MB87P2020 Datasheet, PDF (215/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

1 Introduction
CCFL Driver
The Cold Cathode Fluorescence Light Driver is used to generate the needed signals for controlling a
switched power supply and ionisation circuit of a cold cathode lamp. The intention was that brightness of
the lamp should be adjustable in a wide range.
Following figure shows a block diagram of the circuit driving the cold cathode lamp which can be used for
generating high voltage supplying the displays back light.
CTRL
CBP
CCFL
OFF
IGNIT
FET1
FET2
Supply
Inverter
GPU
SYNC
VIDEO
Display
GDC
Figure 1-1: Application overview for the CCFL circuit
In general CCFL is independent from other GDC components. It is initialized via the Control Bus Port
(CBP) interface which is used to setup almost all GDC control registers. After initialization CCFL works
as stand-alone circuit.
To avoid interferences between back light flashing frequency and picture refresh rate of the display a syn-
chronization input is provided which internally is connected with the video frame synchronization signal of
the Graphic Processing Unit (GPU). Another synchronization method is possible by the connected MCU
over the control interface when writing to the synchronization flag of the control register.
MB87P2020-A has a connection to GPU sync mixer 5 as third synchronization possibility. Because a sync
mixer can match many display coordinates within one GPU frame (see GPU description for details about
sync signal generation) a higher CCFL frequency compared to simple frame synchronization can be
achieved without losing synchronization between CCFL and display output.
In short terms the CCFL has the following synchronization possibilities:
• Internal GPU frame synchronization
• Software synchronization
• Internal sync mixer synchronization (MB87P2020-A only)
Simply spoken the CCFL circuit is a kind of pulse width modulation of lightning duration of the fluores-
cence lamp within one frame period of the display. If the lamp is switched on CCFL provides bi-phase pulse
signals (pins CCFL_FET1, CCFL_FET2) for direct controlling the complementary FET gates of primary
inductance of the voltage transverter. Additional to controlling the lightning and off durations the ignition
of the lamp is handled (pins: CCFL_OFF, CCFL_IGNIT).
Introduction
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