Daewoo 2898ST Service Manual page 20

No Name
1 SOUND IF INPUT
2 EXT AUDIO INPUT
3 VCO REF FILTER
4
5 PLL LOOP FILTER
6 IF VIDEO OUTPUT
7 BUS INPUT : SCL
8 BUS INPUT : SDA
9 BANDGAP
DECOUPLING
10 CHROMA INPUT
11 Y/CVBS INPUT
12 MAIN
37 POSITIVE SUPPLY
Description
not used.
not used.
The IF VCO tuned circuit is applied to these pin.
Its resonance frequency must be two times the IF-frequency and in between a
range of 64-120MHz.
This range is suitable for the IF standards as 33.4, 38.9, 45.75 and 58.75MHz.
The VCO frequency can be adjusted by I2C bus so a fixed coil can be used.
The PLL loopfilter is a first order filter with R=390 ohm and C = 100nF in
series to ground.
The loopfilter bandwidth is 60kHz and is optimal for both fast catching and
sufficient video suppression for optimal sound performance.
Sound performance can theoretically be improved by adding a small
capacitor (approx.0- 4.7nF) between pin 5 and ground.
This however must be evaluated further because the normal video signal
response should not be effected.
Although the video output impedance is low it is recommended to avoid
high frequency current in the output due to for instance sound trap filters.
This can be achieved by means of an emitter follower at the video output with
a 1 resistor in series with the base.
Serial clock line
Serial data line
The bandgap circuit provides a very stable and temperature independent
reference voltage.
This reference voltage (6.7V) ensures optimal performance of the TDA8375
and is used in almost all functional circuit blocks.
The supplied C S-VHS input burst amplitude should be nominally 300mVpp
(assumed is a colour bar signal with 75% saturation and with chroma/burst
ratio of 2.2/1 ). The C S-VHS input is internally clamped to 4V via 50 .
The external AC coupling capacitor with 50
A recommended coupling capacitor is 1 nF; the high pass filter cut off
frequency is then approximately 3KHz.
The Y S-VHS signal of 1Vpp ( inclusive sync amplitude) is AC coupled to pin11.
The TDA8375 has a main supply pin 12 and a horizontal supply pin 37. Both
pins have to be supplied simultaneously.
Notice that the IC has not been designed to use this pin 37 as start pin.
(pin 37 supplies the horizontal oscillator, PHI-1 and PHl-2)
(pin 12 supplies the rest of the circuits in the IC)
The nominal supply voltage is 8V. With min/max values of 7.2-8.8V.
Also in stand-by condition the IC must be supplied with 8V.
A voltage detection circuit is connected to both pins.
- pin12 if V12 <6.8V than a power on reset, POR, is generated. The Hout
output is disabled immediate.
- pin37 if V37 <5.8V than the horizontal output is disabled immediate.
20
forms a high pass filter.