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TPS6507x burned due to short-circuit

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Noah Harris
Posted by
on Apr 22 2012 12:18 PM
Intellectual360 points
Hi,
We have a board which is supplied by a TPS65070 PMU and the PMU has been working reliably for all of outputs. Today after doing a solder work however, I forgot to take the solder wire off the table before plugging in DC 5V power to the power. In a pretty dramatic fashion the board smoked and it took me over 15 seconds to react and turn off the power due to surprise.
After I turned off the power, took away the solder wire and turned on the power again, oscilloscope show that the SYS pin of TPS65070 is outputting straight something close to the input 5V, approximate 4.7~4.9V, rather than the normal 3.7V around which I previously for many times recorded.
As the datasheet suggests that the SYS pin is “System voltage; output of the power path manager. All voltage regulators are typically powered from this output.” Does the 4.8V output indicate that the power path manager has been damaged?
I also measured the voltages of VDCDC1, VDCDC2, VDCDC3, VLDO1 and VLDO2, and all of them give nearly 0V output.
So in this case, is it possible that the damage is only locally on the TPS65070? Circuit theory suggest that current always take the path of lowest resistance, and since CPUs and other ICs all have non-zero resistance, it looks unlikely that current would prefer the path through them, thus chances are that they remain intact despite the burning of PMU. Would this very fortunate result be possible?
 
Noah
TPS6507x power-path manager short-circuit
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  • Daniel Acevedo
    Posted by
    on Apr 23 2012 12:28 PM
    Verified Answer
    Verified by
    Genius16920 points

    If you are seeing different behavior before and after your incident, the board is likely damaged and should be replaced; including the TPS65070. Smoke is probably a bad sign.

    The voltage at SYS is the output of the power path and its value depends on voltage at VAC, VUSB, VBAT and on charge status among other factors.

    If a piece of solder wire shorted a number of contacts on the board, excess current could have passed through (in or out of) sensitive circuitry, damaging the device.

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  • Noah Harris
    Posted by
    on Apr 24 2012 07:33 AM
    Intellectual360 points

    We have fixed the board by replacing the TPS65070 part, all other parts seem to be intact and are functional as before. Thank you for your advices.

     

    Noah

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