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LM5064: Output shottky diode for inductive load

K. Sasaki14
Guru 10200 points
Part Number: LM5064
Other Parts Discussed in Thread: LM5067

Is LM5064 output shottky diode placed to protect which pin?

Is it for protection of Vcc negative voltage? If it is yes, I think it should be placed between VCC and VEE.

I would like to know protected pin and protection situation.

Best Regards,
Kohei Sasaki

  • 0
    TI__Expert 5940 points

    Kohei,

    The TVS protects the Vcc pin from excesive positive transient.  The Schottky protects the OUT pin from excessive negative transient.  This during fault condition that turns off the FET rapidly, creating a di_dt impact on line inductance that will cause Vin to rise to a very high level and the output to go very negative.  Both devices need to clamp the entire short circuit current - that will be higher than the CB setpoint due to ~ 1usec delay (de glitch).  The inductance in the lines determines the energy (time duration of the spike) mostly but also the amplitude to a lesser degree.  So use very large clamping TVS and a good Schottky that has very low Vf at the short circuit current.  See the LM5064 for a good example and placement.

    Brian

    Input TVS Output Schottlky.pdf0207.Voltage transient protection for HS due to di_dt CB event.pdf

  • 0 in reply to Brian Daugherty
    Guru 10200 points

    Brian-san,

    Thank you for your response.
    I can understand the OUT pin negative voltage about positive Hot Swap. However LM5064 is negative Hot Swap. Then the circuit is different from positive hot swap circuit.
    Does the negative voltage occur on negative Hot swap circuit?

    And I think OUT pin has shottky diode to VEE for surge event protection.

    Best Regards,
    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    Guru 10200 points

    Brian-san,


    Is the datasheet description correct?
    I think it is mis-description. And I found the comment which I can understand on LM5067 datasheet P.26.
    There is a following comment,

    "Adding the diode prevents possible damage to the LM5067 as the OUT pin will be taken above ground by the inductive load at shutoff."

    From this, I think the output shottky is required for protection positive over voltage.

    What do you think about my idea?

    Best Regards,
    Kohei Sasaki