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TVS SMCG33A fails to short.

Narayan P Sangale
Prodigy 120 points


Dears,

We are using TVS diode SMCG33A from vishay to protect signal line which has voltage range from 0-24VDC.

We found that this TVS diode connected to signal line is getting short.

Signal line has a cable length near about 30 meter.

Signal line is continuously switch between 0 and 24V state to give signal state.

After several months (not fixed) of operation the TVS diode connected between signal line and ground gets short.

Cable length of signal is 30 meter approximate and has 10 nodes connected to it.

Request you please help us to find out possible causes of TVS fail and how can we improve design and is any other better TVS option is available with TI to protect circuit and improve robustness.

  • 0
    TI__Genius 12410 points

    Hello,

    We do not design SMC diodes so I will not be able to help you with replacing it. As far as protecting it I am not sure what the damage is coming from? What is the maximum voltage that can be seen on the line? Long cables typically give themselves to surge events but an SMC diode should be able to protect up to 100s of amps. We do not have the capability of sustaining 100s of amps for our devices.

  • 0 in reply to Cameron Phillips
    Prodigy 120 points

    Dear Cameron,

    Thanks for your reply.

    Maximum voltage is upto 26V max in normal condition.

    Please help me to find answers to below questions.

    When to use unidirectional or bidirectional TVS?

    If signal has some negative spike (not big) then can we use bidirectional TVS?

    What can additional taken care along with TVS?

    Does adding ferrite bead and series resistor help and how?

    Can you suggest probable causes of TVS failure? 

    Thanks in advance.

  • 0 in reply to Narayan P Sangale
    TI__Genius 12410 points

    Hello,

    Please see our two training's online about esd and surge

    Adding impedance in front of a TVS diode just means that those components will have to take the full pulse. However if you add them after the TVS then they don't have to take as much energy.