LM3554TMXSLASHNOPB datasheet(13/47 Pages) TI1

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VREF

PWM

Control

2 MHz

Oscillator

Thermal

Shutdown

+150

VREF

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 m

150 m:

Over Voltage

Comparator

VTRIP

ILEDI

ILED2

ILED1

LM3554

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SNVS549C – JUNE 2009 – REVISED FEBRUARY 2016

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7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Start-Up

The device is turned on 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 start-up, when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers

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

When the voltage across the output capacitor reaches 2.2 V, the current sources can turn on. At turnon 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 turnon and limits inrush current from the VIN supply.

7.3.2 Overvoltage Protection

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

the LM3554 raises the output voltage in order to keep the LED current at its target value. When VOUT reaches 5.6

V the overvoltage comparator trips and turns off both the internal NFET and PFET. When VOUT falls below 5.4 V

(typical), the LM3554 begins switching again.

7.3.3 Current Limit

The LM3554 features four selectable current limits: 1 A, 1.5 A, 2 A, and 2.5 A. 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 device stops switching for the remainder of the switching cycle.

LM3554TMX/NOPB Datasheet(PDF) 13 Page - Texas Instruments

LM3554TMX/NOPB Datasheet(HTML) 13 Page - Texas Instruments

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