Datasheet

LT1167
16
1167fc
APP
LIC
A
TI
ON
S I
N
F
ORMA
TI
ON
–
+
–
+
–
+
350Ω
350Ω
350Ω
350Ω
10V
10k**
PRECISION BRIDGE TRANSDUCER
LT1167 MONOLITHIC
INSTRUMENTATION AMPLIFIER
G = 100, R
G
= ±10ppm TC
SUPPLY CURRENT = 1.3mA MAX
“ROLL YOUR OWN” INST AMP, G = 100
* 0.02% RESISTOR MATCH, 3ppm/°C TRACKING
** DISCRETE 1% RESISTOR, ±100ppm/°C TC
100ppm TRACKING
SUPPLY CURRENT = 1.35mA FOR 3 AMPLIFIERS
1167 F06
R
G
499Ω
1/4
LT1114A
1/4
LT1114A
1/4
LT1114A
10k**
202Ω**
10k*
10k*
10k*
10k*
–
+
LT1167C
REF
Figure 6. “Roll Your Own” vs LT1167
Table 1. “Roll Your Own” vs LT1167 Error Budget
ERROR SOURCE LT1167C CIRCUIT CALCULATION
“ROLL YOUR OWN”’ CIRCUIT
CALCULATION
ERROR, ppm OF FULL SCALE
LT1167C “ROLL YOUR OWN”
Absolute Accuracy at T
A
= 25°C
Input Offset Voltage, μV
Output Offset Voltage, μV
Input Offset Current, nA
CMR, dB
60μV/20mV
(300μV/100)/20mV
[(450pA)(350/2)Ω]/20mV
110dB→[(3.16ppm)(5V)]/20mV
100μV/20mV
[(60μV)(2)/100]/20mV
[(450pA)(350Ω)/2]/20mV
[(0.02% Match)(5V)]/20mV
3000
150
4
790
5000
60
4
500
Drift to 85°C
Gain Drift, ppm/°C
Input Offset Voltage Drift, μV/°C
Output Offset Voltage Drift, μV/°C
(50ppm + 10ppm)(60°C)
[(0.4μV/°C)(60°C)]/20mV
[(6μV/°C)(60°C)]/100/20mV
Total Absolute Error
(100ppm/°C Track)(60°C)
[(1.6μV/°C)(60°C)]/20mV
[(1.1μV/°C)(2)(60°C)]/100/20mV
3944
3600
1200
180
5564
6000
4800
66
Resolution
Gain Nonlinearity, ppm of Full Scale
Typ 0.1Hz to 10Hz Voltage Noise, μV
P-P
15ppm
0.28μV
P-P
/20mV
Total Drift Error
10ppm
(0.3μV
P-P
)(√2)/20mV
4980
15
14
10866
10
21
Total Resolution Error
Grand Total Error
29
8953
31
16461
G = 100, VS = ±15V
All errors are min/max and referred to input.
the LT1167 are input offset voltage and CMRR. Note that
for the discrete solution, the noise voltage specification is
multiplied by √2 which is the RMS sum of the uncorelated
noise of the two input amplifiers. Each of the amplifier er-
rors is referenced to a full-scale bridge differential voltage
of 20mV. The common mode range of the bridge is 5V. The
LT1114 data sheet provides offset voltage, offset voltage
drift and offset current specifications for the matched op
amp pairs used in the error-budget table. Even with an
excellent matched op amp like the LT1114, the discrete
solution’s total error is significantly higher than the LT1167’s
total error. The LT1167 has additional advantages over
the discrete design, including lower component cost and
smaller size.
Current Source
Figure 7 shows a simple, accurate, low power program-
mable current source. The differential voltage across
Pins2 and 3 is mirrored across R
G
. The voltage across
R
G
is amplified and applied across R
X
, defining the out-
put current. The 50μA bias current flowing from Pin 5 is
buffered by the LT1464 JFET operational amplifier. This