REF191 Datasheet, PDF (22/24 Pages) Analog Devices – Precision Micropower, Low Dropout Voltage References

REF19x Series
For V_S levels lower than the LOWER threshold, U3’s output is
low, thus U2 and Q1 are OFF, while U1 is ON. For V_S levels
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
is powered from V_S and is arranged so that when V_S fails, the
default output comes from U1.
For the R1–R3 values as shown, the LOWER/UPPER V_S switching
thresholds are approximately 5.5 V and 6 V, respectively. These
can obviously be changed to suit other V_S supplies, as can the
REF19x devices used for U1 and U2, over a range of 2.5 V to
5 V of output. U3 can operate down to a V_S of 3.3 V, which is
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.
10␮F
REF195
1␮F
100⍀
57k⍀
1%
0.1␮F
10␮F
0.1␮F
10k⍀
1%
1/4
OP492
2N2222
500⍀
0.1%
2.21k⍀
10k⍀
1%
1/4
OP492
10k⍀
1%
1/4
OP492
20k⍀
1%
0.01␮F
20k⍀
1%
1/4
OP492
20k⍀
1%
20k⍀
1%
OUTPUT
Figure 12. A Low Power, Strain Gage Circuit
–22–
REV. E