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BQ24100: Part fails to charge after 3 months in the field

Tim Christensen
Prodigy 90 points
Part Number: BQ24100

I am having field returns with BQ24100 after several month in the field.   The part fails to charge a battery and draws around 10mA in this state.   I want to rule out or in the manufacturing soldering process.   In the spec sheet it states: 

There is an internal electrical connection between the exposed thermal

Exposed pad and VSS. The exposed thermal pad must be connected to the same potential as the VSS pin on the printed circuit board. VSS pin must be connected to ground at all times.

I would like to know if the solder connection to the ground pad is good but the connection to VSS is intermittent,   would this cause the part to fail such that it doesn't charge and draws a continuous burden current less than 10mA.

thank you

  • 0
    TI__Guru**** 166136 points
    Hello Tim,

    Having the pad and VSS at different potentials is something that we have never tested. It is my understanding that the solder pad connects to the die substrate which is somewhat resistively connected to ground. If the external components are ground to VSS and not the pad then I would expect normal operation and not 10mA current to ground. Do you have the resources to order one of our EVMs and then replace its IC with one of your field return ICs? That would quickly determine if the IC is failing.
  • 0 in reply to Jeff F
    Prodigy 90 points

    Thank you for the quick reply.    On the circuit board it is wired to have pin 10 VSS connected to the Thermal Pad thru a large ground plane.   I have a visual indication that the VSS pin is not getting properly soldered to the board and therefore it may intermittent or fail open to the rest of the circuit.    It that happens will the internal connection to the Thermal Pad continue to work properly handling the VSS currents or would the IC fail because the VSS pin was not soldered.    I have removed parts from problem boards and using an ohm meter I read over 40Mohm.    But I also see this on a good IC.   

  • 0 in reply to Tim Christensen
    Prodigy 90 points

    Hello TI,

              Our failure return rate has reached a critical level.    I would like to return 3 chips (or quantity you need) to perform a failure analysis to help us get to root cause.   Can you please direct me to how I can send units to you and open a failure analysis project??

    thanks you

  • 0 in reply to Tim Christensen
    TI__Guru**** 166136 points
    Hi Tim,

    How did you purchase the ICs? From TI directly or through a distributor?
  • 0 in reply to Jeff F
    Prodigy 90 points
    Our contract manufacturer. Do we need to go thru them and a distributor. I really need a short cut to a solution
  • 0 in reply to Tim Christensen
    TI__Guru**** 166136 points
    Tim,

    Unfortunately, you have to return through the distributor. By the way, I confirmed with my design manager that leaving the pad unconnected would cause the charger to run hotter but it has thermal shutdown protection. Do you know if the return parts were power cycling into and out of thermal shutdown? If not, the charger could be running just below the shutdown temperature threshold, which could accelerate lifetime/aging effects.

    Regards,
    Jeff
  • 0 in reply to Jeff F
    Prodigy 90 points
    Jeff. the pad is connected to ground, PGND is also connect to the pad. I do not believe that there was enough solder on pin 10 VSS and this pin was left floating. Therefore the only way pin 10 would be electrically in the circuit would be thru the electrical connection described in the spec sheet to thermal pad. So if all pin are soldered correctly including the thermal pad with is at ground potential and PGND pins, would the IC be damaged at 5V input, 1.7Amp max current if "Only Pin 10 is floating because there is no solder" please reply
  • 0 in reply to Tim Christensen
    Prodigy 90 points
    Hi Jeff, I have just complete some analysis on 8 failures and this is what I found on these devices that will not charge after weeks to months in the field. PG line flips correctly depending on input voltage. STAT1 and STAT2 are both off indicating a fault. CE is at ground potential. VTSB is approximately 3.1 volts and all 8 devices connected to 5V input and charging set for 1.7Amp max. For some reason the TS pin is forcing the input voltage to be from 0.3V to 0.9V which is too low to initiate charge. On a good board the voltage divider and battery thermistor holds this line to 1.6 volts


    When I apply an external voltage to the TS pin thru a 220 ohm resistor to limit current, I can pull the TS line above 1.1 volts and charging works again. As soon as I remove this external voltage the chip stops charge. Please note my VTSB voltage divider is 9.31K over 442K just like the spec sheet recommends and my battery has a 10K thermistor. Even with battery removed this line is held low by the TS pin. also a 100nF cap to VTSB per spec sheet.


    Also the TS pin sinks 1 to 30mA from the external source to pull this pin up to the necessary level for charging. Why would the TS pin fail and appear to have a path of current sinking causing this analog input to pull low?????????????????
  • 0 in reply to Tim Christensen
    TI__Guru**** 166136 points
    Tim,

    Great job debugging! I communicated this to my design and quality teams. Please work with your distributor to return the ICs to TI for failure analysis.

    Regards,
    Jeff
  • 0 in reply to Jeff F
    TI__Guru**** 166136 points
    Tim,

    Any luck getting those damaged ICs return through the distributor?

    Regards,
    Jeff
  • 0 in reply to Jeff F
    Prodigy 90 points

    Hello Jeff,    we are working with the board population contractor to send to their distributor.   I will provide an RMA# or some type of tracking number once parts are in distributors hands.   thank you

  • 0 in reply to Tim Christensen
    TI__Genius 10240 points
    Tim,

    The process will be handled by the quality team and our team and communicate through different channel including distributors. We would like to close this thread on the forum.
  • 0 in reply to Jeff F
    Prodigy 90 points

    We are preparing the paper work today.     Do you have any thoughts on why the TS pin on this BQ24100 part would get damaged in the circuit after weeks to months in the field.  There is nothing connected to this pin that the end user can touch since the board with the BQ and battery is in a metal box

  • 0 in reply to Tim Christensen
    TI__Guru**** 166136 points
    Tim,

    I will try to get priority for this failure analysis once we receive the units. I have asked design and our quality team for possible root cause but they are at a loss, unless the floating thermal pad resulted in device overheating and accelerated aging. Hopefully the failure analysis will show us what has failed.

    Thank you for your patience.

    Regards,
    Jeff