DocID023043 Rev 7

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STPA001

General information

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4

General information

4.1

Operation

The STPA001's inputs are ground-compatible. If the standard value for the input capacitors

(0.22 μF) is adopted, the low frequency cut-off will amount to 16 Hz. The input capacitors

should be 1/4 of the capacitor connected to AC-GND pin for optimum pop performances

(see Figure 2: Application circuit (STPA001)).

Standby and mute pins are both CMOS compatible.

RC cells at both mute and stand-by pins have always to be used in order to smooth the

transitions for preventing any audible transient noise.

In case muting and stand-by functions are not used, they could steadily be connected to VS,

but a 470 kΩ resistance should be present between the power supply and the pins.

The capacitance on SVR sets the start-up and shut-down times and helps to have pop-noise

free transitions. Its minimum recommended value is 10 μF. However, to have a fast start-up

time, the internal resistor on SVR pin, used to set the time constant, is reduced from 50 kΩ

to 3 kΩ till voltage on SVR reaches VCC/4 -2VBE and then released. In this way the

capacitor on SVR is charged very quickly to VCC/4, as shown in the following figure.

The time constant to be assigned to the standby pin in order to obtain a virtually pop-free

transition has to be slower than 2.5 V/ms.

Figure 20. SVR charge diagram

SVR pin accomplishes multiple functions:



it is used as a reference voltage for input pins (VCC/4)



the capacitor connected to SVR helps the supply voltage ripple rejection



it is used as a reference to generate the half supply voltage for the output

When the amplifier goes in standby mode or goes out from this condition, it is suggested to

put the amplifier in mute to ensure the absence of audible noise. Then the stand-by pin can

be set to the appropriate value (ground or > 2.6 V) and the capacitance on SVR pin is

discharged or charged consequently.

4.2

Battery variations

4.2.1

Low voltage operation

The most recent OEM specifications are require automatic stop of car engine at traffic lights,

in order to reduce emissions of polluting substances. The STPA001, thanks to its innovating