MP4248 – Single inductor but two inductance equations?

DC-DC Power Converters
1

Hello!

I am currently implementing the MP4248GQV-0011-P with the specs:

  • Input: 18V–34V (unregulated battery)

  • Output: 24V at 3A (fixed, 72W)

Since my output voltage falls within my input range, the converter will operate across all three modes (buck, boost, and buck-boost)
The typical application circuit shows a single inductor, but the datasheet provides two separate inductance equations: Equation 6 for buck mode and Equation 7 for boost mode. My questions are:

  1. Which one do I use when my design needs to cover all three operating modes?
  2. Do I calculate both and pick the larger value, or is there something else I’m missing?
  3. Is there a design calculator I can use with this converter model for these calculations?

Thanks in advance!

2

Hello @cnune052 ,

Thank you for posting your question on the MPS Technical Forum.

For the Inductor selection of the MP4248, you need an inductor that will satisfy both Buck and Boost Modes of operation. Hence, you have to select the largest inductance value from either Equations 6 and Equation 7.
There is currently no design calculator for this specific IC, nevertheless for Equation 6 (Buck Mode) choose Vin = 34V, and for Equation 7 Vin = 18V.

Regards,
Edgar

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3

Hello Edgar,

Thank you very much for the informative response! I did stumble across this tool: https://www.monolithicpower.com/en/mp4248.html and I was wondering if using the Inductor Selector Tool is suitable for this application? I’ve been using the Buck-Sync and Boost-Sync tabs specifically.
If it is a suitable tool, could you suggest possible input values?

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Thank you!

4

Hi @cnune052 ,

Yes, you can use the Inductor Selector Tool to calculate the inductances for both Buck Mode and Boost Mode of the MP4248 using the Buck-Sync and Boost Sync Tabs respectively.

  • Buck-Mode: Vin = 24V-32V
  • Boost Mode: Vin = 18V-24V

What is important is your nominal voltage value. In other words, the most typical input voltage your will feed the system at both Buck and Boost Modes.
If you do not have a nominal voltage value, then use the Max Voltage for Buck Mode (32V) and the min voltage for Boost Mode (18V) in your calculations to find the Inductances.

I hope this provides some insight.

Regards,
Edgar

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