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INA234: Wrong shunt and current values return

Etienne Droniou
Prodigy 140 points
Part Number: INA234

Hi all, 

I have a issue with the INA234. 
I try to read the Vshunt, VBus and Current values. But the VBus value stays always the same, no variation even some mV.  And Vshunt and current values are both at 0.

I don't understand why.

I configured the config register with 0x2127. I write the calibartion with the value 0x20C4. 

The writting configuration is confirm by a read back register. 

My design is the following: 

Am I missing something ? 

Thank your help. 

Best Regards,

Etienne 

  • 0
    TI__Mastermind 34370 points

    Hi Etienne,

    It is good that you verified read/write communication.

    If Vbus variation is less than ½ LSB, or ~13mV, INA234 will not be able to detect it. If this is the case, it will report a “perfect” reading. You may introduce a controllable Vbus and vary it manually to see if you see corresponding INA234 measurements.

    The schematic doesn’t show a load. If the voltage drop across the shunt resistor is indeed ~0V, INA234 will likely return the same. Again please note the resolution (40uV or 10uV depending on range setting).

    Regards, Guang

  • 0 in reply to Guang Zhou
    Prodigy 140 points

    Hi Guang,

    Sorry for the delay of the response.

    I received the eval board to test if it is my component or the way I use it that is wrong.

    It appears that on one board the component was wrong soldered.

    On the other board I removed the capacitor of the filter and I got some value which was the same on the eval board.

    However, I miss someting on the convertion value because I got 5.7V instead of 3.6V and the current is aroud 30mA instead of 1-2mA

    Vbus value is aroud 0x08C and Current value is aroud 0x006. I don't know how to obtain the good value with the information provied on the datasheet.

    Best regards, 

    Etienne

  • +1 in reply to Etienne Droniou
    TI__Mastermind 34370 points

    Hi Etienne,

    The good news is that your board seems to work properly. The only problem is converting register values into physical quantities as you suspected.

    For Vbus, the decimal value is 140 (0x08C). In terms volts, 140*25.6mV=3.584V.

    For current, I back calculated that the current LSB=195.33uA based on the calibration register value of 0x20C4 and Rshunt=50mOhm. With this the current is 6*195.33uA=1.172mA.

    Both results appear to agree with expected.

    Regards, Guang

  • 0 in reply to Guang Zhou
    Prodigy 140 points

    Hi Guang, 

    Thank you a lot for your response. 

    Best regards, 

    Etienne