Voltage Protect on 2302 with high capacitance load

[GeneWB]

The 2302 manual says that VPT can be set to protect the voltage from rising too much in case a sense line becomes disconnected. We use the 2302 to provide 3.2V to our device under test which most of the time draws very little current (perhaps less than 1mA). Additionally, our test fixuture has a 2800uF capacitor across the voltage supplied by the 2302. We are using remote sense. I did some experiments in which I removed the Sense+ line after power was applied to our device and also prior to applying power. In these experiments VSET = 3.2V and VPT = 0.3V, so I expected the 2302's over voltage protection to trip at 3.5V. In the first case, when I removed the sense line after power-up, the 2302 tripped at around 5V instead of 3.5V. In the second case, when I removed the sense line prior to applying power, the voltage at the DUT shot up to nearly 10V before the 2302 tripped. Is this behaviour to be expected given the fact that our device draws so little current and with such a large capacative load? Could you provide a brief description of how overvoltage protection is implemented in the 2302?

[Dale C]

The Model 2302 can be used in 2 wire or four wire mode.
But the sense lines should never be left "open" in 2 wire or 4 wire for that matter.
The Sense+ and Sense- pins provide output voltage
sensing. Without these terminals connected, the power supply operates without voltage feedback
and therefore supplies an unregulated voltage. This unregulated voltage value can be up to +18V
or down to -5V. Use voltage protection to turn off the output and protect against the extremes.
Take a look at figures 2-1 and 2-2 in the Model 2302/2306 instruction manual.
Here is the link to the manual.
http://www.keithley.com/support/data?asset=870

[GeneWB]

In section 2-5 of the manual, it says "VPT circuitry is useful in protecting the load from a high positive voltage if one of the remote sensing leads is disconnected." I was trying to determine whether or not
an appropriate VPT setting could protect our device from an accidently disconnected Sense line and hold the voltage seen by our device to Vset + VPT. Evidently with a sense line disconnected, the voltage protect feature is not able to function as it should.

[Dale C]

I agree, all bets are off when the sense lines are open.