TDA7406T datasheet(10/49 Pages) STMICROELECTRONICS

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TDA7406T

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2.2 AutoZero

The AutoZero allows a reduction of the number of pins as well as external components by canceling any offset

generated by or before the In-Gain-stage (Please notice that externally generated offsets, e.g. generated

through the leakage current of the coupling capacitors, are not canceled).

The auto-zeroing is started every time the DATA-BYTE 0 is selected and needs max. 0.3ms for the alignment.

To avoid audible clicks the Audioprocessor have to be muted by soft mute or hard mute during this time.

2.2.1 AutoZero for Stereodecoder-Selection

A special procedure is recommended for selecting the stereodecoder at the input-selector to guarantee an op-

timum offset-cancellation:

(Step 0: SoftMute or Mute the signal-path)

Step 1: Temporary deselect the stereodecoder at the input-selector

Step 2: Configure the stereodecoder via IIC-Bus

Step 3: Wait 1ms

Step 4: Select the stereodecoder

The root cause of this procedure is, that after muting the stereodecoder (Step 1), the internal stereodecoder

filters have to settle in order to perform a proper offset-cancellation.

2.2.2 AutoZero-Remain

In some cases, for example if the µP is executing a refresh cycle of the IIC-Bus-programming, it is not useful to

start a new AutoZero-action because no new source is selected and an undesired mute would appear at the

outputs. For such applications the TDA7406T could be switched in the AutoZero-Remain-Mode (Bit 6 of the

subaddress-byte). If this bit is set to high, the DATABYTE 0 could be loaded without invoking the AutoZero and

the old adjustment-value remains.

2.2.3 PAUSE Detector

A pause detector stage with programmable threshold (40/80/160mV) is provided (see data Byte 14).

The pause detector info is available at the PAUSE pin; a capacitor must be connected between this pin and

GND.

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.

The pause status can be detected in two ways:

reading directly the PAUSE pin level

Pause Off = level low (<3.0V)

Pause On = level high (>3.0V)

by reading the I2C transmitted byte, bit P

P = 1 pause active

P = 0 no pause detected

The external capacitor value fixes the time constant. The pull up current is 25

µA typical.

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