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Original question:

BQ24780S: Charge current of BQ24780S

BQ24780S: BQ24780S charging a few minutes charging current reduce.

Star Xu
Genius 9645 points
Part Number: BQ24780S

Hi

The customer design with BQ24780S. When charging in low battery voltage mode, the current of CC mode is set to 3A, but after the charging continues for a while, the current will be reduced to about 1.8A. At this time, the battery power is still very low. 

Attached the log data.

Why the charging current will reduce in CC mode？

Thanks

Star

  • 0
    TI__Genius 11385 points

    Hi Star,

    Can you send the register values before this occurred and after this occurred? What is the VIN voltage and SYS load at this time?

    One possibility is that the SYS load suddenly increased, so the charger reduce the charge current in order to provide power to the system. The input current limit can be increased to help with this situation. Note that the input current limit is limited by the lower of the input current register and ILIM pin. User can also disable the external current limit using the "EN_EXTILIM" pin.

    Meanwhile, please let me know if you see the same problem on the EVM.

    https://www.ti.com/tool/BQ24780SEVM-583 

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    TI__Genius 9645 points

    Hi Peng

    Thanks for your reply.

    the register value as below.

    vin =20V, under the WINDOWS system, and it is in no-load state.

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Genius 11385 points

    Hi Star,

    Are you sure this is the register list when it is charging at 1.8A? I put the values in and I see this:



    I would recommend the following:

    1. Isolate charger from rest of the system (isolate VSYS). Set "EN_EXTILIM" to 0. Use a benchtop power supply instead of an adaptor.
    2. Compare schematic to EVM.
    3. Pay attention to VBAT, IBAT, VBUS, IBUS when this is happening.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    Prodigy 220 points

    This is the initialization setting and assignment of the internal register of BQ24780S according to the EC of the paired battery. The paired battery is three batteries of 6300mAH.

  • 0 in reply to Verna Hong
    TI__Genius 11385 points

    Hi Verna,

    If there is an issue, you need to isolate in order to find out the root cause.

    I would recommend the following:

    1. Isolate charger from rest of the system (isolate VSYS). Set "EN_EXTILIM" to 0. Use a benchtop power supply instead of an adaptor.
    2. Compare schematic to EVM. 
    3. Pay attention to VBAT, IBAT, VBUS, IBUS when this is happening.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    TI__Genius 11385 points

    Hi Verna,

    Another thing to try is to see what the actual voltage at SRN pin is when the charge current is dropping. The charger uses SRN to sense battery voltage. Your input current limit looks ok (20@4A) but I would double check that as well.

    My previous comments and recommendations still apply. Isolate to debug is the best option.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    Prodigy 220 points

    What is the maximum resistance of SRP and SPN in series?

    Replacing these two 10ohm resistors with 100ohm can solve the previous problem of abnormal charging current.

  • 0 in reply to Verna Hong
    TI__Genius 11385 points

    Hi Verna,

    Those are just used for RC filters. 10 ohms and 100 ohms should not make a difference. Is it possible that the resistors are damaged? Can they try a bigger (such as 0201 to 0402), higher power/surge rated, 10 ohm package?

    Thanks,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory