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BQ25616: Package Impedance and Charging Time

Ryoma Miyazawa
Prodigy 115 points
Part Number: BQ25616

Tool/software:

Hello expert, 

Let me confirm the relationship between package impedance and charging time.

When two types of batteries with the same cell but different package impedance were charged using BQ25616, 
the higher the internal resistance, the shorter the time until switching to constant voltage (CV) charging, 
and the longer it took to complete charging.

Could you explain this phenomenon as follows?

Hereafter, the one with the higher impedance will be referred to as A, and the other as B.
・Note1: A:200 mΩ / B:160 mΩ
・Note2: the cells are the same, but the protection circuits and cable diameters differ.
・Note3: Full charge: 4.1 V


(1) Regarding the time until switching to CV charging
      Can the following diagram explain why "A" switches to CV charging earlier than "B"?


(2) Regarding the time until charging is complete
      Can the following diagram explain why "A" takes longer to complete charging than "B"?



Regards, 
Ryoma

  • 0
    TI__Mastermind 40635 points

    Hi Ryoma,

    When the device switches from CC to CV, the BAT pin is currently at regulation. With a higher cell impedance with the same charge current, the higher impedance cell will enter CV at a lower cell voltage. As it is a lower cell voltage, it takes longer in CV to fully charge it to regulation.

    Regards,

    Mike Emanuel