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LT1167

APPLICATIONS INFORMATION

Figure 6. “Roll Your Own” vs LT1167

“ROLL YOUR OWN”’ CIRCUIT

ERROR SOURCE

LT1167C CIRCUIT CALCULATION

CALCULATION

LT1167C “ROLL YOUR OWN”

Absolute Accuracy at TA = 25°C

Input Offset Voltage,

µV60µV/20mV

100

µV/20mV

3000

5000

Output Offset Voltage,

µV

(300

µV/100)/20mV

[(60

µV)(2)/100]/20mV

150

Input Offset Current, nA

[(450pA)(350/2)

Ω]/20mV

[(450pA)(350

Ω)/2]/20mV

CMR, dB

110dB

→[(3.16ppm)(5V)]/20mV

[(0.02% Match)(5V)]/20mV

790

500

Total Absolute Error

3944

5564

Drift to 85

°C

Gain Drift, ppm/

°C

(50ppm + 10ppm)(60

°C)

(100ppm/

°C Track)(60°C)

3600

6000

Input Offset Voltage Drift,

µV/°C

[(0.4

µV/°C)(60°C)]/20mV

[(1.6

µV/°C)(60°C)]/20mV

1200

4800

Output Offset Voltage Drift,

µV/°C[6µV/°C)(60°C)]/100/20mV

[(1.1

µV/°C)(2)(60°C)]/100/20mV

180

Total Drift Error

4980

10866

Resolution

Gain Nonlinearity, ppm of Full Scale

15ppm

10ppm

Typ 0.1Hz to 10Hz Voltage Noise,

µVP-P

0.28

µVP-P/20mV

(0.3

µVP-P)(√2)/20mV

Total Resolution Error

Grand Total Error

8953

16461

G = 100, VS = ±15V

All errors are min/max and referred to input.

Table 1. “Roll Your Own” vs LT1167 Error Budget

ERROR, ppm OF FULL SCALE

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 RG. The voltage across RG is

amplified and applied across RX, defining the output

current. The 50

µA bias current flowing from Pin 5 is

buffered by the LT1464 JFET operational amplifier. This

has the effect of improving the resolution of the current

source to 3pA, which is the maximum IB of the LT1464A.

Replacing RG with a programmable resistor greatly

increases the range of available output currents.

–

350

Ω

350

Ω

350

Ω

350

Ω

10V

10k**

PRECISION BRIDGE TRANSDUCER

LT1167 MONOLITHIC

INSTRUMENTATION AMPLIFIER

G = 100, RG = ±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

499

Ω

1/4

LT1114A

1/4

LT1114A

1/4

LT1114A

10k**

100

Ω**

10k*

LT1167C

REF

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