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LM2936Q high voltage transients - ISO7637-2

Alexander Schaeder
Prodigy 415 points
Other Parts Discussed in Thread: LM2936

Hi team,

         I would like to verify quickly if the LM2936Q device can deal with high voltage transients up to 58V. This is typically requiredin a  24V boardnet.

Transient: 

Impuls U_transient = 58V (vbat 28V+ transient 30V) for 40ms duration , td 250ms Ri=2R; Impuls is repeated 5s at 25°C.

In the attachment you can find the impuls defined as ISO7637-2.

Please confirm that the following devices can be used  24v boardnet applications.

LM2936QM-5.0/NOPB

LM2936QM-3.3/NOPB

Vin 40V max, transients up tu 60V.

Regards,

Alex

 

  • 0
    TI__Mastermind 22610 points

     This looks to be the standard automotive 'Test Pulse 2a'

    "... for 40ms duration , td 250ms ..."

     However, ISO 7637-2:2011 defines the pulse duration, td , to be 50 us (i.e. 0.05 ms).

    From your description, you appear to have a non-standard pulse requirement. If this is the case, then knowing the pulse rise time, tr , and the LM2936 load current would be helpful. If the rise time is fast and load current is low, it is simple to RC filter the Pulse 2a peak voltage.

    Input voltage pulse amplitude and duration are important, along with load current, since they all affect the device dissipation, and thus the average junction temperature.

    The LM2936QM-x.x (8-pin SOIC) has a thermal resistance (Theta ja) of 110 °C/W when mounted on a PCB where additional copper area is allocated at the device pins for enhanced thermal dissipation.

    The 58V peak voltage is not a problem.

    My concern is : if the duration, td , is really 250ms, the LM2936QM-x.x may likely go into thermal shutdown.

    If survivability is the only requirement, you should be OK.

    However, if continuous operation during the pulse string with a long duration time (td) is a requirement, then there might be a dissipation problem.