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INA240: Common Mode Voltage

Ray Vincent Aranzaso
Genius 13535 points
Part Number: INA240

Hi,

Good Day. I have customer who is working with INA240. Please see below his query for your reference. Thank you very much.

I have a question regarding the error analysis tool for INA240. What value should be chosen for "common-mode voltage". In my opinion it is a working point. Am I wrong with this? I am not sure regarding this common-mode voltage. I think it is the voltage drop across the shunt. But the current varies and this value is fix in the tool. In this tool the VCM is a fix value. I thought that the common-mode voltage will vary at different currents flowing through the shunt resistor. Is this true or not?

Best Regards,

Ray Vincent

  • 0
    TI__Mastermind 18780 points

    Ray,

    The common mode is the voltage shared by both input nodes. This is often determined mainly by whether you are sensing on the high side or the low side. The differential voltage you mention is commonly referred to as either VSHUNT or VSENSE, but this is a very small value. So, for example, if you were running an application with a 24V as the power supply (Power Supply = Vcc in the below diagram), and the sense voltage was 50mV, the upper node would see 24V, and the lower node would see 23.95V, so you can approximate the common mode voltage as 24V. The same applies on the low side, but here, the VCM is approximately GND. I included the below figure to help visualize this. 

    Please let me know if this makes sense.