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Current Measurement Circuit

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Hi Guys,


I am trying to build a circuit that the MCU can measurement the current consumption of the circuit. I have read a few things and decided to go with the "low side" measurement.

Incidentally I have some BB INA's laying around from my previous project, so I use it as the amplifier of choice.

I am confused that which "Ground" should I connect the amplifier ref. and Voltage ref GND to - the ground of the load (virtual ground) or the ground of the system (0V)?

Most importantly, will the circuit work?

I am more a digital guy than analog - help appreciated. Thank you!


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I think you can remove virtual ground entirely.  Since you are using an IA, which does a great job of rejecting common mode voltage, you are able to use a small value resistor value for your current measurement and still achieve good accuracy. This will reduce the need for a high wattage resistor (assuming your load is high current). You should be able to tie the ref pin on the IA directly to ground (0v).


Also since you are running a +5v supply please note that your output swing will be limited to ground+1.4V and Vcc-1.4V worst case (typical is .8v to .9v).


TI has some great app notes on instrumentation amplifiers so you may want to search their site. 

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Oh, I almost forgot the INA128 could not produce rail-to-rail outputs and I will probably lose the low current measurements.

After reading some application notes, I guess I should use some proper current shunt amplifiers. INA214 looks good to me...

Thanks a lot!

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