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# N channel low current sensing after biasing with AD5686

Category: Software

Hi folks,

I have a question regarding multichannel current sensing. First a description of the application: So far I have the AD5686R as a 16 bit, 4-channel precision voltage source (0-5V). At each channel of the voltage source I connect a 50kOhm resistor and in series to this, I connect our device that has typically a very low resistance (few ohms) and at a certain voltage switches to high resistance (few 10 kOhm). In the end, I want to sweep the voltage and measure the current for each voltage step. To depict this easy circuit for one channel:
AD5686R voltage source channel ------- 50kOhm resistor ------- my device ------ GND

What we are now interested in, is to sense the current flowing through the device (=the current through the 50kOhm resistor) that is typically in the order of 10µA (up to a few 10µA). How and with which of the plenty of different devices in the AD product line would you measure the current passing through each of the channels? Two ideas I have in mind so far: Measure the voltage drop over the 50kOhm resistor by measuring the voltage drop over my device and subtract it from the applied voltage from the AD5686R and subsequently convert it with the given 50kOhm resistance to the corresponding current value. Or by adding a small shunt resistor over which to measure a voltage drop and converting it to the corresponding current.

As I want to scale the whole application to N channels, I chose as voltage source the AD5686R that one can daisy chain and thus obtain N*4 channels with N AD5686R. Also, I want to communicate with the corresponding device via SPI or I2C, similar to the AD5686R and for rapid prototyping it would be great to choose a device where there exists a similar evaluation board like the one for the AD5686R such that I can quickly build up the test system by connecting a similar evaluation board with the Arduino that already controls the AD5686R on the EVAL-AD5686R.

I am looking forward to your ideas and suggestions!

Best regards,

Stefan

added the information about the switching between low resistance and high resistance state of my device
[edited by: stefanE24 at 11:55 AM (GMT -4) on 19 May 2022]