The 34925A 40/80-Channel Optically-Isolated FET Multiplexer (40/80-Ch FET MUX) module is a high-speed and high-density FET MUX for high throughput production test. This module is divided into two equal banks of non-latching FET switches. This module also contains four armature Analog Bus relays. Through ABus1 and ABus2 you can connect any of the channels to the internal DMM for voltage or resistance measurements. When the power is off, all channel and Analog Bus relays open.

Using program commands or the mainframe front panel, you can control each of the FET channel switches individually, and configure this module for differential (2-wire or 4-wire) or single-ended (1-wire) mode.

Terminal blocks

If you are using a Keysight 34925T-00x terminal block to connect your DUT to this module, be sure to use the terminal block that corresponds to your module configuration mode.

• 34925T-001 (Option 001) Terminal block for differential (two- or four-wire) mode
• 34925T-002 (Option 002) Terminal block for single-ended (1-wire) mode

Two wire mode

• Two independent 20-channel 2-wire MUXes. This configuration requires neither using external wiring nor connecting through the internal Analog Bus relays
• One 40-channel, 2-wire MUX. You must use external wiring or connect through the Analog Bus relays to for this configuration

Four wire mode

You may configure the 34925A as a single 20-channel 4-wire MUX. This configuration requires using neither external wiring nor connecting through the internal Analog Buses. For 4-wire resistance measurements, the instrument automatically pairs channel n on Bank 1 (source) with channel n+20 on Bank 2 (sense) to provide these connections. Four-wire controls occur only when doing 4-wire measurement operations through the internal DMM, or scanning a channel previously configured as 4-wire.

One wire mode

• Two independent 40-channel 1-wire MUXes. This configuration requires neither using external wiring nor connecting through the Analog Bus relays
• One 80-channel 1-wire MUX. You must use external wiring or connect through the Analog Bus relays for this configuration

Interlock protection

This module is interlock protected, which means whenever the D-sub connector end of the modules is exposed, the Analog Bus relays immediately open and disconnect from the Analog Buses.

Overvoltage protection

This module also features high voltage detection (< 100 V) and current limiting circuitry to protect the FET relays. This circuitry senses current flows from input overvoltages. These overvoltages may come from either the MUX input or from the Analog Buses. In addition, each channel is also protected from input overvoltages with a resistor.

When overvoltage is detected, all relays (Analog Bus and FET) are opened. While in the overvoltage state, any attempts to close any Analog Bus or FET switch, results in an error status response from the module.

For additional information on the 34925A, please see the document linked here beginning on page 25.

The chart below provides a brief overview of multiplexer modules for the 34980A.