Only For Training And Service Purposes - LG GB220 Service Manual

3. TECHNICAL BRIEF
LED Backlight Current Sinks
The backlight current is set via the SemWire interface. The current is regulated to one of 32 values between
0.5mA and 25mA. The step size varies depending upon the current setting. Between 0.5mA and 12mA, the
step size is 0.5mA. The step size increases to 1mA for settings between 12mA and 15mA and 2mA for settings
greater than 15mA. This feature allows fi ner adjustment for dimming functions in the low current setting
range and coarse adjustment at higher current settings where small current changes are not visibly
noticeable in LED brightness.
All backlight current sinks have matched currents, even when there is variation in the forward voltages (ΔVF )
of the LEDs. A ΔVF of 1.2V is supported when the input voltage is at 3.0V. Higher ΔVF LED mis-match is
supported when VIN is higher than 3.0V. All current sink outputs are compared and the lowest output is used
for setting the voltage regulation at the VOUT pin. This is done to ensure that sufficient bias exists for all LEDs.
The backlight LEDs default to the off state upon powerup. For backlight applications using less than four LEDs,
any unused output must be left open and the unused LED driver must remain disabled. When writing to the
Backlight Enable Control register, a zero
Backlight Quiescent Current
The quiescent current required to operate all four backlights is reduced by 1.5mA when backlight current is
set to 4.0mA or less. This feature results in higher efficiency under light-load conditions. Further reduction in
quiescent current will result from using fewer than four LEDs.
LGE Internal Use Only
LGE Internal Use Only
(0) must be written to the corresponding bit of any unused output.
- 50 - Copyright © 2009 LG Electronics. Inc. All right reserved.

Only for training and service purposes

Copyright © 2007 LG Electronics. Inc. All right reserved.
Only for training and service purposes