STA541SA

Practical information

Doc ID 16988 Rev 2

17/26

7

Practical information

7.1

Internally fixed gain

The advantages in internally fixing the gain to 26 dB are:

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components and space saving

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output noise, supply voltage rejection and distortion optimization.

7.2

Silent turn on/off and muting/standby function

The standby mode can be easily activated by means of a CMOS logic level applied to

pin STBY through a RC filter.

In standby, the device is turned of, drawing typically 1 mA from the supply and the output

attenuation is 80 dB minimum.

All switch-on and switch-off operations are virtually pop-free. Furthermore, at turn-on the

device stays muted for a time determined by the value of the capacitor on pin SVR. This

prevents transients coming from previous stages which otherwise could produce unpleasant

acoustic effects at the speakers.

7.3

Driving circuit for standby mode

Some precautions need to be taken when designing the driving circuit for pin 7, STBY. For

instance, the pin cannot be directly driven by a voltage source having a current capability

higher than 5 mA. In practical cases a series resistor must be inserted, giving it the double

purpose of limiting the current at pin 7 and to smooth down the standby on/off transitions.

When done in combination with a capacitor it prevents output pop.

A capacitor of at least 100 nF from pin 7 to SGND is necessary to ensure correct turn-on

(see also Figure 14: Applications circuit on page 13).