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LM5088: Transient performance & Load regulation Issue

PRAHLAD Supeda
Expert 6180 points
Part Number: LM5088


My customer is using LM5088 for 12V DC fan. Where he is observing that on applying power to the module the fan voltage VFAN shoots to more than 40V and then stabilizes.

Also, the voltage regulations is poor and varying with load. I am yet to get more details on this.

Schematic: 

Please share your comments.

  • 0
    TI__Mastermind 40310 points

    Also if you have a filter on the input, make sure its well damped, that is it has high RDCR, ferrite Beads typically have high enough resistance to be well dampen.  However, if this is a typical inductor with a low DCR mR's then you will need to dampen.  The easiest way to do this is to add an input cap parallel to C500, such that the Cd>>C500 (at least 5 x larger) and the ESR is in the range of 100's mR's, say 0.5ohm.

     

    Regarding the Start up times, increasing Css from 10nF to 100nF, will help with the over shoot, but we need to determine if the supply is stable.  Check the switch node with a scope in steady state to confirm stability is a good idea. 

     

    Kind regards,

     

    David.