CS5181 datasheet(10/24 Pages) CIRRUS

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CS5181

DS250PP1

Analog Input

The analog signal to the converter is input into the

AIN+ and AIN- pins. The input signal is fully dif-

ferential with the maximum peak-to-peak ampli-

tude of VREFIN X 1.6 V. The signal needs to have

a common mode voltage in a range from 1.0 V to

VREF + 0.25 V for minimum distortion. A resis-

tor-capacitor filter should be included on the AIN+

and AIN- inputs of the converter. This should con-

sist of a 20

Ω resistor and a 2200 pF capacitor on

each input to ground as illustrated in the system

connection diagram (Figure 11).

Output Coding

Table 1 illustrates the output coding for the con-

verter when operating with the digital filter

(MODE = 1). The converter outputs its data from

the serial port in twos complement format, MSB

first.

The chip offers an MFLAG signal to indicate when

the modulator has gone unstable. MFLAG is set

when an overrange signal forces the modulator into

an unstable condition. Under this condition, output

codes from the converter will be locked to either

plus or minus full scale as is appropriate for the

overrange condition.

Modulator-Only mode

The CS5181 can be operated in modulator-only

mode by connecting the MODE pin to a logic 0

(DGND).

In modulator-only mode the noise-shaped bit-

stream from the fifth-order delta-sigma modulator

is output from the SDO and SDO (inverse bit-

stream) pins.

10 µF

0.1 µF

VREFIN

VREF+

VREF-

VREFOUT

VREFCAP

X1.6

Modulator

Reference

CS5181

10 µF

0.1 µF

1 µF

0.1 µF

10 µF

0.1 µF

2.5 V

10 µF

0.1 µF

Figure 4. CS5181 connection diagram for using an external voltage reference.

Fully Differential Bipolar

Input Voltage1

Twos Complement

>(VFS - 1.5 LSB)

7FFF

VFS - 1.5 LSB

7FFF

7FFE

-0.5 LSB

0000

FFFF

-VFS + 0.5 LSB

8001

8000

<(-VFS + 0.5 LSB)

8000

Notes: 1. VFS = VREFIN x 1.6

Table 1. Output Coding.

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