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TPS62135: Recreating a failure

TI_Lover
Prodigy 160 points
Part Number: TPS62135
Other Parts Discussed in Thread: TPS563200

Hello!

Thanks in advance for your help. A bit of an unorthodox question, but I need your help to break this chip! We have several boards coming back from the field with this IC burnt (some look okay, some burnt to a crisp, but all have SW shorted to ground internally) and I need to see how it can be recreated.

Some application background: Input is a 4-series cell Li-ion pack (we limit it to 12V-16.4V) and output is 12V to an outward facing barrel jack. We picked this IC for its 100% duty cycle (many others that advertise 100% duty require split power, Vin > PVin). Max load is 3.5A.

Since this IC has both over-current protection and thermal shutdown, there aren't many easy ways to recreate a failure such as this. Looking at the functional block diagram, it looks like current is measured using the Rds(on) of the high side and low side FETs.

  1. Is the only way to defeat both the OCP and thermal shutdown for one/both of the FETs to fail as shorts?
  2. If you wanted to recreate a thermal failure for this IC, what would you do? (Maybe apply an excessive voltage to the output?)

Let me know if you need any other info! 

  • 0
    TI__Guru**** 191445 points

    TI_L

    Generally that indicates LS FET shorted to ground.  When the high side FET is on, then an over voltage at VIN will cause EOS on the low side FET.  It may be tricky to get the timong right so the LSfFET is damaged and not the high side (or both).

  • 0 in reply to JohnTucker
    Prodigy 160 points

    Hi John,

    Thanks for your quick response and insight. 

    My first thought was since the output of the TPS62135 goes to a customer facing port that they are mistakenly putting a power source into it. However, after testing that, the voltage actually propagates back through the HS FET body diode, charges up the input bus, and caused a different IC on that bus to fail first (TPS563200, which has a lower Abs Max than the TPS62135).

    Anyways, I think I need to do more testing before I can come up with additional questions for you, so I will mark the thread closed in the mean time. 

    Regards,,