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I see that MAX6126 even has a GNDS spin, with 300mV max compliance, so you could test relative to ground if the load values will drop < 300mV. If this is an aging test, you need something better than a LM317, and a precision reference is the right part - get the highest spec you can afford.Īlmost ANY Logic level mosfet will do, just choose a package with some thermal margin, and voltage margin I figure with a good steady 10 mA current source and a 16-bit differential input ADC I should be able to easily detect aging of at least 1% in the resistance.

I will probably also put and ADC across Rest and to measure the current to correct for any drift and help maximize the accuracy and repeatability of the measurement.Ĭan any of you MOSFET savvy out there help with selecting a suitable device?

The most important aspect of the current source is repeatability and stability over time and temperature (<0.1% would be nice over weeks/months and as much as ☑5☌). Assuming the MOSFET has a negligible “Vce”(?) and Rset for 10 mA is about 200 Ω then the maximum resistance for the DUT would be 200 Ω. I assume as long as I keep “Vin” less than 4.096 V that should protect the ADC if any of the samples break (high resistance). I would like the Vref to the ADC to be 4.096 V to make the math simple so the maximum voltage at ∺DC (+) needs to be less than 4.096 V. The DUTs (samples) will generally range from about 10 to 200 Ω. This is where I am stuck – I have no idea how to spec out which MOSFET would be suitable. The figure shows an n-type bipolar transistor but the text suggests using a MOSFET for better accuracy (I assume this is because the base current is much less than a transistor?). MAX6126) and an n-type MOSFET (see Figure 2 on page 15). I came across what looks to me to be a very simple two-device circuit to generate a 5 mA source. So now I am looking for a circuit that will produce a nice steady and repeatable 10 mA of current that I can send to each sample via some DPDT relays. I am currently using the Propeller to automate the thermal cycling of these samples and now I want to add the ability to automatically measure their resistance values periodically (ranging from once to several times each day).

I need to measure the resistance aging of several samples over a long period of time (ranging from a few hours to several months).