Application hints

TDA7850

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4

Application hints

Referred 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

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 470k



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

ST-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 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

DC offset detector

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

inputs of the amplifier may be multiplied by the gain and result in a dangerous large offset on

the outputs which may lead to speakers damage for overheating. The feature is enabled by

the MUTE pin (according to table 3) and works with the amplifier unmuted and with no signal

on the inputs.

The DC offset detection is signaled out on the HSD pin. To ensure the correct functionality of

the Offset Detector it is necessary to connect a pulldown 10 kW resistor between HSD and

ground.

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

cause Pdiss = 26 W. Assuming Tamb = 70 °C and TCHIP = 150 °C as boundary conditions, 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.