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BQ25858-Q1: Inductor Min DCR Inquiry - Also For BQ25858B-Q1 and BQ25758A

Nicholas Leak
Prodigy 10 points
Part Number: BQ25858-Q1

Tool/software:

Considering these ICs for a Buck/Boost design, and am challenged by Table 7-1. MODE Pin Resistance Configuration Options.

Comment 1 appears to indicate a minimum DCR regardless of whether it is buck/boost or buck only.

Can you confirm If i am looking to operate in buck/boost that minimum DCR for a 10uH inductor must be 7.9mOhm, or does this only hold true for Buck only mode?

The Ideal inductor I've selected for the circuit is ~2.6mOhm DCR and I'd like to run this in buck/boost if possible.

I do not see this limitation on other similar battery charge ICs so clarification would be helpful.

Thanks!
-Nick

  • +1
    TI__Expert 6245 points

    Hi Nicholas,

    7.9 mOhm would be the minimum DCR for the 10 uH inductor for both buck-only and buck-boost modes. The formula given for buck-boost R-dcr is how the buck-only values are calculated.

    • L / DCR = 1260 us
    • DCR = L / 1260 us
    • DCR = 10 uH / 1260 us = 7.9 mOhms

    The inductor you have selected will unfortunately not be within the accepted DCR range for this part. Let me know if you have any other questions.

    Best,

    Michael

  • 0 in reply to Michael Bradbourne
    Prodigy 10 points

    Michael,

    Thank you for confirming that my understanding is correct.
    Does TI provide any other Battery Charger ICs that do not have this limitation, while still allowing I2C setting of output voltage and current for CCCV charging?

  • 0 in reply to Nicholas Leak
    TI__Expert 6245 points

    Hi Nicholas,

    We might have a charger that does not have this limitation, but I am not sure so I would have to go through and look. Typically, our compensation loops for the converter are designed internal to the chip expecting a certain range of DCR for proper operation.

    If you would like me to look for a different part, I need to know more about your design.

    • What are your input voltage and current requirements?
    • What is your output voltage and current?
    • Are there any features of the BQ25858 that you need in a different chip?

    Best,

    Michael