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LM3409HV: Hot-plugging

Ryanton
Prodigy 85 points
Part Number: LM3409HV
Other Parts Discussed in Thread: LM3409

Has anyone had issues with hot-plugging an LED driver using this IC/topology. Application would be 54Vin and ~45Vout up to 5A.

  • 0
    TI__Mastermind 25500 points

    Hello Ryanton,

    It does not have an issue with hot-plugging in and of itself and I'm certain it was tested under certain conditions during development.

    However, any device can have issues with hot-plugging depending on the system characteristics. It depends on the source output capacitance and output impedance, the parasitics between the source and the LED driver, and the LED driver input capacitance (and possibly EMI filter). At a high input voltage such as this and depending on those characteristics you could have voltage overshoots at the input of the LED driver that could exceed the abs max rating of the device and/or the PFET and diode.

    I would place a footprint for a TVS that can be loaded if you see excessive overshoot during your initial testing. If the overshoots exceed the abs max you can then load an appropriate TVS to clamp the overshoots to below the LM3409 abs max rating.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 85 points

    Thanks for the info Clint. 

    Next question. Reading through the datasheet for this chip, I didn't see any means of protection from an output short. Has TI tested any short circuit protection circuits with this chip/topology?

  • 0 in reply to Ryanton
    TI__Mastermind 25500 points

    Hello Ryanton,

    The LM3409 is designed with output shorts in mind, that is how shunt FET PWM dimming works, you are shorting the output with a FET. It is a peak detect topology so it inherently current limits. So yes, that was tested extensively and it performs very well.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 85 points
    Are you saying the shunt FET circuit has to be used for short circuit protection? Or the LM3409 by itself has short circuit protection?
  • 0 in reply to Ryanton
    TI__Mastermind 25500 points

    The shunt FET is not required for short circuit protection, that is inherent in the device and the reason a shunt FET can be used if desired. There are no worries about shorting the output whether there is a shunt FET or not. Sorry, I could have made that more clear. I hope that helps.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 85 points
    I have some proprietary information to discuss not for a public forum. Please contact me directly.
  • 0 in reply to Ryanton
    TI__Mastermind 25500 points
    Private message sent.