TDA8722 Philips Semiconductors, TDA8722 Datasheet - Page 17

• Manufacturer Part Number: TDA8722
• Description: I2C-bus programmable modulator for negative video modulation and FM sound
• Manufacturer: Philips Semiconductors

Philips Semiconductors
In the design of the application, it is highly recommended
to separate the part of the RF oscillator as much as
possible from the part of the RF outputs in order to avoid
parasitic coupling between these two parts.
A good solution is shielding the RF oscillator part to avoid
radiation from and to this part. The pin 5 (OGND) must be
connected to the shielding box and to ground.
RF outputs
For inexpensive applications, it is possible to use the IC
with an asymmetrical output (pins 15 or 16). In this event,
the unused output pin must be loaded with a load as
1998 Jun 23
handbook, full pagewidth
I
negative video modulation and FM sound
2
C-bus programmable modulator for
VIDEO
AUDIO
R1
R2
Fig.9 Application using a symmetrical output with a balun transformer.
20
100 nF
1
C19
100 nF
C20
2
L3
15 H
56 pF
C3
R3
19
18
3
15 pF
C17
4
17
33 pF
C5
100 pF
R5
C16
BB215
TDA8722
L5
10 nF
16
D5
6
1
5
C7
TR1
17
2
6
33 pF
C6
R6
15
similar as possible to the load connected to the used pin,
see Fig.8.
A good improvement in performance is obtained using a
1 : 4 symmetrical to asymmetrical transformer
(balun; balance-to-unbalance) connected between the
two outputs. In this event both outputs have their loads
matched. The level of the RF second harmonic, and the
spurious outside channel is decreasing. The parasitic
coupling between RF outputs and RF oscillator is also
reduced (see Fig.9).
4
3
100 pF
R7
C15
617DB - 1010
7
TOKO - B4F
T8
14
8
150 nF
C8
R8
BC547B
13
R9
12
9
11
10
10 nF
C11
10 nF
C30
MBE404
Product specification
Q9
4 MHz
27 pF
C9
TDA8722
33 V
GND
PORT
SCL
SDA
5 V