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LM3450: Hold-Pin floating

Claus Wassmuth
Prodigy 20 points
Part Number: LM3450
Other Parts Discussed in Thread: LM3409,

Hello,

Our power supply is based upon LM3450A having LM3409 on secondary side. On Primary side we don't use dynamic hold functionality comming with LM3450. So Pin "HOLD" is floating and Pin "ISens" is connected to primary ground.

Unfortunately in datasheet I cannot find a hint if there are any side-effects leaving Pin "Hold" floating and Pin "ISens" connected to Ground. Does anybody have experience with that topology?

Thanks for your help.

Regards

Claus

  • 0
    TI__Mastermind 28655 points
    Hello Claus,

    Looking at how the hold works it should be okay the way you have it set up. It's trying to regulate -200 mV on the Isen resistor but I don't see anywhere it will cause issues if it cannot do that.

    The block diagram shows a 5 uA current source across a 40 Kohm resistor creating a 200 mV offset for the Isen threshold. The hold would add additional current to try and get Isen to -200 mV, if it's not able to hold should just be railed low.

    This is not being used on a triac or reverse phase dimmer?

    Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points
    Hello Irwin,

    thanks for the quick reply.
    No, we're not using triac or reverse phase dimmer in that use case.

    Regards,
    Claus