TDA7377
Reliable and safe operation, in presence of all
kinds of short circuit involving the outputs is as-
sured by BUILT-IN protectors. Additionally to the
AC/DC short circuit to GND, to V
S
, across the
speaker, a SOFT SHORT condition is signalled
out during the TURN-ON PHASE so assuring cor-
rect operation for the device itself and for the
loudspeaker.
This particular kind of protection acts in a way to
avoid that the device is turned on (by ST-BY)
when a resistive path (less than 16 ohms) is pre-
sent between the output and GND. As the in-
volved circuitry is normally disabled when a cur-
rent higher than 5mA is flowing into the ST-BY
pin, it is important, in order not to disable it, to
have the external current source driving the ST-
BY pin limited to 5mA.
This extra function becomes particularly attractive
when, in the single ended configuration, one ca-
pacitor is shared between two outputs (see fig.
21).
Figure 21.
Figure 22:
Clipping Detection Waveforms
A current sinking at pin 10 is triggered when a
certain distortion level is reached at any of the
outputs. This function allows gain compression
possibility whenever the amplifier is overdriven.
Thermal Shutdown
In this case the output 10 will signal the proximity
of the junction temperature to the shutdown
threshold. Typically current sinking at pin 10 will
start ~10°C before the shutdown threshold is
reached.
HANDLING OF THE DIAGNOSTICS INFORMA-
Figure 23:
Output Fault Waveforms (see fig. 24)
Supposing that the output capacitor C
out
for any
reason is shorted, the loudspeaker will not be
damaged being this soft short circuit condition re-
vealed.
Diagnostics Facility
The TDA7377 is equipped with a diagnostic cir-
cuitry able to detect the following events:
Clipping in the output signal
Thermal shutdown
Output fault:
– short to GND
– short to V
S
– soft short at turn on
The information is available across an open
collector output (pin 10) through a current sink-
ing when the event is detected
TDA7377
6/10
STMICROELECTRONICS [ STMICROELECTRONICS ]
