TDA4687 Philips Semiconductors, TDA4687 Datasheet - Page 16

• Manufacturer Part Number: TDA4687
• Description: Video processor with automatic cut-off control
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Notes to the characteristics
1. The values of the (B
2. The pins are capacitively coupled to a low ohmic source, with a recommended maximum output impedance of 600 .
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
6. Vertical signal blanking is determined by the vertical component of the sandcastle pulse. The leakage and the RGB
7. If no VFB pulse is applied, pin 18 can be left open-circuit or connected to V
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.
10. During leakage current measurement, the RGB channels are blanked to ultra-black level. During cut-off
11. During picture cathode warming up (first switch-on delay) the RGB outputs (pins 24, 22 and 20) are blanked to the
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 Jun 23
Video processor with automatic cut-off control
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:
The internal threshold voltages (control bit SC5 = 1) are:
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.
automatic cut-off control nor output clamping can happen.
The maximum RGB outputs are determined via the I
the maximum voltage, peak drive limiting is delayed by one horizontal line.
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).
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.
1.5 V for horizontal and vertical blanking pulses
3.5 V for horizontal pulses
6.5 V for the burst key pulse.
1.5 V for horizontal and vertical blanking pulses
3.5 V for the burst key pulse.
Y) and (R
Y) colour difference input signals are for a 75% colour-bar signal.
2
C-bus under subaddress 0AH. When an RGB output exceeds
16
P
. If pin 18 is always LOW neither
P
. The threshold voltages
Product specification
TDA4687