Digital Potentiometer to Analog Input

Thread Starter

fredp

Joined Sep 24, 2009
41
Hi, I was considering using a digital potentiometer (MCP4131) to apply a voltage to an analog input for control. The analog input has a relatively low impedence of 250 Ohms. It is unclear to me if the digi-pot will pass this amount of current. The datasheet says Maximum output current sourced by any Output pin: 25 mA. This is promising since my analog input is maximum at 5 V, so I don't expect more than 20 mA; however, another line on the datasheet concerns me. Maximum current into PXA, PXW & PXB pins: ±2.5 mA Will someone please advise? I'm thinking that these pins are not sinking current in my application, so it shouldn't be an issue, but perhaps I'm wrong.
 

AlbertHall

Joined Jun 4, 2014
12,338
The options for resistance of the track of the MCP4131 range from 5k to 100k so you will get strange results connecting this to a 250Ω load. For instance, if you feed 5V to the pot set to the mid position you won't get the 2.5V you might expect, you will get only about 0.25V.
You would need a buffer in between the pot and the analogue input - for instance an op-amp.
 

OBW0549

Joined Mar 2, 2015
3,566
Hi, I was considering using a digital potentiometer (MCP4131) to apply a voltage to an analog input for control. The analog input has a relatively low impedence of 250 Ohms. It is unclear to me if the digi-pot will pass this amount of current. The datasheet says Maximum output current sourced by any Output pin: 25 mA. This is promising since my analog input is maximum at 5 V, so I don't expect more than 20 mA; however, another line on the datasheet concerns me. Maximum current into PXA, PXW & PXB pins: ±2.5 mA Will someone please advise? I'm thinking that these pins are not sinking current in my application, so it shouldn't be an issue, but perhaps I'm wrong.
That 20 mA rating applies only to digital output pins (such as SDO), NOT to the potentiometer connections. There is absolutely no way this digital pot will be able to directly drive a 250Ω analog input without being buffered by an op amp or other suitable device.
 
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