TDA7801PDTR datasheet(23/48 Pages) STMICROELECTRONICS

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TDA7801

Functional description

6.1

Voltage supplies timing

TDA7801 internal voltage supplies rise time and fall time are determined by the two

capacitors at pin 16 and 17, respectively digital supply pin (D3V3) and analog supply pin

(A3V3). Capacitor on analog supply pin, (pin 17), and capacitor on digital supply, (pin 16),

should respect the ratio 2:1. It is suggested to fix a minimum value of 22 µF on digital supply

pin and 47 µF on analog supply pin, which correspond to a typical Turn-on time of 1.5 ms

and a typical turn-off time of 8.5 ms.

6.2

Turn-on diagnostic description

Turn-on diagnostic is activated under I2C bus request. Detectable output faults are:



Short to GND



Short to Vs



Short across the speaker



Open load

In the TDA7801 a new diagnostic that exploits the presence of D/A converters has been

implemented. To verify if some of the above connections are in place, a subsonic (inaudible)

voltage pulse is digitally and internally generated and converted (Figure 27). The amplitude

of this pulse is stopped when the current flowing through the speaker is the same as the

prefixed one corresponding to a specified load. The exact knowledge of the voltage drop

across the load in any phase of the diagnostic time gives the possibility to know the

connected load.

During the observation time, the measured load is compared with tabled values in order to

determine the result.

The turn-on diagnostic status is internally stored until a successive diagnostic pulse is

requested.

Figure 27. Turn-on diagnostic cycle. Positive and negative output behaviour

A turn-on diagnostic cycle is activated writing '1' on the D7 of byte IB0 only when the

amplifier is in Tristate-mode. Note that the turn-on diagnostic state machine is sensible to

the rise edge of this bit. To run another cycle of turn-on diagnostic it is necessary to:

wait that the previous cycle ends;

clear the D7-IB0 bit.

write '1' on D7-IB0 bit.

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