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TVS3300: Power line protecting

D3j4nHr01
Intellectual 410 points
Part Number: TVS3300
Other Parts Discussed in Thread: TSM36A

Hello,

I would like to protect a power line from overvoltage events. Maximum expected voltage on the line is 33.6 V. Firstly I'm thinking about using SMAJ33A diode, which has Vwrm of 33 V, minimum breakdown voltage (voltage where current equals 1 mA) of 36.7 V and maximum of 40.6 V. Maximum clamping voltage for this diode is a little bit higher than 53 V. Although expected maximum voltage on the line is 0.6 V higher than Vrwm voltage of diode, I think that everything would still work great, since there is still a sifficient gap between maximum expected voltage and minimum breakdown voltage. SMAJ36A diode would be a next diode from the list, but it has also higher clamping voltage - I'm using DC/DC converter with absolute maximum input voltage of 50 V and I'm worry that 36 V would not sufficiently protect this converter, because clamping voltage is higher than 50 V.

However, because of limited space on the board, I'm now thinking about using TVS3300 TVS diode for protection, but I'm worry about this idea, because this diode has much more "shaper" characteristic.

What do you think?

Many thanks, Kind regards, Dejan.

  • 0
    TI__Expert 6165 points

    Hi Dejan,

    Please see the comparison table below between the potential candidates, and TSM36A, another TI device that may be of interest:

      SMAJ33A SMAJ36A TVS3300 TSM36A
    Vrwm (V) 33 36 33 36
    Package Type SMA (DO-214AC) SMA (DO-214AC) WSON SOT-23
    Nominal Package Size            (L x W) (mm) 4.3 x 2.6 4.3 x 2.6 2 x 2 2.92 x 2.37
    Bi-/uni-directional Uni-directional Uni-directional Uni-directional Uni-directional
    Breakdown Voltage (min) (V) 36.7 40 34 37.8
    Number of Channels 1 1 1 1
    Clamping Voltage (V) 53.3 58.1 38 50
    IO Capacitance (typ) (pF) ~700 ~700 130 50
    IEC 61000-4-5 (A) 7.5 6.9 35 41
    IEC 61000-4-2 Contact (kV) 30 30 11 30
    Max Leakage Current (nA) 1000 1000 150 1000

    It seems if you wanted some more tolerance regarding the breakdown region, TSM36A may be more desirable, especially because it clamps right at 50V (at 25A, clamping is 57V at 40A). 

    Please let me know if you have any additional questions!

    Best Regards,

    Josh Prushing

  • 0 in reply to Josh Prushing
    Intellectual 410 points

    Hello Josh,

    thanks for this comparison. TSM36A looks very interesting. However, what do you think regarding gap between maximum expected voltage on the line (33.6 V) and breakdown voltage of TVS3300 which equals 34 V. Would be this gap sufficient?

    Many thanks, Kind regards, Dejan.

  • 0 in reply to D3j4nHr01
    TI__Expert 6165 points

    Hi Dejan,

    I think that TSM36A would be the safer option here, as a 0.4V tolerance is very tight. Is there anything about the TSM36A that is not suitable for this opportunity?

    Best Regards,

    Josh Prushing

  • 0 in reply to Josh Prushing
    Intellectual 410 points

    Hello Josh,

    I have many TVS3300 in house stock already, but I ordered TSM36A also and I will try with it.

    Additionaly, I worry that at the end a TVS with even higher power capability would be needed if TSM36A would not bring a sufficient protection. I'm thinking about SMLJ series.

    SMLJ33A has a Vwrm of 33 V, Vbr(min) of 36.7 V and Vbr(max) of 40.6 V. However, Vclamp is a little bit higher than 50 V - it equals 53.3 V at Ipp. Using that diode on power line with a maximum voltage of 34 V (1 V higher than Vwrm) means that there will a constant current flowing through the diode which means a constant power dissipation on the diode. However, because Vbr(min) is 36.7 V, current at 34 V would be smaller than 1 mA, so power dissipation on the diode would be lower than 34 V × 1 mA = 34 mW which is acceptable for me. I don't like to think about using SMLJ36A, although power dissipation would be smaller (maximum voltage would be lower than Vwrm), but clamping voltage will be even higher. Did I forget somehing within this calculation or constant power dissipation is only thing I need to worry about? I really don't expect that Vbr will goes lower than 36.7 V, so I think that more than 2.5 V of gap between actual applied voltage and Vbr(min) would be enough?

    Many thanks, Kind regards, Dejan.

  • 0 in reply to D3j4nHr01
    TI__Expert 6165 points

    Hi Dejan,

    I agree that SMLJ36A's high clamping voltage makes the device a weaker option. I don't see anything wrong with your calculations.

    Could you please inform me of what your specific power needs are? What is the maximum current your system can handle?

    Please keep me posted on how TSM36A testing goes!