TDA7415CB Datasheet, PDF (31/50 Pages) STMicroelectronics – Car radio multimedia signal processor

TDA7415CB
Description of the audio processor
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:
a) All PA-outputs (front and rear) are inside zero crossing windows.
b) 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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