Pumping Effects - Philips TDA8920B Product Data Sheet

Philips Semiconductors

13.7 Pumping effects

TDA8920B_2
Product data sheet
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.
In a typical stereo half-bridge SE application the TDA8920B class-D amplifier is supplied
by a symmetrical voltage (e.g V
in a SE configuration, a so-called 'pumping effect' can occur. During one switching
interval, energy is taken from one supply (e.g. V
delivered back to the other supply line (e.g. V
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).
Rev. 02 — 07 November 2005
= −27 V). When the amplifier is used
= +27 V and V
DD SS
), while a part of that energy is
DD
) and visa versa. When the voltage supply
SS
TDA8920B
2 × 100 W class-D power amplifier
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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