TDA7566 Datasheet, PDF (12/19 Pages) STMicroelectronics – MULTIFUNCTION QUAD POWER AMPLIFIER WITH BUILT-IN DIAGNOSTICS FEATURES

TDA7566
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 double-fault possible. 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. GND (so)
S. GND
S. GND
S. GND (sk)
/
S. GND
S. Vs
S. Vs + S. GND
S. Vs
S. Across L.
S. GND
S. GND
Open L.
S. GND
Open L. (*)
S. Vs
/
S. Across L.
/
Open L.
/
/
S. Vs
S. Vs
S. Vs
/
/
S. Across L.
N.A.
/
/
/
Open L. (*)
S. GND (so) / S. GND (sk) in the above table make a distinction according to which of the 2 outputs is shorted
to ground (test-current source side= so, test-current sink side = sk). More precisely, in channels LF and LR, so
= CH+, sk = CH-; in channels LR and RF, so = CH-, SK = CH+.
In Permanent Diagnostic the table is the same, with only a difference concerning Open Load (*), which is not
among the recognisable faults. Should an Open Load be present during the device's normal working, it would
be detected at a subsequent Turn on Diagnostic cycle (i.e. at the successive Car Radio Turn on).
FAULTS AVAILABILITY
All the results coming from I2Cbus, by read operations, are the consequence of measurements inside a defined
period of time. If the fault is stable throughout the whole period, it will be sent out. This is true for DC diagnostic
(Turn on and Permanent), for Offset Detector, for AC Diagnostic (the low current sensor needs to be stable to
confirm the Open tweeter).
To guarantee always resident functions, every kind of diagnostic cycles (Turn on, Permanent, Offset, AC) will
be reactivate after any I2C reading operation. So, when the micro reads the I²C, a new cycle will be able to start,
but the read data will come from the previous diag. cycle (i.e. The device is in Turn On state, with a short to Gnd,
then the short is removed and micro reads I²C. The short to Gnd is still present in bytes, because it is the result
of the previous cycle. If another I²C reading operation occurs, the bytes do not show the short). In general to
observe a change in Diagnostic bytes, two I²C reading operations are necessary.
I²C PROGRAMMING/READING SEQUENCE
A correct turn on/off sequence respectful of the diagnostic timings and producing no audible noises could be as
follows (after battery connection):
TURN-ON: (STAND-BY OUT + DIAG ENABLE) --- 500 ms (min) --- MUTING OUT
TURN-OFF: MUTING IN --- 20 ms --- (DIAG DISABLE + STAND-BY IN)
Car Radio Installation: DIAG ENABLE (write) --- 200 ms --- I2C read (repeat until All faults disappear).
AC TEST: FEED H.F. TONE -- AC DIAG ENABLE (write) --- WAIT > 3 CYCLES --- I2C read
(repeat I2C reading until tweeter-off message disappears).
OFFSET TEST: Device in Play (no signal) -- OFFSET ENABLE - 30ms - I2C reading
(repeat I2C reading until high-offset message disappears).
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