INA159 datasheet(21/51 Pages) TI2

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10 kΩ

OPA333

±10 mV

Adjustment Range

100 Ω

100 mA

1/2 REF200

100 mA

1/2 REF200

V+

V-

INA826

REF

IN-

IN+

INA826

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SBOS562G – AUGUST 2011 – REVISED JUNE 2020

Product Folder Links: INA826

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8.3.3 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 the Output Offset Voltage

8.3.4 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 and maintains 84-dB (minimum) common-mode rejection throughout this range. The

common-mode range for most common operating conditions is described in the input common-mode voltage

versus output voltage Typical Characteristics curves (Figure 9 through Figure 15) and the offset voltage versus

common-mode voltage curves (Figure 41 through Figure 43). The INA826 operates over a wide range of power

supplies and VREF configurations, thus providing a comprehensive guide to common-mode range limits for all

possible conditions is impractical.

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 58) 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 can still be in linear operation, responding to changes in the noninverting input

voltage. This difference can 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 58. 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 differential measurements to be made 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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