TDA8950
NXP Semiconductors
13.5 Noise
2 × 150 W class-D power amplifier
Noise should be measured using a high order low-pass filter with a cut-off frequency of
20 kHz. The standard audio band pass filters, used in audio analyzers, do not suppress
the residue of the carrier frequency sufficiently to ensure a reliable measurement of the
audible noise. Noise measurements should preferably be carried out using AES 17
(‘brickwall’) filters or an audio precision AUX 0025 filter, which was designed specifically
for measuring class-D switching amplifiers.
13.6 Heatsink requirements
In many applications it may be necessary to connect an external heatsink to the
TDA8950.
Equation 5 shows the relationship between the maximum power dissipation, before
activation of the TFB, and the total thermal resistance from junction to ambient
T j – Tamb
Rth( j – a)
=
(5)
-----------------------
Pdiss
Power dissipation (Pdiss) is determined by the efficiency of the TDA8950. The efficiency
measured as a function of output power is given in Figure 21. The power dissipation can
be derived as a function of output power (Figure 20).
mbl469
30
P
(W)
(1)
20
(2)
10
(3)
(4)
(5)
0
0
20
40
60
80
T
100
(°C)
amb
(1) Rth(j-a) = 5 K/W.
(2) Rth(j-a) = 10 K/W.
(3) Rth(j-a) = 15 K/W.
(4) Rth(j-a) = 20 K/W.
(5) Rth(j-a) = 35 K/W.
Fig 9. De-rating curves for power dissipation as a function of maximum ambient
temperature
In the following example, a heatsink calculation is made for an 8 Ω BTL application with a
±35 V supply:
TDA8950_1
© NXP B.V. 2008. All rights reserved.
Preliminary data sheet
Rev. 01 — 9 September 2008
19 of 39
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