LM3559 datasheet(11/50 Pages) TI1

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LM3559

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SNVS624B – JUNE 2011 – REVISED JUNE 2016

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8 Detailed Description

8.1 Overview

The LM3559 is a high-power white LED flash driver capable of delivering up to 1.8 A of LED current into a single

LED, or up to 900 mA into two parallel LEDs. The device incorporates a 2-MHz constant frequency, synchronous

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

voltage range.

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

maintains at least 270 mV across both current sources (LED1 and LED2). This minimum headroom voltage

ensures that the current sinks 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 × RON_P) and the voltage across the LEDs is dropped across the current

sources.

Four hardware control pins provide control of the LM3559 device. 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 LM3559 include an internal 4-bit ADC for LED voltage monitoring, an

internal comparator for LED thermal sensing via an external NTC thermistor, a battery voltage monitor during

flash current turnon which monitors VIN and optimizes the flash current during low-battery voltage conditions, an

input voltage monitor that can force torch mode or LED shutdown of the flash current during input undervoltage

conditions, a low-power Indicator current source with programmable patterns, and a mode for utilizing the flash

LEDs as a privacy indicator.

Control of the LM3559 is done via an I2C-compatible interface. This includes adjustment of the flash and torch

current levels, adjustment of the indicator LED currents and indicator pattern, 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 timeout, LED overtemperature, LED failure (by sensing LED short or output OVP

condition during flash, torch, or privacy modes), device thermal shutdown, VIN undervoltage condition, tripping of

the VIN flash monitor, and the occurrence of a TX interrupt (both TX1 and TX2).

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