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INA219 - Wrong shunt voltage reading

Kawai
Guru 19775 points
Other Parts Discussed in Thread: INA219

Hi Team,

Please let me ask you about the shunt voltage reading of INA219.

Our customer designed a board using this device to monitor the load current. Shunt resistor value is 0.002 ohm.

When they read the shunt voltage with no current flow, it reads out 29h which is 0.41mV.
When they read the shunt voltage with 1A current, it reads out F9h which is 2.49mV.

It seems that the device reading has an offset of 29h and if you subtract 29h form F9h, it is D0h which is 2.08mV (1.04A).

Here are my questions.

[Q1]
Is this offset due to the trace issue from shunt resistor to INA219 pins?
They do have difference in the measured value for shunt voltage and pin voltage.

[Q2]
I cannot understand why there is an offset when there is no current at the shunt resistor. Could you please explain how this voltage appear ?
Load is physically cut off with a switch and INA219 is placed at the load side.

[Q3]
Could you give us the recommended PCB design information, gerber data ?
I would appreciate it if you could give us the data in PDF format, in case I cannot open the gerber data.

[Q4]
Could you also give us the information If there is anything else what the user would need to take care when using this device ?

Thanks and Best Regards,
Kawai

  • 0
    TI__Genius 14825 points

    Kawai,


    I'd like to help you with these questions, but may I first ask you for more information?  I would like to see the customer's schematic and pcb layout.  I need to know if there is an input filter.  I would also like to know the bias conditions of the device; the common mode and the supply voltages for sure.


    Without knowing anything else about the application, I wonder if the customer might be seeing artifacts due to the VIN- to VIN+ input impedance imbalance.  Does the customer also measure the Vbus?  If so, is it accurate?

    Please email me at bridgmon_jason@ti.com if you don't want to share the customer's designs publicly.

    Thanks!

    Jason Bridgmon

  • 0 in reply to Jason Bridgmon
    Guru 19775 points

    Hi Jason-san,

    Thank you very much for your support. It would be a great help.

    I will send you the information to your email address shortly.

    Best Regards,
    Kawai