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WEBENCH® Tools/THVD2450: TVS selection of THVD2450 design circuit

Part Number: THVD2450

Tool/software: WEBENCH® Design Tools

Can I use CPDQR24V-HF instead of SMAJ30CA? We need a TVS with the same package size as CPDQR24V-HF. Do you have a better recommendation?

  • Hello,

    Yes, the TVS component selection is flexible.  The part number in the datasheet is just one provided for reference.  In general, you should choose a TVS whose working voltage exceeds the normal operating voltages in your system, and the peak voltage during a current surge should not exceed the maximum voltage rating of the RS-485 transceiver.  For a more detailed description on how to choose a TVS for RS-485 applications, you could reference this blog:

    https://e2e.ti.com/blogs_/b/industrial_strength/archive/2017/11/13/how-to-choose-a-tvs-diode-for-rs-232-rs-485-and-can-based-on-voltage-ratings

    Please let us know if you have any further questions.

    Regards,
    Max

  • Hello,

    I don’t understand why I look at the output voltage range instead of the input voltage range in the blog.

  • Good question.  In this datasheet it is a little confusing since there are both drivers and receiver channels and each has an input and an output.  In the case of the driver channel (which you've circled), the absolute maximum input voltage refers to the "DIN" port while the absolute maximum output voltage refers to the "DOUT" port.  The DOUT port is what would connect to a cable, so it would be the one which typically requires ESD protection.  So, the absolute maximum voltage range is +/- 13.2 V per this table and the expected working voltage range is +/- 5.4 V (plus some margin).  Based on these requirements, a TVS can be chosen.

    Please let us know if it is not clear.

    Regards,
    Max