TDA7801 datasheet(29/48 Pages) STMICROELECTRONICS

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TDA7801

Functional description

6.11

Under-voltage threshold

6.11.1

Supply voltage auto-mute threshold

The device in play-mode is put in mute when the supply voltage gets lower than the VAM

threshold.

When the supply voltage gets lower than the VAM threshold the device is put in mute. The

muting strategy in this case is reported in Figure 33: once the supply voltage Vs becomes

lower than VAM_HIGH, analog mute and digital mute are activated. The analog mute

attenuation is proportional to the Vs voltage and becomes equal to AM when the Vs gets

lower than VAM_LOW. Note that once the digital mute procedure is started, it cannot be

stopped to move back the device in play, the procedure is going on until the attenuation

level has reached AM. This mechanism avoids that a fast oscillation on Vs cause a similar

oscillation on the output.

Figure 33. Low voltage mute attenuation, supply voltage variation (Vs); result digital

attenuation (At)

6.11.2

Digital mute disabling

The digital mute is disabled in the following conditions:



when TW1 threshold is trespassed (to avoid simultaneous intervention of digital mute

and thermal mute)



when the bit IB3-D5 is set to '1'



during the start-up diagnostic

When the digital mute is disabled, the analog mute is kept active.

6.11.3

Power-on reset threshold

When the ENABLE pin is low or the supply voltage value doesn't guarantee the integrity of

The I2C bus registers (VPOWERONRESET) the TDA7801 is put in tristate-mode and the

registers are set to the initial state. The event is signalled by the low value of DIAG pin and

the '0' value of bit D7 of byte DB0. The DIAG pin is set to high after a POR when the bit D7

of byte IB1 is set to '1' (amplifier mode on) if no other event on DIAG pin is present. The

same I2C bus write operation automatically set to '1' the bit D7 of byte DB0. When the

device is programmed with the D7=1 of IB0 and D7=1 of byte IB1 the device turns-on after a

diagnostic cycle and the DIAG pin stays low for the whole duration of the diagnostic cycle.

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