INA826 datasheet(19/40 Pages) TI

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10kW

OPA333

±10mV

AdjustmentRange

100 W

100 A

1/2REF200

100 A

1/2REF200

V+

V-

INA826

REF

IN-

IN+

INA826

www.ti.com

SBOS562B

– AUGUST 2011 – REVISED DECEMBER 2011

OFFSET TRIMMING

Most applications require no external offset adjustment; however, if necessary, adjustments can be made by

applying a voltage to the REF terminal. Figure 59 shows an optional circuit for trimming the output offset voltage.

The voltage applied to the REF terminal is summed at the output. The op amp buffer provides low impedance at

the REF terminal to preserve good common-mode rejection.

Figure 59. Optional Trimming of Output Offset Voltage

INPUT COMMON-MODE RANGE

The linear input voltage range of the INA826 input circuitry extends from the negative supply voltage to 1 V

below the positive supply, while maintaining 84-dB (minimum) common-mode rejection throughout this range.

The common-mode range for most common operating conditions is described in the typical characteristic curves

(Input Common-Mode Voltage vs Output Voltage, Figure 9 through Figure 16) and Offset Voltage vs

Common-Mode Voltage (Figure 41 through Figure 44). The INA826 can operate over a wide range of power

supplies and VREF configurations, making it impractical to provide a comprehensive guide to common-mode

range limits for all possible conditions.

The most commonly overlooked overload condition occurs when a circuit exceeds the output swing of A1 and A2,

which are internal circuit nodes that cannot be measured. Calculating the expected voltages at the output of A1

and A2 (see Figure 60) provides a check for the most common overload conditions. The designs of A1 and A2 are

identical and the outputs can swing to within approximately 100 mV of the power-supply rails. For example, when

the A2 output is saturated, A1 may continue to be in linear operation, responding to changes in the noninverting

input voltage. This difference may give the appearance of linear operation but the output voltage is invalid.

A single-supply instrumentation amplifier has special design considerations. To achieve a common-mode range

that extends to single-supply ground, the INA826 employs a current-feedback topology with PNP input

transistors; see Figure 60. The matched PNP transistors Q1 and Q2 shift the input voltages of both inputs up by a

diode drop, and through the feedback network, shift the output of A1 and A2 by approximately +0.8 V. With both

inputs and VREF at single-supply ground (negative power supply), the output of A1 and A2 is well within the linear

range, allowing users to make differential measurements at the GND level. As a result of this input level-shifting,

the voltages at pin 2 and pin 3 are not equal to the respective input terminal voltages (pin 1 and pin 4). For most

applications, this inequality is not important because only the gain-setting resistor connects to these pins.

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