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BQ27520-G4: Behavior When Charging is Stopped

Ryan.Bishop
Expert 3900 points
Part Number: BQ27520-G4

Hello,

It is my understanding that there are two steps:
Step 1: If voltage is greater than charge voltage – taper voltage, then it goes to the next step 2.
Step 2: If current is less than taper current, then charge is completed.

The settings in the fuel gauge are charge voltage = 4.3V, taper voltage = 0.13V, and taper current = 300mA.  The steps become:
Step 1. If voltage > 4.17V, then it goes to step 2
Step 2.If current < 300mA, then charge is completed

Can you help comment on the following scenarios?

  1. When charging stops, there is a voltage drop after the current goes to zero . If the voltage drops from greater that 4.17V to less than 4.17V, does the logic still continue to the next step?
  2. If charging is stopped before 300mA is reached, and assuming step 1 condition is met, is step 2 satisfied because the current goes to zero when stopped?

Thank you,
Ryan B.

  • 0
    TI__Guru* 76230 points
    1. I don't see how that would happen, but if it does the logic will not continue to the next step.
    2. No. There is usually an accumulated passed charge condition attached as well.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    TI__Expert 3900 points

    Hi Onyx,

    Thanks for the reply. Is my understanding correct: In order for the FC(Fully Charged) bit to be set, all three conditions must be met before the charger stops delivering charge. 1) Voltage is greater than its threshold 2) Current is less than its threshold 3)Accumulated charge is greater than its threshold.

    I see those conditions on page 42 of the TRM. Is there anyway the accumulated charge threshold can be set above 0? How is it possible for the accumulated charge to ever NOT be > 0?

    Thank you!

    Ryan B.

  • 0 in reply to Ryan.Bishop
    TI__Guru* 76230 points
    Hi Ryan,
    like in the case where instead of the current tapering, it drops to 0 right away. In that case, you will not have accumulated passed charge. In some of our gauges, that number is not "0", but rather "25mAh" just to make sure you actually have some passed accumulated charge and not the charger turning off , cutting the current to 0 and fooling the gauge making it think it is fully charged..

    thanks
    Onyx