TDA8841-N2 Philips Semiconductors, TDA8841-N2 Datasheet - Page 16

• Manufacturer Part Number: TDA8841-N2
• Description: I2C-bus controlled PAL/NTSC/SECAM TV processors
• Manufacturer: Philips Semiconductors

Philips Semiconductors
An important property of the 2-point stabilisation is that the
off-set as well as the gain of the RGB path is adjusted by
the feedback loop. Hence the maximum drive voltage for
the cathode is fixed by the relation between the test
pulses, the reference current and the relative gain setting
of the 3 channels. This has the consequence that the drive
level of the CRT cannot be adjusted by adapting the gain
of the RGB output stage. Because different picture tubes
may require different drive levels the typical “cathode drive
level” amplitude can be adjusted by means of an I
setting. Dependent on the chosen cathode drive level the
typical gain of the RGB output stages can be fixed taking
into account the drive capability of the RGB outputs (pins
19 to 21). More details about the design will be given in the
application report.
The measurement of the “high” and the “low” current of the
2- point stabilisation circuit is carried out in 2 consecutive
fields. The leakage current is measured in each field. The
maximum allowable leakage current is 100 A
When the TV receiver is switched-on the RGB output
signals are blanked and the black current loop will try to set
the right picture tube bias levels. Via the AST bit a choice
can be made between automatic start-up or a start-up via
the -processor. In the automatic mode the RGB drive
signals are switched-on as soon as the black current loop
has been stabilised. In the other mode the BCF bit is set to
0 when the loop is stabilised. The RGB drive can than be
switched-on by setting the AST bit to 0. In the latter mode
some delay can be introduced between the setting of the
BCF bit and the switching of the AST bit so that switch-on
effects can be suppressed.
It is also possible to start-up the devices with a fixed
internal delay (as with the TDA 837X and the TDA884X/5X
N1). This mode is activated with the BCO bit.
The vertical blanking is adapted to the incoming CVBS
signal (50 Hz or 60 Hz). When the flyback time of the
vertical output stage is longer than the 60 Hz blanking time
the blanking can be increased to the same value as that of
the 50 Hz blanking. This can be set by means of the LBM
bit.
December 16, 1997
I
processors
2
C-bus controlled PAL/NTSC/SECAM TV
2
C-bus
16
For an easy (manual) adjustment of the V
the VSD bit is available. When this bit is activated the black
current loop is switched-off, a fixed black level is inserted
at the RGB outputs and the vertical scan is switched-off so
that a horizontal line is displayed on the screen. This line
can be used as indicator for the V
of the different requirements for the optimum cut-off
voltage of the picture tube the RGB output level is
adjustable when the VSD bit is activated. The control
range is 2.5
brightness control DAC.
It is possible to insert a so called “blue back” back-ground
level when no video is available. This feature can be
activated via the BB bit in the control2 subaddress.
I
The slave address of the IC’s is given in Fig.7. The circuit
operates up to clock frequencies of 400 kHz.
Start-up procedure
Read the status bytes until POR = 0 and send all
subaddress bytes. The horizontal output signal is
switched-on when the oscillator is calibrated.
Each time before the data in the IC is refreshed, the status
bytes must be read. If POR = 1, the procedure mentioned
above must be carried out to restart the IC.
When this procedure is not followed the horizontal
frequency may be incorrect after power-up or after a
power dip.
2
handbook, halfpage
C-BUS SPECIFICATION
A6
1
0.7 V and can be controlled via the
A5
Fig.7 Slave address (8A).
0
TDA884X/5X-N2 series
A4
0
A3
0
Tentative Device Specification
A2
1
g2
A1
0
adjustment. Because
A0
g2
1
control voltage
MLA743
R/W
1/0