Application hints

TDA7851F

12/18

DocID17714 Rev 4

4

Application hints

4.1

SVR

Besides its contribution to the ripple rejection, the SVR capacitor governs the turn ON/OFF

time sequence and, consequently, plays an essential role in the pop optimization during

ON/OFF transients.To conveniently serve both needs, its minimum recommended value

is 10

μF.

4.2

Input stage

The TDA7851's inputs are ground-compatible and can stand very high input signals

(± 8 Vpk) without any performance degradation.

If the standard value for the input capacitors (0.1 μF) is adopted, the low frequency cut-off

amounts to 16 Hz.

The input capacitors should be 1/4 of the capacitor connected to AC-GND pin for optimum

pop performance.

4.3

Standby and muting

Standby and muting facilities are both CMOS-compatible. In absence of true CMOS ports or

microprocessors, a direct connection to Vs of these two pins is admissible but a 470 k



equivalent resistance should be present between the power supply and muting and standby

pins.

R-C cells have always to be used in order to smooth down the transitions for preventing any

audible transient noise.

About standby, the time constant to be assigned in order to obtain a virtually pop-free

transition has to be slower than 2.5 V /ms.

4.4

Heatsink definition

Under normal usage (4 Ohm speakers) the heatsink's thermal requirements have to be

deduced from Figure 16, which reports the simulated power dissipation when real

music/speech programmers are played out. Noise with Gaussian-distributed amplitude was

employed for this simulation. Based on that, frequent clipping occurrence (worst-case)

the heatsink's thermal resistance should be approximately 2 °C/W. This would avoid any

thermal shutdown occurrence even after long-term and full-volume operation.