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INA220: INA220 readding issue

Hailiang Zhang
Expert 7035 points
Part Number: INA220
Other Parts Discussed in Thread: INA238, INA237, INA226

Hi Team,

My customer report that the current measured by INA220 is always lower than the real current. I see  a describe "in continuous mode, so the INA220 will capture new data between reads by the customer. If the customer wants to calculate the data results like this they will need to put the device in shutdown or triggered mode" in this thread. (+) INA220: Reg value calculation review - Amplifiers-INTERNAL Forum - Amplifiers-INTERNAL - TI E2E support forums

It seems that when the devices is configured to continuous mode, the host can not read the data in the register. Right? 

Also, if the max expected current  is 60A, and the Rshunt is 2.5mohm, could you pls recommend a set of configure, including the PGA? And the current register should be equal to shunt voltage register * Calibration register / PGA /4096t, right?

Thanks in advance.

Regards,
Hailiang 

  • 0
    TI__Expert 6602 points

    Hi Hailiang,

    • You can read the register while in continuous mode, however for this device it is best to try to avoid reading the result while the register is being updated (ie, at the end of a conversion). 
    • Based off your current and Rshunt, the most appropriate PGA setting would be PGA = /4. However, the rest of the configuration register would depend on your desired settings or preferences. I gathered this by calculated V=IR: V = (60A)(2.5mohm) =  150mV which is closest to the PGA setting of 160mV: 

    • Yes. The current register should be the shunt voltage register multiplied by the calibration register and dividing by 4096. However, to get a current value in Amps, you must multiply the current register value by Current_LSB.

    Please let me know if you have any further questions. 

    Best,

    Mohamed 

  • 0 in reply to Mohamed Hamida
    TI__Expert 7035 points

    Hi Mohamed，

    Sorry for my mistake. Customers use a 0.25mohm shunt resistor.

    When the Iload = 20A, the register data and log are shown below. The current reading out is 18.799A. Do you have any suggestion? 

    Here is the schematic for your reference.

    Regards,
    Hailiang

  • 0 in reply to Hailiang Zhang
    TI__Expert 6602 points

    Hi Hailiang, 

    It seems as though you're overloading your calibration register. The decimal value of E492 is 58514 and the limit of the register is 15 bits, which is 32,767: 

    In order to alleviate this, you could either increase your shunt size or your current_lsb. Alternatively, you could look into using a different device such as the INA226, INA237, or INA238. These are all alternative devices that could handle your design parameters. However, you may need to fiddle with the ADCRANGE and shunt size to use the full-scale range of your part. Please let me know if you have any questions.

    Best,

    Mohamed