1 MW

50 kW

52.6316 kW

50 kW

2.7778 kW

1 MW

R

C

R

S

I

L

V

CM

7

3

200 V

2

6

4

1

A1

INA148

–15 V

V

O

+15 V

Load

V

O = IL × RS

Copyright © 2016, Texas Instruments Incorporated

1 MW

50 kW

52.6316 kW

50 kW

2.7778 kW

1 MW

7

3

2

6

4

1

A1

INA148

–15 V

V

O

+15 V

±15-mV Offset Trim Range, RTI

100 kW

100 kW

100 W

+15 V

–15 V

V

REF

OPA171-Q1

V

+IN

V

–IN

V = (V

– V

)

O

+IN

–IN

Copyright © 2016, Texas Instruments Incorporated

12

INA148-Q1

SBOS472B – MARCH 2009 – REVISED JUNE 2016

www.ti.com

Product Folder Links: INA148-Q1

Submit Documentation Feedback

Copyright © 2009–2016, Texas Instruments Incorporated

Feature Description (continued)

Figure 22. Preferred Offset Trim Circuit

7.3.5 Input Impedance

The input resistor network determines the impedance of each of the INA148-Q1 inputs. The impedance is

approximately 1 M

Ω. Unlike an instrumentation amplifier, signal source impedances at the two input pins must be

nearly equal to maintain good common-mode rejection.

A mismatch between the two input source impedances causes a differential amplifier's common-mode rejection

to be degraded. With a source impedance imbalance of only 500

Ω, CMR can fall to approximately 66 dB.

Figure 23 shows a common application, measuring power supply current through a shunt resistor (RS). A shunt

resistor creates an unbalanced source resistance condition that can degrade a differential amplifier's common-

mode rejection.

Figure 23. Shunt-Resistor Current Measurement Circuit

Unless the shunt resistor is less than approximately 100

Ω, TI recommends an additional equal compensating

resistor (RC) to maintain input balance and high CMR.