LP8545 datasheet(13/44 Pages) TI1

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LP8545

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SNVS635D – APRIL 2010 – REVISED DECEMBER 2013

FUNCTIONAL DESCRIPTION

LP8545 is a high voltage LED driver for medium sized LCD backlight applications. It includes high voltage boost

converter which can be used either with internal FET or with external FET depending on boost output voltage

requirements. Boost voltage automatically sets to the correct level needed to drive the LED strings. This is done

by monitoring LED output voltage drop in real time.

Six constant current sinks with PWM control are used for driving LEDs. Constant current value is set with

EEPROM bits and with RISET resistor. Brightness (PWM) is controlled either with I

2C 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 LP8545 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 LP8545 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. LP8545 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.

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