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LM5180-Q1: Reason for BCM

RYO
Intellectual 2000 points
Part Number:

RI have three questions about this IC. Can you answer to those?

  • Why do you utilize boundary conduction mode (BCM) at heavy load? What is the merit to use BCM?
  • In the figure below, is each range of current correct, such as FFM, DCM, BCM and current limit region?
  • In the figure below, why does the output voltage go down by increasing the output current? Do you have any methods to calculate the output voltage drop?

Regards,
RYO

  • 0
    TI__Guru 74032 points

    Hi Ryo,

    See answers below.

    Regards,

    Tim

    RYO said:

    Part Number: LM5180-Q1

    RI have three questions about this IC. Can you answer to those?

    • Why do you utilize boundary conduction mode (BCM) at heavy load? What is the merit to use BCM? BCM allows more output current while still preserving DCM like behavior in terms of the mag current reverting to zero each cycle.
    • In the figure below, is each range of current correct, such as FFM, DCM, BCM and current limit region? Yes.
    • In the figure below, why does the output voltage go down by increasing the output current? Do you have any methods to calculate the output voltage drop? The converter effectively regulates at the top of the output ripple waveform (depending on Cout and its ESR). As BCM has lower switching frequency and higher output current, the pk-pk output ripple tends to increase and thus Vout decreases slightly. This is mitigated by using a larger output cap. You can use the LM5180 quickstart calculator to assist with component selection.

    Regards,
    RYO