TDA7402 Datasheet, PDF (12/59 Pages) STMicroelectronics – CARRADIO SIGNAL PROCESSOR

TDA7402
Mono-differential Input 1 (MD1)
The MD1-input is designed as a basic differential stage with 56kΩ input-impedance. This input is configurable
as a single-ended stereo input (see pin-out).
Mono-differential Input 2 (MD2)
The MD2-input has the same topology as MD1, but without the possibility to configure it to single ended.
Single-ended stereo Input (SE1), single-ended mono input (AM) and FM-MPX input
All single ended inputs offer an input impedance of 100kΩ. 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.
1.2 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.
AutoZero for Stereodecoder-Selection
A special procedure is recommended for selecting the stereodecoder at the main input-selector to guarantee
an optimum offset-cancellation:
(Step 0: SoftMute or Mute the signal-path)
Step 1: Temporary deselect the stereodecoder at all input-selectors
Step 2: Configure the stereodecoder via IIC-Bus
Step 3: Wait 1ms
Step 4: Select the stereodecoder at the main input-selector first
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.
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 A619 could be switched in the AutoZero-Remain-Mode (Bit 6 of the subad-
dress-byte). If this bit is set to high, the DATABYTE 0 could be loaded without invoking the AutoZero and the
old adjustment-value remains.
1.3 Pause Detector / MUX-Output
The pin number 40(Pause/MUX) is configurable for two different functions:
1. During Pause-Detector OFF this pin is used as a mono-output of the main input-selector. This signal is often
used to drive a level-/equalizer-display on the carradio front-panel.
2. During Pause-Detector ON the pin is used to define the time-constant of the detector by an external capacitor.
The pause-detector is driven by the internal stereodecoder-outputs in order to use pauses in the FM-signal
for alternate-frequency-jumps. If the signal-level of both stereodecoder channels is outside the programmed
voltage-window, the external capacitor is abruptly discharged. Inside the pause-condition the capacitor is
slowly recharged by a constant current of 25µA. The pause information is also available via IIC-Bus (see IIC-
Bus programming).
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