TDA7803A-QLX datasheet(26/72 Pages) STMICROELECTRONICS

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Functional description

TDA7803A

26/72

DS12195 Rev 7

Open Load: it detects a non connected speaker condition.

The diagnostic's results are stored into DB1, DB2, DB3 and DB4 data registers (one for

each channel) after the diagnostic is over.

The flow of the diagnostic includes some steps as described below.



During the first part, the soft-short evaluation is performed. The outputs and an internal

reference line are pulled up to a voltage of 2/5*Vbattery in a time TSTR and then

compared for a time TPLS. During the plateau time, the comparator outputs are read

from the digital part. The outputs are then pulled down to zero (see Figure 31). The

A3V3 supply is 0V and the output stage is in tri-state during this phase.

Figure 31. Soft short diagnostic



If a soft short is detected, the short to GND/VCC evaluation follows. Pin A3V3 goes up

as the amplifier stage is turned on; the power and the outputs are risen up to

1/2*Vbattery and then compared to (Vbattery - 1.5 V) and 1.5 V for a time TPLS. At the

end of the plateau (TPLS) output and A3V3 go back to 0V and the results obtained are

written into the I2C Bus registers once the diagnostic is over. For soft short resistance

above the defined thresholds, the normal, short or open load recognition is guaranteed.

In case the short to VCC or GND is detected during this phase a '1' is written in DBx-D1/D0

(VCC/GND) but not in DBx-D6. In case the hard short is not detected a '1' is written all DBx-

D6.

The turn-on diagnostic is then completed and the amplifier goes back to the ECO - mode.



However, if a soft short is not detected, then we can also exclude the Short to Vs/GND,

and don't need to be checked. In this case, short across the speaker and the open load

evaluation can be performed. Pin A3V3 goes up as the amplifier stage is turned on and

the outputs are risen up to 1/2*Vbattery. A first pulse for "Short load detection" is done:

exploiting the presence of a D/A converter, a subsonic (inaudible) voltage pulse is

digitally and internally generated and converted. The pulse amplitude increasing is

stopped when the current flowing through the speaker Ispeaker is the same as a prefixed

one Ihigh (high current) or because it reaches the maximum value permitted. Since the

differential output voltage Vo is well known, it is possible to keep monitored the value of

the connected speaker during the transition and plateau. In the case the Ispeaker will get

to an higher value then Ihigh, Vo< Vshort (short circuit threshold) the result is short load

(DBx - D3 ='1'), otherwise it is normal load (DBx - D3 = '0'); when Ispeaker does not

reach Ihigh the turn-on diagnostic is not completed yet because the result could be still

normal or open load.



This is called "Open load detection". If IB4 D1/D2 = 1 the power DMOS need to be

changed again: the outputs are pulled down to zero, the DMOS are switched and then

the outputs raised up to 1/2*Vbattery again. This sequence is done in order to avoid any

pop noise during the power set. The procedure is the same as the previous case or in

Output

+/-

2/5*Vs

time

Soft Short

thresholds

TPLS

TSTR

TSTF

GAPGPS00805

TDA7803A-QLX Datasheet(PDF) 26 Page - STMicroelectronics

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