September 1990

8

Philips Semiconductors

Preliminary specification

Horizontal/vertical synchronization circuit

TDA2579B

If the new TV station is weak, the sync-noise detector is activated. This will result in a change over of pin 18 voltage from

6.5 V to

≈10 V. When pin 18 exceeds the level of 7.8 V the phase detector is switched to slow time constant and gated

sync pulse condition. The current is also reduced during the vertical blanking period by 1 mA. When desired, most

conditions of the phase detector can also be set by external means in the following way:

a. Fast time constant TV transmitter identification circuit not active, connect pin 18 to earth (pin 9).

b. Fast time constant TV transmitter identification circuit active, connect a resistor of 220 k

Ω between pin 18 and ground.

This condition can also be set by using a 3.6 V stabistor diode instead of a resistor.

c. Slow time constant, (with exception of frame blanking period), connect pin 18 via a resistor of 10 k

Ω to + 12 V, pin 10.

In this condition the transmitter identification circuit is not active.

d. No switching to slow time constant desired (transmitter identification circuit active), connect a 6.8 V zener diode

between pin 18 and ground.

Fig.2 illustrates the operation of the 3 phase detector circuits.

Fig.2 Timing diagram, phase detectors.