MB87P2020 Datasheet, PDF (221/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

4 Application Notes
CCFL Driver
4.1 CCFL Setup Example
The time base of CCFL Driver should be near 800 ns. Assumed we have a system clock frequency CLKK
of 60 MHz (16.6 ns).
t_bper = 800 ns
CCFL1_SCL = t_CLKK / t_bper = 800 ns / 16.6 ns = 48 = 0x30
We have to setup a prescaler value of 0x30 in the SCALE register.
Possible values for Ignition duration and Pause can be 0x10 and 0x80 for instance. This depends mainly on
the lamp characteristics and is not too critical for setting up the right value.
If we have a frame rate of 60 Hz so we get nearly
1 / 60Hz / 800ns = 20833 t_bper = 0x5161 t_bper cycles.
Due to the fact that setup duration values are interpreted as macro cycles of 4 times t_bper one period has a
duration of
0x5161 t_bper cycles / 4 = 0x1458 macro cycles.
After subtraction of 0x10 ignition time and 0x80 pause duration and 1 for the start-up phase we got the re-
sulting dimming range of 0x0000 to 0x13C7 macro cycles from dark to full luminescence.
Be careful not to setup a larger value for FLASH duration, then the lamp ignition may happen each other
frame only and is flickering then.
4.2 CCFL Protection
During initialization of setup values there is no need to switch off the CCFL driver. To avoid inconsistency
of configuration data a protection mechanism can be used. This method offers a way that no forbidden out-
put timing is generated and the lamp or the supply circuitry would not be damaged. To do a secure config-
uration following sequence should be used:
1. Switch CCFL_PROT to ’1’
2. Configure CCFL2 duration registers.
3. Release protection by setting CCFL_PROT = ’0’
This gives the possibility to modulate the durations without switching the lamp off.
Application Notes
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