Block description

STA7360

16/28

Doc ID 9814 Rev 4

4

Block description

4.1

Polarization

The device is organized with the gain resistors directly connected to the signal ground pin

i.e. without gain capacitors (Figure 2).

The non-inverting inputs of the amplifiers are connected to the SVR pin by means of resistor

dividers, equal to the feedback networks. This allows the outputs to track the SVR pin which

is sufficiently slow to avoid audible turn-on and turn-off transients.

4.2

SVR

The voltage ripple on the outputs is equal to the one on the SVR pin: with appropriate

selection of CSVR, more than 60 dB of ripple rejection can be obtained.

4.3

Delayed turn-on (muting)

The CSVR sets a signal turn-on delay too. A circuit is included which mutes the device until

the voltage on the SVR pin reaches ~2.5 V typ. (Figure 25). The mute function is obtained

by duplicating the input differential pair (Figure 24); it can be switched to the signal source or

to an internal mute input. This feature is necessary to prevent transients at the inputs

reaching the loudspeaker(s) immediately after power-on).

Figure 25 represents the detailed turn-on transient with reference to the stereo

configuration. At power-on the output decoupling capacitors are charged through an internal

path but the device itself remains switched off (phase 1 of the represented diagram).

When the outputs reach the voltage level of about 1 V (this means that there are no short-

circuits) the device switches on, the SVR capacitor starts charging itself and the output

tracks exactly the SVR pin. During this phase the device is muted until the SVR reaches the

"Play" threshold (~2.5 V typ.), after which the music signal starts being played.

4.4

Stereo/bridge switching

There is also no need for external components for changing from stereo to bridge

configuration (Figure 2, 3). A simple short-circuit between two pins allows phase reversal at

one output, yet maintaining the quiescent output voltage.

4.5

Standby

The device is also equipped with a standby function, so that a low current, and hence a low

cost switch, can be used for turn-on/off.

Obsolete

Product(s)

- Obsolete

Product(s)