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BQ25302: Inductor Selection

Mark Ackerson
Genius 10190 points
Part Number: BQ25302

BQ25302EVM uses 1 uH MAPM0420LA1R0M-LF inductor that is difficult to source.  I'm working with the customer on alternatives, preferably physically smaller.  If you have suggestions, they would appreciated.

For 2A charge current what would be the minimum inductor Isat requirement with margin?  Can we get by with Isat = 4A?  MAPM0420LA1R0M-LF has Isat = 8.7A typ.

ISAT ≥ ICHG + (1/2) IRIPPLE

Usually inductor ripple is designed in the range between 20% and 40% maximum charging current as a trade-off between inductor size and efficiency for a practical design.

Thanks,
Mark

  • 0
    TI__Mastermind 24075 points

    Hi Mark,

      Yes, an ISAT of 4A would definitely be fine. Inductors have a lot of different factors when choosing, but I would focus primarily on the DCR and ISAT. The smaller the package, the more the limitation on the ISAT. The 20%-40% limitation is a good rule of thumb when choosing an inductor. As I designed the EVM with other IC in mind, I had to take the upper charge current limit of those IC as well (302,300,303J all share the same EVM).

  • 0 in reply to Kedar Manishankar
    TI__Genius 10190 points

    What would be a reasonable DCR for BQ25302 inductor with 4A Isat?

    Any inductor recommendations from a main stream supplier?

    Thanks,
    Mark

  • +1 in reply to Mark Ackerson
    TI__Mastermind 24075 points

    Hi Mark,

       It really  depends as we are seeing some shortages throughout the market so the onus is really on the customer/end designer to verify supplier stock with mainstream suppliers. Again, there are a lot of different factors going on behind choosing an inductor and tradeoffs have to be made with price vs footprint size vs saturation current vs temp rise vs core material vs DCR vs core loss. Most of these are parameters in the parametric search tool on digikey along with stock availability. Since there are so many factors we don't give generic recommendations apart from the validated solution on the EVM. This is also because there are factors I look for with specific manufacturers (example: core loss) that aren't readily available on inductor datasheets, and my main care about is the effect on efficiency and not so much the price, as the aim of the EVM is to show best performance of IC.

    DCR selection really depends on how much power budget the customer has, as it is easy to calculate the efficiency loss due to conduction loss across the DCR of the inductor. Lower is always better but if some efficiency loss is acceptable (depends on end designer) then choosing a higher DCR for smaller package/lower cost isn't a problem.