INA219: INA219 mathoverflow

Thank you Mohamed,

Will fix it 

No problem, feel free to let me if there are any further questions!

Hello Mohamed,

My new setup is as follows:

• INA219_CONFIG_VALUE = 0x0773
• INA219_CURRENT_LSB_mA = 0.0004
• INA219_CALIB_VALUE = 0xC800 (after the shift operation)

However, I still encounter "math overflow" occasionally (less that I used to before the change). Do you have any insights into what might be causing this issue?

Best regards, Genadi.

Hi Genadi, 

It's possible that you're overflowing because the max current is above the limit given those parameters. What's the max expected current you intend on measuring? 

Best, 
Mohamed

Hello Mohamed,

It's unlikely. The device is powered by a battery with a maximum output current of about 2 A, and in its current state, it's drawing only around 20 mA.

Is there a chance that the Vshunt value might exceed the range I've configured, leading to issues with the sampling math overflow?

Sincerely, Genadi.

Hi Genadi, 

This is strange, the math flag should not be tripping with your current configuration. Could you let me know the VBUS so I can recreate the test? It is worth noting however that your configuration doesn't yield good results, even if it were to work. I ran the parameters you provided through our error calculation tool (you can find this here: https://www.ti.com/tool/CS-AMPLIFIER-ERROR-TOOL) and it gave the following results: 

At 20mA you will be getting very high error. It is worth playing with the tool to find a new configuration that yields better results for your setup. 

Best, 

Mohamed 

Hi Mohamed,

The V_BUS varies from 3.2 up to 4.1 Volt.
The current is going to be increased from 20 up to about 1 Arms.

P.S. the link you provided doesn't work. I guess something with the server.

thanks, Genadi.

My apologies, here is the updated link: Error Tool. Note that using the tool may even solve the math overload issue when finding a calibration value that works better for your setup. 

Hi Mohamed.
Thank you very much for the tool. 

Unfortunately, I did not fine the sections with configuration and calibration values. Could you please guide me where can I find it?
BR, Genadi.

Hi Mohamed.

I noticed that this occurs when one of the peripherals turns on. It's an analog front device that uses I2C and toggles LEDs and photodiodes at a high frequency. Could the reason for the math overflow issues be the large variance in current measurements caused by this?

Have a good day, Genadi

This could be the case. Do you know what the variance may be between the current measurements? 

The difference between the On and Off LED states is up to 200 mA. Each LED turns on for 2 microseconds and then turns off for about 40 microseconds. This pattern repeats continuously.

By the way:

The calibration value I am trying to write to the register is: 1100100000000000

But when I read the register (after the write operation) I get: 1100100001000100

The same about writing to config register. I am sending - 11101110011, and reading 11101001111.

Does it make sense to you?

Interesting fact:

When I configure the BADC and SADC to a single sample (no oversampling), this problem occurs much less frequently..