LP8543 datasheet(13/40 Pages) TI

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LP8543

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SNVS604D – AUGUST 2009 – REVISED MARCH 2013

Brightness Control Methods

1. CURRENT CONTROL

–

The 8-bit LED current default value is read from EEPROM when the chip is activated. Current value can

be used for fine tuning the backlight brightness between panels. This current setting can be overridden by

a register write from the serial interface. Current control range is from 0 to 60 mA with 0.23 mA step. This

fine grained current control gives backlight manufacturer possibility to adapt different LED bins in one

product and maintain the full PWM control range. There are separate controls for both Display1 and

Display2.

2. INTERNAL PWM CONTROL

–

The basic brightness control is register based 8-bit PWM control. There is a piecewise linear transfer

curve from register value to LED PWM value and the curve coefficients are stored in the EEPROM. This

makes possible to calibrate the 100% brightness and the dimming behavior. LED PWM frequency is

selectable from 229 Hz to 19.5 kHz. In addition PSPWM can be used.

3. EXTERNAL PWM CONTROL

–

An external PWM signal can be used to set the brightness of the display. LP8543 measures the duty

cycle of this input signal to calculate the output PWM value. Input PWM frequency can vary from 100 Hz

to 25 kHz. Based on the configuration selected, this external PWM control can linearly reduce the

brightness from the value set by the Brightness Register. This external PWM control can also be used as

the only control for LP8543. In this case, when PWM input is permanently low, the chip is turned off.

When there is signal in PWM input, the chip turns on and adjusts brightness according to PWM signal

duty cycle. In addition, PSPWM can also be used in this mode.

4. AMBIENT LIGHT SENSING

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External ambient light sensor can be used for controlling the brightness of the LEDs. Light-to- Frequency

type light sensor can be connected to ALSI input in LP8543 for ambient light compensation. Transfer

curve coefficients for response setting are stored in EEPROM. LP8543 has an enable output, ALSO to

activate the light sensor (active high/low, programmed to EEPROM). Light sensor supply voltage can be

taken from the 5V regulator in LP8543. Ambient light control is possible for Display1 (4-7 outputs).

Calibration

LP8543 has an internal EEPROM to store different control parameters which allows calibrating the backlight

brightness at various brightness settings so that every display has exactly the same brightness and several

LP8543 circuits can be used in the same display if needed.

Programming the EEPROM is easy. User needs to write the data in the shadow RAM memory and give the

EEPROM write command. On-chip boost converter produces the needed erase and program voltages, no

external voltages other than normal input voltage are required.

Calibration in backlight or display production can be done according to the flowchart below

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