Philips Semiconductors
Preliminary specification
26 W BTL and 2 × 13 W SE or
4 × 13 W SE power amplifier
TDA8512J
11 THERMAL CHARACTERISTICS
In accordance with IEC 60747-1.
SYMBOL
PARAMETER
CONDITIONS
VALUE
UNIT
Rth(j-a)
Rth(j-c)
thermal resistance from junction to ambient
thermal resistance from junction to case
in free air
see Fig.5
40.0
1.3
K/W
K/W
The measured thermal resistance of the IC-package (Rth(j-c)) is maximum 1.3 K/W if all four channels are driven. For a
maximum ambient temperature of 60 °C and VP = 15 V, the following calculation for the heatsink can be made:
For the application two SE outputs with 2 Ω load, the measured worst-case sine-wave dissipation is 2 × 7 W
For the application BTL output with 4 Ω load, the worst-case sine-wave dissipation is 12.5 W.
So the total power dissipation is Pd(tot) = 2 × 7 + 12.5 W = 26.5 W.
At Tj(max) = 150 °C the temperature increase, caused by the power dissipation, is: ∆T = 150 °C − 60 °C = 90 °C.
90
26.5
So Pd(tot) × Rth(tot) = ∆T = 90 K. As a result: Rth(tot)
th(hs) = Rth(tot) − Rth(j-c) = 3.4 − 1.3 = 2.1 K/W.
=
= 3.4 K/W which means:
-----------
R
The above calculation is for application at worst-case (stereo) sine-wave output signals. In practice, music signals will be
applied. In that case the maximum power dissipation will be about the half the sine-wave power dissipation, which allows
the use of a smaller heatsink.
90
13.25
So Pd(tot) × Rth(tot) = ∆T = 90 K. As a result: Rth(tot)
=
= 6.8 K/W which means:
--------------
Rth(hs) = Rth(tot) − Rth(j-c) = 6.8 − 1.3 = 5.5 K/W.
virtual junction
output 3 output 4
handbook, halfpage
output 1 output 2
3.0 K/W
3.0 K/W
3.0 K/W
3.0 K/W
0.7 K/W
0.7 K/W
MEA860 - 2
0.2 K/W
case
Fig.5 Equivalent thermal resistance network.
2001 Nov 16
8
NXP [ NXP ]
