Gain Error (%) = 100

(100

Gain Error Factor)

-

´

IN+

IN±

OUT

V

CM

-

+

Buffer

Current

Feedback

V

S

GND

RL

R1

R1

Bias

Load

R

SENSE

I

SENSE

R

IN

R

IN

C

IN

f

1

15

INA281

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SBOSA29 – JUNE 2020

Product Folder Links: INA281

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Copyright © 2020, Texas Instruments Incorporated

Application Information (continued)

(1)

Design example with 10-A full-scale current with maximum output voltage set to 5 V.

(1)

PARAMETER

EQUATION

A1, B1

DEVICES

A2, B2

DEVICES

A3, B3

DEVICES

A4, B4

DEVICES

A5, B5

DEVICES

G

Gain

20 V/V

50 V/V

100 V/V

200 V/V

500 V/V

Ideal differential input voltage

250 mV

100 mV

50 mV

25 mV

10 mV

Current sense resistor value

25 mΩ

10 mΩ

5 mΩ

2.5 mΩ

1 mΩ

Current-sense resistor power dissipation

2.5 W

1 W

0.5W

0.25 W

0.1 W

8.1.2 Input Filtering

NOTE

Input filters are not required for accurate measurements using the INA281, and use of

filters in this location is not recommended. If filter components are used on the input of the

amplifier, follow the guidelines in this section to minimize the effects on performance.

Based strictly on user design requirements, external filtering of the current signal may be desired. The initial

location that can be considered for the filter is at the output of the current-sense amplifier. Although placing the

filter at the output satisfies the filtering requirements, this location changes the low output impedance measured

by any circuitry connected to the output voltage pin. The other location for filter placement is at the current-sense

amplifier input pins. This location also satisfies the filtering requirement, but the components must be carefully

selected to minimally impact device performance. Figure 29 shows a filter placed at the input pins.

Figure 29. Filter at Input Pins

External series resistance provides a source of additional measurement error, so keep the value of these series

resistors to 10 Ω or less to reduce loss of accuracy. The internal bias network shown in Figure 29 creates a

mismatch in input bias currents (see Figure 7, Figure 8, and Figure 9) when a differential voltage is applied

between the input pins. If additional external series filter resistors are added to the circuit, a mismatch is created

in the voltage drop across the filter resistors. This voltage is a differential error voltage in the shunt resistor

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.

(4)