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BQ24765: Trickle charging of deep discharged battery

Thomas CN1
Intellectual 300 points
Part Number: BQ24765

Is the trickle charging by BQ24765 gets enabled automatically when a battery detected with less than 2.5V on FB pin or is there any other enable procedure has to be done? We are using BQ24765 in our design and the deep discharged battery charging back is not happening automatically.

  • 0
    TI__Expert 4780 points

    Hi Thomas,

    There is no special enable setting for trickle charging specifically. If the requirements to conditions to enable charging are met (listed below) then charging is enabled. Trickle charging at 220mA is enabled when the VFB voltage is <2.5V.

    The following conditions must be valid before charging is enabled:

    • Not in UVLO (DCINA > 4.5 V, and VDDSMB > 2.5 V)
    • Adapter is detected (ACIN > 2.4 V)
    • Adapter – Battery voltage is higher than V(DCINA-VFB) Comparator threshold
    • SMBus ChargeVoltage(),ChargeCurrent(), and InputCurrent() DAC registers are inside the valid range
    • CE is HIGH
    • 2 ms delay is complete after adapter detected and CE goes high
    • VDDP and VREF are valid
    • Not in Thermal Shutdown (TSHUT)

    Thank you and hope this helps,

    Khalid

  • 0 in reply to Khalid Bairuti
    Intellectual 300 points

    Hi Khalid,

    Thanks for the reply.

    Regarding the point:

    • SMBus ChargeVoltage(),ChargeCurrent(), and InputCurrent() DAC registers are inside the valid range

    We are trying to set the ChargeCurrent() value to 128mA when there is a deep discharged battery present. Is that a valid settings and will BQ24765 automatically start trickle charging with  220mA if the set value by us is 128mA?

    Regards,

    Thomas CN

  • 0 in reply to Thomas CN1
    TI__Expert 4780 points

    Hi Thomas,

    The datasheet indicates that the device reduces the charge current limit to 220mA if the VFB pin falls below 2.5V. This indicates that if the charge current is set to 128mA then it should charge at 128mA, since it is below that current limit.

    Thanks,
    Khalid

  • 0 in reply to Khalid Bairuti
    Intellectual 300 points

    Hi Khalid,

    Thanks for the clarification.

    We had some issues with the voltage and current settings registers and fixed it. Now we are able to get the charger enabled. But now what we see is a different behavior. Once the charger is enabled with constant 128mA charge current. The charger output initially goes to the set 12V and then see a ramp down as the battery is deep discharged. Then once the battery voltage falls below 3.6V, the charger get disabled. This is understood as the battery short protection method explained in the data sheet. But the charger doesn't get enabled after the 2mS time mentioned in data sheet. The charger remains disabled thereafter. Can you please give any suggestion to the possible cause for this behavior? 

    Regards,

    Thomas CN

  • 0 in reply to Thomas CN1
    TI__Expert 4780 points

    Hi Thomas,

    As you mentioned upon BAT_LOWV detection (<3.6V) the charger should stop for 2ms, and then soft start again.

    The soft-start typically has 10ms rise time. If you are not seeing charging start again after a few ms, I would suggest to re-check the required charging conditions after BAT_LOWV is detected to make sure the requirements for charging are all met.

    Specifically I would check to make sure that ChargeVoltage() and ChargeCurrent() remain set, since these will get cleared during a reset condition. Note, they are not supposed to be cleared with just a LOWV condition.

    Thanks,

    Khalid

  • 0 in reply to Khalid Bairuti
    Intellectual 300 points

    Hi Khalid,

    Thanks for the reply. We found some other issues with the register setting operation and could get it fixed and enable the charging for deep discharged batteries.

    But the charge current during trickle charging get set to 220mA irrespective of what we set as 128mA. Can you please reconfirm on this? Whether  the charger takes the lowest value (128mA) or it takes 220mA by default, the charge current mentioned in data sheet for trickle charging?

    Regards,

    Thomas CN

  • 0 in reply to Thomas CN1
    TI__Mastermind 25065 points

    Today is a US holiday, please check it back after Tuesday. 

  • 0 in reply to Thomas CN1
    TI__Expert 4780 points

    Hi Thomas, 

    As this device is quite old we don't have much support for it. I will check this behavior locally and get back to you. It will likely take a few days.

    Thanks,

    Khalid

  • 0 in reply to Khalid Bairuti
    Intellectual 300 points

    Hi Khalid,

    Can you please further update on this?

    Regards,

    Thomas CN

  • 0 in reply to Thomas CN1
    TI__Expert 4780 points

    Hi Thomas,

    As this device is quite old I did not have an EVM here to reproduce the behavior on. I have ordered one and I will have it soon. I can confirm the behavior by this Thursday.

    Khalid

  • 0 in reply to Khalid Bairuti
    TI__Expert 4780 points

    Thomas,

    I confirmed the behavior you saw on my setup. If the charge current is set to 128mA, if VFB > 2.5V then the charge current will be 128mA, however, if it falls below 2.5V then the trickle charging of 220mA will override the ChargeCurrent set to 128mA.

    Thanks,

    Khalid