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Teflon standoffs?

Randy Mitchell
Intellectual 330 points

The spec sheet for FET operational amplifiers like the OPA128 and OPA111 say that "to avoid leakage problems, it is recommend that input signal of the device be wired to a Teflon standoff."  I'm not clear on what they are talking about -- where do you get the standoffs and now do you use them?  Thank you in advance for any insite you can give me!!!

  • 0
    TI__Guru* 93105 points

    Hello Randy,

    The OPA128 and OPA111 FET-input operational amplifiers were developed about a quarter-century ago when round, 8-pin , metal TO-99 package was commonly in use. Assembly methods of the time were less automated and didn't necessarily include a printed circuit board. Devices were sometimes installed in Teflon(TM) PTFE, sockets or hand wired to insulated circuit terminal pins. This is where the mention of Teflon(TM) standoffs enters into the OPA111/OPA128 datasheet applications. The standoff most often consists of a plated, conductive pin centered and held in a very low-loss, insulating plug. The plug is inserted in an appropriately sized hole which was part of a metal chassis or circuit board assembly. Wires and component leads such as the OPA111 or OP128 inputs are then soldered to the terminal pin. It is important to keep all of the circuitry very clean such that circuit leakage currents do not exceed the ultra-low bias current of the amplifiers.

    I did quick web search and found that Keystone produces PTFE insulated terminal pins. Here is the URL:

    http://www.keyelco.com/products/specs/PTFE-11065THRU11074.ASP

    Likely, other terminal manufactures produce them as well. I hope this helps.

    Regards, Thomas

    Thomas Kuehl

    Senior Applications Engineer

    HPA - Linear Products

    Texas Instruments - Tucson