TDA7402 datasheet(18/71 Pages) STMICROELECTRONICS

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Audioprocessor part

TDA7402

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4.1.3

Mono differential Input 1 (MD1)

The MD1 input is designed as a basic differential stage with 56k

Ω input impedance. This

input is configurable as a single ended stereo input (see pin-out).

4.1.4

Mono differential Input 2 (MD2)

The MD2 input has the same topology as MD1, but without the possibility to configure it to

single ended.

4.1.5

Single ended stereo Input (SE1), single ended mono input (AM) and

FM-MPX input

All single ended inputs offer an input impedance of 100k

Ω. The AM pin can be connected by

software to the input of the stereo-decoder in order to use the AM noiseblanker and AM High

Cut feature.

4.2

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 is muted before the loudness

stage during this time. The AutoZero feature is only present in the main signal path.

4.2.1

AutoZero for stereo decoder selection

A special procedure is recommended for selecting the stereo decoder at the main input-

selector to guarantee an optimum offset cancellation:

SoftMute or Mute the signal-path

Temporary deselect the stereo decoder at all input selectors

Configure the stereo decoder via IIC-Bus

Wait 1ms

Select the stereo decoder at the main input selector first

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

internal stereo decoder filters have to settle in order to perform a proper offset cancellation.

4.2.2

AutoZero remain

In some cases, for example if the µP is executing a refresh cycle of the I2C 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

A619 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.

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