Figure 17. Restart timing without Diagnostic Enable (Permanent)
Each 1mS time, a sampling of the fault is done
1-2mS
1mS
1mS
1mS
1mS
Overcurrent and short
circuit protection intervention
(i.e. short circuit to GND)
t
Short circuit removed
Figure 18. Restart timing with Diagnostic Enable (Permanent)
1mS
100mS
1mS
1mS
TDA7561
Out
Overcurrent and short
(i.e. short circuit to GND)
t
Short circuit removed
OUTPUT DC OFFSET DETECTION.
Any DC output offset exceeding ±2V are signalled out. This inconvenient might occur as a consequence of ini-
tially defective or aged and worn-out input capacitors feeding a DC component to the inputs, so putting the
speakers at risk of overheating.
This diagnostic has to be performed with low-level output AC signal (or Vin = 0).
The test is run with selectable time duration by microprocessor (from a "start" to a "stop" command):START =
Last reading operation or setting IB1 - D5 - (OFFSET enable) to 1STOP = Actual reading operation
Excess offset is signalled out if persistent throughout the assigned testing time. This feature is disabled if any
overloads leading to activation of the short-circuit protection occurs in the process.
MULTIPLE FAULTS.
When more misconnections are simultaneously in place at the audio outputs, it is guaranteed that at least one
of them is initially read out. The others are notified after successive cycles of I2C reading and faults removal,
provided that the diagnostic is enabled. This is true for both kinds of diagnostic (Turn on and Permanent).
The table below shows all the couples of possible double-fault. It should be taken into account that a short circuit
with the 4 ohm speaker unconnected is considered as double fault.
Double fault table for Turn On Diagnostic
S. GND (so)
S. GND (sk)
S. Vs
S. Across L.
Open L.
S. GND (so) S. GND
S. GND
S. Vs + S. GND
S. GND
S. GND
S. GND (sk) /
S. GND
S. Vs
S. GND
Open L. (*)
S. Vs
/
/
S. Vs
S. Vs
S. Vs
S. Across L. /
/
/
S. Across L.
N.A.
Open L.
/
/
/
/
Open L. (*)
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