LM3560 datasheet(13/48 Pages) TI1

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LM3560

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SNOSB43B – SEPTEMBER 2011 – REVISED AUGUST 2013

DEVICE INFORMATION

Overview

The LM3560 is a high-power white LED flash driver capable of delivering up to 2A of LED current into a single

LED, or up to 1A into two parallel LEDs. The device incorporates a 2MHz constant frequency, synchronous boost

converter, and two high-side current sources to regulate the LED current over the 2.5V to 5.5V input voltage

range.

During operation when the output voltage is greater than VIN – 150 mV the boost converter switches and

maintains at least 300 mV across both current sources (LED1 and LED2). This minimum headroom voltage

ensures that the current sources remain in regulation. When the input voltage rises above the LED voltage +

current source headroom voltage, the device stops switching and turns the PFET on continuously (Pass mode).

In Pass mode the difference between (VIN - ILED x RON_P) and the voltage across the LED's is dropped across the

current sources.

Four hardware control pins provide control of the LM3560. These include a hardware Flash Enable (STROBE),

Dual Flash Interrupt inputs (TX1 and TX2) designed to interrupt the flash pulse during high battery current

conditions, and a logic high hardware enable (HWEN) that can be pulled low to rapidly place the device into

shutdown. Additional features of the LM3560 include an internal 4-bit ADC for LED voltage monitoring, an

internal comparator for LED thermal sensing via an external NTC thermistor, an input voltage monitor that can

reduce the Flash current during input undervoltage conditions, a low-power message indicator LED current

source, and a mode for utilizing the flash LEDs as a privacy indicator.

Control of the LM3560 is done via an I2C-compatible interface. This includes adjustment of the Flash and Torch

current levels, adjustment of the indicator LED currents, changing the Flash Timeout Duration, changing the

switch current limit, and reading back the ADC results. Additionally, there are 8 flag bits that indicate flash current

time-out, LED over-temperature, LED failure (LED short or output OVP condition), device thermal shutdown, VIN

under voltage condition, VIN Flash Monitor undervoltage condition, and the occurrence of a TX1 or TX2 interrupt.

STARTUP (ENABLING THE DEVICE)

Turn-on of the LM3560 is done through bits [1:0] of the Enable Register. These bits enable the device in Torch

mode, Flash mode, or Privacy Indicate mode. Additionally, bit 6 of the Enable Register enables the message

indicator at the LEDI/NTC pin. On startup, when VOUT is less than VIN, the internal synchronous PFET turns on

as a current source and delivers 350 mA to the output capacitor. During this time both current sources (LED1,

and LED2) 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 and TORCH level until their target LED current is

reached (32 µs/step). This gives the device a controlled turn-on and limits inrush current from the VIN supply.

INDEPENDENT LED CONTROL

Bits [4:3] of the Enable register provide for independent turn-on and turn-off of the LED1 or LED2 current

sources. Once enabled, the LED current is adjusted by writing to the Torch Brightness or Flash Brightness

Registers depending on whether Flash or Torch mode is selected. Both the Torch Brightness and the Flash

Brightness Registers provide for independent current programming for the LED currents in either LED1 or LED2.

(See TORCH BRIGHTNESS REGISTER DESCRIPTIONS (Address 0xA0) and FLASH BRIGHTNESS

PASS MODE

On turn-on when the output voltage charges up to ( VIN – 150 mV), the LM3560 will decide if the part operates in

Pass Mode or Boost mode. If the voltage difference between VOUT and VLED is less then 300 mV, the device

operates in Boost Mode. If the difference between VOUT and VLED is greater then 300 mV, the device operates in

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

VOUT up to (VIN – IIN x RPMOS) where RPMOS = 80 mΩ. In Pass Mode the inductor current is not limited by the

peak current limit. In this situation the output current must be limited to 3A.

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