1 MW

50 kW

52.6316 kW

50 kW

10 kW

10 kW

+15 V

–15 V

10 W

2.7778 kW

1 MW

190 W

7

3

2

6

4

1

A1

INA148

–V

S

V

O

+V

S

±15-mV Offset Trim Range, RTI

V

REF

V

+IN

V

–IN

V = (V

– V

)

O

+IN

–IN

Copyright © 2016, Texas Instruments Incorporated

11

INA148-Q1

www.ti.com

SBOS472B – MARCH 2009 – REVISED JUNE 2016

Product Folder Links: INA148-Q1

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Feature Description (continued)

7.3.3 Common-Mode Range

The 20:1 input resistor ratio of the INA148-Q1 provides an input common-mode range that extends well beyond

its power supply rails.

The exact input voltage range depends on the amplifier's power-supply voltage and the voltage applied to the

REF pin. See Typical Applications for typical input voltage ranges at different power supply voltages.

7.3.4 Offset Trim

The INA148-Q1 is laser-trimmed for low offset voltage and drift. Most applications require no external offset

adjustment.

Because a voltage applied to the reference (REF) pin is summed directly into the amplifier's output signal, this

technique can be used to null the amplifier's input offset voltage. Figure 21 shows an optional circuit for trimming

the offset voltage.

Figure 21. Optional Offset Trim Circuit

To maintain high common-mode rejection (CMR), the source impedance of any signal applied to the REF pin

must be very low (

≤5 Ω).

A source impedance of only 10

Ω at the REF pin reduces the INA148-Q1's CMR to approximately 74 dB. High

CMR can be restored if a resistor is added in series with the amplifier's positive input pin. This resistor must be

19 times the source impedance that drives the REF pin. For example, if there is a source impedance of 10

Ω to

the REF pin, a 190-

Ω resistor must be added in series with the +IN pin.

Preferably, the offset trim voltage applied to the REF pin must be buffered with an amplifier such as an OPA171-

Q1 (see Figure 22). In this case, the op amp output impedance is low enough that no external resistor is needed

to maintain the INA148-Q1's excellent CMR.