LT1021_15 Datasheet, PDF (13/16 Pages) Linear Technology – Precision Reference

LT1021
TYPICAL APPLICATIONS
Strain Gauge Conditioner for 350Ω Bridge
Negative Shunt Reference Driven
by Current Source
R1
357Ω
1/2W
LT1021-10
28mA
28.5mA
15V
IN
OUT
GND
5V
350Ω STRAIN
R3
GAUGE BRIDGE**
2M
3
6
LM301A^†
2
1
100pF 8
R2
20k
2_–
R4
20k
LT1012C
3₊
6
V_OUT
× 100
R5
2M
R6*
2M
–5V
1021 TA09
357Ω
1/2W
–15V
*THIS RESISTOR PROVIDES POSITIVE FEEDBACK TO
THE BRIDGE TO ELIMINATE LOADING EFFECT OF
THE AMPLIFIER. EFFECTIVE Z_IN OF AMPLIFIER
STAGE IS ≥1MΩ. IF R2 TO R5 ARE CHANGED,
SET R6 = R3
**BRIDGE IS ULTRALINEAR WHEN ALL LEGS ARE
ACTIVE, TWO IN COMPRESSION AND TWO IN TENSION,
OR WHEN ONE SIDE IS ACTIVE WITH ONE COMPRESSED
AND ONE TENSIONED LEG
†_{OFFSET AND DRIFT OF LM301A ARE VIRTUALLY}
ELIMINATED BY DIFFERENTIAL CONNECTION OF LT1012C
LT1021-10
OUT
GND
–10V (I_LOAD ≤ 1mA)
2.5mA
LM334
27Ω
–11V TO – 40V
1021 TA14
Precision DAC Reference with System TC Trim
LT1021-10
15V IN
OUT
GND
8.87k
1%
1.24k
1%
D1
1N457
10k
50k
1%
TC TRIM*
50k
ROOM TEMP
TRIM
10k
D2
200k
1%
1N457
1%
10.36k
1%
50k
1mA
8.45k
*TRIMS 1mA REFERENCE CURRENT
TC BY ± 40ppm/°C. THIS TRIM SCHEME HAS
VERY LITTLE EFFECT ON ROOM TEMPERATURE
CURRENT TO MINIMIZE ITERATIVE TRIMMING
DAC
1021 TA17
Handling Higher Load Currents
15V _30mA
IN
LT1021-10
OUT
GND
R1*
169Ω
V_OUT
10V
R_L
TYPICAL LOAD
CURRENT = 30mA
1021 TA08
*SELECT R1 TO DELIVER TYPICAL LOAD CURRENT.
LT1021 WILL THEN SOURCE OR SINK AS NECESSARY
TO MAINTAIN PROPER OUTPUT. DO NOT REMOVE LOAD
AS OUTPUT WILL BE DRIVEN UNREGULATED HIGH. LINE
REGULATION IS DEGRADED IN THIS APPLICATION
1021fc
13