TDA4689 Datasheet, PDF (16/24 Pages) NXP Semiconductors – Video processor with automatic cut-off control

Philips Semiconductors
Video processor with automatic cut-off control
Product specification
TDA4689
Notes to the characteristics
1. The values of the −(B − Y) and −(R − Y) colour difference input signals are for a 75% colour-bar signal.
2. The pins are capacitively coupled to a low ohmic source, with a recommended maximum output impedance of 600 Ω.
3. The white potentiometers affect the amplitudes of the RGB output signals.
4. The RGB outputs at pins 24, 22 and 20 are emitter followers with current sources.
5. Sandcastle pulses are compared with internal threshold voltages independent of V_P. The threshold voltages
separate the components of the sandcastle pulse. The particular component is generated when the voltage on pin 14
exceeds the defined internal threshold voltage.
The internal threshold voltages (control bit SC5 = 0) are:
1.5 V for horizontal and vertical blanking pulses
3.5 V for horizontal pulses
6.5 V for the burst key pulse.
The internal threshold voltages (control bit SC5 = 1) are:
1.5 V for horizontal and vertical blanking pulses
3.5 V for the burst key pulse.
6. Vertical signal blanking is determined by the vertical component of the sandcastle pulse. The leakage and the RGB
cut-off measurement lines are positioned in the first four complete lines after the end of the vertical component.
In this case, the RGB output signals are blanked until the end of the last measurement line; see Fig.7a. If an extra
vertical flyback pulse VFB is applied to pin 18, the four measurement lines start in the first complete line after the end
of the VFB pulse; see Fig.7b. In this case, the output signals are blanked either until the end of the last measurement
line or until the end of the vertical component of the sandcastle pulse, according to which occurs last.
7. If no VFB pulse is applied, pin 18 can be left open-circuit or connected to V_P. If pin 18 is always LOW neither
automatic cut-off control nor output clamping can happen.
8. Average beam current limiting reduces the contrast, at minimum contrast it reduces the brightness.
9. Peak drive limiting reduces the RGB outputs by reducing the contrast, at minimum contrast it reduces the brightness.
The maximum RGB outputs are determined via the I²C-bus under subaddress 0AH. When an RGB output exceeds
the maximum voltage, peak drive limiting is delayed by one horizontal line.
10. During leakage current measurement, the RGB channels are blanked to ultra-black level. During cut-off
measurement one channel is set to the measurement pulse level, the other channels are blanked to ultra-black.
Since the brightness adjust shifts the colour signal relative to the black level, the brightness adjust is disabled during
the vertical blanking interval (see Figs 6 and 7).
11. During picture cathode warming up (first switch-on delay) the RGB outputs (pins 24, 22 and 20) are blanked to the
ultra-black level during line scan. During the vertical blanking interval a white-level monitor pulse is fed out on the
RGB outputs and the cathode currents are measured. When the voltage threshold on pin 19 is greater than 4.5 V,
the monitor pulse is switched off and cut-off control is activated (second switch-on delay). As soon as cut-off control
stabilizes, RGB output blanking is removed.
12. Range of cut-off measurement level at the RGB outputs is 1 to 5 V. The recommended value is 3 V.
13. The hue control output at pin 26 is an emitter follower with current source.
1997 Jul 01
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