LP85571 datasheet(11/49 Pages) TI2

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LED Current Sinks

PWM Control

Headroom

Control

LED1

LED2

LED3

LED4

LED5

LED6

Boost Converter

Switching

Frequency

500, 1000 kHz

Oscillator

Thermal

shutdown

Reference

Voltage

VDD

PWM

POR

Digital Logic

Fault Detection

(Open*/Short LED,

OCP, OVP)

VIN

FSET / SDA

ISET /SCL

BRIGHTNESS

CONTROL

EPROM

BOOST_FREQ

VOUT

UVLO

LP8557, LP85571

www.ti.com

SNVSA15B – DECEMBER 2013 – REVISED DECEMBER 2015

8 Detailed Description

8.1 Overview

The LP8557 and LP8557I are high-efficiency LED drivers each featuring an integrated DC-DC inductive boost

converter and six high-precision current sinks. LP8557 is intended for applications that exclusively use a pulse

width modulated (PWM) signal for controlling the brightness while LP8557I is intended for applications that can

utilize an I2C master as well.

The boost converter has adaptive output voltage control. This feature minimizes the power consumption by

adjusting the voltage to the lowest sufficient level under all conditions.

The adaptive current sink headroom voltage control scales the headroom voltage with the LED current for

optimal system efficiency.

The LED string auto-detect function enables use of the same device in systems with 1 to 6 LED strings for the

maximum design flexibility.

Proprietary hybrid PWM plus current mode dimming enables additional system power savings. Phase shift PWM

allows reduced audible noise and smaller boost output capacitors.

Flexible CABC support combines brightness level selections based on the PWM input and I2C commands.

The LP8557 and LP8557I feature a full set of features that ensure robust operation of the device and external

components. The set consists of input undervoltage lockout, thermal shutdown, overcurrent protection,

overvoltage protection, and LED open and short detection.

8.2 Functional Block Diagram

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