I designed a battery-powered LED driver and USB power supply, and this part was used to disconnect the load from the batteries when they get discharged to prevent over-discharge. Most of the time the part works fine, but 20-40% of the new boards that are assembled have this part fail immediately on power up. Another ~10% fail sometime after first power-up, but again when powered up.
The original design is attached. The EN pin is used to enable the output when the input voltage rises above a certain threshold, similar to the example in Fig 18. Thinking that a slower rise time would help, I added a 10nF cap on the CT pin (to ground) to give a 2ms rise time. I noticed on a scope however that the rise time didn't change, and then I noticed in the datasheet that the Vin needs to be stable before EN is asserted in order for this rise time function to work. I increased the cap C27 to 1uF and this caused a larger delay before EN goes high, so then I would see a ~2ms rise time. Unfortunately the chip continued to fail.
The total load on the output rail is about 100uF. The input (at +9V_SW) is typically 9V from batteries, but can be as high as 12V from a wall adapter when the batteries are charging.
The datasheet states: "The device has a thermal protection feature. Due to this device protects itself against thermal damage due to over-temperature and over-current conditions. Safe Operating Area (SoA) requirements are thus inherently met without any special design consideration by the board designer." But this doesn't seem to be the case for me.
Any thoughts or suggestions?
Thanks