I'm thinking of using an mcp41100 digital potentiometer to control an op amp gain. My board will have a split ground plane - digital and analog grounds.

Unfortunately the mcp41100 doesn't have separate digital and analog power/ground rails.

How should I power and ground the chip ? Digital/Analog supply/ground ?


The MCP41100 (along with probably every other digipot I've seen) doesn't need nor use an analogue ground. It is a digitally controlled potentiometer and the three connections to the potentiometer are floating and can be connected to your target analogue circuit however you need them to be (within reason).

Here are a couple of examples from the data sheet - these examples show how the device is wired to test for frequency response and capacitance but, the diagrams serve the purpose of showing the 3 pot connections are not needed to be connected to ground (unless you want them to be): -

enter image description here

Note also that this particular device should not have voltages applied to the pot connections that are outside the absolute maximum ratings for the device (-0.6V to Vdd+1V). If in doubt, read the data sheet.

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  • \$\begingroup\$ So connecting it to digital power rail and ground wouldn't induce noise into the analog supply/circuit through the potentiometer terminals ? Also, would it work normally with a negative couple of hundred mv on the potentiometer's pins (under -0.6v) ? \$\endgroup\$ – Mike Jun 2 '14 at 16:39
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    \$\begingroup\$ As with any circuit that converts digital values into analogue voltages the cleaner you can make your digital supply the better. Digipots are not known for great performance in these areas and the closer you have your analogue signals to the power limits, the worse it can be. Sorry but if you want a really clean control you might have to use other methods. Having said that I'm using one on a 16 bit application before the ADC and I only get noise when the digipot is reconfigured in value - I can live with that though. \$\endgroup\$ – Andy aka Jun 2 '14 at 18:18

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