INA226 Not Getting the Expected Accuracy

Jerry Wong

Other Parts Discussed in Thread: INA226

Hi Mayrim, et al,

I did not see a forum post with exactly the same issue I am facing.

I'm not getting the INA226 accuracy I'm expecting. My calibration calculations are below, as well as comparison with a calculation using a meter.

The meter is reading consistently 9% or 10% higher than the INA226. Can you suggest what I might be doing wrong, or what I can try...

Regards,

Jerry

-------

I’m measuring the voltage across the Shunt Resistors (e.g. R116) manually using a pretty good meter (HP 34401A) at 1.991 mV / 0.005 Ohm = 398mA.

It’s repeatable on 2 of 2 ZCU102 boards (Rev B and Rev C) … And I’ve tried 3 different meters.

I’ve programmed the INA226 to LSB = 100uA for a range of 3.3A maximum.

cal = 5120000L / mOhms0 / uALsb0;

10240 = 5120000L / 5 / 100;

I’m reading iAdc = 3690 counts * 100uA/count = 369mA.

That’s 9 or 10% low. This is systematic on all rails measured.

INA226 says it has a 0.1% Gain Error.

It seems a straight forward implementation, and I can’t find any other explanation to this variation …

over 8 years ago

0 Carolus Andrews over 8 years ago

TI__Mastermind 23165 points

Hi Jerry,

With what parameters are you running the device, i.e., supply voltage, common mode, etc.?

Also, would it be possible for you to send me a picture of your board layout?

Carolus

0 Jerry Wong over 8 years ago in reply to Carolus Andrews

Prodigy 140 points

Hi Carolus,

Thanks for your reply... The schematic is available as a download at
www.xilinx.com/.../zcu102_headstart.html > Documentation and Designs > ZCU102 RevC Schematic

The INA226 and Shunt Resistor R116 are on p71 of the schematic.
Per the schematic, the INA226 supply voltage is 3.3V , and the common mode voltage on the shunt resistor is 0.85V.

Regards,
Jerry

0 Carolus Andrews over 8 years ago in reply to Jerry Wong

TI__Mastermind 23165 points

Hi Jerry,

I can't seem to access the documents from that link without a login ID. Is there any way you can send me a .pdf? Also, while the schematic is also helpful, its the PCB layout I was hoping to see. Let me know if this is possible.

Carolus

0 Jerry Wong over 8 years ago in reply to Carolus Andrews

Prodigy 140 points

Hi Carolus,

You can generate a login ID from that same page. It covers all the legal agreements/notices, etc.

If that doesn't work for you, please reach out to me with a private email, and I can see about providing that schematic page to you in private.

Jerry

0 Carolus Andrews over 8 years ago in reply to Jerry Wong

TI__Mastermind 23165 points

Jerry,

No problem. I established a username, but I have to wait for approval from Xilinx before I can view the file. I'll follow up when they grant me access.

Carolus

0 Jerry Wong over 8 years ago in reply to Carolus Andrews

Prodigy 140 points

Thanks, Carolus ... I look forward to hearing your follow up at that time.

Jerry

0 Carolus Andrews over 8 years ago in reply to Jerry Wong

TI__Mastermind 23165 points

Hi Jerry,

You could also send me the files if you want at

c-andrews@ti.com

This might be faster, as I don't know how long Xilinx takes to approve that usually.

Carolus

Amplifiers

Amplifiers forum

INA226 Not Getting the Expected Accuracy