13
LT1021
1021fc
TYPICAL APPLICATIONS
U
Precision DAC Reference with System TC Trim
Strain Gauge Conditioner for 350Ω Bridge
Negative Shunt Reference Driven
by Current Source
LT1021-10
OUT
IN
GND
1021 TA17
15V
8.87k
1%
1.24k
1%
10k
1%
D1
1N457
50k
TC TRIM*
10k
1%
D2
1N457
50k
200k
1%
50k
ROOM TEMP
TRIM
10.36k
1%
8.45k
1mA
TRIMS 1mA REFERENCE CURRENT
TC BY ± 40ppm/°C. THIS TRIM SCHEME HAS
VERY LITTLE EFFECT ON ROOM TEMPERATURE
CURRENT TO MINIMIZE ITERATIVE TRIMMING
*
DAC
Handling Higher Load Currents
LT1021-10
OUT
GND
IN
1021 TA08
R
L
30mA
15V
R1*
169Ω
V
OUT
10V
TYPICAL LOAD
CURRENT = 30mA
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
*
LT1021-10
OUT
IN
GND
1021 TA09
–
+
–
+
LM301A
†
100pF
8
1
6 6
3
2
–5V
357Ω
1/2W
–15V
R5
2M
R6*
2M
LT1012C
2
3
R4
20k
R2
20k
5V
R3
2M
V
OUT
× 100
350Ω STRAIN
GAUGE BRIDGE**
28mA
28.5mA
R1
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
1021 TA14
2.5mA
–10V (I
LOAD
≤ 1mA)
–11V TO – 40V
27Ω
LM334
