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LM5574: Diode Damage

Part Number: LM5574

Dear forum,

We are facing similar problem with the diode getting burned. We have several different boards using this device, some of them 10 years in production. The burn occurs at the customer. Our input voltage is 48V from backplane power supply, and the output current is ~100mA. The diode is rated for 100V.

1) I checked there is no over-voltage spike on the SW node.

2) It is schotky diode, I don't see dv/dt issues. The diode p/n is ON Semi (Fairchild) S100.

Can you help?

remark: dashed components on the schematic are not populated.  

  • Hello

    There are only three things i can think of that might damage the diode.

    1. Over current/over heat.  You might double check the diode current rating.

    Also, is the diode damaged during a short circuit even?

    2. Over-voltage; it could be a rouge spike; since i assume you can not monitor when the

    fault occurs.  But 100V should be enough for your input.

    3. dv/dt failures.  We have seen these in the past.  First check the slew rate on the switch node.

    Then compare with the data sheet rating.  If the diode has no rating for dv/dt in the data sheet,

    then you may need to find a new diode with a specified rating that is commensurate with your switch dv/dt.


  • Hello Frank,

    1. The max peak current through the diode is 0.5A (steady state current is much lower)
    2. The peak voltage is about 50V (the diode rating is 100V)
    3. dv/ dt is 10V/nsec    (no information in the data sheet regarding  dv/dt )



  • Hello

    I would look for a diode with a dv/dt rating and substitute and see if the failures go away.

    Also, be sure that the diodes are being well soldered down in production.


  • Hello

    I will close this post due to inactivity.