• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 471 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25155: TS pin accidentally left floating instead of GND when we don't plan to use it

Lukas Brchl
Prodigy 90 points

Part Number: BQ25155

Hi,

in the latest revision of our product, we accidentally left TS pin floating and the battery management started to behave strangely. When no battery is inserted and we plug in USB to power up the VIN, the MR pin quickly goes up and then falls to the low, which means that the device won't boot because it is in the reset state. However, when we plug in the battery and USB, everything works as expected. All power rails all good no matter if the battery is inserted or not.

The MR pin is weird only without the battery and we hadn't this trouble in the last revision where we had the TS pin grounded. I suppose that the TS pin needs to be grounded to be able to operate the BQ25155 without a battery. Could you please confirm this information?

Best regards,

Lukas

  • 0
    TI__Mastermind 21590 points

    Hello,

    The /MR pin is pulled up to VBAT and since the battery is absent, you'll see the capacitor on battery pin get charged and discharged. This will also be seen on /MR. The VDD and PMID pins should be powered when on VIN plugin only. 

  • 0 in reply to Raheem
    Prodigy 90 points

    Hi,

    > The /MR pin is pulled up to VBAT and since the battery is absent, you'll see the capacitor on battery pin get charged and discharged

    Yeah, this is the expected behavior we saw on our previous revisions. The /MR was oscillating between 1.5 and 4.2 V. 

    But we have now new revision, where we forget to ground the TS pin, and when the battery is removed the /MR is permanently pulled low (not oscillating). Could you please confirm this could be caused by TS pin grounded? 

    Thanks,

    Lukas

  • 0 in reply to Lukas Brchl
    TI__Mastermind 21590 points

    Hello,

    Can you share your schematic? What is VDD and PMID voltage when you have only VIN present? 

    If you can write to the registers, can you try disabling the TS function and see if the behavior changes?

  • 0 in reply to Raheem
    TI__Mastermind 21590 points

    Hello,

    Any updates here?

  • 0 in reply to Raheem
    Prodigy 90 points

    Hi Sharafadeen,

    Sorry for the late reply, but for some reason I didn't receive any notification about your comments.

    TS function was disabled in the registers, but it had no impact. However, we solved the issue by making a new hardware revision where we added a 5k resistor from TS to ground. Nothing else changed. So the issue was caused by TS pin left floating. It would be nice if TI could specify in the datasheet to not leave the TS pin floating otherwise it will behave weird.

    Btw, could you please more elaborate on how to use the BQ25155 without battery? Is it possible to prevent the MR from voltage oscillating? 

    Best regards,

    Lukas

  • 0 in reply to Lukas Brchl
    TI__Mastermind 21590 points

    Hello,

    The BQ25155 reports a fault when TS is left open.

    One way to do is to disable charging. This will prevent the capacitor on the battery pin to stop getting charged and discharged.