R1

25 k

RB

VB

+VS

-VS

+VS

-VS

+VS

-VS

+VS

-VS

+VS

-VS

Super-

NPN

Super-

NPN

RG

(External)

+VS

-VS

Overvoltage

Protection

Overvoltage

Protection

RB

-IN

+IN

REF

OUT

Q1

Q2

A1

A2

A3

+VS

IB Cancellation

IB Cancellation

R2

25 k

40 k

40 k

40 k

40 k

Copyright © 2017, Texas Instruments Incorporated

RG

RG

16

INA828

SBOS792A – AUGUST 2017 – REVISED JANUARY 2018

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Product Folder Links: INA828

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Copyright © 2017–2018, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The INA828 is a monolithic precision instrumentation amplifier incorporating a current-feedback input stage and a

4-resistor difference amplifier output stage. The differential input voltage is buffered by Q1 and Q2 and is forced

across RG, which causes a signal current to flow through RG, R1, and R2. The output difference amplifier, A3,

removes the common-mode component of the input signal and refers the output signal to the REF terminal. The

VBE and voltage drop across R1 and R2 produce output voltages on A1 and A2 that are approximately 0.8 V lower

than the input voltages.

Each input is protected by two field-effect transistors (FETs) that provide a low series resistance under normal

signal conditions, and preserve excellent noise performance. When excessive voltage is applied, these

transistors limit input current to approximately 8 mA.

7.2 Functional Block Diagram