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TDA8366

I2C-bus controlled PAL/NTSC TV processor

Philips Electronics 

Philips Semiconductors

I2C-bus controlled PAL/NTSC TV

processor

Objective specification

TDA8366

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 µA. The nominal value of the

‘black current’ is 10 µA. 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 kΩ. 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

visible on the screen. As soon as the current supplied to

the measuring input exceeds a value of 190 µA 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.

I2C-BUS SPECIFICATION

handbook, halfpage

A6 A5 A4 A3 A2 A1 A0 R/W

1 0 0 0 1 0 1 1/0

MLA743

X = don’t care.

Fig.4 Slave address (8A).

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.

January 1995

11

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