Datasheet REF198x (Analog Devices) - 25

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Data Sheet REF19x Series +VBAT 2 +VS C2 R1 0.1µF U1 R3 R6 1.1MΩ 3 REF195 6 10MΩ 100Ω Q1 (SEE TABLE) 2N3904 5.000V 4 C1 3 + 0.1µF 7 6 4 2 – U3 2 AD820 U2 +C3 3 6 1µF R2 REF195 (SEE TABLE) 100kΩ R4 4 900kΩ C4 R5 V 0.1µF 100kΩ S, VBAT VOUT
30
COMMON
-0
COMMON
71 03 0 Figure 32. Fail-Safe 5 V Reference For V
100
Ω S levels lower than the lower threshold, the output of U3 is low, thus U2 and Q1 are off and U1 is on. For VS levels higher
REF195 10
μ
F
than the upper threshold, the situation reverses, with U1 off and
2 6
both U2 and Q1 on. In the interest of battery power conserva-
+ + 10
μ
F 4 1
μ
F
tion, all of the comparison switching circuitry is powered from VS and is arranged so that when VS fails, the default output
57k
Ω
1% 0.1
μ
F
comes from U1. For the R1 to R3 values, as shown in Figure 32, lower/upper VS
3 + 4
switching thresholds are approximately 5.5 V and 6 V, respec-
1/4 1 2N2222 OP492
tively. These can be changed to suit other VS supplies, as can the
10k
Ω
0.1
μ
F 2 – 11 1%
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 VS of 3.3 V, which is
500
Ω generally compatible with all REF19x family devices.
0.1% LOW POWER, STRAIN GAGE CIRCUIT 10k
Ω As shown in Figure 33, the REF19x family of references can be
1% 0.01
μ
F
used in conjunction with low supply voltage operational ampli-
20k
Ω
1%
fiers, such as the OP492 or the OP747, in a self-contained strain
20k
Ω
13 –
gage circuit in which the REF195 is used as the core. Other
1/4 1% 14 6 –
references can be easily accommodated by changing circuit
OP492 1/4 12 + 7 OUTPUT OP492
element values. The references play a dual role, first as the
2.21k
Ω
10k
Ω
5 + 1%
voltage regulator to provide the supply voltage requirements of the strain gage and the operational amplifiers, and second as a
9 – 20k
Ω precision voltage reference for the current source used to
1/4 1% 8
stimulate the bridge. A distinct feature of the circuit is that it
OP492 20k
Ω
10 +
can be remotely controlled on or off by digital means via
1%
00371-031 the SLEEP pin. Figure 33. Low Power, Strain Gage Circuit Rev. L | Page 25 of 28 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION TEST PINS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS—REF191 @ TA = 25°C ELECTRICAL CHARACTERISTICS—REF191 @ −40°C ≤ +85°C ELECTRICAL CHARACTERISTICS—REF191 @ −40°C ≤ TA ≤ +125°C ELECTRICAL CHARACTERISTICS—REF192 @ TA = 25°C ELECTRICAL CHARACTERISTICS—REF192 @ −40°C ≤ TA ≤ +85°C ELECTRICAL CHARACTERISTICS—REF192 @ −40°C ≤ TA ≤ +125°C ELECTRICAL CHARACTERISTICS—REF193 @ TA = 25°C ELECTRICAL CHARACTERISTICS—REF193 @ −40°C ≤ TA ≤ +85°C ELECTRICAL CHARACTERISTICS—REF193 @ TA ≤ −40°C ≤ +125°C ELECTRICAL CHARACTERISTICS—REF194 @ TA = 25°C ELECTRICAL CHARACTERISTICS—REF194 @ −40°C ≤ TA ≤ +85°C ELECTRICAL CHARACTERISTICS—REF194 @ −40°C ≤ TA ≤ +125°C ELECTRICAL CHARACTERISTICS—REF195 @ TA = 25°C ELECTRICAL CHARACTERISTICS—REF195 @ −40°C ≤ TA ≤ +85°C ELECTRICAL CHARACTERISTICS—REF195 @ −40°C ≤ TA ≤ +125°C ELECTRICAL CHARACTERISTICS—REF196 @ TA = 25°C ELECTRICAL CHARACTERISTICS—REF196 @ −40°C ≤ TA ≤ +85°C ELECTRICAL CHARACTERISTICS—REF196 @ −40°C ≤ TA ≤ +125°C ELECTRICAL CHARACTERISTICS—REF198 @ TA = 25°C ELECTRICAL CHARACTERISTICS—REF198 @ −40°C ≤ TA ≤ +85°C ELECTRICAL CHARACTERISTICS—REF198 @ −40°C ≤ TA ≤ 125°C ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS APPLICATIONS INFORMATION OUTPUT SHORT-CIRCUIT BEHAVIOR DEVICE POWER DISSIPATION CONSIDERATIONS OUTPUT VOLTAGE BYPASSING SLEEP MODE OPERATION BASIC VOLTAGE REFERENCE CONNECTIONS MEMBRANE SWITCH-CONTROLLED POWER SUPPLY SOLDER HEAT EFFECT CURRENT-BOOSTED REFERENCES WITH CURRENT LIMITING NEGATIVE PRECISION REFERENCE WITHOUT PRECISION RESISTORS STACKING REFERENCE ICs FOR ARBITRARY OUTPUTS PRECISION CURRENT SOURCE SWITCHED OUTPUT 5 V/3.3 V REFERENCE KELVIN CONNECTIONS FAIL-SAFE 5 V REFERENCE LOW POWER, STRAIN GAGE CIRCUIT OUTLINE DIMENSIONS ORDERING GUIDE