TDA8944J datasheet(15/21 Pages) PHILIPS

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Philips Semiconductors

TDA8944J

2 x 7 W stereo BTL audio ampliﬁer

Product speciﬁcation

Rev. 02 — 14 February 2000

15 of 21

9397 750 06861

14.2 Thermal behaviour and heatsink calculation

The measured maximum thermal resistance of the IC package, Rth(j-mb) is 6.9 K/W.

A calculation for the heatsink can be made, with the following parameters:

Tamb(max) =50 °C

VCC = 12 V and RL =8 Ω

Tj(max) = 150 °C.

Rth(tot) is the total thermal resistance between the junction and the ambient

including the heatsink. In the heatsink calculations the value of Rth(mb-h) is ignored.

At VCC = 12 V and RL =8 Ω the measured worstcase sine-wave dissipation is 8 W;

see Figure 11. For Tj(max) = 150 °C the temperature raise - caused by the power

dissipation - is: 150 – 50 = 100

°C.

× R

th(tot) = 100 °C

Rth(tot) = 100/8 = 12.5 K/W

Rth(h-a) =Rth(tot) –Rth(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:

× R

th(tot) = 100 °C

Rth(tot) = 100/4 = 25 K/W

Rth(h-a) =Rth(tot) –Rth(j-mb) = 25 – 6.9 = 18.1 K/W.

To increase the lifetime of the IC, Tj(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

Tamb =25 °C; VCC = 12 V; f = 1 kHz; RL =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.

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