TDA8722 Datasheet, PDF (17/28 Pages) NXP Semiconductors – I2C-bus programmable modulator for negative video modulation and FM sound

Philips Semiconductors
I²C-bus programmable modulator for
negative video modulation and FM sound
Product specification
TDA8722
handbook, full pagewidth
VIDEO
R20
470 Ω
100 nF
C19
RF
75 Ω
R18
82 Ω
R19
470 Ω
6
4
TR1
12 3
TOKO - B4F
617DB - 1010
100 nF
C20
C17
15 pF
R17
120 kΩ
100 pF
C16
R15
300 Ω
100 pF
C15
20
19 18
17
16
15
14 13 12 11
TDA8722
12
3
AUDIO
C1
220 pF
R1
220 kΩ
R2
12 kΩ
C3
56 pF
R3
15 kΩ
L3
15 µH
4
56
78
9 10
150 nF
L5
C8
33 pF
C5
D5
33 pF
C6
BB215
R5
22 kΩ
R6
22 kΩ
R7
R8
12 kΩ
R9
22 kΩ
10 nF
C7
12 kΩ
T8
BC547B
PORT
SCL
SDA
5V
10 nF
C11
Q9
4 MHz
27 pF
C9
33 V
C30
10 nF
MBE404
GND
Fig.9 Application using a symmetrical output with a balun transformer.
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
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).
1998 Jun 23
17