AD7707 datasheet(35/40 Pages) AD

35 / 40 page

REV. A

AD7707

–35–

Pressure Measurement

Other typical applications for the AD7707 include temperature

and pressure measurement. Figure 27 shows the AD7707 used

with a pressure transducer, the BP01 from Sensym. The

pressure transducer is arranged in a bridge network and gives 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 (i.e., the voltage between its IN(+) and IN(–)

terminals). Assuming a 5 V excitation voltage, the full-scale

output range from the transducer is 15 mV. The low level input

channels are ideal for this type of low signal measurement appli-

cation. The excitation voltage for the bridge is also used to

generate the reference voltage for the AD7707. Therefore,

variations in the excitation voltage do not introduce errors in

the system. Choosing resistor values of 24 k

Ω and 15 kΩ, as

per Figure 27, gives a 1.92 V reference voltage for the AD7707

when the excitation voltage is 5 V.

Using the part with a programmed gain of 128 results in the

full-scale input span of the AD7707 being 15 mV, which corre-

sponds with the output span from the transducer.

AD7707

DVDD

+5V

REF IN(–)

AGND

MCLK IN

MCLK OUT

DRDY

REF IN(+)

24k

AVDD

AIN1

LOCOM

DGND

OUT(–)

SCLK

DIN

DOUT

CONTROLLER

15k

OUT(+)

EXCITATION VOLTAGE = +5V

IN(–)

IN(+)

Figure 27. Pressure Measurement Using the AD7707

Thermocouple Measurement

Another application area for the AD7707 is in temperature

measurement. Figure 28 outlines a connection from a thermo-

couple to the AD7707. In this application, the AD7707 is oper-

ated in its unbuffered mode to accommodate signals of

±100 mV

on the front end. Cold conjunction compensation is imple-

mented using the AD590 temperature transducer that produces

an output current proportional to absolute temperature.

AD7707

DVDD

+5V

AIN2

REF IN(–)

AGND

MCLK IN

MCLK OUT

DRDY

REF IN(+)

8.2k

CJC

AVDD

AD590

+5V

AIN1

LOCOM

DGND

OUT

SCLK

DIN

DOUT

THERMOCOUPLE

JUNCTION

CONTROLLER

REF192

+5V

GND

Figure 28. Thermocouple Measurement Using the

AD7707

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