CS4525 View Datasheet(PDF) - Cirrus Logic

Part Name

Description

MFG CO.

CS4525

30 W Digital Audio Amplifier with Integrated ADC

Cirrus Logic 

CS4525

6.4 Output Filters

The filter placed after the PWM outputs can greatly affect the output performance. The filter not only reduces

radiated EMI (snubber filter), but also filters high frequency content from the switching output before going

to the speaker (low-pass LC filter).

6.4.1

Half-Bridge Output Filter

Figure 26 shows the output filter for a half-bridge configuration. The transient-voltage suppression circuit

(snubber circuit) is comprised of a capacitor (680 pF) and a resistor (5.6 Ω, 1/8 W) and should be placed

as close as possible to the corresponding PWM output pin to greatly reduce radiated EMI.

VP

OUTx

680 pF

5.6 Ω

L1

*Diode is Rohm

RB160M-30 or

equivalent

C2

+-

C1

Figure 26. Output Filter - Half-Bridge

The inductor, 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 18 shows the component values

for L1 and C1 based on nominal speaker (load) impedance for a corner frequency (-3 dB point) of approx-

imately 35 kHz.

Load

4Ω

6Ω

8Ω

L1

22 µH

33 µH

47 µH

C1

1.0 µF

0.68 µF

0.47 µF

Table 18. Low-Pass Filter Components - Half-Bridge

C2 is the DC-blocking capacitor. Table 19 shows the component values for C2 based on corner frequency

(-3 dB point) and a nominal speaker (load) impedances of 4 Ω, 6 Ω, and 8 Ω. This capacitor should also

be chosen to have a ripple current rating above the amount of current that will passed through it.

Load

4Ω

6Ω

8Ω

Corner Frequency

40 Hz

58 Hz

120 Hz

39 Hz

68 Hz

120 Hz

42 Hz

60 Hz

110 Hz

C2

1000 µF

680 µF

330 µF

680 µF

390 µF

220 µF

470 µF

330 µF

180 µF

Table 19. DC-Blocking Capacitors Values - Half-Bridge

DS726PP1

59

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