voltage. In addition to the absolute resistor value, mismatch resulting from resistor tolerance can significantly

impact the error because this value is calculated based on the actual measured resistance.

The measurement error expected from the additional external filter resistors can be calculated using Equation 4,

and the gain error factor is calculated using Equation 5.

Gain Error (%) = 100

(100

Gain Error Factor)

-

´

(4)

The gain error factor, shown in Equation 4, can be calculated to determine the gain error introduced by the

additional external series resistance. Equation 4 calculates the deviation of the shunt voltage, resulting from

the attenuation and imbalance created by the added external filter resistance. Table 7-2 provides the gain error

factor and gain error for several resistor values.

Gain Error Factor =

RB × R1

(RB × R1) + (RB × RIN) + (2 × RIN × R1)

(5)

Where:

• RIN is the external filter resistance value.

• R1 is the INA281-Q1 input resistance value specified in Table 6-1.

• RB in the internal bias resistance, which is 6600 Ω ± 20%.

Table 7-2. Example Gain Error Factor and Gain Error for 10-Ω External Filter Input Resistors

DEVICE (GAIN)

GAIN ERROR FACTOR

GAIN ERROR (%)

A1 devices (20)

0.99658

–0.34185

A2 devices (50)

0.99598

–0.40141

A3 devices (100)

0.99598

–0.40141

A4 devices (200)

0.99499

–0.50051

A5 devices (500)

0.99203

–0.79663

7.2 Typical Application

The INA281-Q1 is a unidirectional, current-sense amplifier capable of measuring currents through a resistive

shunt with shunt common-mode voltages from –4 V to +110 V.

GND

MCU

24 V

Solenoid

5 V

INA

R

SENSE

I

SENSE

ADC

Figure 7-2. Current Sensing in a Solenoid Application

7.2.1 Design Requirements

In this example application, the common-mode voltage ranges from 0 V to 24 V. The maximum sense current

is 1.5 A, and a 5-V supply is available for the INA281-Q1. Following the design guidelines from Section 7.1.1, a

RSENSE of 50 mΩ and a gain of 50 V/V are selected to provide good output dynamic range. Table 7-3 lists the

design setup for this application.

INA281

SBOSA29A – JUNE 2020 – REVISED NOVEMBER 2023

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