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LM3410XSDSEPEV: Efficienc in SEPIC Configuration

Franz Schellhase
Expert 3605 points
Part Number: LM3410XSDSEPEV
Other Parts Discussed in Thread: LM3410

Hi team,

My customer is evaluating LM3410 in SEPIC configuration to power an LED at Vf=3.1V and Vin between 3V to 4.2V. They see an efficiency of only 73%/74%. Can do you have suggestions on why this could be the case and how to increase it?

Thank you,

Franz

  • 0
    TI__Mastermind 28655 points

    Hello Franz,

    The efficiency will not be very high due to a few factors.  The fb threshold is approximatley 0.2V, the diode Vf is about 0.3V which, by itself, will make the efficiency 86%.  Then you have to add in all of the other losses, switching losses of the LM3410, IC operating current, the loss in the inductors, etc.

    The way to increase it is to figure out where the losses are and try to improve.  This isn't the best topology for efficiency, however there aren't many choices if it has to both boost and buck.  1.6 MHz may not be helping either however going to 525 KHz will probably make the design physically larger.

    The LED current will also have an effect since some losses are fixed, such as the IC operating current.

    Best Regards,

  • 0
    TI__Mastermind 18890 points

    Franz,

    In general, that's around what we would expect the efficiency to be around depending on whether the input voltage is less than the output and the load.  You can try going to a the 500Khz version (Y) of this part to try and reduce the switching loss but the external components will be larger to handle the lower switching frequency.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    TI__Expert 3605 points

    Hi Irwin, Tuan,

    Thank you for the inputs. Do you have an alternative higher efficiency constant current IC suggestion for this application?

    Vin = 3.0 - 4.2V

    Vf_LED = 3.25V

    Iout = 700mA

    Thank you,

    Franz

  • 0 in reply to Franz Schellhase
    TI__Mastermind 28655 points

    Hello Franz,

    Unfortunately no.  There range makes it necessary for a both a boost and a buck solution.  At the low Vf a synchronous part would help with efficiency, we do not have that.  Possibly a better option would be a synchronous buck.  It would be more efficient and, guessing the application, would probably run longer on a lithium battery.  This is also a part we do not have.  And yet another option would be a linear.

    Best Regards,