INA181 datasheet(30/62 Pages) TI2

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8.2 Typical Application

One application for the INAx181 is to monitor bidirectional currents. Bidirectional currents are present in systems

that have to monitor currents in both directions; common examples are monitoring the charging and discharging

of batteries and bidirectional current monitoring in motor control. The device configuration for bidirectional

current monitoring is shown in Figure 8-7. Applying stable REF pin voltage closer to the middle of device supply

voltage allows both positive- and negative-current monitoring, as shown in this configuration. Configure the

INAx181 to monitor unidirectional currents by grounding the REF pin.

Power Supply, VS

2.7 V to 5.5 V

CBYPASS

0.1 µF

Single-Channel

TI Device

Bus Voltage

±0.2 V to +26 V

RSENSE

GND

Load

IN±

IN+

REF

OUT

Output

Reference

Voltage

Figure 8-7. Measuring Bidirectional Current

8.2.1 Design Requirements

The design requirements for the circuit shown in Figure 8-7, are listed in Table 8-3.

Table 8-3. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Power-supply voltage, VS

5 V

Bus supply rail, VCM

12 V

RSENSE power loss

< 450 mW

Maximum sense current, IMAX

±20 A

Current sensing error

Less than 3.5% at maximum current, TJ = 25°C

Small-signal bandwidth

> 100 kHz

8.2.2 Detailed Design Procedure

The maximum value of the current sense resistor is calculated based on the maximum power loss requirement.

By applying Equation 2, the maximum value of the current-sense resistor is calculated to be 1.125 mΩ. This is

the maximum value for sense resistor RSENSE; therefore, select RSENSE to be 1 mΩ because this value is the

closest standard resistor value that meets the power-loss requirement.

The next step is to select the appropriate gain and reduce RSENSE, if needed, to keep the output signal swing

within the VS range. The design requirements call for bidirectional current monitoring; therefore, a voltage

between 0 and VS must be applied to the REF pin. The bidirectional currents monitored are symmetric around 0

(that is, ±20 A); therefore, the ideal voltage to apply to VREF is VS / 2 or 2.5 V. If the positive current is greater

than the negative current, using a lower voltage on VREF has the benefit of maximizing the output swing for

the given range of expected currents. Using Equation 3, and given that IMAX = 20 A , RSENSE = 1 mΩ, and

VREF = 2.5 V, the maximum current-sense gain calculated to avoid the positive swing-to-rail limitations on the

output is 122.5. Likewise, using Equation 4 for the negative-swing limitation results in a maximum gain of 124.75.

INA181, INA2181, INA4181

SBOS793H – APRIL 2017 – REVISED NOVEMBER 2023

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