AN10436 PHILIPS [NXP Semiconductors], AN10436 Datasheet - Page 31

• Manufacturer Part Number: AN10436
• Description: TDA8932B/33(B) Class-D audio amplifier
• Manufacturer: PHILIPS [NXP Semiconductors]

NXP Semiconductors
AN10436_1
Application note
3.5.4 Voltage clamp diodes
3.6 Single ended capacitor
Remark: If the amplifier is driven at the resonance frequency (f
power dissipation in the resistor will rise causing the resistor to overheat.
For a voice coil inductance L
effectiveness of the zobel damping network is limited and the power dissipation in the
resistor grows high, requiring bulky power resistors. In general, mostly subwoofer voice
coils and HIFI multi-way speakers have such a high inductance.
Remark: Applications for which the end user is able to disconnect the speaker and
operate the amplifier without speaker, might also suffer from issues of robustness
because of the inductor saturation.
To avoid inductor saturation in case of high inductive load or no load, it is recommended to
apply voltage clamp diodes at the output to the supply rails (see
Relatively cheap general purpose diodes, like the 1N4001 (V
1N4002 (V
should be at least 1.2 times the supply voltage and the repetitive peak current should be
1.2 times the maximum current of the amplifier.
A single ended amplifier (Class-AB or Class-D) operating at an asymmetrical supply
voltage will require an AC couple capacitor (SE capacitor) in series with the speaker.
Especially for a low output power (< 25 W) it is a very cost effective solution compared to
a BTL configuration. It should be noted, the SE capacitor has no major drawback on THD
and audio performance in general.
The SE capacitor forms a high-pass filter with the speaker impedance. Therefore, the
frequency response will roll off with 20 dB per decade below the cut-off frequency f
The cut-off frequency is equal to:
Where:
f
–
Fig 28. Voltage clamp diodes
3dB
R
C15 (C24) = Single Ended capacitance (F) (see schematic
L
= load impedance (Ω).
=
------------------------------- -
2π R
R
⋅
= 100 V) can be used for this purpose. The reverse voltage of the diode
1
L
⋅
C15
Rev. 01 — 12 December 2007
V DD
V SS
E
greater than 10 times the filter inductance (L
PWM
D cl2
D cl1
L LC
TDA8932B/33(B) Class-D audio amplifier
R Z
C Z
C LC
equivalent
voice coil
R
010aaa428
circuit
Section
o
= 50 V) or the
L E
= 40 kHz) of the filter, the
R E
Figure
3.10).
AN10436
© NXP B.V. 2007. All rights reserved.
28).
LC
) the
−3dB
31 of 55
(19)
.