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LTC3803 soft start issue

Hi ADI Experts

I am using LTC3803 for POE at application. but I have some inrush current issue that needs to be reduced.

since the SS is internally controlled by LTC3803, May I know if it is possible to build a external SS circuit on Ith pin?

Does ADI/LTC have reference circuit for external soft start for LTC3803?



  • Hi Ken:

    If this is isolated application and you are using OPTO feedback circuit the soft start should be implemented on the secondary side. We have LT4430 part that addresses that issue.

    The internal soft-start should be adequate for non-isolated application. If not, there is a circuit in LTC1871 data sheet that shows how to add external soft-start in non-isolated application.

  • HI Gperica

    thanks for your prompt reply.  My application is an isolated power supply but I used a Aux winding for FB

    I checked the reference schematicn of  LTC1871 with external SS and ran a simple simulation(added the circuit at the output of the Aux winding),

    I think the circuit is work!~

    thanks for the suggestion