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TDA7437N

The detection works separately for the left and the right channels (see Figg. 10, 11). Four different windows

threshold are software selectable by two dedicated bits.

bit D6 bit D5 WINDOW

0

0

Vref DC +/-280mV

0

1

Vref DC +/-140mV

1

0

Vref DC +/-70mV

1

1

Vref DC +/-35mV

The zero crossing mute activation/deactivation starts when the AC signal level falls inside the selected window

(internal comparator).

The ZEROCROSS Mute (and Pause) detector is always active. It can be disabled, if the feature is not used, by

forcing the bit D4 = 1 Zero crossing and Pause detector reset.

In this way the internal comparator logic is stopped, eliminating its switching noise.

The zero cross mute status is detected reading the Transmitted Byte bit ZM.

bit ZM = 1 zero cross mute status ON

bit ZM = 0 zero cross mute status OFF

PAUSE FUNCTION

On chip is implemented a pause detector block.

It uses the same 4 windows threshold selectable for the zero crossing mute, bit D6,D5 byte MUTE (see above).

The detector can be put in OFF by forcing bit D4 = 1, otherwise it is active.

The Pause detector info is available at PAUSE pin. A capacitor must be connected between PAUSE pin and

Ground.

When the incoming signal is detected to be outside the selected window, the external capacitor is discharged.

When the signal is inside the window, the capacitor is integrating up (see Figg.12 and 13).

a by reading directly the Pause pin level.The ON/OFF voltage threshold is 3.0V typical.Pause OFF = level

low (< 3.0V)Pause ON = level high ( ; 3.0V)

b by reading via I2C bus the Transmitted Byte, bit PP = 0 pause active.P = 1 no pause detected. The ex-

ternal capacitor value fixes the time constant.

The pull up current is 25uV typicalWith input signal

Vin = 1Vrm --; Vdc pin pause = 15mV

Vin = 0Vrms --; Vdc pin pause = 5.62V

For example choosing Cpause = 100nF the charge up constant is about 22ms. Instead with Cpause = 15nF the

charge up constant is about 360

µs.

The Pause detection is useful in applications like RDS, to perform noiseless tuning frequeny jumps avoiding to

mute the signal.

NO SYMMETRICAL BASS CUT RESPONSE

bit D7 = 0 No symmetrical

bit D7 = 1 Symmetrical

The Bass stage has the option to generate an unsymmetrical response, for cut mode settings (bass level from

-2db to - 14dB)

For example using a T-type band pass externa

The feature is useful for human ear equalization in noisy enviroments like cars etc.

See examples in Fig. 14 (symmetrical response) and Fig. 15 (unsymmetrical response).