Application hints

TDA7850

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4

Application hints

Ref. to the circuit of Figure 2.

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 10µF.

4.2

Input stage

The TDA7850's inputs are ground-compatible and can stand very high input signals (±

8Vpk) without any performance degradation.

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

will amount to 16 Hz.

4.3

Stand-by and muting

STAND-BY 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

470k

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

and stand-by pins.

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

audible transient noises.

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

transition has to be slower than 2.5V/ms.

4.4

DC offset detector

The TDA7850 integrates a DC offset detector to avoid an anomalous DC offset on the inputs

of the amplifier which may be multiplied by the gain, and result in a dangerous large offset

on the outputs, which may lead to speaker damage through overheating.

The feature is enabled by the MUTE pin and works with the amplifier unmuted and with no

signal on the inputs. The DC offset detection is signaled out on the HSD pin.

4.5

Heatsink definition

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

deduced from Figure 18, which reports the simulated power dissipation when real

music/speech programmes are played out. Noise with gaussian-distributed amplitude was

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

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.