16

DS749A1

CS4412

4.4.2

Full-Bridge Output Filter (Stereo or Parallel)

Figure 6 shows the output filter for a full-bridge configuration. The transient-voltage suppression circuit

(snubber circuit) is comprised of a resistor (20

Ω) and capacitor (330 pF) and should be placed as close

as possible to the corresponding PWM output pins to greatly reduce radiated EMI. The inductors, L1, and

capacitor, C1, comprise the low-pass filter. Along with the nominal load impedance of the speaker, these

values set the cutoff frequency of the filter. Table 5 shows the component values based on nominal speak-

er (load) impedance for a corner frequency (-3 dB point) of approximately 35 kHz.

Load

Corner Frequency

C2

4

Ω

40 Hz

1000 µF

58 Hz

680 µF

120 Hz

330 µF

6

Ω

39 Hz

680 µF

68 Hz

390 µF

120 Hz

220 µF

8

Ω

42 Hz

470 µF

60 Hz

330 µF

110 Hz

180 µF

Table 4. DC-Blocking Capacitors Values - Half-Bridge

Load

L1

C1

4

Ω

10 µH

1.0 µF

6

Ω

15 µH

0.47 µF

8

Ω

22 µH

0.47 µF

Table 5. Low-Pass Filter Components - Full-Bridge

330 pF

20

Ω

C1

L1

L1

*Diode is Zetex

ZHCS400 or

equivalent

VP

VP

+ PWM

Output

- PWM

Output

Figure 6. Output Filter - Full-Bridge