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 10μF.
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)
causes P
diss
= 26 W. Assuming T
amb
= 70 °C and T
CHIP
= 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.
