CS4525 datasheet(59/98 Pages) CIRRUS

59 / 98 page

DS726PP3

CS4525

6.4

Output Filters

The output filter configuration of the CS4525 can greatly affect device performance. These components re-

duce radiated EMI, protect the output transistors of the device, attenuate the high frequency content of the

output signal, and, in the half bridge configuration, block DC current from reaching the loudspeaker.

6.4.1

Half-Bridge Output Filter

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

implemented as an RC snubber network comprised of a resistor Rs (5.6 Ω, 1/8 W) and a capacitor Cs

(680 pF). This should be placed as close as possible to the corresponding output pin. This circuit decreas-

es the slew rate of the output signal and reduces high frequency ringing which can lead to increased EMI.

The Schottky diodes protect the body diodes of the output devices by conducting load current during

switching transitions; these diodes must be present to ensure proper device operation.

The inductor L1 and capacitor C1 form a low-pass filter to remove high frequency switching content from

the output signal. These values combine with the nominal load impedance of the speaker to set the cut-

off frequency of the filter. Table 18 shows the component values for L1 and C1 based on nominal speaker

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

C2 serves to block DC from the output. Table 19 shows the component values for C2 based on desired

corner frequency (-3 dB) and nominal speaker impedances of 4

Ω, 6 Ω, and 8 Ω. This capacitor should be

chosen to have a ripple current rating higher than the amount of current that will pass through it.

Load

Ω

22 µH

1.0 µF

Ω

33 µH

0.68 µF

Ω

47 µH

0.47 µF

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

Load

Corner Frequency

Ω

40 Hz

1000 µF

58 Hz

680 µF

120 Hz

330 µF

Ω

39 Hz

680 µF

68 Hz

390 µF

120 Hz

220 µF

Ω

42 Hz

470 µF

60 Hz

330 µF

110 Hz

180 µF

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

* ROHM RB160 M-30

or equivalent

D1*

D2*

5.6

Ω

680 pF

OUTx

Figure 26. Output Filter - Half-Bridge

CS4525

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