TDA8722 Datasheet, PDF (6/28 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
To bias the audio input it is necessary to put a resistor in
the application between pin 1 and ground. The resistor
has a typical value of 12 kΩ.
The RF part of the oscillator consists of:
• An oscillator which operates at the required video
carrier frequency. The range of the oscillator is
determined in the application by C5, C6, L5 and D5.
• An RF mixer. It first combines the video signal and the
sound subcarrier to build a baseband TV channel.
Then the baseband signal is mixed with the oscillator
signal to get the RF TV channel. The mixer has two
outputs which can be used as two independent
asymmetrical outputs, or as one symmetrical output. In
the event of asymmetrical use, the unused output must
be loaded with a 75 Ω resistor (see Fig.7).
The oscillator frequency is set by a programmable PLL
frequency synthesizer in accordance with equation:
f_osc = 8 × N × f_ref
Where:
f_osc is the local oscillator frequency.
N is a 12-bit dividing number (10 bits are programmable
by the I²C-bus).
f_ref is the crystal frequency (4 MHz) divided by 128
(31.25 kHz).
The circuit allows a step of 250 kHz but because only
10 bits are programmable, the programming steps are
1 MHz.
When the PLL loop is locked, both inputs of the phase
comparator are equal, which gives equation:
f_DIV = _8---f--^o_×--^s---^c_N--- = _1-f-^x--2-^t--^a_8--^l = f_ref
During the test mode operation, f_DIV and f_ref can be
monitored on the output Port pin (pin 14).
Software information
The synthesizer is controlled via a two-wire I²C-bus
receiver. For programming, the address byte (C8 HEX)
has to be sent first. Then one or two data bytes are used
to set the 10 programmable bits of the dividing number N,
the test bits (see Table 1) and the output Port state. Note
that after power-up of the IC, the two data bytes must be
sent.
handbook, full pagewidth
MBE395
0
10
20
30
40
50
60
70
t (µs)
64
Fig.3 Test pattern signal.
1998 Jun 23
6