TDA7360 Datasheet, PDF (14/22 Pages) STMicroelectronics – 22W BRIDGE / STEREO AUDIO AMPLIFIER WITH CLIPPING DETECTOR

TDA7360
Figure 33: A Classical Output Stage
Figure 34: Amplifier Block Diagram
BUILT-IN PROTECTION SYSTEMS
Short Circuit Protection
The maximum current the device can deliver can
be calculated by considering the voltage that may
be present at the terminals of a car radio amplifier
and the minimum load impedance.
Apart from consideration concerning the area of
the power transistors it is not difficult to achieve
peak currents of this magnitude (5 A peak).
However, it becomes more complicated if AC and
DC short circuit protection is also required.In par-
ticular, with a protection circuit which limits the
output current following the SOA curve of the out-
put transistors it is possible that in some condi-
tions (highly reactive loads, for example) the pro-
tection circuit may intervene during normal
operation. For this reason each amplifier has
been equipped with a protection circuit that inter-
venes when the output current exceeds 4A
Fig 35 shows the protection circuit for an NPN
power transistor (a symmetrical circuit applies to
PNP).The VBE of the power is monitored and
gives out a signal,available through a cascode.
This cascode is used to avoid the intervention of
the short circuit protection when the saturation is
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below a given limit.
The signal sets a flip-flop which forces the amplifier
outputs into a high impedance state.
In case of DC short circuit when the short circuit
is removed the flip-flop is reset and restarts the
circuit (fig. 39). In case of AC short circuit or load
shorted in Bridge configuration, the device is con-
tinuously switched in ON/OFF conditions and the
current is limited.
Figure 35: Circuitry for Short Circuit Detection