CS4811 datasheet(13/24 Pages) CIRRUS

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CS4811

DS486PP2

3.3

Analog Outputs

3.3.1

Line Level Outputs

The CS4811 contains on-chip differential buffer

amplifiers that produce line level outputs AOUT+

and AOUT-, which are capable of driving 10 k

Ω

loads. These amplifiers are internally biased to the

CMOUT voltage of 2.3 V.

The recommended off-chip analog filter is a 2nd

order Butterworth with a -3 dB corner at Fs. A third

order Butterworth filter with a -3 dB corner at

0.75 Fs can be used if greater out of band noise fil-

tering is desired. These filters can be easily inte-

grated into a differential-to-single-ended converter

circuit as shown in the 2-pole and 3-pole Butter-

worth filters of Figure 7. Figure 8 shows the rec-

ommended mute circuit referenced in Figure 7.

Activating the mute circuit is recommended on

power-up and power-down to avoid the output of

undesirable audio signals.

3.4

Clock Generation

The master clock to operate the CS4811 may be gen-

erated by using the on-chip oscillator with an exter-

nal crystal or may be input from an external clock

source.

3.4.1

Clock Source

The CS4811 requires a 256 Fs master clock to run

the internal logic. The two possible clock sources

are the on-chip crystal oscillator or an external clock

input to the XTI pin.

The master clock may be generated directly from

the on-chip crystal oscillator circuit. When using

the on-chip crystal oscillator, external loading ca-

pacitors are required. (see Figure 3) High frequen-

cy crystals (>8 MHz) should be parallel resonant,

fundamental mode and designed for 20 pF loading.

(equivalent to 40 pF to ground on each leg)

The master clock may also be generated directly

from an external CMOS clock input to the XTI pin.

2-Pole Butterworth Filter

BUFFERED

CMOUT

Example

Op-Amps

are

MC33078

AOU T-

MUTE

Line

Out

14.0 k

Ω

14.0 k

Ω

AOUT+

3.24 k

Ω

3.24 k

Ω

1000 pF

14.0 k

Ω

220 pF

14.0 k

Ω

GND

+5 V

BUFFERED

CMOUT

MUTE

Line

Out

AOUT+

AOU T-

220 pF

2200 pF

2.8k

Ω

2.8k

Ω

2.8kΩ

11.0kΩ

14.0k

Ω

14.0k

Ω

2200 pF

GND

+5 V

3-Pole Butterworth Filter

Figure 7. Butterworth Output Filters

Line Out

From

CS4811

PIO

MMBT3906

MMBT3904

MMBT3906

10 k

Ω

10 k

Ω

10 k

Ω

GND

3.3 k

Ω

µF

1 k

Ω

µF

Figure 8. Output Mute Circuit

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