Philips TDA8946J - Manual (Page 16)

Philips Semiconductors
TDA8946J
2 x 15 W stereo BTL audio amplifier
Product specification Rev. 02 — 14 March 2000 16 of 23
9397 750 06863 © Philips Electronics N.V. 2000. All rights reserved.
14.2 Thermal behaviour and heatsink calculation
The measured maximum thermal resistance of the IC package, R
th(j-mb)
is 4.5 K/W.
A calculation for the heatsink can be made, with the following parameters:
T
amb(max)
= 50
°
C
V
CC
= 18 V and R
L
= 8
Ω
T
j(max)
= 150
°
C.
R
th(tot)
is the total thermal resistance between the junction and the ambient
including the heatsink. In the heatsink calculations the value of R
th(mb-h)
is ignored.
At V
CC
= 12 V and R
L
= 8
Ω
the measured worst-case sine-wave dissipation is 18 W;
see Figure 11 . For T
j(max)
= 150
°
C the temperature raise - caused by the power
dissipation - is: 150 – 50 = 100
°
C.
P
×
R
th(tot)
= 100
°
C
R
th(tot)
= 100/18 = 5.56 K/W
R
th(h-a)
= R
th(tot)
– R
th(j-mb)
= 5.56 – 4.5 = 1.06 K/W.
The calculation above is for an application at worst-case (stereo) sine-wave output
signals. In practice music signals will be applied, which decreases the maximum
power dissipation to approximately half of the sine-wave power dissipation (see
Section 8.2.2 ). This allows for the use of a smaller heatsink:
P
×
R
th(tot)
= 100
°
C
R
th(tot)
= 100/8 = 12.5 K/W
R
th(h-a)
= R
th(tot)
– R
th(j-mb)
= 12.5 – 4.5 = 8.0 K/W.
To increase the lifetime of the IC, T
j(max)
should be reduced to 125
°
C. This requires a
heatsink of approximately 4 K/W for music signals.
15. Test information
15.1 Quality information
The General Quality Specification for Integrated Circuits, SNW-FQ-611D is
applicable.
15.2 Test conditions
T
amb
= 25
°
C; V
CC
= 18 V; f = 1 kHz; R
L
= 8
Ω
; audio pass band 22 Hz to 22 kHz;
unless otherwise specified.
Remark: In the graphs as function of frequency no bandpass filter was applied; see
Figure 7 , 12 and 13 .