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LMP91200: ESD protection for pH sensor based on LMP91200

user5329941
Prodigy 100 points
Part Number: LMP91200

Hi,

I am designing a medical-grade pH meter that needs to pass the Level 4 ESD test. The pH electrodes have very high internal resistance, so the op amp must have a very low input bias current (the LMP91200 has an input bias current of less than 1 pA). Can you recommend any ESD protection solutions for such applications? I cannot use TVS diodes because most of them have leakage currents greater than 1 nA, which is an order of magnitude higher than the input bias current of the op amp

I am considering placing a large value pulse-withstand resistor (10 MΩ) in series with the input and a 100 pF capacitor to ground. Additionally, I plan to add a low leakage current TVS diode between the guard ring and ground.

I would be very grateful for any advice.

  • 0
    TI__Expert 5670 points

    Hello,

    Given that the input bias current is so low on the LMP91200, I would avoid connecting anything to INP or GUARD1 with leakage current, I would only connect those pins to the PH electrode sensor. Could you tell me a little more about the Level 4 ESD test you are trying to pass? Is this an end-application specific test?

    Realistically, I think your best bet is to create an E2E thread with the ESD diodes team, you can start by choosing one of their parts and opening a thread asking what the right TVS diode to choose is.

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    TI__Expert 5670 points

    Here is the link to TI's ESD diodes page: https://www.ti.com/interface/diodes/overview.html

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 100 points

    Hi Alex,

    we are working on a special pH monitor that is a medical-grade device with a single-use pH electrode attached to the device connector. The pH electrodes are detachable components, and therefore we need ESD protection on this connector. In accordance with the IEC 60601-1-2 standard, the medical equipment must meet Level 4 ESD discharge requirements (8 kV contact and 15 kV air). In my opinion, we need to implement ESD protection because, without it, the device has no chance of passing the ESD test.

    As you recommended, I will create a thread with the ESD diodes team. Thanks.

    Mateusz

  • 0 in reply to user5329941
    TI__Expert 5670 points

    Thank you for the additional information. I will go ahead and close the thread, but if you have more questions about using the LMP91200, please feel free to reopen the thread by responding with a new question.

    Thanks

    -Alex Thompson