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TIC12400-Q1: Use in 24V system with TVS3301 input clamp

Jessica Riley
Intellectual 490 points
Part Number: TIC12400-Q1
Other Parts Discussed in Thread: TVS3301

Tool/software:

Hello,

I am considering using the TIC12400-Q1 MSDI device in a 24V system.  I have reviewed the app note, but it seems to me adding the resistive divider stage will make it so that it is not possible to use the wetting current feature.  Is that correct?

As an alternative, I was thinking I might be able to use the TVS3301 flat clamp device to protect the inputs (instead of the TVS + resistive divider stage).  Is that a reasonable solution?  I believe it will still require the Schottky diode in series to protect against negative voltage swings.

  • +1
    TI__Mastermind 33330 points

    Hello Jessica,

    You are correct, that the resistor divider needed to protect the inputs also prevents the use of wetting current.  This is basic Ohm's Law (V=I*R) and the voltage drop across the large resistance will prevent the full amount of wetting current.  The devices are more like current limiters and do not "force" a constant voltage.  The maximum voltage that can be sourced is limited by the VS supply voltage.  Therefore if the resistive load is small, the maximum wetting current will flow and the device will limit the current to the set level.  If however, the resistive load is large, the actual amount of current that flows will be based on Ohm's Law.

    Using a flat clamping diode is a possible solution, but it should clamp to a voltage of 16V or less, and certainly less than 40V because that is the abs max at which the internal ESD cells may start to engage.

    The transistors in the device are sized to tolerate voltages up to 40V and can do so for short periods of time without issue.  Subjecting the device to operating voltages of 24V will not immediately break the device.  Instead, the issue is that prolonged exposure to voltages greater than 16V may reduce the life expectancy for some devices based upon the semiconductor manufacturing process used with these devices. 

    Therefore to ensure all devices have reliable operation over their full life expectancy, we recommend the voltage levels remain less than 16V.

    Regards,

    Jonathan