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THVD1406: About the location of the Varistor

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Guru 21045 points
Part Number: THVD1406

Hi Team,

 

We understand that your recommended ESD protection device is CDSOT23-SM712.

However, our customer would like to use Varistor(AVRM1608C270MTABB) for two connecters of daisy chain.

 

Could you please let us know if you know the recommended placement location for Varistor?

 

  1. Are Varistor needed for both CN1 and CN2?
  2. Are Varistor needed for CN1(Upstream side) only if CN2 is connected to the same application?
  3. Where is it appropriate to place Varistor near THVD1406(Point1), near the connector(CNx)(Point2), or in between(Point3)?

 

[daisy chain Image]

https://www.ti.com/lit/ds/symlink/thvd1400.pdf

Regards,

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  • +1
    Guru 244350 points

    Protection components should go as near the connector as possible (to prevent the overvoltage from affecting anything else on the board).

    In theory, you should have two varistors, at CN1 and CN2 (if it is possible for overvoltage to come from either one). In practice, if the connectors are near each other, they can share one.

  • +1
    TI__Mastermind 43696 points

    Hi Hide,

    1. Not necessarily. Point 1 should have the varistor - and it should be installed in the same manner as a the TVS diode shown in our datasheet. Essentially 1 varistor from B to GND at point 1 and 1 varistor from A to GND at point 1 is recommended. Each line should be protected as the common mode overvoltage events won't be clamped unless there are varistors to ground on the A and B line. 

    2. No - see answer to 1. Point 1 is the main point of protection - but a device is needed for the A and B lines (both to ground) 

    3.Point 1, one varistor on A to GND and one varistor on B to GND. 

    Essentially the Varistor eq. circuit is same as a TVS diode - so they should be used in the same way. We haven't tested with the varistor - while I don't think there should be concerns - there may differences in performance. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Guru 21045 points

    Hi Clemens-san, Parker-san,

    Thank you for the information and your advice.

    Regards,

    Hide