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BQ25895EVM-664: IC burns down when 5V applied at Vbus in custom PCB design. Works fine on battery and able to communicate over I2C

Junaid Alam
Prodigy 40 points
Part Number: BQ25895

We initially developed our systems using BQ25895 evaluation kit and later on followed the reference design available in the data sheet for BQ25895 evaluation kit manual given at link given at the end (Page 18) to design custom PCB. Also, the picture of schematic for our custom PCB is attached. In the custom PCB, system works fine when powered by a 4V lithium-ion battery at Vbat. We get stable output voltage and are able to communicate with it through the host controller over the I2C. When PCB is powered from the Vbus at 5V through a type C connector, BQ25895 burns down and stops working. Even the BATFET. We have been debugging the issue but haven’t found anything different from the reference design. It simply burns down upon powering up the IC at Vbus with 5 volts. I hope to get some help in the regard. If you need any more details, I shall be providing them. Reference design link (Page 18): http://www.ti.com/lit/ug/sluuba2b/sluuba2b.pdf

Input current at Vbus is limited to 1A max.

Powering up at Vbus using a USB Type-C dedicated connector.

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  • 0
    TI__Guru**** 152796 points

    Hi Junaid,

    I assume in your debugging you removed all power and then measured the resistance of each charger non-GND pin to GND to confirm there are no solder shorts?  For example, the IC has several protection features against shorts to GND but if PMID is shorted to GND when VBUS is applied the IC could be damaged. 

    I don't see any obvious errors with the schematic; although, I have some questions:

    1. With OTG grounded, you can never enter OTG boost.  Therefore, there is no need for the external Schottky diode.

    2. With D+/D- floating, the charger defaults to an unknown adapter and set input current limit to 500mA.  I assume you are setting input current limit to 1A using I2C registers?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Guru**** 152796 points

    Hi Junaid,

    I haven't heard from you in a while. I am going to assume that you solved your issue and close this thread.  If you have more questions, you can reopen for a few more days but after that, you will need to post a new thread.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hello Jeff, really sorry for the late response we ran into some problems and were trying to sort them out before posting the response.

    1. Considering we are not using the OTG boost, do you recommend removing the Schottky diode? Could Schottky diode be causing any issues?

    2. Yes, we are controlling & limiting the current using I2C registers. Would that cause any issues?

     

    I tested all the non-GND pins with GND which were fine. There was no ground-shorts/solder-shorts.

    Also measured resistances physically if they are rightly placed. Came to know there were a few following mistakes during the manufacturing:

    • R92 (TS Pin) was valued at 30 OHM instead of 30.1K OHM
    • R94 (REGN Pin) was valued at 82 OHM instead of 5.23K OHM

    We ran a few tests again on our PCB with following changes being made:

    • Replaced the BQ25895 IC in one of our PCB (the one that got burned and stopped working completely) with a new IC. The circuit started working fine as it was working before on battery. We were getting back the right output voltage and were able to communicate with the BQ25895 over i2c.
    • Replaced the resistors (R92, R94) with correct values.
    • Almost isolated BQ25895 part of the circuit from rest of the circuit.
    • Made sure there are no solder-shorts in the IC non-ground pins.

    Connected the battery and it was working fine just like before.

    Then, applied 5V at Vbus via USB Type-C connector and it got damaged again instantly. Totally stopped working...

  • 0 in reply to Junaid Alam
    TI__Guru**** 152796 points

    Hi Junaid,

    If you power a known working board with a bench power supply instead of USB-C, does it work?  Is there a problem with the USB-C connector? USB-C should power up to provide only 5-V and 1.5A unless configured by host to provide otherwise.  This should not damage the part. 

    The Schottky diode is required to reach OTG output current of 3.1A.  I would not expect it to be an issue.

    The IC has redundant current limiting protection (ILIM pin, I2C register, cycle by cycle current limit). 

    In my experience, the only two faults that can cause similar failures are extreme over fault on VBUS or reverse voltage on VBUS.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hello Jeff, thanks for all your efforts but we are still stuck with the same issue.

    We reviewed the USB-C part (jack, connectors, cable etc) both physically and in the schematic as well. There are no problems there. Also we removed "L5" on Vbus to isolate type-C jack and checked input voltage on "TP2". It gives stable 5.1V approx at TP2. 

    About reverse voltage, that might be possible in the case of Vbat but should this be a concern at Vbus? 

    Also, we added ferrite bead inductors at Vbus and Vbatt in addition to the reference design given in BQ25895 EVM kit data sheet. Can they cause any issues?

    What do you suggest how do we proceed now literally everything seems to have been correct.

    Thanks again, regards,
    Junaid 

  • 0 in reply to Junaid Alam
    TI__Guru**** 152796 points

    Hi Junaid,

    Reverse voltage at VBUS is destructive to the charger.

    Ferrite beads should not be destructive to the charger.

    Can you identify the exact current path, i.e. from VBUS through the IC through inductor to SYS or is VBUS to ground? 

    Maybe try applying a small, current limited (500mA or less) voltage to VBUS and trace what voltages you see on the other pins?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hello Jeff, 

    We sent the damaged PCBs for IC replacements. Will run the above test you said and a few more once we get them back in a couple of days and will share with you the results ASAP.

    Hope to get the issue resolved and thankyou so much for your appreciated efforts.

    Regards,
    Junaid   

  • 0 in reply to Junaid Alam
    TI__Guru**** 152796 points

    HI Junaid,

    Any update on this?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Guru 51901 points

    Junaid,

    We haven’t heard back from you for a while, the thread is considered solved and closed.

    Thanks,

    Ning.