TDA8922BTH View Datasheet(PDF) - Philips Electronics
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TDA8922BTH Datasheet PDF : 32 Pages
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Philips Semiconductors
TDA8922B
2 Ć 50 W class-D power ampliļ¬er
The TDA8922B ampliļ¬er can distinguish between a low-ohmic short circuit condition and
other overcurrent conditions like dynamic impedance drops of the used loudspeakers. The
impedance threshold (Zth) depends on the supply voltage used.
Depending on the impedance of the short circuit the ampliļ¬er will react as follows:
1. Short-circuit impedance > Zth:
The maximum output current of the ampliļ¬er is regulated to 5 A, but the ampliļ¬er will
not shut-down its PWM outputs. Effectively this results in a clipping output signal
across the load (behavior is very similar to voltage clipping).
2. Short-circuit impedance < Zth:
The ampliļ¬er will limit the maximum output current to 5 A and at the same time the
capacitor on the PROT pin is discharged. When the voltage across this capacitor
drops below an internal threshold voltage the ampliļ¬er will shut-down completely and
an internal timer will be started.
A typical value for the capacitor on the PROT pin is 220 pF. After a ļ¬xed time of
100 ms the ampliļ¬er is switched on again. If the requested output current is still too
high the ampliļ¬er will switch-off again. Thus the ampliļ¬er 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 ampliļ¬er will
remain in Operating mode once restarted.
In this way the TDA8922B ampliļ¬er 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 TDA8922B class-D
ampliļ¬er is supplied by a symmetrical voltage (e.g VDD = +26 V and VSS = ā26 V). When
the ampliļ¬er is used in a SE conļ¬guration, a so-called āpumping effectā 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:
ā¢ Speaker impedance
ā¢ Supply voltage
ā¢ Audio signal frequency
ā¢ Value of decoupling capacitors on supply lines
ā¢ Source and sink currents of other channels.
The pumping effect should not cause a malfunction of either the audio ampliļ¬er 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 ampliļ¬er.
Best remedy for pumping effects is to use the TDA8922B in a mono full-bridge application
or in case of stereo half-bridge application adapt the power supply (e.g. increase supply
decoupling capacitors).
9397 750 13357
Preliminary data sheet
Rev. 01 ā 1 October 2004
Ā© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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