General information

STPA008

16/29

DocID027887 Rev 2

4

General information

4.1

Operation

STPA008's inputs are ground-compatible. If the standard value for the input capacitors (0.22

μF) is adopted, the low frequency cut-off is 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 (STPA008-4WX)).

Standby and mute pins are both 3.3 V 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.

kohm resistance should be present between the power supply and the pin.

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. 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

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 improves the supply voltage ripple rejection



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

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 capacitor on SVR pin is

discharged or charged consequently.

4.2

Battery variations

4.2.1

Low voltage operation

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

order to reduce emissions of polluting substances. STPA008, thanks to its innovating