I want to design a simple circuitry for testing a bench top current source through a load resistor. I want to use MAX9611, and read data through I2C by a micro-controller. The rough circuit schematic I came up with is this: MAX9611 current sense As you can see, the current source comes to RS- pin and goes through r1 to the ground plane.

My problem is, the current source and the power supply for my micro controller and the current sense chip are two different units. e.g. the VCC comes from a 9V wall adapter but the current I want to sense is through a bench top current source equipment.

I am wondering how can I have a common ground? can I just connect the two grounds together? if not, what should I do? Not to mention that I would like to have a clean ground so no noise affects the ADC inside the maxim chip.

Please let me know if I should provide more details

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The output of the 9V adapter is floating. The output of the bench-top power supply is probably floating too. If at least one of them is floating, then you can connect grounds grounds with a wire. The current through the wire will be negligible.

Whether or not connecting the grounds would cause noise issues depends on the nature of the device. If it generates EMI, then be prepared to deal with it (that would be a subject for a separate question, and similar questions have been asked on EE.SE).

On a different note, your current-sense inputs are wired wrong. If RS+ and RS- are tied together, then the current sense amplifier will always read 0 (zero). RS- should be connected to the low side of the current sense resistor (maybe via a Kelvin connection).

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  • \$\begingroup\$ Thanks, do you suggest e.g. a SMD ferrite bead between the two grounds? the max current through the current source will be 1A. \$\endgroup\$ – Sean87 May 14 '16 at 18:52

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