Table Of Contents

Increasing SMU Output Current by Merging Channels

Last Modified: December 3, 2020

Merging channels of an NI SMU allows you to use multiple channels in unison to increase the current you can source beyond the normal maximum for any one channel of the SMU.

  • Not all NI SMUs support merging channels. Your SMU must support the Merged Channels property to merge channels.
  • Merging channels is supported with remote sense only.
  • You cannot change the merge configuration when channels are in the Running state.
  • You cannot merge channels across different physical instruments.

Complete the following steps to increase the current you can source your SMU.

  1. Choose a valid merge configuration that supports the output current you need.
  2. Design your merge circuitry based on that merge configuration and Connection Guidelines for Merged Channels.
  3. Follow Programming the SMU for Merged Channels.

Valid Merge Configurations

Only certain primary channel–merge channels combinations are supported for each merge count.

The potential merge configurations depend on how many and which channels you want to merge.

The valid merge configuration(s) for each primary channel are as follows.

Table 1. Valid Merge Configurations
Primary Channel Possible Merge Counts Required Merge Channel(s)
0 ×2 1
×4 1,2,3
2 ×2 3

Channel 1 and channel 3 cannot be designated as primary channels for merging channels.

Connection Guidelines for Merged Channels

To use merged channels for a higher maximum current, you must design the interface that conveys and the circuitry that combines the current output from the SMU accordingly.

A test system using merged channels comprises the following general components:

  1. The SMU to source the current
  2. Cabling or wiring to convey current from the SMU
  3. An interconnect between the SMU cabling and the circuitry on the opposite end from the SMU
  4. Circuitry at the destination that combines the current from the SMU
  5. The destination device to which you are delivering the current

The specific interconnect and circuitry you need depend on your application, but refer to the following general guidelines for designing these elements:

  • Ensure your design corresponds to a valid merge configuration for the SMU.
  • Design your circuitry to connect the merged channels at the destination in parallel.

    Connect only those channels that you intend to merge.

  • If your application does not involve switching between merge configurations, short the Output HI pins of the primary channel and merge channels together, and short the Output LO pins of the primary channel and merge channels together; otherwise, connect all Output HI and all Output LO as described and ensure your switching circuitry presents as little resistance as possible when merging channels.
  • Tie the Sense HI and Sense LO pins of the primary channel only; the Sense pins of the merge channels do not need to be tied together.
  • For merged channels applications that use screw terminal connectivity, use 22 AWG (0.33 mm2) wire for connecting to the Output HI and Output LO pins of each SMU channel.

Programming the SMU for Merged Channels

Use the NI-DCPower API to program the SMU for merged channels.

Before you program your SMU for merged channels using the NI-DCPower API, ensure your destination circuitry is designed accordingly. Refer to Connection Guidelines for Merged Channels for general information.

Complete the following steps to increase the current you can source from your SMU.

  1. Based on the merge configuration you chose, initialize your NI-DCPower session to the primary channel only.
  2. (LabVIEW, LabVIEW NXG only) Write the primary channel to the Active Channel property.
  3. Depending on your merge configuration, use the Merged Channels property to specify the required merge channel(s).
  4. Use the Configure Sense function or Sense property to configure the primary channel for remote sense.
  5. Use the Commit With Channels function to apply the merge configuration to the SMU. Commiting the session properties reserves the channels you specified for merging, which prevents them from being used independently.
  6. Call the Initiate With Channels function to begin sourcing current according to the merge configuration.
The maximum current you can now source from your SMU in this merge configuration is equal to the merge count times the per-channel maximum of your instrument.

Merging Channels in Practice

For example, for a four-channel SMU that can source up to 3 A on an independent channel, designating channel 0 as the primary channel and using the Merged Channels property to specify channel 1 as the merge channel yields a merge count of ×2.

This configuration would allow you to source up to 6 A from the combined channels.

You could then either use the remaining two channels independently or you could merge them in another ×2 configuration, using channel 2 as the primary channel and channel 3 as the merge channel.


If you want to change the merge configuration, first disable the outputs of any sourcing channels before initiating the new merge configuration in order to avoid output glitches.

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