INA4181A1IPWR.B datasheet(31/62 Pages) TI2

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Selecting the gain-of-100 device maximizes the output range while staying within the output swing range. If the

maximum calculated gains are slightly less than 100, the value of the current-sense resistor can be reduced to

keep the output from hitting the output-swing limitations.

To calculate the accuracy at peak current, the two factors that must be determined are the gain error and the

offset error. The gain error of the INAx181 is specified to be a maximum of 1%. The error due to the offset is

constant, and is specified to be 500 µV (maximum) for the conditions where VCM = 12 V and VS = 5 V. Using

Equation 7, the percentage error contribution of the offset voltage is calculated to be 2.5%, with total offset error

= 500 µV, RSENSE = 1 mΩ, and ISENSE = 20 A.

SENSE

Total Offset Error (V)

Total Offset Error (%) =

100%

(7)

One method of calculating the total error is to add the gain error to the percentage contribution of the offset error.

However, in this case, the gain error and the offset error do not have an influence or correlation to each other. A

more statistically-accurate method of calculating the total error is to use the RSS sum of the errors, as shown in

Equation 8:

Total Error (%) =

Total Gain Error (%) + Total Offset Error (%)

(8)

After applying Equation 8, the total current sense error at maximum current is calculated to be 2.7%, and that is

less than the design example requirement of 3.5%.

The INA181A3 (gain = 100) also has a bandwidth of 150 kHz that meets the small-signal bandwidth requirement

of 100 kHz. If higher bandwidth is required, lower-gain devices can be used at the expense of either reduced

output voltage range or an increased value of RSENSE.

8.2.3 Application Curve

An example output response of a bidirectional configuration is shown in Figure 8-8. With the REF pin connected

to a reference voltage (2.5 V in this case), the output voltage is biased upwards by this reference level. The

output rises above the reference voltage for positive differential input signals, and falls below the reference

voltage for negative differential input signals.

Time (500 µs/div)

VOUT

VREF

C002

Figure 8-8. Bidirectional Application Output Response

8.3 Power Supply Recommendations

The input circuitry of the INAx181 accurately measures beyond the power-supply voltage, VS. For example, VS

can be 5 V, whereas the bus supply voltage at IN+ and IN– can be as high as 26 V. However, the output voltage

range of the OUT pin is limited by the voltages on the VS pin. The INAx181 also withstand the full differential

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SBOS793H – APRIL 2017 – REVISED NOVEMBER 2023

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