TDA8920BTH datasheet(17/34 Pages) PHILIPS

17 / 34 page

9397 750 13356

Preliminary data sheet

Rev. 01 — 1 October 2004

17 of 34

Philips Semiconductors

TDA8920B

× 100 W class-D power ampliﬁer

If two or more class-D ampliﬁers are used in the same audio application, it is strongly

recommended that all devices run at the same switching frequency. This can be realized

by connecting all OSC pins together and feed them from an external central oscillator.

Using an external oscillator it is necessary to force pin OSC to a DC-level above SGND for

switching from the internal to an external oscillator. In this case the internal oscillator is

disabled and the PWM will be switched on the external frequency. The frequency range of

the external oscillator must be in the range as speciﬁed in the switching characteristics;

see Section 12.1.

In an application circuit:

• Internal oscillator: ROSC connected between pin OSC and VSSA

• External oscillator: connect the oscillator signal between pins OSC and SGND; delete

ROSC and COSC.

13.5 Heatsink requirements

In some applications it may be necessary to connect an external heatsink to the

TDA8920B. Limiting factor is the 150

°C maximum junction temperature T

j(max) which

cannot be exceeded. The expression below shows the relationship between the maximum

allowable power dissipation and the total thermal resistance from junction to ambient:

(5)

Pdiss is determined by the efﬁciency (η) of the TDA8920B. The efﬁciency measured in the

TDA8920B as a function of output power is given in Figure 21.The power dissipation can

be derived as function of output power (see Figure 20).

The derating curves (given for several values of the Rth(j-a)) are illustrated in Figure 8.

A maximum junction temperature Tj = 150 °C is taken into account. From Figure 8 the

maximum allowable power dissipation for a given heatsink size can be derived or the

required heatsink size can be determined at a required dissipation level.

th j

–

()

j max

()

amb

–

diss

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