AN10436 PHILIPS [NXP Semiconductors], AN10436 Datasheet - Page 28

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

NXP Semiconductors
AN10436_1
Application note
3.5.1 Filter inductor
Table 4.
There are two main types of inductors:
An air coil is used often in HiFi audio equipment, but is not very useful in mainstream
audio because of the physical size.
The major benefit of an unshielded inductor is cost. However, the magnetic stray field can
cause either crosstalk issues or interference with other sensitive parts inside an audio or
TV system (AM-receiver, picture interference, etc.).
The benefit of the shielded magnetic inductor is that the magnetic field is captured inside
the core, reducing the magnetic stray field.
The most important parameters of an inductor are:
The DC current capability needs to be high enough to avoid magnetic saturation. High
peak currents are a result of saturation because the inductor tends to acts like a short.
Therefore, for a proper inductor selection it is important to consider the maximum current
delivered by the amplifier, and the temperature of the inductor (higher inductor
temperature will decrease the saturation level). The maximum current occurs at voltage
clipping and can be calculated through the use of either
or
Example:
For a 2 × 15 W SE amplifier operating at 22 V the maximum output current is equal to
2.1 A (R
to select an inductor that retains still at least 80 % of the nominal inductance at the
maximum current of 2.1 A.
Configuration
SE
BTL
•
•
•
•
•
Equation 13
Air coil, current independent inductance and no saturation effect.
Inductor with a magnetic core (ferrite or iron powder):
– Magnetically unshielded version (pot core).
– Magnetically shielded version (pot core or toroidal core).
DC current rating to avoid magnetic saturation, causing an increase in audio
distortion.
Linearity of the inductor, causing an increase in audio distortion (especially above
1 kHz).
DC resistance having a direct impact on efficiency.
DSon
Filter component values
= 0.15 Ω and R
for BTL configuration.
Rev. 01 — 12 December 2007
Impedance (Ω)
4
6
8
4
6
8
s
= 0.05 Ω and R
ESR
L2 / L3 (μH)
22
33
47
10
15
22
TDA8932B/33(B) Class-D audio amplifier
= 0.06 Ω). Therefore, it is recommended
Equation 12
C14 / C23 (nF)
680
470
330
1500
1000
680
for SE configuration
AN10436
© NXP B.V. 2007. All rights reserved.
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