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TSM36A: Need help with Load dump calculations

BOOM
Prodigy 85 points
Part Number: TSM36A

I have a load dump requirement. I am planning to use a bi-directional TVS diode at the power input. Can anyone help on how to find out the conduction time of a TVS diode, energy calculations of the pulse, amount of energy that TVS can withstand and how the diode performance degrades over each dump.

Any calculations that can help me find this out?

Surge Requirements: UA (28V), US (100V), Ri (0.5 ohm), td (50 ms), Tr (1<tr<10ms), No. of pulses (5), Time between pulses (5 sec)

  • 0
    TI__Genius 14240 points

    Hi Joseph,

    Below are some estimations for conduction time of the TVS diode and energy of the TVS will need to withstand for this pulse. It was assumed that the TVS diode is clamping at the typical voltage for a 41 A peak surge event. This also doesn't take into account number of pulses and the intervals between as well as degradation between each load dump.

     

    Now with the internal resistance of the alternator being 0.5 Ohms, our device won't be able to dissipate this amount of power. Would you consider a solution using a current limiting resistor? 

    Regards,

    Sebastian 

  • 0 in reply to Sebastian Muriel
    Prodigy 85 points

    I cannot use a limiting resistor for now. Is there any way to conclude on the TVS diode that can be used? Maybe two in series, thinking of the Ri value? A possibility?

  • 0 in reply to BOOM
    TI__Genius 14240 points

    Hi Joseph,

    You would need to put three of these devices in parallel to have enough surge current capability. That being said they would need to share the current evenly and there is typically a slight variation between the turn on time of each device. This could lead to unenven sharing of the current and cause one of the devices to be damaged.You could prevent this with series resistors at each input. 

    The pulse width of the load dump is also quite long, our devices are designed to clamp for durations in the nS- uS range so the load dump transient waveform would need to be tested to see if it can withstand the pulse. 

    Regards,

    Sebastian