TDA8944J Datasheet, PDF (15/21 Pages) NXP Semiconductors – 2 x 7 W stereo Bridge Tied Load BTL audio amplifier

Philips Semiconductors
TDA8944J
2 x 7 W stereo BTL audio amplifier
14.2 Thermal behaviour and heatsink calculation
The measured maximum thermal resistance of the IC package, R_th(j-mb) is 6.9 K/W.
A calculation for the heatsink can be made, with the following parameters:
T_amb(max) = 50 °C
V_CC = 12 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 worstcase sine-wave dissipation is 8 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) = 100/8 = 12.5 K/W
R_th(h-a) = R_th(tot) – R_th(j-mb) = 12.5 – 6.9 = 5.6 K/W.
The calculation above is for an application at worstcase (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) = 100/4 = 25 K/W
R_th(h-a) = R_th(tot) – R_th(j-mb) = 25 – 6.9 = 18.1 K/W.
To increase the lifetime of the IC, T_j(max) should be reduced to 125 °C. This requires a
heatsink of approximately 12 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 = 12 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.
9397 750 06861
Product specification
Rev. 02 — 14 February 2000
© Philips Electronics N.V. 2000. All rights reserved.
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