STA7360 datasheet(8/18 Pages) STMICROELECTRONICS

8 / 18 page

STA7360

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Figure 17. Power Dissipation& Efficiency vs.

Output Power(Stereo)

Figure 18. Power Dissipation& Efficiency vs.

Output Power (Stereo)

Figure 19. Power Dissipation& Efficiency vs.

Output Power (Bridge)

BLOCK DESCRIPTION

PolarizationThe device is organized with the gain re-

sistors directly connected to the signal ground pin i.e.

without gain capacitors (fig. 20).

The non inverting inputs of the amplifiers are con-

nected to the SVR pin by means of resistor dividers,

equal to the feedback networks. This allows the out-

puts to track the SVR pin which is sufficiently slow to

avoid audible turn-on and turn-off transients.

SVR

The voltage ripple on the outputs is equal to the one

on SVR pin: with appropriate selection of CSVR,

more than 60dB of ripple rejection can be obtained.

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

SVR pin reaches ~2.5V typ. (fig. 22). The mute func-

tion is obtained by duplicating the input differential

pair (fig. 21): 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 loud-

speaker(s) immediately after power-on).

Fig. 22 represents the detailed turn-on transient with

reference to the stereo configuration.At the 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 1V

(this means that there is no presence of 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 (~2.5V typ.), after

that the music signal starts being played.

Stereo/Bridge Switching

There is also no need for external components for

changing from stereo to bridge configuration (figg. 20,

22). A simple short circuit between two pins allows

phase reversal at one output, yet maintaining the quies-

cent output voltage.

Stand-by

The device is also equipped with a stand-by function,

so that a low current, and hence low cost switch, can

be used for turn on/off.

Stability

The device is provided with an internal compensation

wich allows to reach low values of closed loop gain.In

this way better performances on S/N ratio and SVR

can be obtained.

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