TDA7360 Datasheet, PDF (17/22 Pages) STMicroelectronics – 22W BRIDGE / STEREO AUDIO AMPLIFIER WITH CLIPPING DETECTOR

TURN-OFF
A turn-off pop can occur if the st-by pin goes low
with a short time constant (this can occur if other
car radio sections, preamplifiers,radio.. are sup-
plied through the same st-by switch).
This pop is due to the fast switch-off of the inter-
nal current generator of the amplifier.
If the voltage present across the load becomes
rapidly zero (due to the fast switch off) a small
pop occurs, depending also on Cout,Rload.
The parameters that set the switch off time con-
stant of the st-by pin are:
♦ the st-by capacitor (Cst-by)
♦ the SVR capacitor (Csvr)
♦ resistors connected from st-by pin to ground
(Rext)
The time constant is given by :
T ≈ Csvr • 2000Ω // Rext + Cst-by • 2500Ω // Rext
The suggested time constants are :
T > 120ms with Cout=1000µF,RL = 4ohm,stereo
T > 170ms with Cout=2200µF,RL = 4ohm,stereo
If Rext is too low the Csvr can become too high
and a different approach may be useful (see next
section).
Figg 41, 42 show some types of electronic
switches (µP compatible) suitable for supplying
the st-by pin (it is important that Qsw is able to
saturate with VCE ≤ 150mV).
Also for turn off pop the bridge configuration is su-
Figure 41
TDA7360
perior, in particular the st-by pin can go low faster.
GLOBAL APPROACH TO SOLVING POP
PROBLEM BY USING THE MUTING/TURN ON
DELAY FUNCTION
In the real case turn-on and turn-off pop problems
are generated not only by the power amplifier,but
also (very often) by preamplifiers,tone controls,ra-
dios etc. and transmitted by the power amplifier to
the loudspeaker.
A simple approach to solving these problems is to
use the mute characteristics of the TDA7360.
If the SVR pin is at a voltage below 1.5 V, the
mute attenuation (typ) is 30dB .The amplifier is in
play mode when Vsvr overcomes 3.5 V.
With the circuit of fig 43 we can mute the amplifier
for a time Ton after switch-on and for a time Toff
after switch-off.During this period the circuitry that
precedes the power amplifier can produce spuri-
ous spikes that are not transmitted to the loud-
speaker. This can give back a very simple design
of this circuitry from the pop point of view.
A timing diagram of this circuit is illustrated in fig
44. Other advantages of this circuit are:
- A reduced time constant allowance of stand-by
pin turn off.Consequently it is possible to drive all
the car-radio with the signal that drives this pin.
-A better turn-off noise with signal on the output.
To drive two stereo amplifiers with this circuit it is
possible to use the circuit of fig 45.
Figure 42
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