TDA4504B Datasheet, PDF (8/26 Pages) NXP Semiconductors – Small signal combination for multistandard colour TV

Philips Semiconductors
Small signal combination for multistandard colour TV
Product specification
TDA4504B
50/60 Hz Information
In the external video mode and with a resistor of 1 MΩ from pin 25 to V_CC the mute is overruled by the 50/60 Hz
information from the divider system.
50/60 Hz Truth Table:
Input Signal
Pin 9/10
Pin 25
Pin 28
Pin 18
Pin 14
50 Hz
9.5
50 Hz
LOW
12
60 Hz
9.5
60 Hz
LOW
9
None
0.3
None
LOW
0.3
Don’t care
Don’t care
Don’t care
9.5
50 Hz
HIGH
12
9.5
60 Hz
HIGH
9
9.5
None
HIGH
12
VCR switch
Flywheel horizontal synchronization is desirable when receiving weak signals marred by noise but is usually unnecessary
when receiving stronger off-air signals unless certain types of interference or multipath reception are apparent. Due to
the inherent instability of VCR signals, however, the horizontal time constant should be shorter to prevent loss of
horizontal synchronization in the early part of the scan. Provision is therefore incorporated to automatically switch the
short time constant such that a strong signal instigates the 'VCR' mode and a weak signal triggers the 'TV' mode.
The connection of a switch to pin 17 provides for this to be accomplished manually and may take the form of an auxiliary
switching function associated with a designated program selector button.
The TDA4504B has a separate pin (pin 17) for the VCR switch:
pin 17
HIGH:
VCR mode
pin 17
pin 17
n.c.:
LOW:
auto VCR mode
TV mode
fast time constant; ungated
slow time constant; gated
Video-switch
Video output from the demodulator is filtered to remove the audio carrier and DC-coupled to pin 16. If AC-coupling is
employed the internal noise clamp will operate on sync. tips.
The TDA4504B provides the opportunity for a direct video connection (e.g. via a peritel connector) to be made to the
device at pin 13. Selection between internal and external video is made by applying a switching potential to pin 18.
Video switch:
pin 18
pin 18
LOW:
HIGH:
internal video
external video
Gain reduction
To prevent crosstalk between the IF stages and the horizontal oscillator when the device is operated in its external video
mode with no RF input, the TDA4504B incorporates an option to reduce IF gain by 20 dB. This is accomplished by
connecting a 39 kΩ resistor between pin 17 and ground. Omission of this component results in the IF amplifier remaining
at full gain.
In the internal video mode the resistor must be disconnected to achieve the auto-VCR mode.
February 1992
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