6 Replies Latest reply on Nov 19, 2012 4:12 PM by geoffrey.budd

    Shorted CY8CKIT-050

    geoffrey.budd

       Hi all,

         

      I managed to short Vin to ground while I had a 12v supply hooked up to the barrel plug on my board. No magic smoke came out of any of the chips (that I saw), but my board no longer works. When the j10 jumper is set to 3.3v the 3.3v regulator just above it gets rather hot (might burn me if I left it on). Also my VDDD has continuity to VSSD (ie, it's shorted to ground) when j10 is in any position (including not attached). I would geuss my 3.3v regulator was blown, but it's doing its job just fine (tested with a mulitmeter and I get 3.3v on the middle pin and the big tab). I also checked  and confirmed that the caps in the power supply circuitry don't have continuity to gound. Any ideas on what to check next? or where I can buy another dev kit (everyone seems to be out of stock)?

         

      Thanks,

         

      Geoff

        • 1. Re: Shorted CY8CKIT-050
          user_14586677

          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.

             

           

             

          Regards, Dana.

          • 2. Re: Shorted CY8CKIT-050
            geoffrey.budd

            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.

               

             

               

            -Geoff

            • 3. Re: Shorted CY8CKIT-050
              user_14586677

              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.

                 

               

                 

              Regards, Dana.

              • 4. Re: Shorted CY8CKIT-050
                kishore.kumar

                 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?

                • 5. Re: Shorted CY8CKIT-050
                  user_14586677

                  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

                     

                  diode.

                     

                   

                     

                  Regards, Dana.

                  • 6. Re: Shorted CY8CKIT-050
                    geoffrey.budd

                    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 :(