CS5522-AP datasheet(43/56 Pages) CIRRUS

43 / 56 page

CS5521/22/23/24/28

DS317F2

2.8 Power Supply Arrangements

The CS5521/22/23/24/28 A/D converters are de-

signed to operate from a single +5 V analog supply

and a single +5 V or +3 V digital supply. A -2.1 V

supply is usually generated from the charge pump

drive to provide power to the instrumentation am-

plifier’s

NBV

(negative

bias

voltage)

pin.

Figure 21 illustrates the CS5522 connected with a

+5 V analog supply and with the external compo-

nents required for the charge pump drive. This en-

ables the CS5522 to measure ground referenced

signals with magnitudes down to ±100 mV.

Figure 22 illustrates the CS5522 connected to mea-

sure ground referenced unipolar signals of a posi-

tive polarity using the 1 V, 2.5 V, and 5 V ranges

on the converter. For the 25 mV, 55 mV, and

100 mV ranges, the signals being digitized must

have a common mode between +1.85 to +2.65 V

(NBV = 0 V).

Although CS5521/22/23/24/28 are optimized for

the measurement of thermocouple outputs, they are

also well suited for the measurement of ratiometric

bridge transducer outputs. Figure 23 illustrates the

CS5522 connected to measure the output of a rati-

ometric differential bridge transducer while operat-

ing from a single +5 V supply. Bridge outputs may

range from 5 mV to 400 mV. See the Digital Gain

Scaling section about manipulating the gain regis-

ter to achieve optimum gain scaling.

XOUT

VD+

VA+

VREF+

VREF-

DGND

NBV

AIN1+

SCLK

SDO

SDI

CS5522

XIN

CPD

Ω

+5V

Analog

Supply

0.1

µF0.1 µF

AGND

214

Optional

Clock

Source

Serial

Data

Interface

32.768 ~ 100 kHz

2.5V

Up to ± 100 mV Input

AIN1-

10 k

Ω

0.1

µF

1N4148

BAV199

AIN2+

AIN2-

Charge-pump network

for VD+ = 5V only and

XIN = 32.768 kHz.

Logic Outputs:

A0 - A1 Switch from

VA+ to AGND.

10 k

Ω

301

Ω

499

Ω

+5V

V+

LM334

Absolute

Current

Reference

V-

Cold Junction

BAT85

0.033

µF

Figure 21. CS5522 Configured to use on-chip charge pump to supply NBV

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