How to set up ADC for measuring current across low side shunt

scott_2272156 Sep 19, 2018 10:49 AM

I am trying to measure the current across a low side shunt as shown below. My question is can I do this as I show in my schematic? If I can do it what is the proper configuration of the ADC? Do I need to make sure I set it up a non-signed or some other configuration?

I have tried it in the signed configuration and it works fine as long as i do not ground either input. When I ground the bottom input as shown in my schematic the ADC only reports zero basically when i run any current through shunt. I am using a CY8CKIT-043 prototyping board mounted to a PCB I had made for a production test project I am trying to implement.

Thanks

1. Re: How to set up ADC for measuring current across low side shunt

VasanthR_91 Sep 21, 2018 2:29 AM (in response to scott_2272156)

Hi,

PSoC opamp output range is from 0.2-VDDA( or 0.5 to VDDA in high power mode). The instrumentation amplifier configuration you use needs the opamp output to go to negative voltage range(when the negative input is grounded) which is not supported by the device. You may need the psoc ground to be at a lesser voltage than the shunt ground for the instrumentation amplifier to work.

Best Regards,
VRS
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2. Re: How to set up ADC for measuring current across low side shunt

scott_2272156 Sep 21, 2018 6:57 AM (in response to VasanthR_91)

Thank you for getting back to me ... I will switch this measurement to a current shunt monitor with a large common mode (-14V to 80V) voltage range that can run from a single supply. This will also allow me to move sense resistor to high side so i can detect a short to ground.

Thanks again for your help
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