Output States of PXI(e) SMUs When Output is Disabled

Issue Details

• I've noticed that when I disable the outputs of my SMU, it can still sink current if I have an active DUT connected to my SMU.  What is the output state of my SMU when the output is disabled?
• Does disabling the output of a PXIe-414x disconnect the output from the circuit?

Solution

When the output of an NI SMU is disabled either by toggling the Output Enabled checkbox on the Soft Front Panel or by writing a False to the Output Enabled property node, it will not supply any power.  It can, however, still sink power if the DUT is an active device such as a power supply or a battery. 

Disabling the output generates a 0 V output, but does not disconnect the output. Some SMU cards support an option to disconnect the output fully. 

The following table describes the voltage levels and current limits that are enforced for each SMU when the output is disabled.

Note: Only devices and channels that can sink power are listed below.

Additional Information

If less current draw from the DUT is required when it's not actively being tested, there are a few options to eliminate or minimize the current draw.
 
For the PXI-4132, PXIe-4154, PXIe-4136/4137, and PXIe-4138/4139 only, you can set the Source:Output Connected property node to False to disconnect the DUT from the SMU by opening the SMU's on-board relay.  This will make the SMU transparent to the DUT so the SMU can't sink any current.
For the PXIe-414x, PXIe-4136/4137, and PXIe-4138/9 only, you can set the current level to 0 A in Constant Current mode. This will make the SMU appear 'open' and no current will flow from the DUT into the SMU. Note: only the PXIe-414x, PXIe-4136/4137, and PXIe-4138/9 will allow you to set the current level to 0; all other NI SMUs have a minimum current level, typically 2% of the current range.
For the PXI-4130, to minimize current draw from the DUT, leave the output enabled in Constant Current mode and set the current range to 200 uA.  Setting the SMU to the smallest current range allows you to set the current level to its smallest possible value. For the PXI-4130, in the 200 uA range the minimum programmable current level is 4 uA.  If 4 uA is still too large of a current draw from your DUT, you may need to consider installing an external relay to disconnect your DUT from your PXI-4130.