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INA226: 1uA measure current resolution for INA226

Part Number: INA226

Hi.

I'm testing INA226EVM.

Shunt resistor is 8.2ohm.

because 81.92mV / 10mA = 8.192ohm

When I connected 100 kilo ohm for load, INA226's current displayed 39.34uA and ampere meter is 33.2uA.

What's my fault?

• Hi Joseph,

have you forgotten the input bias current of INA226?

Kai
• Hello Joseph,

Thanks for considering to use Texas Instruments. Your issue is likely related to input bias current as kai noted above as well as input offset voltage, both of which can cause considerable error for measurements on the lower end of the measurement range. Where was your amp meter located? Was it at the high-side or low-side? Have you tried shorting VIN+ and VIN- together? Ideally your current register would show zero. However, due to the input offset which is related to input bias, you will likely see a non-zero current or non-zero shunt voltage value. Also since the INA226 has an input bias current, the current pulled from the source on the high-side should be higher than the current passing through the low-side.

What is the input bias current of INA226?

I think low-side measurement.

Currency is about 400mA through shunt  resistor(8.2ohm).

I = 3.3V / 8.2 = 0.4024

Calibration registor value is attached file.

• Hello Han,

The typical input bias current can be found in the electrical characteristics section of our datasheets.  I have it attached below for your convenience.  Beneath that I have a figure that explains how the input  bias current may be affecting your measurements.

• I got it.
Input bias current of my INA226EVM is 3.07uA.

Does the input bias current vary each INA226?

When mass production process, how does input bias current measure?

• Hi Joseph,

the usual way to cope with the input bias currents of INA is to keep the current through the shunt much much higher than the input bias currents.

Kai
• thank you everybody. ^^