Hi,
We have been using TPS54302 successfully since some years. Se schematic below.
No problem with this board.
We are now using TPS54302 on a new board. See schematic below.
The differences are: the output voltage is now 5V instead of 12V. The input of the previous board was from a rectifier, but now is from a 24Vdc external supply, so the big 4700uF capacitor on the input has been removed.
We power this new board from an external 24Vdc power, as said, through a machanical switch.
On two boards that were functioning we turned on the switch, the LED showing precence of the +5V flashed and then went off and the external power supply behaved as if its output was short circuited. We check the boards and we found that the TPS54302 was short circuited (less than 1 ohm) between pin 1 and 3. We replaced the TPS54302 on both boards and both boards started to work again regularly.
We try to reproduce the fault and, suspecting that the cause was the bounces of the switch, we connect oscilloscope: yellow plot=voltage across C32, green plot=voltage between pin 2 and ground.
The bounces of the switch end in less than 200 usec, while the TPS54302 starts switching only after about 2 msec. So the cause of the fault cannot be the bounces of the switch.
Any idea on what was the cause of the fault?
