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Original question:

BQ25120: BQ25120

BQ25120A: BQ25120A PCM Lock

sebastian
Prodigy 95 points
Part Number: BQ25120A

Hello,

Although mentioned in a previous thread that the BQ25120A was going to solve the issue of not charging a battery when the PCM has locked it out, we find that the problem still exists.

We are using the BQ25120A for charging a 3.7V Li battery. When the battery is first inserted, the PCM goes into overdischarge protection mode and essentially cuts off the discharge FET.

Upon application of 5V from USB, we found that the BQ25120A will not charge the battery. Removing the USB 5V and re-applying, the BQ25120A starts charging the battery and the PCM is unlocked. 

Are there any guidelines on this issue?

Thank you.

  • 0
    TI__Mastermind 21590 points

    Hello,

    Can you show a scope capture of VIN and VBAT when this happens.

  • 0 in reply to Raheem
    Prodigy 95 points

    Hello Raheem,

    Thanks for your quick reply.

    Please check below:

    Blue is Vbat with respect to USB GND (i.e after the PCM)

    Yellow is Vin (USB 5V) with respect to USB GND.

    Also, if this helps, in this condition, the VPMID is about 520mV which looks like as if the power management path is not completely open to Vin.

    Please let me know of your thoughts.

    Thank you.

  • 0 in reply to sebastian
    TI__Mastermind 21590 points

    Hello,

    Can you check that the device is properly soldered. PMID should be close to VIN as long as VIN is within the operation range.

  • 0 in reply to Raheem
    Prodigy 95 points

    Hello Raheem,

    Thanks for coming back. 

    As you know, the package is a BGA. It is not easy to check the soldering, however, I don't think the problem is related to soldering. 

    I am saying this because 100% of the tested boards present exactly the same bahaviour. 

    Also, the BQ25120A indeed, unlocks the PCB and charges the battery on the second application of USB voltage. If it was a soldering issue, I guess it would not have been possible to unlock the PCM at all.

    Any other suggestions?

  • 0 in reply to sebastian
    TI__Mastermind 21590 points

    Hello,

    Can you please post your schematic.

  • 0 in reply to Raheem
    Prodigy 95 points

    Hello Raheem,

    Please send me a company email address where I can send you the schematic.

    Thanks.

  • 0 in reply to sebastian
    TI__Mastermind 21590 points

    Hello Sebastian,

    I took a look at your schematic. I noticed you have TS connected to PMID, this is not correct. TS should be connected to a voltage divider which is pulled up to VIN. Can you please share a scope capture showing VIN, VBAT and PMID.

    I'm curious as to why PMID is 520mV and VBAT is 2V when VBAT is supplied by PMID.

  • 0 in reply to Raheem
    Prodigy 95 points

    Hello Raheem,

    Thanks for coming back. 

    You are indeed correct. TS is connected to PMID. We misinterpreted the way you can disable TS and connected to PMID without any pull up resistor or divider. 

    I am not sure if this is the problem however. I need to test connecting TS to Vin. 

    At the moment I don't have a 3 channel scope to show you Vin,Vbat and PMID at the same time. 

    I will correct the error on the next revision of our PCB and check if it resolves the problem. 

    Is there anything else I can send you in terms of captures that may help?

    Thank you.

  • 0 in reply to sebastian
    TI__Mastermind 21590 points

    Hello Sebastian,

    I don't expect to see 2V on PMID when 5V is on input. Did you see this in multiple units? The PCM would not affect the PMID voltage when VIN is present.

  • 0 in reply to Raheem
    TI__Mastermind 21590 points

    Hello,

    Any updates here?

  • 0 in reply to Raheem
    Prodigy 95 points

    Hello Raheem and Happy New Year,

    I have nothing new to report on this. Indeed our tests show that the problem is the same for all the units that we tested. 

    The problem may be related to us connecting the TS to PMID instead of Vin but it is not possible to change it without a new board re-spin.

    We plan to re-spin the board within the next couple of months so we will correct it. 

    If you need to close the thread, do so and I will re-open it when I have the new boards. Otherwise let's leave the thread open and I will update in a couple of moths. 

    Thank you for your help.

    Best regards