We've found an unusual shutdown problem in a few TPS40061 devices, about 7 or 8 so far.
The faulty devices would appear to exhibit thermal shutdown at a case temperature of 60C to 65C. As the case temperature increases the duty cycle slowly drops from a nominal 30% until regulation is lost. A quick squirt of freezer spray brings the duty cycle back to normal and replacing the faulty device fixes the problem.
Initially it was thought that the thermal tab wasn't soldered to the PCB so we mounted a known good working chip to a board and isolated the thermal tab just to see how hot it got. Measured case temperature was around 90C and the power supply performed as normal. When heating the same test chip to 160C, using a hot air gun, the duty cycle could be seen to drop in the same manner as the faulty devices, and returned to normal when the chip cooled down.
Copy of schematic attached. 6318.TPS40061 schematic.pdf
Date/batch code for one device reads: 40061 05T CGND. Has anyone else seen this behaviour in the TPS40060/61 ?
Chris
