TDA7572 Datasheet, PDF (51/64 Pages) STMicroelectronics – 200W mono bridge PWM amplifier with built-in step-up converter

TDA7572
Diagnostics
10.1.8
Events that put in tri-state the Modulator:
– Diagnostic on
– Offset detection
– Output over-current second threshold trespassed
Events that enable the Fault Pin without I²C bus:
– Diagnostic Fault
– Junction thermal warning
– External thermal warning
– Supply current over-threshold
– Offset detection
Events that enable the SCR:
– Over-temperature protection
– Output over-current second threshold trespassed
– Supply current over-threshold
Faults during power-up:
This is a power-up diagnostic useful to detect: load short to ground, load short to supply,
short across the transducer, open transducer. The PUD could be performed with and
without I²C bus.
● I²Cbus: setting the bit 4 of Fault1 register the diagnostic begin. The capacitor TestC is
then charged by a Thevenin circuits with R = 155 kOhm and supply equal to 1.75V. The
value of capacitor is choose in order to have an audible charge ramp and at the same
time in order to have an acceptable charge time. The diagnostic time start when the
TestC pin reaches the 98% of full charge. During the diagnostic time of 100 ms a
current equal to
I = ₃-----_â‹--²-_R--^.--⁴-_I--_S5----_e----_t
The drop across the load produced by this current is continuously monitored. A fault is
detected if the drop and/or the absolute value of pin HB1Out and HB2Out are abnormal
for the full 100 ms period set when a fault is detected the correspondent bit in the Fault1
register is set and the diagnostic keep running until the fault is present. In case no fault
is detected after the 100 ms period the capacitor is discharged and the current on the
load is reduced down to zero. When this current is at the 2% of is nominal value the bit
4 of Fault1 register is set to zero. Pulling this register the operator could understand the
state of diagnostic. Note that during diagnostic cycle the output FET are in tristate.
● No I²C bus: The operation of diagnostic is equal to the one with I²C bus. The only
differences are about the habilitation, which is selected by the mode, and the assertion
of fault presence, which is done trough the addr0/Fault pin. At the end of diagnostic the
Fault pin is for sure low and the external FET start to commute.
These are the thresholds to take into account for short to ground and short to supply
Voltage threshold
SGND
X
Normal
operation
X
SVCC
VSM VSM+1V
VSM+2V VSM+5.5V VSM+8V VSP
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