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LM27313 DCM Operation

tateo yamashiro
Guru 10890 points
Other Parts Discussed in Thread: LM27313

Hi,

My customer has question about LM27313.
Could you tell me about questoin?

[Question]
 My customer consider to design DCM operation under the following condition.

  Vin=3.0V to 4.2V
  Vout=17V
  Iout=50mA max
  L=2.2uH
  peak inductor current=650mA at Vin=3.0V

 If the device is designed CCM operation, there is concern about maximum Duty limit.
 Could you recommend that the device operates in discontinuous mode in this case?

Best Regards,
tateo

  • 0
    Prodigy 10 points
    Hi,

    I don't think CCM or DCM mode will make any difference if you have duty cycle limitation.

    Webench suggests that you may hit the duty cycle limit with this device for 3Vin and 17Vout.

    - Denka
  • 0
    TI__Expert 4365 points

    Well this is interesting. I just posted an answer to a different but similar application issue.

    It the incentive is to use DCM mode to skirt the issue of maximum duty cycle, then try the attached doubler schematic. This changes the loop situation so the duty cycle limit is as though you are only generating 1/2 the actual Vout.  

    This approach does add more parts, but at least some of the diodes can be co-packaged as SOT523 versions of BAT54S, which may save a slight amount of space. The upper feedback resistor will need to be about 158K rather than 287K.

    Alan

    4604.5to30Boost.pdf