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BQ25628E: Inductor sizing and current queestion

s_breakpoint
Prodigy 60 points
Part Number: BQ25628E

Tool/software:

Hi! I am pretty new to switching battery chargers, and have a design in which I'd like to try out the BQ25628E. 

In the "Inductor Selection" section of the datasheet for this part, there's mention of using I_chg for calculating the ripple and saturation currents needed to pick an inductor part. But, if I understand this part correctly, it is able to both charge a battery AND power a system simultaneously...is that right? If so, wouldn't I have an I_chg (the current being used to charge the battery) and - at times - I_sys (the current being used separately to power the system)? And, if so, would I then want to use the sum of these two currents to calculate inductor size? 

I'm sure this is a pretty entry-level question, I'm just a little confused why the datasheets seems to assert that I_chg is sufficient and complete for calculating saturation current. 

Thanks so much!

  • 0
    TI__Mastermind 31650 points

    Hello, 

    Thank you for reaching out via E2E. Please see my comments below. 

    s_breakpoint said:
    And, if so, would I then want to use the sum of these two currents to calculate inductor size? 

    You are correct that you will want to consider the total output current expected in your system when deciding the required saturation current for the inductor you select. Total output current will be ISYS plus ICHG. 

    Additionally, for your information the BQ25628E is designed to work with an inductor in range of 1uH to 2.2uH and then you have more flexibility when considering DCR and saturation current requirement of the inductor. A lower DCR inductor will result in better efficiency.

    You can also start by referencing the inductor used on our BQ25628EVM board. I have linked the user guide, which includes BOM for the board below. 

    https://www.ti.com/lit/ug/sluucq9/sluucq9.pdf 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 60 points

    Amazing, so super helpful. Thank you so much!