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LM117HV overvoltage transient

Karl Strauss
Prodigy 55 points

A review of a Worst Case Analysis revealed that an LM117HVHRLQMLV can have a transitory overvoltage condition applied where in  Vin - Vout > 60 V.    For a set 15V output, nominal Vin is 38 V, Iout is 22 mA.  For a period of 10 microseconds, Vin might surge to 75.2 volts.

The concern is that this may damage the device.  Understand that operating parameters are not guaranteed for out of spec operating conditions; but will this cause some latch-up or other induced failure?   This sort of thing cannot be modeled reliably as the existing models work on optimal parameters - even the schematic supplied does not reflect the true design.  This is, I think, process related.

Thoughts?

  • 0
    TI__Intellectual 2010 points

    Karl,

    The absolute maximum input to output voltage differential is +60V for this device and the Vin-Vout exceeding 60V can be demaging for the part. Unfortunately this device does't have over voltage protection built in. Despite the voltage overshoot time is low (10usec), it can still damage the device. You can use a positive Transient voltage suppression diode or TVS. You can clamp  and divert or shunt voltage spikes from a circuit in order to protect that circuit with a TVS. 

    In this case you may choose 40V TVS, they are typically small and inexpensive but work great for positive and negative voltage spikes. 

  • 0 in reply to Kaisar Ali
    Prodigy 55 points

    Thank you.  Are these particular devices factory tested at the extreme delta-V condition  (i.e.60 volt differential)?

  • 0 in reply to Karl Strauss
    TI__Intellectual 2010 points
    Karl,
    These devices are tested for the EC table specs but only at room temperature, unless otherwise noted below the EC table.