Datasheet

Applications information TDA7491LP
32/37 Doc ID 13541 Rev 5
5.9 Heatsink requirements
Due to the high efficiency of the class-D amplifier a 2-layer PCB can easily provide the
heatsinking capability for low to medium power outputs.
Using such a PCB with a copper ground layer of 3 x 3 cm
2
and 16 vias connecting it to the
contact area for the exposed pad, a thermal resistance, junction to ambient (in natural air
convection), of 24 °C/W can be achieved.
The dissipated power within the device depends primarily on the supply voltage, load
impedance and output modulation level. With the TDA7491LP driving 2 x8 Ω with a supply
of 9 V then the maximum device dissipation is approximately 1 W.
When this power is dissipated at the maximum ambient temperature of 85 °C and the device
is mounted on the above PCB then the junction temperature could reach:
Tj = Tamb + Pd * Rj-amb = 85 + 1 * 24 = 109 °C
However, this temperature is sufficiently low to avoid triggering thermal warning.
With a musical program the dissipated power is about 40% less than the above maximum
value. This leads to a junction temperature of around only 99 °C with the 9 cm2 copper
ground. A commensurately smaller heatsink can thus be used.
Figure 36 shows the power derating curve for the PowerSSO-36 package on PCBs with
copper areas of 2 x 2 cm
2
and 3 x 3 cm
2
.
Figure 36. Power derating curves for PCB used as heatsink
0
1
2
3
4
5
6
7
8
0 20 40 60 80 100 120 140 160
g
Pd (W)
Tamb ( °C)
Copper Area 2x2 cm
and via holes
TDA7491P
PSSO36
Copper Area 3x3 cm
and via holes
TDA7491LP
PowerSSO-36