6.4 Device Functional Modes

6.4.1 Unidirectional Operation

The INA281-Q1 measures the differential voltage developed by current flowing through a resistor that is

commonly referred to as a current-sensing resistor or a current-shunt resistor. The INA281-Q1 operates in

unidirectional mode only, meaning it only senses current sourced from a power supply to a system load as

shown in Figure 6-2.

IN+

IN±

OUT

-

+

Buffer

Current

Feedback

5 V

GND

RL

R1

R1

Bias

RSENSE

ISENSE

48-V

Supply

Load

Figure 6-2. Unidirectional Application

The linear range of the output stage is limited to how close the output voltage can approach ground under

zero-input conditions. The zero current output voltage of the INA281-Q1 is very small, with a maximum of GND +

20 mV. Make sure to apply a differential input voltage of (20 mV / Gain) or greater to keep the INA281-Q1 output

in the linear region of operation.

6.4.2 High Signal Throughput

With a bandwidth of 1.3 MHz at a gain of 20 V/V and a slew rate of 2.5 V/µs, the INA281-Q1 is specifically

designed for detecting and protecting applications from fast inrush currents. As shown in Table 6-2, the INA281-

Q1 responds in less than 2 µs for a system measuring a 75-A threshold on a 2-mΩ shunt.

Table 6-2. Response Time

PARAMETER

EQUATION

INA281-Q1

AT VS = 5 V

G

Gain

20 V/V

IMAX

Maximum current

100 A

IThreshold

Threshold current

75 A

RSENSE

Current sense resistor value

2 mΩ

VOUT_MAX

Output voltage at maximum current

VOUT_MAX = IMAX × RSENSE × G

4 V

VOUT_THR

Output voltage at threshold current

VOUT_THR = ITHR × RSENSE × G

3 V

SR

Slew rate

2.5 V/µs

Output response time

Tresponse= VOUT_THR / SR

< 2 µs

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INA281

SBOSA29A – JUNE 2020 – REVISED NOVEMBER 2023

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