CS4220 datasheet(22/32 Pages) CIRRUS

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CS4220 CS4221

DS284PP3

8. APPLICATIONS

8.1

Overview

The CS4220 is a stand-alone device controlled

through dedicated pins. The CS4221 is controlled

with an external microcontroller using the serial

control port.

8.2

Grounding and Power Supply

Decoupling

As with any high resolution converter, the

CS4220/1 requires careful attention to power sup-

ply and grounding arrangements to optimize per-

formance.

Figures

and

shows

the

recommended power arrangement with VA, VD

and VL connected to clean supplies. Decoupling

capacitors should be located as close to the device

package as possible. If desired, all supply pins may

be connected to the same supply, but a decoupling

capacitor should still be used on each supply pin.

8.3

High Pass Filter

The operational amplifiers in the input circuitry

driving the CS4220/1 may generate a small DC off-

set into the A/D converter. The CS4220/1 includes

a high pass filter after the decimator to remove any

DC offset which could result in recording a DC lev-

el, possibly yielding "clicks" when switching be-

tween devices in a multichannel system.

8.4

Analog Outputs

The recommended off-chip analog filter is either a

2nd order Butterworth or a 3rd order Butterworth,

if greater out-of-band noise filtering is desired. The

CS4220/1 DAC interpolation filter has been pre-

compensated for an external 2nd order Butterworth

filter with a 3 dB corner at Fs, or a 3rd order But-

terworth filter with a 3 dB corner at 0.75 Fs to pro-

vide a flat frequency response and linear phase over

the passband (see Figure 14 for Fs = 48 kHz). If the

recommended filter is not used, small frequency re-

sponse magnitude and phase errors will occur. In

addition to providing out-of-band noise attenua-

tion, the output filters shown in Figure 14 provide

differential to single-ended conversion.

8.5

Master vs. Slave Mode

The CS4220/1 may be operated in either master

mode or slave mode. In master mode, SCLK and

LRCK are outputs which are internally derived

from MCLK. The device will operate in master

mode when a 47 k

Ω pulldown resistor is present on

SDOUT at startup or after reset, see Figure 5.

LRCK and SCLK are inputs to the CS4220/1 when

operating in slave mode. See Figures 8-11 for the

available clocking modes.

8.6

De-emphasis

The CS4220/1 includes digital de-emphasis for 32,

44.1, or 48 kHz sample rates. The frequency re-

sponse of the de-emphasis curve, as shown in Fig-

ure 15, will scale proportionally with changes in

samples rate, Fs. The de-emphasis feature is in-

cluded to accommodate older audio recordings that

utilize pre-emphasis as a means of noise reduction.

De-emphasis control is achieved with the DEM1/0

pins on the CS4220 or through the DEM1-0 bits in

the DSP Port Mode Byte (#5) on the CS4221.

8.7

Power-up / Reset / Power Down

Calibration

Upon power up, the user should hold RST = 0 for

approximately 10 ms. In this state, the control port

is reset to its default settings and the part remains in

the power down mode. At the end of RST, the de-

vice performs an offset calibration which lasts ap-

proximately 50 ms after which the device enters

normal operation. In the CS4221, a calibration may

also be initiated via the CAL bit in the ADC Con-

trol Byte (#1). The CALP bit in the ADC Control

Byte is a read only bit indicating the status of the

calibration.

Reset/Power Down is achieved by lowering the

RST pin causing the part to enter power down.

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