TDA7462 datasheet(9/25 Pages) STMICROELECTRONICS

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offers the full common-mode rejection even with

those CD players.

AutoZero Stage

In order to reduce the number of pins there is no

AC coupling between the In-Gain and the follow-

ing stage, so that any offset generated by or be-

fore the stage would be transferred or even am-

plified to the output. To avoid that effect, a special

offset cancellation stage called AutoZero is imple-

mented. This stage is located before the mixing

block to eliminate all offsets generated by the in-

put and the In-Gain (notice that externally gener-

ated offsets, e.g. generated through the leakage

current of the coupling capacitors, are not can-

celled).

The auto-zeroing is started every time the data-

byte 0 is selected and takes a time of max.

0.3ms. To avoid audible clicking the audioproces-

sor is muted before the loudness stage during

this time.

AutoZero Remain

In some cases, for example if the

µP is executing

a refresh cycle of the I

2C 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 applica-

tions the TDA7462 could be switched in the

AutoZeroRemain mode. If this bit is set to high,

the databyte 0 could be loaded without invoking

the AutoZero and the old adjustment value re-

mains.

Full Mixing Stage

The four-level mixing stage offers the possibility

to mix the rear selector signal or the phone signal

to any other source. Due to the fact that the mix-

ing stage is located after the In-Gain stage fine

adjustments of the main source level could be

done in this way.

Figure 2. Signal Flow of Mixing Stage.

TDA7462

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