TDA7415CB datasheet(31/50 Pages) STMICROELECTRONICS

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TDA7415CB

Description of the audio processor

31/50

5.5

DC offset detector

Using the DC offset detection circuit (figure 22) an offset voltage difference between the

audio power amplifier and theTDA7415CB's PA-outputs can be detected, preventing serious

damage to the loudspeakers. The circuit compares whether the signal crosses the zero level

inside the audio power at the same time as in the speaker cell. The output of the zero-

window-comparator of the power amplifier must be connected with the WinIn-input of the

TDA7415CB. The WinIn-input has an internal pull-up resistor connected to 5,5Volts. It is

recommended to drive this pin with open-collector outputs only.

To compensate for errors at low frequencies the WinTC0/1-pins are implemented, with

external capacitors introducing the same delay

τ = 5kΩ * Cext as the AC-coupling between

the TDA7415 and the power amplifier introduces. For the zero window comparators, the

time constant for spike rejection as well as the threshold are programmable.

For electrical characteristics see page 8.

A low-active DC-offset error signal appears at the DCErr output if the next conditions are

both true:

All PA-outputs (front and rear) are inside zero crossing windows.

The Input voltage VWinIn is logic low whenever at least one output of the power

amplifier is outside the zero crossing windows.

After power-on, the external attached capacitor is rapidly charged (fast-charge) to overcome

a false indication. The fast mode has to be turned off by a manual release of the fast-charge

Figure 23.

DC-offset detection circuit (simplified)

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