TDA8920B datasheet(19/34 Pages) PHILIPS

19 / 34 page

9397 750 13356

Preliminary data sheet

Rev. 01 — 1 October 2004

19 of 34

Philips Semiconductors

TDA8920B

× 100 W class-D power ampliﬁer

A typical value for the capacitor on the PROT pin is 220 pF. After a ﬁxed time of

100 ms the ampliﬁer is switched on again. If the requested output current is still too

high the ampliﬁer will switch-off again. Thus the ampliﬁer will try to switch to the

Operating mode every 100 ms. The average dissipation will be low in this situation

because of this low duty cycle. If the overcurrent condition is removed the ampliﬁer will

remain in Operating mode once restarted.

In this way the TDA8920B ampliﬁer is fully robust against short circuit conditions while at

the same time so-called audio holes as a result of loudspeaker impedance drops are

eliminated.

13.7 Pumping effects

In a typical stereo half-bridge (Single-Ended (SE)) application the TDA8920B class-D

ampliﬁer is supplied by a symmetrical voltage (e.g VDD = +27 V and VSS = −27 V). When

the ampliﬁer is used in a SE conﬁguration, a so-called ‘pumping effect’ can occur. During

one switching interval, energy is taken from one supply (e.g. VDD), while a part of that

energy is delivered back to the other supply line (e.g. VSS) and visa versa. When the

voltage supply source cannot sink energy, the voltage across the output capacitors of that

voltage supply source will increase: the supply voltage is pumped to higher levels. The

voltage increase caused by the pumping effect depends on:

• Speaker impedance

• Supply voltage

• Audio signal frequency

• Value of decoupling capacitors on supply lines

• Source and sink currents of other channels.

The pumping effect should not cause a malfunction of either the audio ampliﬁer and/or the

voltage supply source. For instance, this malfunction can be caused by triggering of the

undervoltage or overvoltage protection or unbalance protection of the ampliﬁer.

Best remedy for pumping effects is to use the TDA8920B in a mono full-bridge application

or in case of stereo half-bridge application adapt the power supply (e.g. increase supply

decoupling capacitors).

TDA8920B Datasheet(PDF) 19 Page - NXP Semiconductors