BOOST

LED

DRIVERS

LOGIC

EEPROM

I

2

C/

INTERFACE

LDO

OSC

TSD

PWM

DETECTOR

SW

FB

VLDO

GND

GND_SW

GND_LED

EN

PWM

VDDIO

SCLK

SDA

OUT1

OUT2

OUT3

OUT4

PLL

FAULT

VIN

TEMP

SENSOR

MCU

VIN

FILTER

VSYNC

VSYNC

ISET

FSET

RISET

RFSET

LP8553

SNVS701B – SEPTEMBER 2011 – REVISED JANUARY 2014

www.ti.com

Four LED outputs are driven either with constant current sinks with PWM control or by controlling both PWM and

current. Constant current value is set with EEPROM bits and with RISET resistor. Brightness (PWM) is controlled

either with I2C register or with PWM input. PWM frequencies are set with EEPROM bits and with RFSET resistor.

Special Phase-Shift PWM mode can be used to reduce boost output current peak, thus reducing output ripple,

capacitor size and audible noise.

With LP8553 it is possible to synchronize the PWM output frequency to VSYNC signal received from video

processor. Internal PLL ensures that the PWM output clock is always synchronized to the VSYNC signal.

Special dithering mode makes it possible to increase output resolution during fading between two brightness

values and by this making the transition look very smooth with virtually no stepping. Transition slope time can be

adjusted with EEPROM bits.

Safety features include LED fault detection with open and short detection. LED fault detection will prevent system

overheating in case of open in some of the LED strings. Chip internal temperature is constantly monitored and

based on this LP8553 can reduce the brightness of the backlight to reduce thermal loading once certain trip point

is reached. Threshold is programmable in EEPROM. If chip internal temperature reaches too high, the boost

converter and LED outputs are completely turned off until the internal temperature has reached acceptable level.

Boost converter is protected against too high load current and over-voltage. LP8553 notifies the system about

the fault through I2C register and with FAULT pin.

EEPROM programmable functions include:

•

PWM frequencies

•

Phase shift PWM mode

•

LED constant current

•

Boost output frequency

•

Temperature thresholds

•

Slope for brightness changes

•

Dithering options

•

PWM output resolution

•

Boost control bits

External components RISET and RFSET can also be used for selecting the output current and PWM frequencies.

Block Diagram

12

Submit Documentation Feedback

Copyright © 2011–2014, Texas Instruments Incorporated

Product Folder Links: LP8553