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LM3464 Two Strings Configuration

tateo yamashiro
Guru 10890 points
Other Parts Discussed in Thread: LM3464, LM5122

Hi,

My customer has question about LM3464.
Could you tell me about questoin?

[Question]
My customer considers to use LM3464 under the following condition.

 Vrail(nom)=28V *Boost convertor output
 Vf=30V
 Iled=2A/ch
 LED=two Strings

- Can the device be set two strings configuration?


- How much is the maximum current per channel?
  Does it depend on power dissipation of external FET?


- My customer wants to use boost convertor for the primary power supply.
  e.g. LM5122
  Can the device use boost convertor for the primary power supply?

- My customer wants to use the stabilized power source equipment for primary power supply on simple evaluation.
  Can the device use the stabilized power source equipment for primary power supply?

Best Regards,
tateo

  • 0
    TI__Mastermind 28655 points

    Hello,


    Vboost at 28 volts and Vf at 30 volts won't work.  Vboost has to be higher than the LED stack voltage plus some headroom.

    I have the question to another engineer about paralleling outputs this way, I don't see why this wouldn't work but I want to confirm it.

    I also have the question about maximum current out to another engineer.  I don't see why that should be limited except for watch the power dissipation of the regulating MOSFET

    It should work from a boost converter.  Do you plan on using the headroom control by regulating the boost with the LM3464?

    The circuit can be used from a stabilized power source provided the control loops don't interact with each other.  If the LM3464 response is faster than the power source it can go unstable.

  • 0 in reply to Irwin Nederbragt
    Guru 10890 points

    Thank you for your support.
    My customer plans on using the headroom control by regulating the boost with the LM3464.

    And sorry for rush, but could you give us the answer by this Friday?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Mastermind 28655 points

    Hello,

    The response is:

    I don’t see there is any limit on the output current as long as it’s just an op-amp inside of LM3464.

    If the voltage rail is properly setup, I believe it should work using 2 strings parallel.

    So they should be able to parallel the outputs as they asked or use two channels for 2A each and disable the other two.

    Thanks,