TDA7564 Datasheet, PDF (11/20 Pages) STMicroelectronics – MULTIFUNCTION QUAD POWER AMPLIFIER WITH BUILT-IN DIAGNOSTICS FEATURES

TDA7564
– After a diagnostic cycle, the audio channel interested by the fault is switched to RESTART mode. The
relevant data are stored inside the device and can be read by the microprocessor. When one cycle has
terminated, the next one is activated by an I²C reading. This is to ensure continuous diagnostics
throughout the car-radio operating time.
– To check the status of the device a sampling system is needed. The timing is chosen at microprocessor
level (over half a second is recommended).
Figure 19. Restart timing without Diagnostic Enable (Permanent) - Each 1mS time, a sampling of
the fault is done
1-2mS
1mS
1mS 1mS
1mS
Out
Overcurrent and short
circuit protection intervention
(i.e. short circuit to GND)
t
Short circuit removed
Figure 20. Restart timing with Diagnostic Enable (Permanent)
1-2mS
100/200mS
1mS
1mS
Overcurrent and short
circuit protection intervention
(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 1
– STOP = 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.
AC DIAGNOSTIC.
It is targeted at detecting accidental disconnection of tweeters in 2-way speaker and, more in general, presence
of capacitively (AC) coupled loads.
This diagnostic is based on the notion that the overall speaker's impedance (woofer + parallel tweeter) will tend
to increase towards high frequencies if the tweeter gets disconnected, because the remaining speaker (woofer)
would be out of its operating range (high impedance). The diagnostic decision is made according to peak output
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