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BQ24195L: PMID is not being stable at 5.1 V

Elie Wakim
Prodigy 120 points
Part Number: BQ24195L

Hey ,

we tried to used bq24195L in our project, and it is working properly.

However, we wanted to changed our design by adding a coulomb counter, so we faced a major problem with the Boost mode provided by the BQ24195L:

we made sure that all the necessary conditions are true to set the boost mode ( OTG pin , Vbat > Vbat low , and REG01[5:4] = 10 and the watchdog timer is disabled)

so in the last project we were working on, the PMID voltage was stabilized at 5.1 V regardless of the current consumption ( max 1 A ) , but in the new one , the PMID is generating 5.1 V when there is no load and the voltage starts to drop progressively ( from 5.1 V to 4.6 V ) wen the current drained by PMID starts to increase ( Max 1 A ) .

I will be glad to know what could possibly affect the regulation of the PMID voltage, because we don t have enough details in your datasheet to see how the boost mode regulation is made.

I will be waiting forward for your answer

Thank you in advance.

Elie Wakim

  • 0
    TI__Genius 10385 points

    Elie,

    Let me clarify that the boost mode was operating properly with the same setup before you added the coulomb counter and once the coulomb counter was added the boost mode was not operating properly, correct?

    Also, could you please send me more details about the coulomb counter schematic and how you are measuring from it? Are you measuring VBAT at the pin?

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 120 points

    Hey  Ricardo,

    First of all i would like to thank you for your support services.

    Let me explain in details about the issue we are facing in the new project knowing that the old one is working properly.

    Here is the schematic of the Coulomb Counter that we are using in the NEW project. We have shorted Rcg the shunt resistor to make sure we have the same reference ground all over the board just for troubleshooting purposes (the problem remains the same) :

    The Best way to diagnosis is to compare the OLD project (in which PMID is stable at 5.1 V regardless of the current consumption) to the NEW one (PMID is Dropping down).

    Result of the functional (OLD) project:

    CASE

    V PMID

    I PMID

    V BAT

    A

    5.1 V

    0 A

    3.3 V < V BAT < 4.2 V

    B

    5.1 V

    1 A

    3.3 V < V BAT < 4.2 V

    Result of the NEW project:

    CASE

    V PMID

    I PMID

    V BAT

    A

    5.1 V

    0 A

    3.3 V < V BAT < 4.2 V

    B

    4.75 V

    0.73 A

    3.3 V < V BAT < 4.2 V

    We have mounted the same components in both projects, based on the application note of TI. I think that the control of the boost converter that adjusts the duty cycle (or any other parameter ) of its dedicated MOSFET in order to provide a stable output (V PMID = 5.1 V) regardless of its drained current (0 < I < 1 A) is not working properly.

    We will be glad to get an answer or a proposition to solve this unpredicted issue.

    Thank you again.

    Elie Wakim

  • 0 in reply to Elie Wakim
    TI__Guru**** 166996 points

    Hi Elie,

    In boost mode, the LSFET cycle-by-cycle current limit (IOTG_ILIM) is 2.76 A min and 3.8 A typical.  If the charger is hitting the cycle-by-cycle current limit, the duty cycle will be clamped and the output will droop. Just to confirm, you are using the same inductor in the new project as the old?  Do you have a method to measure the inductor current?   If the inductor is saturating, the current will spike and hit IOTG_ILIM.

    Regards,

    Jeff

     

  • 0 in reply to Jeff F
    TI__Guru**** 166996 points

    Hi Elie,

    I haven't heard back from you so I am going to assume your issue is resolved and close this thread.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 120 points

    hey jeff,

    I am sorry i did not answer you bcak because i had some complications and could not try your suggested precedure.

    Please keep this case on hold, i will get back to you and update you as soon as I start tweaking on my project.

    Thank you for your comprehension.

    Elie Wakim

  • 0 in reply to Elie Wakim
    TI__Genius 10385 points

    Elie,

    Do you have any updates on this issue? If not, I am going to assume it has been resolved and close the thread.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 120 points

    hello,

    Riccardo i think the batch was damaged, because in the latest version (newest one) we did not face this problem.

    Thank you