Microsemi

Linfinity Microelectronics Division

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Page 12

Copyright

© 2000

Rev. 1.1, 2000-12-01

The output filter inductors are key elements in the

performance of the Class-D audio power amplifier.

Inductor selection criteria also involves tradeoffs

between performance (efficiency) and component

costs. The critical specifications for the inductor are

the DC resistance, DC current, and peak current

ratings.

The inductors should be able to handle the

amplifier’s power as well as operate within its linear

region.

Saturating the inductors could decrease

performance (increase THD) and even produce a

short, which may damage either the circuit or the

speaker.

Other variables when selecting an inductor depend on

the switching frequency of the designed amplifier. A

higher switching frequency implies that the corner

the inductor value is smaller.

The amplifier’s application and design constraints will

help determine whether the inductors are selected for

size, power, or performance. Various inductors such

as those that are shielded may also have different EMI

effects and distortion performance.

The overall efficiency (

) of the amplifier circuit is given

in the previous MOSFET section.

The inductor’s

power loss contribution is a function of the inductor’s

   

)

)(

2

)(

(

Loss

Power

Inductor

2

IND

IND

R

I

P

=

=

The LX1710 Evaluation board utilizes two 15µH radial

leaded R.F. inductors from Inductor Supply, Inc. (ISI).

When evaluating component options, inductors such

as from Coilcraft can be used for other performance /

price tradeoffs. See inductor table below.

W

7

.

0

)

056

)(.

2

)(

5

.

2

(

2

=

=

The efficiency approximation can now be completed.

%

2

.

90

25

45

.

7

.

56

.

1

25

]

)

(

2

[

2

2

2

2

=

+

+

+

=

+

+

+

=

+

+

+

+

=

=

L

CROSS

IND

DS

L

CROSS

L

IND

PDS

NDS

L

IN

OUT

R

I

P

P

P

R

I

P

R

R

R

R

I

R

I

P

P

The efficiency is a function of the power and switching

loss in the MOSFETs and inductors.

Manufacturer

Part Number

Inductance



Q min

Test

Frequency

DC Resistance

 

DC Current

Self Resonant

Frequency min

(MHz)

ISI

RL622-150K

15.0

50

2.520MHz

56

2.50

12.0

Coilcraft

DO5022P-153HC

15.0

100kHz

32

4.4

20

  Inductor Component Options