AD7193 datasheet(52/56 Pages) AD

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AD7193

MCLK1 MCLK2

REFIN2(+)

REFIN2(–)

DVDD DGND

Rev. A | Page 52 of 56

APPLICATIONS INFORMATION

The AD7193 provides a low cost, high resolution analog-to-

digital function. Because the analog-to-digital function is

provided by a Σ-Δ architecture, the part is more immune to noisy

environments, making it ideal for use in sensor measurement and

industrial and process control applications.

FLOWMETER

Figure 67 shows the AD7193 being used in a flowmeter application

that consists of two pressure transducers with the rate of flow

being equal to the pressure difference. The pressure transducers

are arranged in a bridge network and give a differential output

voltage between its OUT+ and OUT– terminals. With rated

full-scale pressure (in this case 300 mmHg) on the transducer,

the differential output voltage is 3 mV/V of the input voltage

(that is, the voltage between the IN+ and IN– terminals).

Assuming a 5 V excitation voltage, the full-scale output range

from the transducer is 15 mV. The excitation voltage for the

bridge can be used to directly provide the reference for the

ADC, because the reference input range includes the supply

voltage.

A second advantage of using the AD7193 in transducer based

applications is that the bridge power-down switch can be fully

utilized in low power applications. The bridge power-down switch

is connected in series with the cold side of the bridges. In normal

operation, the switch is closed and measurements are taken.

In applications where power is of concern, the AD7193 can be

placed in power-down mode, thus significantly reducing the

power consumed in the application. In addition, the bridge

power-down switch can be opened while the AD7193 is in power-

down mode, thus avoiding unnecessary power consumption

by the front-end transducers. When the parts are taken out of

power-down mode and the bridge power-down switch is closed,

the user should ensure that the front-end circuitry is fully settled

before attempting a read from the AD7193.

In Figure 67, temperature compensation is performed using

a thermistor. In addition, the reference voltage for the temperature

measurement is derived from a precision resistor in series with

the thermistor. This allows a ratiometric measurement so that

variation of the excitation voltage has no affect on the measurement

(it is the ratio of the precision reference resistance to the thermistor

resistance that is measured)

For simplicity, external filters are not shown in Figure 67;

however, an R-C antialias filter must be included on each analog

input. This is required because the on-chip digital filter does

not provide any rejection around the modulator sampling

frequency or multiples of this frequency. Suitable values are a

100 Ω resistor in series with each analog input, a 0.1 μF capacitor

between the analog input pins, and a 0.01 μF capacitor from

each analog input pin to AGND.

AIN1

IN+

IN–

OUT–

OUT+

AIN2

AIN3

AIN4

REFIN1(–)

BPDSW

AGND

AD7193

REFIN1(+)

REFERENCE

DETECT

SERIAL

INTERFACE

AND

CONTROL

LOGIC

CLOCK

CIRCUITRY

AVDD

AGND

DOUT/RDY

DIN

SCLK

SYNC

AVDD

AGND

AIN5

AIN6

IN+

IN–

OUT–

OUT+

Σ-Δ ADC

PGA

MUX

Figure 67. Typical Application (Flowmeter)

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