This is a well understood poroblem, shorting Vin to a 3 terminal regulator the
output cap discharges back thru the regulator, and can destroy or damage
it. From the LM117 datasheet -
When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will
discharge into the output of the regulator. The discharge current depends on the value of the capacitor,
the output voltage of the regulator, and the rate of decrease of VIN. In the LM117, this discharge path is
through a large junction that is able to sustain a 20A surge with no problem. This is not true of other types
of positive regulators. For output capacitors of 20 µF or less, there is no need to use diodes.
The fix, which Cypress board does not have, is a diode strapped across regulator, input to output.
Thanks for the reply!
The regulator going seemed most likely to me as well, which is why I checked that it is stil putting out 3.3v. It still outputs 3.3v but it does get really hot when it's being used (becasue something is shorted). I'll try sourcing another regulator and giving that a go.
A quick check of a regulator is lift the ref leg (while powered down), insert
ammeter, power up, and if you see large current in ref leg that regulator is hosed.
Why don't you create a Tech Support case and ask for a replacement Kit as the Kit doesn't even have the short circuit protection?
Actually the kit does have short circuit protection, virtually all 3 terminal
regulators now have both current and thermal overload protection. It is
this case often missed in most designs, what happens to the charge on
the regulator output cap if the input is shorted, which takes a seperate
discrete diode to resolve strapped across the regulator input to output.
But it still would not hurt to ask, and maybe mention the needed protection
Regulators (5 and 3.3v) are fine. WIth both regulators pulled off the board I still had a short between VSSD and VDDD :( I found that C41 had been blown off the board, replaced it but that obviously didn't fix the short.\
I supplied 3.3v to the VDDD pin and ground to the gound plane and the ARM core got rather warm. Time for a new board :(