TDA7719
Description
4.11
DC offset detector and level meter option
This device provide DC offset detector function and level meter function option. In one
specific application, only one of the function can be used. The configuration of the function
2
is controlled by I C bus (Byte3 Bit7).
When the device uses DC offset detector function, Pin22, Pin27 and Pin28 are used as
WinTC, DCErr and WinIN for DC offset detector. When it is configured as level meter, DCErr
becomes level meter output. In the mean time, WinIN is used as beep input (Mono single-
ended input for mixing), and WinTC becomes a reference voltage output (4V external DC
voltage or 3.3V internal reference voltage).
Caution:
DC offset detector and level meter / Vref output / Beep / (mono single sided input) can not
be used at the same time.
4.12
DC offset detector
Using the DC offset detection circuit (Figure 19) an offset voltage difference between the
audio power amplifier and the APR's Front and Rear 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 APR. 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 WinTC-pin are implemented, with external
capacitors introducing the same delay τ = 7.5kΩ * C as the AC-coupling between the APR
ext
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 Chapter 3 on page 9.
A low-active DC-offset error signal appears at the DCErr output if the next conditions are
both true:
a) Front and rear outputs 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.
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STMICROELECTRONICS [ ST ]
