TDA8366 Philips Semiconductors, TDA8366 Datasheet - Page 11

• Manufacturer Part Number: TDA8366
• Description: I2C-bus controlled PAL/NTSC TV processor
• Manufacturer: Philips Semiconductors

Philips Semiconductors
RGB output circuit and black-current stabilization
The colour-difference signals are matrixed with the
luminance signal to obtain the RGB-signals. For the
RGB-inputs linear amplifiers have been chosen so that the
circuit is suited for signals coming from the SCART
connector. The contrast and brightness control operate on
internal and external signals.
The output signal has an amplitude of approximately 2 V
black-to-white at nominal input signals and nominal
settings of the controls.
The black current stabilization is realized by means of a
feedback from the video output amplifiers to the RGB
control circuit. The ‘black current’ of the 3 guns of the
picture tube is internally measured and stabilized. The
black level control is active during 4 lines at the end of the
vertical blanking. During the first line the leakage current is
measured and the following 3 lines the 3 guns are
adjusted to the required level. The maximum acceptable
leakage current is 100 A. The nominal value of the
‘black current’ is 10 A. The ratio of the currents for the
various guns automatically tracks with the white point
adjustment so that the back-ground colour is the same as
the adjusted white point.
The input impedance of the ‘black-current’ measuring pin
is 15 k . Therefore the beam current during scan will
cause the input voltage to exceed the supply voltage. The
internal protection will start conducting so that the
excessive current is bypassed.
When the TV receiver is switched-on the black current
stabilization circuit is not active, the RGB outputs are
blanked and beam current limiting input pin is
short-circuited. Only during the measuring lines will the
outputs supply a voltage of 5 V to the video output stage
so that it can be detected if the picture tube is warming up.
These pulses are switched-on after a waiting time of
approximately 0.5 s. This ensures that the vertical
deflection is activated so that the measuring pulses are not
January 1995
I
processor
2
C-bus controlled PAL/NTSC TV
11
visible on the screen. As soon as the current supplied to
the measuring input exceeds a value of 190 A the
stabilization circuit is activated. After a waiting time of
approximately 0.8 s the blanking and the beam current
limiting input pin are released. The remaining switch-on
behaviour of the picture is determined by the external time
constant of the beam current limiting network.
I
Valid subaddresses: 00 to 13; subaddress FE is reserved
for test purposes. Auto-increment mode is available for
subaddresses.
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. It is possible
to have the horizontal output signal available before
calibration. Then the SFM bit must be set to logic 0.
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
X = don’t care.
A6
1
A5
Fig.4 Slave address (8A).
0
A4
0
A3
0
A2
1
A1
Objective specification
0
A0
1
TDA8366
MLA743
R/W
1/0