AN10436 Datasheet, PDF (42/55 Pages) NXP Semiconductors – TDA8932B/33(B) Class-D audio amplifier

NXP Semiconductors
AN10436
TDA8932B/33(B) Class-D audio amplifier
POWER SUPPLY
GND
SOUND
PROCESSOR
DAC ^OUT
GND
GND
LEAVE FLOATING
FROM GROUND
(OR USE RC)
Fig 39. Supply GND connection
DIFFERENTIAL INPUT
AMPLIFIER TDA8932B/33(B)
FERRITE
BEAD
100nF
SPEAKER
LP
FILTER
STAR GROUND
AMPLIFIER SIDE
GND
SOLID GROUND PLANE
010aaa079
4.3 Low frequency supply pumping effect
A Single Ended (SE) Class-D amplifier will deliver energy back to the supply line (V_P)
during the negative part of the audio signal. Because most power supplies are not capable
of sinking energy, the supply voltage will increase especially when driving the amplifier at
low audio frequencies. This phenomenon is often called the pumping effect.
The voltage increase caused by the pumping effect depends on:
• The speaker impedance.
• The supply voltage.
• The audio signal frequency.
• The capacitance value of the supply line.
• The source/sink current of other channels (including the quiescent current of the
amplifier).
• The current drawn from other circuits attached to the same supply line.
This voltage increase might trigger the OVP of the audio amplifier and/or cause incorrect
control behavior of the regulated power supply.
The most effective way to overcome the pumping effect in a stereo SE application is to
apply one of the input signals to the negative input to invert the phase of that particular
output (see Figure 40).
AN10436_1
Application note
Rev. 01 — 12 December 2007
© NXP B.V. 2007. All rights reserved.
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