DocID023917 Rev 1

17/23

AN4199

Design guidelines for schematic and PCB layout

23

6.3.2

Main filter

The main filter is an L and C based Butterworth filter. The cut-off frequency must be chosen

between the upper limit of the audio band (~20 kHz) and the carrier frequency (384 kHz).

Figure 18. Main filter

6.3.3

Damping network

The C-R-C is a damping network. It is mainly intended for high inductive loads where the

speaker load could be disconnected.

Figure 19. Damping network

Rload

Cload

Lload

Lload

INxA

INxB

2

Π

2

*

*

*

----------------

-----------------

=

1

2

Π

*

2

load

*

*

*

-----------------------------------------------------------------------

=

1

2

Π

*

*

*

-----------------------------------------------------------------

=

C

----------------

-

Table 2. Recommended values for main filter and damping network

Rload

16



12



8



6



4



Main filter

Lload

47 µH

33 µH

22 µH

15 µH

10 µH

Cload

220 nF

330 nF

470 nF

680 nF

1 µF

Damping network

C damp-S

100 nF

100 nF

100 nF

100 nF

220 nF

C damp-P

100 nF

100 nF

100 nF

100 nF

220 nF

R damp

10



8.2



6.2



4.7



2.7

