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UCD9240 temperature issues on start-up

EDGAR BROWN
Intellectual 450 points
Other Parts Discussed in Thread: UCD9240, PTD08A006W

We have a design with an UCD9240 and three single-phase power rails. We have found that after the system warms-up (UCD9240 case temperature with a thermocouple attached ~65°C) we get semi-random rail failures.

Some rails will come up, but at least one of the rails will fail to start. This shows a very strong temperature dependency, 0 failures below 55°C or so, ~ 50% failures around 65°C and ~100% failures around 70°C. We see multiple rail faults being logged, but looking at another system we notice that these might happen on start-up or shut down.

We are trying to debug the system, and we applied external heat to a separate, known-good UCD on a different system with four rails (the ones in the failing system have a known calibration issue). We started getting failures at ~75°C (unfortunately we seem to have damaged two PTD08A006W in the process, even though their logged internal temperatures never exceeded the indicated 80°C maximum).

According to the datasheet I should be able to approach or exceed 80°C without too much problem.

Is there something in the set-up that could be causing this problem? How can we avoid or recover from these rail failures?

 

  • 0
    Intellectual 450 points

    This problem is still happening. No responses from anyone at TI after 3 weeks?

    We are starting to consider removing these parts from our next design revision.

  • 0
    Intellectual 450 points

    After more testing and some board modifications we realized that the problem was not the UCD9240 but the PTD08A006W modules, the faults seemed to be _somewhat_ legitimate.

    Under hot conditions the module voltage might be transiently dipping below the minimum of 4.75V causing an apparent drive transistor over-current. The gate voltage might be reduced enough to cause an over-current detection problem on part of the on-cycle when we reach ~65°C on the module transistors, or there might be an internal glitch that crosses the fault threshold. This happens even though we have 22µF ceramic decoupling capacitors directly attached to the module pin,  we have multiple supply and GND planes, and more than 1000µF of low-ESR capacitance on the module proximity.

    In our system, we are using 5V input voltage, and relatively few elements that depend on this voltage being exact, we solved the problem by increasing this voltage to 5.3V (although I suspect that as little as 5.1V should work).