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ISO1228: ISO1228 surge protection for source inputs

Anicia Yu
Prodigy 40 points

Part Number: ISO1228

Do I need to add Rsurge and Csurge for sourcing type inputs?

  • +1
    TI__Mastermind 25225 points

    Hello Anicia,

    For sourcing type inputs, Rsurge and Csurge are not required. 

    However, in order to have surge protection for the device when in source mode an external TVS diode is required. 

    You may also refer to this page for the setup in source mode - https://www.ti.com/lit/ds/sllsfn5b/sllsfn5b.pdf#page=29 

    Do you need help with TVS diode selection for this application? If so, what is the surge immunity target and field supply voltage? 

    Best,
    Michael

  • 0 in reply to Michael J Schultis
    Prodigy 40 points

    Thank you, Michael, for the information. Unfortunately, I am unable to open the E2E post you referenced. I plan to use a 33 V TVS for the local ISO1228 source input protection.

  • 0 in reply to Anicia Yu
    TI__Mastermind 25225 points

    Anicia,

    Ah you are correct, that one is inaccessible, let me correct that post.

    In any case, it sounds like the response helped, please let us know if you have additional questions and we will be happy to support you.

    Best,

    Michael

  • 0 in reply to Michael J Schultis
    Prodigy 40 points

    Hi Michael,

    I am using the recommended values for RILIM type 3 (RILIM = 0 ohms). The datasheet recommends using a MELF resistor, but I noticed that the ISO1228EVM uses an 0603 resistor for this location. I am using ISO1228DFBR. For my design, should I follow the datasheet recommendation and use a MELF resistor, or is an 0603 package acceptable when RILIM is 0 ohms?

    I also wanted to double check my wiring for OUT_EN, nFAULT, F0, and F1. I want to keep the isolator enabled and use no internal filtering. My current connections are:

    • OUT_EN tied to VCC1
    • F0 tied to GND
    • F1 tied to GND
    • nFAULT pulled up to VCC1 with 4.7 kΩ

    Is this correct?

    Also, if I do not need to monitor fault status, can nFAULT be left open, or should it still have the pullup?

    Thanks,

    Anicia

  • +1 in reply to Anicia Yu
    TI__Genius 15920 points

    Hi Anicia,

    The datasheet's MELF recommendation is for surge-proof applications especially in sink mode where the resistor must withstand impulse energy. Since in source mode, a TVS diode is required, there is no need to use MELF resistors

    Control Pin Wiring

    Your connections are correct for enabled operation with no internal filtering

    Pin Connection Function
    OUT_EN Tied to VCC1 Outputs enabled
    F0 Tied to GND No internal filtering
    F1 Tied to GND No internal filtering
    nFAULT 4.7 kΩ pullup to VCC1 Fault monitoring active

    nFAULT — Pullup vs. Floating

    If you don't need fault monitoring, nFAULT can be left floating It is an open-drain output 1, so leaving it unconnected won't cause any functional issues. That said, including the pullup is low-cost insurance—it gives you diagnostic capability without requiring a board re-spin if your requirements change later.

    Regards
    Varun

  • 0 in reply to Varun Kumar
    Prodigy 40 points

    Thank you for confirming the resistor type and the wiring!

  • 0 in reply to Anicia Yu
    TI__Genius 15920 points

    Hi Anicia,

    Glad to help :)

    Closing this thread now.

    Regards
    Varun