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ADC Current sensing using a Potential Divider

Question asked by Thomas Carrington on Jan 20, 2018
Latest reply on Jan 20, 2018 by Andrew Neil

Hi All,


I'm going to be building a motor control circuit, and what I would like is to be able to monitor the voltage and current going into the motor.

Was going to use the STM32F108's inbuild ADC to measure this, so I am limited to an input voltage of ~3.3Vs - the motor is going to be connected to a 12V @ ~2A power supply.

From a datasheet that I found on the web, I saw that I can use a potential divider to step down the voltage to within the ADCs input range - Datasheet on the LTC2991 p.25 - shows a circuit with a 0 to 40V & 0 to +/-2.2A power supply.

I understand how the calculation for the voltage resolution is done - its the inverse of the potential divider multiplied by the single point resolution.

I have NO idea how the current resolution is calculated and was hoping that someone within this community might be able to educate me on what I am missing in getting to the number stated on this sheet.