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Original question:

BQ25820: Input voltage is getting stuck when AC is removed

BQ25820: Follow-up on Previous Power Stuck Issue

Tung Nguyen
Prodigy 35 points
Part Number: BQ25820


Hi Christian Moyer,

Apologize for getting this late response to your suggestion related to previous issue due to other work priorities were taken over.

For an update:

  1. I replaced the input MOSFETs with your suggested part, AON6276 Alpha & Omega Semiconductor Inc. | Discrete Semiconductor Products | DigiKey , but the issue still exists --> Make sense since I'm also seeing it on EVM board which has these MOSFETs
  2. I removed one of the three input 47uF capacitors, issue still exists; the same result when repeating the same for output capacitors
  3. I retried again changing the UVLO resistors setting to increase limit to 33V and observed the Gate voltage got increased to ~35V (as described in original post); hence, the issue still exists

I remember you mentioned that you're trying to replicate this issue in your lab. Just wondering how it went.

Also, I'm looking forward to any other suggestions to try now. This has become a serious issue when the prototype unit stays ON when AC is removed but it should not.

Best Regards,

Tung.

  • 0
    TI__Mastermind 34381 points

    Hello Tung,

    Have you tried enabling EN_IAC_LOAD=1, wih the new fets?

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 35 points

    Hello Christian,

    FYI, enabling EN_IAC_LOAD=1 does not solve the issue. 

    Best Regards,

    Tung.

  • +1 in reply to Tung Nguyen
    TI__Mastermind 34381 points

    Hello Tung,

    Tung Nguyen said:
    I remember you mentioned that you're trying to replicate this issue in your lab. Just wondering how it went.

    I have not been able to replicate it in the lab. You mentioned that you were able to see it on the EVM? What were you exact test conditions? Did you make any changes to the EVM?

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    TI__Mastermind 34381 points

    Hello Tung,

    Can you try these options:

    • Lower the VAC_DPM/ACUV threshold below the battery voltage?
    • Is this application for a sink/source or just sink? If it is just a sink, the ACFETS can be replace with a schottky diode.
  • 0 in reply to Christian Moyer
    Prodigy 35 points

    Hi Christian,

    First of all, I'm sorry but I accidentally clicked "This resolved my issue" when I meant to reply to your question. Not sure how to remove that yet.

    About the EVM, I tried to replicate the same conditions as my design circuit since they are similar, which were:

    • VIN went to external DC supply with 36V
    • VOUTs went to my actual battery through a custom cable
    • For ICHG, JP3 is placed to remove charge current limit
    • Nothing else was modified on the EVM board

    The issue occurred only when I turned off DC supply while battery is in middle of charging cycle. The only difference I observed when on EVM board that the "stuck" voltage appeared to be the same as battery voltage.

  • 0 in reply to Christian Moyer
    Prodigy 35 points

    Christian,

    I'll try lowering the ACUV threshold in the lab today and let you know the result. However, it's not ideal because doing that equals to battery won't be fully charged.

    Can you elaborate more of what you meant by a sink/source? Also, do you have a recommendation for a Schottky diode that have been tested before with this EVM?

    Best Regards,

    Tung.

  • 0 in reply to Tung Nguyen
    TI__Mastermind 34381 points

    Hello Tung,

    Tung Nguyen said:
    Can you elaborate more of what you meant by a sink/source?

    Are you using the BQ25820 to only charge the battery, or will you also have a load on the VAC side? Will you use the reverse mode feature? If you do not need reverse mode, you can replace the ACFETS with a Schottky, to prevent the VBUS from being held up when adapter is removed.

    Tung Nguyen said:
    I'll try lowering the ACUV threshold in the lab today and let you know the result. However, it's not ideal because doing that equals to battery won't be fully charged.

    As long as the the adapter voltage is higher than the battery voltage, it should reach the max charge voltage..

    Tung Nguyen said:
    Also, do you have a recommendation for a Schottky diode that have been tested before with this EVM?

    I don't have a specific schottky recommendation, but if you find one that you think is suitable. I can confirm if it will work.

    Best Regards,

    christian

  • 0 in reply to Christian Moyer
    Prodigy 35 points

    Hi Christian,

    Currently I'm using the BQ25820 to only charge the battery while I have a separate circuit for battery to power a load with an external switch being turned ON. The issue exists without a load, meaning I just want to charge the battery.

    Lowering ACUV threshold to 28V and 24.5V did not resolve it. I measured that gate voltage was ~30.5V and ~27V respectively.

    Since max charge current for my application is 6A, I'm looking at this Schottky diode that might be suitable. Can you confirm?
    SK810L-TP MCC (Micro Commercial Components) | Discrete Semiconductor Products | DigiKey

    Best Regards,
    Tung.

  • 0 in reply to Tung Nguyen
    TI__Mastermind 34381 points

    Hello Tung,

    Tung Nguyen said:
    Since max charge current for my application is 6A, I'm looking at this Schottky diode that might be suitable. Can you confirm?
    SK810L-TP MCC (Micro Commercial Components) | Discrete Semiconductor Products | DigiKey

    I don't see any obvious issues with this diode.

    Best Regards,

    Christian.