TDA7389A Application hints
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3 Application hints
Ref. to the circuit of Figure 14.
3.1 SVR
Besides its contribution to the ripple rejection, the SVR capacitor governs the turn ON/OFF
time sequence and, consequently, plays an essential role in the pop optimization during
ON/OFF transients.
To conveniently serve both needs, its minimum recommended value is 22µF, 47µF can
be used to optimize pop performances.
3.2 Input stage
The TDA7389A’s inputs are ground-compatible and can stand very high input signals (±
8Vpk) without any performances degradation.
If the standard value for the input capacitors (0.1µF) is adopted, the low frequency cut-off
will amount to 16 Hz.
The input capacitors should be 1/4 of the capacitor connected to AC-GND pin for optimum
pop performances.
3.3 Standby and muting
Standby and muting facilities are both 3.3 V CMOS-compatible. If unused, a straight
connection to V
s
of their respective pins would be admissible.
Conventional/low-power transistors can be employed to drive muting and stand-by pins in
absence of true CMOS ports or microprocessors. R-C cells have always to be used in order
to smooth down the transitions for preventing any audible transient noises.
Since a DC current of about 10µA normally flows out of pin 23, the maximum allowable
muting-series resistance (R
2
) is 70 k, which is sufficiently high to permit a muting capacitor
reasonably small (about 1µF).
If R
2
is higher than recommended, the involved risk will be that the voltage at pin 23 may rise
to above the 1.2 V threshold voltage and the device will consequently fail to turn OFF when
the mute line is brought down.
About the stand-by, the time constant to be assigned in order to obtain a virtually pop-free
transition has to be slower than 2.5V/ms.
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