TDA7854 Datasheet, PDF (9/12 Pages) STMicroelectronics – 4 x 47W MOSFET quad bridge power amplifier

TDA7854
4
Application hints
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 TDA7854's inputs are ground-compatible and can stand very high input signals (±
8Vpk) without any performances 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
R-C cells have always to be used in order to smooth down the transitions for preventing any
audible transient noise.
About 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.
A direct connection to Vs of these two pins is admissible but a 470kOhm equivalent
resistance should be present between the power supply and muting and stand-by pins.
4.4
Heatsink definition
Under normal usage (4 Ohm speakers) the heatsink's thermal requirements have to be
deduced from Figure 4, 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 P_diss = 26W. 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.
Figure 4.
Power dissipation vs. output power (R_L = 4Ω, audio program simulation)
30 ^{Ptot (W)}
V_s = 14.4 V
25
R_L = 4 x 4 Ω
GAUSSIAN NOISE
CLIP START
20
15
10
5
0
1
2
3
4
5
6
P_o (W)
AC00036
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