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Original question:

INA233: Ina233 reads current 4096 when load terminals are floating

INA233: IN+ pin is floating what should I expect on IN- ?

joe lindula
Mastermind 6940 points
Part Number: INA233

Tool/software:

Hello, I am seeing a strange behavior on a custom board that has a INA233 monitor. 

When the voltage that is being monitored is not present and I measure the IN- pin,  I measure 2.6V with my multimeter. 

Here is a simplified diagram:

In the above graphic, if the switch is open what should I measure on IN-?

I am seeing 2.6V which is very strange. Could it be possible that the 3.3V on VS is some how getting on the IN- pin because the IN+ pin is floating?

Can anyone help or give some comments?

Thank you

Joe

  • +1
    TI__Mastermind 26465 points

    Hello Joe,

    If you float IN+ then IN- would have the voltage present on the IN- side of the resistor (it will not produce a voltage). Since the IN-side of the resistor goes to your load, it is likely a voltage from that (which would usually be close to GND, depending on your load setup).  Also, you need to make sure that the GND of the load is the same as the GND of the INA. If those are not the same, then you could see weird voltage measurements as well.

    Regards,

    Mitch