HI
I am having a problem with a power supply based on the LM2655 switching regulator operating in synchronous mode.
The design is based very closely on the example circuits in the data sheet. We have 12V input and 1.2V output. We have many of these boards running with no problem but I have one board that refuses to work. The regulator fails with a short between the Pvin and SW pin. The input supply goes into current limit.
The device fails immediately the power is applied but I can find no short on the output. This has happened twice on the same board - when first built and following a replacement of the regulator. I have also had the lower FET, Schottky diode Cboot, Css and Cdelay replaced just in case one of these was faulty/wrong value.
I can find no obvious differences between a good board and this failing board.
Can anybody suggest a failure mechanism that would cause the device to fail in this way; normally these devices are pretty well self protected to prevent this sort of thing happening.