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TPS65218: something wrong with DCDC5 channel of TPS65218

user4999129
Intellectual 550 points
Part Number: TPS65218
Other Parts Discussed in Thread: AM4378,

Hi, everyone:

I power am4378 by TPS65218, But its DCDC5 output is 4.72V which cause the RTC don' t work. I wonder why this may happen? 

My board has already work properly for about 1 mouth. This problem occurs last week.

  • 0
    TI__Mastermind 30260 points

    Can you provide a screen shot from an oscilloscope showing the issue occurring?

    Do you have a schematic you can share?

  • 0 in reply to Brian Berner
    Intellectual 550 points

    Hi, Brian:

    I designed my TPS65218 reference to GPEVM of am4378. Here is the DCDC5 part :

    The waveform of the DCDC5 channel is as below:

  • 0 in reply to user4999129
    TI__Mastermind 30260 points
    Please share the full orderable part # of the TPS65218 device that is assembled on your PCB.
    It should be TPS65218B1, TPS65218B101, or TPS65218D1 and end in lettering to designate the package type.
  • 0 in reply to Brian Berner
    Intellectual 550 points

    Hi, Brian:

     It is the TPS65218B1RSLR which we use in our board

  • 0 in reply to user4999129
    TI__Mastermind 30260 points

    If these PCBs have been working for a month and suddenly began to exhibit this behavior, my guess is you have had an EOS (electrical over-stress) event on the IN_BU pin.

    An EOS event can commonly result in FETs that are damaged and are permanently shorted (closed circuit). This would mean the VDCDC5 = VIN_BU and DCDC5 would be stuck in 100% duty cycle. In other words, it is no longer switching. EOS can also result in FETs that are also permanently open circuit, but it depends on many factors.

    Notice in the Absolute Maximum Ratings table on page 9 that IN_BU has a Max of 5.8V while all other IN_xxx pins have a Max of 7V.

    To prove this theory, you will need to monitor the main input power rail to your system when it first turns on and see if there is any overshoot beyond the expected value of approximately 5V.

  • 0 in reply to Brian Berner
    TI__Mastermind 30260 points
    When DCDC5 is damaged and outputting 4.72V, what are the voltages on DCDC6 and SYS_BU?

    This EOS event could have happened upstream at the IN_BU input load switch or downstream only for the DCDC5 converter, but if DCDC6 and SYS_BU are also providing a strange output voltage then it would mean the damage first occurred upstream and propagated down.