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LM3409: Higher current capability.

Shinya Sawamoto
Expert 5285 points
Part Number: LM3409
Other Parts Discussed in Thread: TPS92640, TPS92641

Hello team,

I have a question about LM3409 LED current capability.
I found the description of "These features combine to make the LM3409 family of devices ideal for use as constant current sources for driving LEDs where forward currents up to 5 A are easily achievable." on the datasheet.
My question is that if LM3409 can accept higher current up to 10A depends on the external FET&SKD choice.
Or do you have any other recommendation for 10A LED current? (I want buck controller solution.)

Thanks in advance.
S.Sawamoto

  • 0
    TI__Mastermind 28655 points

    Hello S.Sawamoto,

    Since the LM3409 is a controller it can be used at 10A provided it is designed correct around the LM3409.  One section to read is section 9.1.8 in the datasheet, specifically:  "A good rule of thumb is to limit Qg < 30nC (if the switching frequency remains below 300kHz for the entire
    operating range then a larger Qg can be considered). If a PFET with small RDS-ON and a high voltage rating is
    required, there may be no choice but to use a PFET with Qg > 30nC."  There are other design considerations so I'll ask for more information to help.

    Can I ask what this application is for?  What is the input voltage, output voltage and desired switching frequency and anything specific to other operation such as PWM dimming or Shunt FET dimming?  This is driving LEDs?

    Another part to look at is the TPS92640/TPS92641.  There is a reference design for 20A with this part, PMP8016, it comes up when searching for TPS92641 on TI's website.

    The LM3409 is an easier part to design around since it is not synchronous and is hysteretic control though the TPS92641 may have other advantages.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    TI__Expert 5285 points

    Thanks a lot, Irwin.

    I'll send you an email for more detail.

    Regards,
    S.Sawamoto