Hi,
I have an application where I'm using an LM5069 to control and current limit a battery input which can be from 42-60V. This has been working fine and rolled out to a wider population of boards but I've now had a failure of a part on a customer unit. This part was tested when built and has been running successfully for many hours (probably several hundred). Now it will not power up.
We've taken scope traces and can see that Ctimer voltage increases up to, and stays at, 6V as soon as VIN is applied with UVLO held low. This normally ramps to ~4V and then is discharged. When UVLO is negated (using an opto), there is no change of state of the device. The Gate-Source voltage remains around -1V.
We have performed an A-B-A test, replacing the part on the board, and the fault follows the LM5069 component. We've also taken resistance measurements of each pin to GND when the part was removed which shows a lower resistance (500kOhm) on the TIMER pin compared to new parts.
Results, schematic and part marking can be seen in the presentation here.
The only risk factor I am aware of is that there is a high inrush condition on this variant of the design when a large external capacitance is connected to the supply once it is up and which occurs on each startup cycle. That causes the LM5069 to go into "circuit breaker" mode (current > 2x configured limit) and then restart by charging the additional load in power limit. Though the output voltage drops substantially during this time, this has been characterised and found to work successfully in our application.
I really need to understand the root cause and whether there is anything in the design that could have caused it and whether the remaining field population are at risk of the same failure occurring.
Thanks,
Paul.