TDA7572 datasheet(51/64 Pages) STMICROELECTRONICS

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TDA7572

Diagnostics

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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

10.1.8

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

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

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

SGND

Normal

operation

SVCC

Voltage threshold

VSM

VSM+1V

VSM+2V

VSM+5.5V

VSM+8V

VSP

2.45

3RISet

⋅

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