTC), and a VIN Monitor Flag. Additionally, two interrupt flag bits TX1 interrupt and TX2

interrupt indicate a change of state of the TX1/TORCH pin (TX1 mode) and ENVM/TX2 pin (TX2 mode). Reading

back a "1" indicates the TX lines have changed state since the last read of the Flags Register. A read of the

Flags Register resets these bits.

Thermal Shutdown

When the LM3554’s die temperature reaches +150°C the boost converter shuts down, and the NFET and PFET

turn off. Additionally, all three current sources (LED1, LED2, and LEDI) turn off. When the thermal shutdown

threshold is tripped a (1) gets written to bit [1] of the Flag Register (Thermal Shutdown bit). The LM3554 will start

up again when the die temperature falls to below +135°C.

During heavy load conditions when the internal power dissipation in the device causes thermal shutdown, the

part will turn off and start up again after the die temperature cools. This will result in a pulsed on/off operation.

The OVT bit however will only get written once. To reset the OVT bit pull HWEN low, power down the LM3554,

or read the Flags Register.

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LED Fault

The LED Fault flag (bit 2 of the Flags Register) reads back a (1) if the part is active in Flash or Torch mode and

either LED1 or LED2 experience an open or short condition. An LED open condition is signaled if the OVP

threshold is crossed at OUT while the device is in Flash or Torch mode. An LED short condition is signaled if the

voltage at LED1 or LED2 goes below 500mV while the device is in Torch or Flash mode.

There is a delay of 250µs before the LEDF flag is valid on a LED short. This is the time from when VLED falls

below the LED short threshold of 500mV (typical) to when the fault flag is valid. There is a delay of 2µs from

when the LEDF flag is valid on an LED open. This delay is the time between when the OVP threshold is

triggered and when the fault flag is valid. The LEDF flag can only be reset to (0) by pulling HWEN low, removing

power to the LM3554, or reading the Flags Register.

Flash Timeout

The TO flag (bit [0] of the Flags Register) reads back a (1) if the LM3554 is active in Flash mode and the

Timeout period expires before the Flash pulse is terminated. The flash pulse can be terminated before the

Timeout period expires by pulling the STROBE pin low (with STR bit '0'), or by writing a ‘0’ to bit 0 or 1 of the

Torch Brightness Register or the Flash Brightness Register. The TO flag is reset to (0) by pulling HWEN low,

removing power to the LM3554, reading the Flags Register, or when the next Flash pulse is triggered.

LED Thermal Fault

The NTC flag (bit [5] of the Flags Register) reads back a (1) if the LM3554 is active in Flash or Torch mode, the

device is in NTC mode, and the voltage at LEDI/NTC has fallen below VTRIP (1.05V typical). When this has

happened and the LM3554 has been forced into Torch or LED shutdown (depending on the state of

Configuration Register 2 bit [1], the Flags Register must be read in order to place the device back in normal

operation. (See Thermal Comparator Mode (NTC) section for more details.)

Input Voltage Monitor Fault

The VIN Monitor Flag (bit [6] of the Flag Register) reads back a '1' when the Input Voltage Monitor is enabled and

VIN falls below the programmed VIN Monitor threshold. This flag must be read back in order to resume normal

operation after the LED current has been forced to Torch mode or turned off due to a VIN Monitor event.

TX1 and TX2 Interrupt Flags

The TX1 and TX2 interrupt flags (bits [3] and [4]) indicate a TX event on the TX1/TORCH and ENVM/TX2 pins.

Bit 3 will read back a (1) if TX1/TORCH is in TX1 mode and the pin has changed from low to high since the last

read of the Flags Register. Bit 4 will read back a (1) if ENVM/TX2 is in TX2 mode and the pin has had a TX

event since the last read of the Flags Register. A read of the Flags Register automatically resets these bits.

The ENVM/TX2/GPIO2 pin, when configured in TX2 mode, has a TX event that can be either a high-to-low

transition or a low-to-high transition depending on the setting of the TX2 polarity bit (see Table 7).

I2C-Compatible Interface

Start And Stop Conditions

The LM3554 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning

and end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL is

HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master

always generates the START and STOP conditions.

Product Folder Links: LM3554

R/W

Bit 0

Bit 1

Bit 2

Bit 3

Bit 4

Bit 5

Bit 7 0

Bit 6

MSB LSB

I2C Slave Address (chip address)

SCL

SDA_IN

SDA_OUT

SDA

Start Condition Stop Condition

SCL S P

LM3554

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Figure 62. Start and Stop Sequences

The I2C bus is considered busy after a START condition and free after a STOP condition. During data

transmission the I2C master can generate repeated START conditions. A START and a repeated START

condition are equivalent function-wise. The data on SDA must be stable during the HIGH period of the clock

signal (SCL). In other words, the state of SDA can only be changed when SCL is LOW. Figure 3 and Figure 63

show the SDA and SCL signal timing for the I2C-Compatible Bus. See Electrical Characteristics for timing values.

Figure 63. I2C-Compatible Timing

I2C-Compatible Chip Address

The device address for the LM3554 is 1010011 (53). After the START condition, the I2C master sends the 7-bit

address followed by an eighth bit, read or write (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 64. Device Address

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 (write mode). The LM3554

pulls down SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each

byte has been received.

Product Folder Links: LM3554

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5

IND1

Bit 7 Bit 6

MSB LSB

Torch Brightness Register

IND0 TC2 TC1 TC0 VM EN1 EN0

LM3554

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Table 2. LM3554 Internal Registers

Torch Brightness 0xA0 0x50

Flash Brightness 0xB0 0x68

Flash Duration 0xC0 0x4F

Flag Register 0xD0 0x40

Configuration Register 1 0xE0 0x42

Configuration Register 2 0xF0 0xF0

GPIO Register 0x20 0x80

VIN Monitor Register 0x80 0xF0

TORCH Brightness Register

Bits [2:0] of the Torch Brightness Register, or bits [2:0] of the Flash Brightness Register place the device in

shutdown or control the on/off state of Torch, Flash, the Indicator LED and the Voltage output mode (see

Table 3). Writing to Torch Brightness Register bits [2:0] automatically updates the Flash Brightness Register bits

[2:0]; writing to bits [2:0] of the Flash Brightness Register automatically updates bits [2:0] of the Torch Brightness

(see Table 3).

Figure 65. Torch Brightness Register Description

Table 3. Torch Brightness Register Bit Settings

Bit 7 (IND1) Bit 6 (IND0) Bit 5 (TC2) Bit 4 (TC1) Bit 3 (TC0) Bit 2 (VM) Bit 1 (EN1) Bit 0 (EN0)

Indicator Current Select Bits Torch Current Select Bits Enable Bits

00 = 2.3mA 000 = 17mA (34mA total) 000 = Shutdown (default)

01 = 4.6mA (default state) 001 = 35.5mA (71mA total) 001 = Indicator Mode

10 = 6.9mA 010 = 54mA (108mA total) default state 010 = Torch Mode

11 = 8.2mA 011 = 73mA (146mA total) 011 = Flash Mode (bits reset at timeout)

100 = 90mA (180mA total) 100 = Voltage Output Mode

101 = 109mA (218mA total) 101 = Voltage Output + Indicator Mode

110 = 128mA (256mA total) 110 = Voltage Output + Torch Mode

111 = 147.5mA (295mA total) 111 = Voltage Output + Flash Mode (bits [1:0] are

reset at end of timeout)

Flash Brightness Register

Bits [2:0] of the Torch Brightness Register, or bits [2:0] of the Flash Brightness Register place the device in

shutdown or control the on/off state of Torch, Flash, the Indicator LED and the Voltage output mode. Writing to

the Flash Brightness Register bits [2:0] automatically updates the Torch Brightness Register bits [2:0]. Bits [6:3]

set the current level in Flash mode (see Table 4). Bit [7] sets the STROBE Termination select bit (STR) (see

Table 4).

Product Folder Links: LM3554

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5

N/A

Bit 7 Bit 6

MSB LSB

Flash Duration Register

CL1 CL0 T4 T3 T2 T1 T0

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5

STR

Bit 7 Bit 6

MSB LSB

Flash Brightness Register

FC3 FC2 FC1 FC0 VM EN1 EN0

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Figure 66. Flash Brightness Register Description

Table 4. Flash Brightness Register Bit Settings

Bit 7 (STR) Bit 6 (FC3) Bit 5 (FC2) Bit 4 (FC1) Bit 3 (FC0) Bit 2 (VM) Bit 1 (EN1) Bit 0 (EN0)

STROBE Edge or Level Flash Current Select Bits Enable Bits

Select 0000 = 35.5mA (71mA total) 000 = Shutdown (default)

0 = (Level Sensitive) When 0001 = 73mA (146mA total) 001 = Indicator Mode

STROBE goes high, Flash 0010 = 109mA (218mA total) 010 = Torch Mode

current will turn on and 0011 = 147.5mA (295mA total) 011 = Flash Mode (bits reset at timeout)

remain on for the duration the 0100 = 182.5mA (365mA total) 100 = Voltage Output Mode

STROBE pin is held high or 0101 = 220.5mA (441mA total) 101 = Voltage Output + Indicator Mode

when Flash Timeout occurs, 0110 = 259mA (518mA total) 110 = Voltage Output + Torch Mode

whichever comes 111 = 298mA (596mA total) 111 = Voltage Output + Flash Mode (bits [1:0]

first.(default) 1000 =326mA (652mA total) are reset at end of timeout)

1 = (Edge Triggered) When 1001 = 364.5mA (729mA total)

STROBE goes high , Flash 1010 = 402.5mA (805mA total)

current will turn on and 1011 = 440.5mA (881mA total)

remain on for the duration of 1100 = 480mA (960mA total)

the Flash Timeout. 1101 = 518.5mA (1037mA total) Default

1110 = 556.5mA (1113mA total)

1111 = 595.5mA (1191mA total)

FLASH DURATION REGISTER

Bits [4:0] of the Flash Duration Register set the Flash Timeout duration. Bits [6:5] set the switch current limit. Bit

[7] defaults as a '1' and is not used (see Table 5).

Figure 67. Flash Duration Register Description

Product Folder Links: LM3554

Bit 0

Bit 1

Bit 2

Bit 3

Bit 4Bit 5

Bit 7

MSB LSB

Flags Register

VIN Monitor

Fault LED Thermal

Fault TX2

Interrupt LED

Fault Thermal

Shutdown Flash

Timeout

TX1

Interrupt

N/A

Bit 6

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Table 5. Flash Duration Register Bit Settings

Bit 7 (Not Bit 6 (CL1) Bit 5 (CL0) Bit 4 (T4) Bit 3 (T3) Bit 2 (T2) Bit 1 (T1) Bit 0 (T0)

used)

Reads Back '0' Current Limit Select Bits Flash Timeout Select Bits

00 = 1A Peak Current Limit 00000 = 32ms timeout

01 = 1.5A Peak Current Limit 00001 = 64ms timeout

10 = 2A Peak Current 00010 = 96ms timeout

Limi(default) 00011 = 128ms timeout

11 = 2.5A Peak Current Limit 00100 = 160ms timeout

00101 = 192ms timeout

00110 = 224ms timeout

00111 = 256ms timeout

01000 = 288ms timeout

01001 = 320ms timeout

01010 = 352ms timeout

01011 = 384ms timeout

01100 = 416ms timeout

01101 = 448ms timeout

01110 = 480ms timeout

01111 = 512ms timeout (default)

10000 = 544ms timeout

10001 = 576ms timeout

10010 = 608ms timeout

10011 = 640ms timeout

10100 = 672ms timeout

10101 = 704ms timeout

10110 = 736ms timeout

10111 = 768ms time-out

11000 = 800ms timeout

11001 = 832ms timeout

11010 = 864ms timeout

11011 = 896ms timeout

11100 = 928ms timeout

11101 = 960ms timeout

11110 = 992ms timeout

11111 = 1024ms timeout

Flags Register

The Flags Register holds the status of the flag bits indicating LED Failure, Over-Temperature, the Flash Timeout

expiring, VIN Monitor Fault, LED over temperature (NTC), and a TX interrupt. (See Figure 67 and Table 6.)

Figure 68. Flags Register Description

Product Folder Links: LM3554

Bit 0Bit 1

Bit 2

Bit 3Bit 4Bit 5

TX1/

TORCH

Bit 7 Bit 6

MSB LSB

Configuration Register 1

TX2

Polarity ENVM/TX2 HYST Ext Flash

Inhibit OV LL

Disable

LEDI/NTC

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Table 6. Flags Register Bit Settings

Bit 7 (VIN Bit 6 (Unused) Bit 5 (LED Bit 4 (TX2 Bit 3 (TX1 Bit 2 (Led Bit 1 (Thermal Bit 0 (Flash

Monitor Fault Thermal Interrupt) Interrupt ) Fault) Shutdown) Timeout)

Fault) Fault)

0=No Fault at Not Used 0=LEDI/NTC 0=ENVM/TX2 0=TX1/TORCH 0 = Proper 0 = Die 0 = Flash

VIN (default) (Reads Back pin is above has not has not changed LED Operation Temperature TimeOut did not

'1') VTRIP (default) changed state state (default) (default) below Thermal expire (default)

(default) Shutdown Limit

(default)

1=Input 1=LEDI/NTC 1=ENVM/TX2 1=TX1/TORCH 1 = LED Failed 1 = Die 1 = Flash

Voltage has fallen has changed pin has changed (Open or Short Temperature TimeOut

Monitor is below state (TX2 state (TX1 mode has crossed Expired

enabled and VTRIP(NTC mode only) only) the Thermal

VIN has fallen mode only) Shutdown

below the Threshold

programmed

threshold

Configuration Register 1

Configuration Register 1 holds the light load disable bit, the voltage mode select bit (OV), the external flash

inhibit bit, the control bit for the LEDI/NTC pin, the control bit for ENVM to TX2 mode, the polarity selection bit for

the TX2 input, and the control bit for the TX1/TORCH bit (see Figure 69 and Table 7).

Figure 69. Configuration Register 1 Description

Table 7. Configuration Register 1 Bit Settings

Bit 7 Bit 6 (TX2 Bit 5 Bit 4 (N/A) Bit 3 Bit 2 (External Bit 1 (OV, Bit 0

(Hardware Polarity) (ENVM/TX2) (LEDI/NTC) Flash Inhibit) Output (Disable Light

Torch Mode Voltage Load )

Enable) Select)

0 = 0 = ENVM/TX2 0 = ENVM Reads Back '0' 0 = LEDI/NTC 0 = STROBE 0 = Voltage 0 = Light load

TX1/TORCH is pin is an active Mode The pin in Indicator Input Enabled Mode output comparator is

a TX1 flash low Flash ENVM/TX2 pin mode (default) (default) voltage is 4.5V enabled. The

interrupt input inhibit is a logic input LM3554 will go

(default) to enable into PFM mode

Voltage Mode. at light load

A high on (default).

ENVM/TX2 will

force Voltage

Output Mode

(default)

1 = 1 = ENVM/TX2 1 = TX2 Mode 1 = LEDI/NTC 1 = STROBE 1 = Voltage 1 = Light load

TX1/TORCH pin is an active The ENVM/TX2 pin in Thermal Input Disabled Mode output comparator is

pin is a high Flash is a Power Comparator voltage is 5V disabled. The

hardware inhibit (default) Amplifier Mode. Indicator (default) LM3554 will not

TORCH enable Synchronization current is go into PFM

input. A high on disabled. mode at light

ENVM/TX2 will load.

force the

LM3554 from

Flash to Torch

mode.

Product Folder Links: LM3554

Bit 0Bit 1

Bit 2

Bit 3Bit 4Bit 5

Not

Used

Bit 7 Bit 6

MSB LSB

GPIO Register

NTC

External

Flag Data Data

Direction Data Data

Direction TX1/TORCH/

GPIO1

ENVM/

TX2/GPIO2

Bit 0Bit 1

Bit 2

Bit 3Bit 4Bit 5

N/A

Bit 7 Bit 6

MSB LSB

Configuration Register 2

N/A AET

Mode NTC

Shutdown TX2

Shutdown

VIN Monitor

Mode

N/AN/A

LM3554

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SNVS549B –JUNE 2009–REVISED MAY 2013

Configuration Register 2

Configuration Register 2 contains the bits to select if TX2, NTC, and the VIN monitor force Torch mode or force

the Flash LEDs into shutdown. Additionally, bit [2] (AET bit) selects the Alternate External Torch mode (see

Figure 70 and Table 8).

Figure 70. Configuration Register 2 Description

Table 8. Configuration Register 2 Bit Settings

Bit 7 (Not Bit 6 (Not Bit 5 (Not Bit 4 (Not Bit 3 (VIN Bit 2 (AET Bit 1 Bit 0

used) used) used) used) Monitor mode) (NTC (TX2

Shutdown) Shutdown) Shutdown)

Reads Back '1' Reads Back '1' Reads Back '1' Reads Back '1' 0 = If IN drops 0 = Normal 0 = LEDI/NTC 0 = TX2 event

below the operation for pin going below forces the

programmed TX1/TORCH VTRIP forces the LEDs into

threshold and high before LEDs into Torch mode

the VIN Monitor STROBE (TX1 Torch mode (TX2 mode

feature is mode only) (NTC mode only) default

enabled, the default only) default

LED's are

forced into

Torch mode

(default)

1 = If IN drops 1 = Alternative 1 = LEDI/NTC 1 = TX2 event

below the External Torch pin going below forces the

programmed operation. VTRIP forces the LEDs into

threshold and TX1/TORCH LEDs into shutdown (TX2

the VIN Monitor high before shutdown (NTC mode only)

feature is STROBE mode only)

enabled, the forces Torch

LED's turn off mode with no

timeout (TX1

mode only)

GPIO Register

The GPIO register contains the control bits which change the state of the TX1/TORCH/GPIO1 pin and the

ENVM/TX2/GPIO2 pin to general purpose I/O’s (GPIO’s). Additionally, bit[6] of this register configures the

ENVM/TX2/GPIO2 as a hardware interrupt output reflecting the NTC flag bit in the Flags Register. Figure 71 and

Table 9 describe the bit description and functionality of the GPIO register.

Figure 71. GPIO Register Description

Product Folder Links: LM3554

Bit 0

Bit 1

Bit 2

Bit 3Bit 4Bit 5

N/A

Bit 7 Bit 6

MSB LSB

VIN Monitor Register

N/A Enable

N/A N/A N/A ThresholdThreshold

VIN VIN VIN

Monitor

LM3554

SNVS549B –JUNE 2009–REVISED MAY 2013

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Table 9. GPIO Register Bit Settings

Bit 7 (Not Bit 6 (NTC Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

Used) External Flag) (ENVM/TX2/GP (ENVM/TX2/GP (ENVM/TX2/GP (TX1/TORCH/G (TX1/TORCH/G (TX1/TORCH/G

IO2 data) IO2 data IO2 Control) PIO1 data) PIO1 data PIO1 Control)

direction) direction)

Reads Back '1' 0 = NTC This bit is the 0 = 0 = This bit is the 0 = 0 =

External Flag read or write ENVM/TX2/GPI ENVM/TX2/GPI read or write TX1/TORCH/G TX1/TORCH/G

mode is data for the O2 is a GPIO O2 is data for the PIO1 is a GPIO PIO1 pin is

disabled ENVM/TX2/GPI Input (default) configured TX1/TORCH/G input (default) configured as

(default) O2 pin in GPIO according to PIO1 pin in an active low

mode (default the GPIO mode reset input

is 0) Configuration (default is 0) (default)

(default)

1 = When 1 = 1 = 1 = 1 =

ENVM/TX2/GPI ENVM/TX2/GPI ENVM/TX2/GPI TX!/TORCH/GP TX1/TORCH/G

O2 is O2 is a GPIO O2 is IO1 is an PIO1 pin is

configured as a Output configured as a output configured as a

GPIO output GPIO GPIO

the

ENVM/TX2/GPI

O2 pin will pull

low when the

LED Thermal

Fault Flag is set

VIN MONITOR REGISTER

The VIN Monitor Register controls the on/off state of the VIN Monitor comparator as well as selects the 4

programmable thresholds. Figure 72 and Table 10 describe the bit settings of the VIN Monitor feature.

Figure 72. VIN Monitor Register Description

Table 10. VIN Monitor Register Bit Settings

Bit 7 (Not Bit 6 (Not Bit 5 (Not Bit 4 (Not Bit 3 (Not used) Bit 2 (VIN Bit 1 (VIN Bit 0 (VIN

used) used) used) used) Threshold) Threshold) Monitor Enable)

Reads Back '1' Reads Back '1' Reads Back '1' Reads Back '1' Reads Back '0' 00 = 3.1V threshold (VIN falling) 0 = VIN

Default Monitoring

01=3.2V threshold (VIN falling) Comparator is

10 = 3.3V threshold (VIN falling) disabled

11 = 3.4V threshold (VIN falling) (default)

1 = VIN

Monitoring

Comparator is

enabled.

Product Folder Links: LM3554

where IN INOUT

( )

- VV

L=I'

OUTSW V

I+

xR=V L

ESRESR '

'VxI OUTLED VIN ¹

Q=V'( )

INOUTLED - VVxI

OUTOUTSW CxVxf

LM3554

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SNVS549B –JUNE 2009–REVISED MAY 2013

APPLICATIONS INFORMATION

Output Capacitor Selection

The LM3554 is designed to operate with a at least a 4.7µF ceramic output capacitor in LED mode and a 10µF

output capacitor in Voltage Output Mode. When the boost converter is running the output capacitor supplies the

load current during the boost converters 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.

For proper LED operation the output capacitor must be at least a 4.7µF ceramic (10µF in Voltage Output Mode).

Larger capacitors such as 10µF or 22µF can 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

ESR (ΔVESR) use the following equations:

For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:

(9)

The output voltage ripple due to the output capacitors ESR is found by:

(10)

In ceramic capacitors the ESR is very low so assume that 80% of the output voltage ripple is due to capacitor

discharge and 20% from ESR. Table 11 lists different manufacturers for various output capacitors and their case

sizes suitable for use with the LM3554.

Input Capacitor Selection

Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching

of the LM3554’s boost converter and reduces noise on the devices input terminal that can feed through and

disrupt internal analog signals. In the Typical Application Circuit a 4.7µF ceramic input capacitor works well. It is

important to place the input capacitor as close as possible to the LM3554’s input (IN) terminals. This reduces the

series resistance and inductance that can inject noise into the device due to the input switching currents.

Table 11 lists various input capacitors that or recommended for use with the LM3554.

Table 11. Recommended Input/Output Capacitors (X5R Dielectric)

Manufacturer Part Number Value Case Size Voltage Rating

TDK Corporation C1608JB0J475K 4.7µF 0603(1.6mm×0.8mm×0.8mm) 6.3V

TDK Corporation C1608JB0J106M 10µF 0603(1.6mm×0.8mm×0.8mm) 6.3V

TDK Corporation C2012JB1C475K 4.7µF 0805(2mm×1.25mm×1.25mm) 16V

TDK Corporation C2012JB1A106M 10µF 0805(2mm×1.25mm×1.25mm) 10V

TDK Corporation C2012JB0J226M 22µF 0805(2mm×1.25mm×1.25mm) 6.3V

Murata GRM188R60J475KE19 4.7µF 0603(1.6mm×0.8mm×0.8mm) 6.3V

Murata GRM21BR61C475KA88 4.7µF 0805(2mm×1.25mm×1.25mm) 16V

Murata GRM21BR61A106KE19 10µF 0805(2mm×1.25mm×1.25mm) 10V

Murata GRM21BR60J226ME39L 22µF 0805(2mm×1.25mm×1.25mm) 6.3V

Product Folder Links: LM3554

R3 is then: .:k= 0719

V1( )

:V - 1V5.2xk047.6

= 047.6 :k

(TR )x:= k100 e -

+ 298

27393 1



( )

TRIP

- V

BIAS

)TRIP(T

TRIP

=3R

( ) C25

R=TR °298

273+C°T 1

E-¹

PEAK

ILOAD

=KxL

I+'where L=I'IN xV ( )

INOUT - VV

OUTSW VxLxfx2

OUT

LM3554

SNVS549B –JUNE 2009–REVISED MAY 2013

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Inductor Selection

The LM3554 is designed to use a 2.2µH inductor. Table 12 lists various inductors and their manufacturers that

can work well with the LM3554. When the device is boosting (VOUT > VIN) the inductor will typically be the biggest

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 should be greater than the maximum operating peak

current of the LM3554. This prevents excess efficiency loss that can occur with inductors that operate in

saturation and prevents over heating of the inductor and possible damage. For proper inductor operation and

circuit performance ensure that the inductor saturation and the peak current limit setting of the LM3554 is greater

than IPEAK can be calculated by:

(11)

ƒSW = 2MHz; ηcan be found in the Typical Performance Characteristics plots.

Table 12. Recommended Inductors

Manufacturer L Part Number Dimensions (L×W×H) ISAT

TOKO 2.2µH FDSE0312-2R2M 3mm×3mm×1.2mm 2A

TDK 2.2µH VLS252012T-2R2M1R3 2mm×2.5mm×1.2mm 1.5A

Coilcraft 2.2µH LPS4018-222ML 3.9mmx3.9mmx1.7mm 2.3A

NTC Thermistor Selection

NTC thermistors have a temperature to resistance relationship of:

(12)

where βis given in the thermistor datasheet and R25C is the thermistors value at +25°C. R3 in Figure 74 is

chosen so that it is equal to:

(13)

where R(T)TRIP is the thermistors value at the temperature trip point, VBIAS is shown in Figure 74, and VTRIP =

1.05V (typical). Choosing R3 here gives a more linear response around the temperature trip voltage. For

example, with VBIAS = 2.5V, a thermistor whose nominal value at +25°C is 100kΩand a β= 4500K, the trip point

is chosen to be +93°C. The value of R(T) at 93°C is:

(14)

Figure 73 shows the linearity of the thermistor resistive divider of the previous example.

Product Folder Links: LM3554

RVTRIP x 3

C°x298EC°273

LNC x°298

CT =° )(

ª(VV TRIPBIAS x- )RC°25

0.5

0.6

0.7

0.8

0.9

1.1

1.2

1.3

1.4

1.5

70 75 80 85 90 95 100 105 110

TEMPERATURE (°C)

VLEDI/NTC (V)

VBIAS = 2.5V,

@ +25°C, B = 4500,

R3 = 9 k:

RTHERMISTOR = 100 k:

LM3554

www.ti.com

SNVS549B –JUNE 2009–REVISED MAY 2013

Figure 73. Thermistor Resistive Divider Response vs Temperature

Another useful equation for the thermistor resistive divider is developed by combining the equations for R3, and

R(T) and solving for temperature. This gives the following relationship.

(15)

Using a spreadsheet such as Excel, different curves for the temperature trip point T(°C) can be created vs R3,

Beta, or VBIAS in order to help better choose the thermal components for practical values of thermistors, series

resistors (R3), or reference voltages VBIAS.

Programming bit [3] of the Configuration register with a (1) selects Thermal Comparator mode making the

LEDI/NTC pin a comparator input for flash LED thermal sensing. Figure 74 shows the internal block diagram of

the thermal sensing circuit which is OR’d with both the TX1 and ENVM/TX2 (TX2 mode) to force the LM3554

from Flash to Torch mode. This is intended to prevent LED overheating during flash pulses.

Product Folder Links: LM3554

1.05V

TX2

TX1/TORCH

Force Torch or

LED Shutdown (VIN Monitor, TX2 or

NTC only)

Internal to

LM3554

LEDI/

NTC

R(T)

0.1 PF

VIN Monitor

VBIAS

LM3554

SNVS549B –JUNE 2009–REVISED MAY 2013

www.ti.com

Figure 74. Thermistor Voltage Divider and Sensing Circuit

NTC Thermistor Placement

The termination of the thermistor must be done directly to the cathode of the Flash LED in order to adequately

couple the heat from the LED into the thermistor. Consequentally, the noisy environment generated from the

switching of the LM3554's boost converter can introduce noise from GND into the thermistor sensing input. To

filter out this noise it is necessary to place a 0.1µF or larger ceramic capacitor close to the LEDI/NTC pin. The

filter capacitor's return must also connect with a low-impedance trace, as close as possible to the PGND pin of

the LM3554.

Layout Recommendations

The high frequency and large switching currents of the LM3554 make the choice of layout important. The

following steps should be used as a reference to ensure the device is stable and maintains proper voltage and

current regulation across its intended operating voltage and current range.

1. Place CIN on the top layer (same layer as the LM3554) and as close to the device as possible. The input

capacitor conducts the driver currents during the low-side MOSFET turn-on and turn-off and can see current

spikes over 1A in amplitude. Connecting the input capacitor through short wide traces on both the IN and

GND terminals will reduce the inductive voltage spikes that occur during switching and which can corrupt the

VIN line.

2. Place COUT on the top layer (same layer as the LM3554) and as close as possible to the OUT and GND

terminal. The returns for both CIN and COUT should come together at one point, and as close to the GND pin

as possible. Connecting COUT through short wide traces will reduce the series inductance on the OUT and

GND terminals that can corrupt the VOUT and GND line and cause excessive noise in the device and

surrounding circuitry.

3. Connect the inductor on the top layer close to the SW pin. There should 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 should be small so as to reduce the capacitive coupling of the high dV/dt present at SW that can

couple into nearby traces.

4. Avoid routing logic traces near the SW node so as to avoid any capacitively coupled voltages from SW onto

any high-impedance logic lines such as TX1/TORCH/GPIO1, ENVM/TX2/GPIO2, HWEN, LEDI/NTC (NTC

mode), SDA, and SCL. A good approach is to insert an inner layer GND plane underneath the SW node and

Product Folder Links: LM3554

LM3554

www.ti.com

SNVS549B –JUNE 2009–REVISED MAY 2013

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 LM3554. If possible, route the LED returns

with a dedicated path so as to keep the high amplitude LED currents out the GND plane. For Flash LEDs

that are routed relatively far away from the LM3554, a good approach is to sandwich the forward and return

current paths over the top of each other on two layers. This will help in reducing the inductance of the LED

current paths.

6. The NTC Thermistor is intended to have its return path connected to the LED's cathode. This allows the

thermistor resistive divider voltage (VNTC) to trip the comparators threshold as VNTC is falling. Additionally, the

thermistor-to-LED cathode junction can have low thermal resistivity since both the LED and the thermistor

are electrically connected at GND. The drawback is that the thermistor's return will see the switching currents

from the LM3554's boost converter. Because of this, it is necessary to have a filter capacitor at the NTC pin

which terminates close to the GND of the LM3554 and which can conduct the switched currents to GND.

Product Folder Links: LM3554

LM3554

SNVS549B –JUNE 2009–REVISED MAY 2013

www.ti.com

REVISION HISTORY

Changes from Revision A (May 2013) to Revision B Page

• Changed layout of National Data Sheet to TI format .......................................................................................................... 39

Product Folder Links: LM3554

PACKAGE OPTION ADDENDUM

www.ti.com 3-May-2013

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish MSL Peak Temp

(3)

Op Temp (°C) Top-Side Markings

(4)

Samples

LM3554TME/NOPB ACTIVE DSBGA YFQ 16 250 Green (RoHS

& no Sb/Br) SNAGCU Level-1-260C-UNLIM -30 to 85 SF

LM3554TMX/NOPB ACTIVE DSBGA YFQ 16 3000 Green (RoHS

& no Sb/Br) SNAGCU Level-1-260C-UNLIM -30 to 85 SF

(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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability

information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that

lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.

Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between

the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.

Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight

in homogeneous material)

(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) Multiple Top-Side Markings will be inside parentheses. Only one Top-Side 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 Top-Side Marking for that device.

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.

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM3554TME/NOPB DSBGA YFQ 16 250 178.0 8.4 1.85 2.01 0.76 4.0 8.0 Q1

LM3554TMX/NOPB DSBGA YFQ 16 3000 178.0 8.4 1.85 2.01 0.76 4.0 8.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 8-May-2013

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM3554TME/NOPB DSBGA YFQ 16 250 210.0 185.0 35.0

LM3554TMX/NOPB DSBGA YFQ 16 3000 210.0 185.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 8-May-2013

Pack Materials-Page 2

MECHANICAL DATA

YFQ0016xxx

www.ti.com

TMD16XXX (Rev A)

0.600±0.075

. 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 =

1.685 mm, Min =

1.624 mm

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