CS4812 datasheet(18/36 Pages) CIRRUS

18 / 36 page

CS4812

DS291PP3

signal swing. DC control input voltages may range

from ground to Vcc.

ADC output data is in twos-complement binary

format. For inputs above full scale, the ADC digital

output saturates. The OVL output pin asserts when

the analog input is out-of-range.

3.2.2

Digital High Pass Filter

In DC coupled systems, a small DC offset may ex-

ist between the input circuitry and the A/D convert-

ers. The CS4812 includes a defeatable high pass

filter after the decimator to remove these DC com-

ponents. The high pass filter response is given in

“High Pass Filter Characteristics” on page 4 and

scales linearly with sample rate. In applications

where DC level measurement is required, as would

occur when one of the ADC inputs is used for mea-

surement of DC control voltages, the high pass fil-

ter may be disabled via a control port register.

Note: The high pass filter defeat operates on both

ADC inputs simultaneously therefore external DC

blocking must be provided in the design of the an-

alog audio input circuit.

3.3

Analog Outputs

3.3.1

Line Level Outputs

The CS4812 contains on-chip differential buffer

amplifiers that produce line level outputs capable

of driving 10 k

Ω loads to full scale. These amplifi-

ers internally biased to the CMOUT voltage of 2.3

The recommended off-chip analog filter is a second

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 filtering

is desired. These filters can be easily integrated into

a differential-to-single-ended converter circuit as

shown in the 2-pole and 3-pole Butterworth filters

of Figure 12. The hardware mute circuit referenced

in Figure 12 is shown in Figure 13. Hardware mut-

ing is recommended on power-up and power-

down.

CS4812

AIN

150

22 µF

2.2 nF

100 µF

0.1 µF

Ω

Figure 11. Single Ended Input

2-Pole Butterworth Filter

BUFFERED

CMOUT

AOU T-

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

Line

Out

AOU T+

AOU T-

220 pF

2200 pF

2.8k

Ω

2.8k

Ω

2.8kΩ

2.8k

Ω

11.0k

Ω

11.0k

Ω

14.0k

Ω

14.0k

Ω

2200 pF

GND

+5 V

3-Pole Butterworth Filter

Output

Mute Ckt

Output

Mute Ckt

Figure 12. Butterworth Output Filters

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