REV. E

–22–

REF19x Series

higher than the UPPER threshold, the situation reverses, with

U1 OFF and both U2 and Q1 ON. In the interest of battery

power conservation, all of the comparison switching circuitry

default output comes from U1.

thresholds are approximately 5.5 V and 6 V, respectively. These

REF19x devices used for U1 and U2, over a range of 2.5 V to

generally compatible with all family devices.

A Low Power, Strain Gage Circuit

As shown in Figure 12, the REF19x family of references can be

used in conjunction with low supply voltage operational amplifi-

ers, such as the OP492 and the OP283, in a self-contained strain

gage circuit. In this circuit, the REF195 was used as the core of

this low power, strain gage circuit. Other references can be easily

accommodated by changing circuit element values. The references

play a dual role as the voltage regulator to provide the supply

voltage requirements of the strain gage and the operational

amplifiers as well as a precision voltage reference for the current

source used to stimulate the bridge. A distinct feature of the

circuit is that it can be remotely controlled ON or OFF by digital

means via the

SLEEP pin.

500

0.1%

57k

1%

0.1 F

10k

1%

0.1 F

1/4

OP492

10 F

1 F

REF195

1/4

OP492

1/4

OP492

1/4

OP492

2.21k

20k

1%

10k

1%

20k

1%

20k

1%

0.01 F

10 F

100

OUTPUT

2N2222

20k

1%

10k

1%

Figure 12. A Low Power, Strain Gage Circuit