[FAQ] What Analog Switch / Multiplexer Should I Use for JTAG applications?

TI signal switches and multiplexers can be used for JTAG (Joint Test Action Group) applications, but a few things need to be considered before selecting a device. The most important is first defining what the JTAG protocol requires:

• 4 Pin Protocol (5^th pin optional) – TCK (Test Clock), TMS (Test Mode Select), TDI (Test Data In), TDO (Test Data Out), TRST (Test Reset – Optional)
• Voltage Levels: 1.8V-5V
• Frequency: 10MHz-100MHz

Now with understanding the requirements of JTAG, we can utilize this information to find some compatible devices that can support all of these determining characteristics:

• JTAG commonly uses 4 pins and for such instances, so a 4-channel device is the minimum requirement given the amount of pins that need to be switched. In this case, 2:1x4 channel devices will be the primary multiplexer used. In the event that the optional 5^th pin is needed, at least a 2:1x6 channel will need to be utilized (as 2:1x5 channel devices are extremely rare).
• In addition, the JTAG protocol can communicate using voltage levels anywhere from 1.8V to 5V. This would indicate the usage of TI’s low voltage multiplexer portfolio for which there are many options that can fit this requirement.
• Bandwidth/Frequency is well within the operating margin of many of TI’s multiplexers as well with only needing a maximum of 100MHz typically.

The below table is a list of recommended TI Multiplexers that would be perfectly suited for JTAG applications: