LP8543 datasheet(12/40 Pages) TI

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LP8543

SNVS604D – AUGUST 2009 – REVISED MARCH 2013

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FUNCTIONAL OVERVIEW

The LP8543 is a high-voltage LED driver for medium-sized LCD backlight applications. It includes 38V boost

converter, 7 current sink outputs for the backlight and an interface for digital Ambient Light Sensor (ALS).

LP8543 can be controlled through SMBus or I2C serial interface or PWM input. Light-to-frequency type ambient

light sensor can be directly connected to LP8543 and the sensor response vs. LED brightness curve can be

programmed in the on-chip EEPROM memory.

LP8543 differs from conventional LED drivers due to following advanced features.

1. PHASE SHIFT PWM FEATURE

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LP8543 supports a state-of-the-art feature called Phase Shift PWM (PSPWM). Key advantages of the

PSPWM is improved power efficiency when there is variation in the forward voltages amongst the LED

strings. Due to an unmatched LED VF there is a random difference in each string forward voltage.

PSPWM optimizes the boost converter output voltage by turning off LED outputs periodically. The lower

the brightness, the more strings can be simultaneously off. When the strings with higher forward voltages

are turned off, the boost voltage is automatically lowered thereby improving efficiency. The second benefit

of PSPWM control is that it will make the boost and battery loading more constant. In other words, the

peak current needed from the battery is greatly reduced beause not all LED outputs are simultaneously

on.

2. PROGRAMMABLE OUTPUT STRINGS

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Programmability helps display manufacturers to fit LP8543 to several sizes of displays. The number of

output strings in use is a parameter in EEPROM and can be fixed during the manufacturing process of

displays. Based on the configuration the device will automatically adjust the phase Shift PWM function for

a given number of output strings. LP8543 supports of minimum of 4 strings and a maximum of 7 strings.

In this datasheet , strings 1 through 6 are classified as Display1, and string 7 is classified as Display2.

3. INDIVIDUALLY CONTROLLED LED STRING FOR BACKSIDE DISPLAY BACKLIGHT

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OUT7 string can be either used for main backlight or for possible back side sub display. Separate control

allows dimming through I2C interface and reduces extra components or ICs in display module.

4. LED FAULT DETECTION

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LED fault detection enables higher yield in display manufacturing process and also makes possible to

monitor backlight faults during normal operation. Fault test detects both open circuit (string with

unconnected or open circuit LED) and short circuit of 2 or more shorted LEDs. Single LED short can also

be detected if the amount of LEDs per string and/or the VF variation are sufficiently low. Threshold levels

are EEPROM programmable. Fault information is available in the status register and in the open drain

active low FAULT output.

5. LED PWM TEMPERATURE REGULATION

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This feature will decrease the effect of high temperature LED lifetime reduction. LP8543 reduces output

PWM of the LEDs at high temperatures and prevents overheating of the device and LEDs. Temperature

threshold can be programmed to EEPROM.

6. AMBIENT LIGHT SENSOR INTERFACE WITH USER PROGRAMMABLE CONTROL CURVE

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Ambient light sensing reduces power consumption and it allows natural backlight in any ambient light

condition. Programmability allows display manufacturer and even end user to control sensor to backlight

control loop. By integrating this feature LP8543 reduces external component count, wiring and complexity

of the design. LP8543 supports digital light-to-frequency type sensors. Prescaler and compensation curve

can be programmed in to the EEPROM.

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