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LM3464A: request for review my customer's circuits(LM3464A)

robin Moon
Expert 1520 points
Part Number: LM3464A
Other Parts Discussed in Thread: LM3464, TPS92640, LM3409

Hi.

please request my customer's circuit reviews.

He is using the LM3464A to have 3A current in each LED channel

Please see the attached file.

thanks.

regards,

  • 0
    TI__Mastermind 28655 points

    Hello Robin,

    What are they intending to drive with these outputs?  What is the LED string voltage?  Are they all the same strings?  What is the tolerance of the LED string voltages including over operating temperature?

    The dynamic headroom control is not being used, at this input voltage and output current there can be a lot of power dissipation in the MOSFETs.

    The current sense resistor values are correct.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Expert 1520 points

    Hi.

    this application is High power Light in outdoor.

    The LED module has arranged 14 LEDs in series and 7 in parallel.

    Up to 48V DC can be supplied to Vin, and up to 3A of current can be supplied to each String.

    refer to LED Datasheet.

    please give additional advice or recommend new LED driver device.

    thanks.

    dsXPL2.pdf

  • 0 in reply to robin Moon
    TI__Mastermind 28655 points

    Hello Robin,

    I did some calculations from the LED datasheet.  This is for outdoor light so I assumed a temperature range for the LED from -25C to 150C for the calculations.  The datasheet does not have Vf versus temperature so I took the lumen output versus temperature to get an idea of what variation there is in Vf.  To actually design this the Vf versus temperature needs to be known as well as the LED junction temperature range.

    With all tolerances at 3A the LED string voltage using 14 LEDs in series can vary from 33.7V to 56V.  Using 1V of overhead for the LM3464 the input would need to be 57V to allow operation over LED Vf variance and temperature (the real data needs to be used in my calculation which I do not have and may change this range).  This means the LED string power is 98W to 168W over this variance.  This also means the MOSFET will have to dissipate 73W when the LED string voltage is 33.7V.  This also places the MOSFET at the DC SOA limit which the MOSFET case held to 25 Celsius.  This also means the LM3464 portion of the circuit will be 57.3% efficient at worst case operation.

    If you are going to use the LM3464 at this power level I recommend using the dynamic headroom control as well as making sure that the LED string temperatures cannot vary much between each other.  What would be better is to use LED drivers for all seven strings, it will, most likely, be more efficient.  Such as using LM3409 or the TPS92640.

    Is this a 1000W LED design?

    Best Regards,