6 Replies Latest reply on Aug 13, 2015 12:04 PM by user_14586677

    WaveDAC8 open load Behavior?

    neal.o'hara

      Hello, 

         

       

         

      I am planning to use a CY8C56xx  with a WaveDAC8 as current source/sink  on a  variable external load. This load includes the possibilities of becoming open or too large to power (ie  Rload * WaveDAC8_Amplitude  >   VCC- Voverhead )  and I would like to know what behavior to expect from the WaveDAC8 module during these time?

         

      Does the WaveDAC8 include protection against these modes, and if so, what are the ranges of this protection?

         

      Are there indicators of these faults occurring? I haven't seen any in the component documentation, but I want to verify this.

         

       

         

      Any advice, or links to appropriate documentation, is appreciated!

         

      ngohara

        • 1. Re: WaveDAC8 open load Behavior?
          user_14586677

          I am planning to use a CY8C56xx  with a WaveDAC8 as current source/sink  on a

             

          variable external load.  This load includes the possibilities of becoming open or too

             

          large to power (ie  Rload * WaveDAC8_Amplitude >   VCC- Voverhead )  and I

             

          would like to know what behavior to expect from the WaveDAC8 module during

             

          these time?

             

           

             

          The current generator will come out of compliance once you exceed its min operating V.

             

           

             

          For the case where external load is a power generator -

             

          If you exceed the rails you will start drawing a lot of current due to pin protection diodes.

             

          Too much current and you will trigger the parasitic SCR which in turn will draw very large\

             

          currents, and or blow the internal power bond wires to chip with permanent damage. The

             

          latchup current rating is 140 mA, enough to generate significant die hot spots and melt

             

          silicon possibly.

             

           

             

          For case where external load is a real resistance, current generator simply out of

             

          compliance, regulation.

             

           

             

          Does the WaveDAC8 include protection against these modes, and if so, what are

             

          the ranges of this protection?

             

           

             

          NO, for external power generator case, otherwise none needed, generator simply not

             

          functioning properly.

             

           

             

          Are there indicators of these faults occurring? I haven't seen any in the component\

             

          documentation, but I want to verify this.

             

           

             

          None that you can get your hands on given scr mechanism can trigger in uS range. Diodes

             

          turn on even faster. You could use a comparator that generates an ISR or the A/D and

             

          measure Vcurrentsource/sink, but thats not fast enough in the power generator case to

             

          protect if its capable of power source/sink > rails.

             

           

             

          Regards, Dana.

          • 2. Re: WaveDAC8 open load Behavior?
            neal.o'hara

            Thank you for the advice.

               

            Just to clarify, by "power generator" you mean the case where  WaveDAC8_current * RLoad is higher than Vsupply, right?

               

            There should be no external power connected to this part of my system.

               

             

               

            Secondly, in the case of exceeding the rails, is there a module or an internal routing scheme I can implement to prevent the drastic hardware failure you describe?  My system Will vary to extremely high Rloads at times, so preventing hardware damage is important in this case. It is understood that we will not be able to actually supply current in this case, or the open load case.

               

            Thirdly, do you know what the WaveDAC8's response is in the open loop case?

               

             

               

            Thank you again for the advice, and any other advice or links to documentation is appreciated!

            • 3. Re: WaveDAC8 open load Behavior?
              user_14586677

              Just to clarify, by "power generator" you mean the case where  WaveDAC8_current * RLoad is higher than Vsupply, right?

                 

               

                 

              By this I mean an Rload in series with another V generator. Such that a condition could

                 

              occur where that generator started supplying current into the pin/Idac output. If you have

                 

              just a R load, nothing else, all that will happen at high values of Rload  or opens is that

                 

              the current source will come out of compliance/regulation. No damage in this case or

                 

              special considerations needed. Other than your own circuit functionality considerations.

                 

               

                 

              Secondly, in the case of exceeding the rails, is there a module or an internal routing scheme I can implement

                 

              to prevent the drastic hardware failure you describe?  

                 

               

                 

              Limit pin currents when any input is outside rails + ~ 1 diode drop with a series R

                 

              between pin and generator of the transient. For example if your signal path to pin

                 

              had a lot of L in it, opr laod dump capacitors.....

                 

               

                 

              My system Will vary to extremely high Rloads at times, so preventing hardware damage is important in this case.

                 

               

                 

              In your case no issue as stated above in first point.

                 

               

                 

              Thirdly, do you know what the WaveDAC8's response is in the open loop case?

                 

               

                 

              You would see the output saturate to ~ 1 volt below Vdd rail. Test it, simple to do in Creator.

                 

               

                 

              Regards, Dana.

              • 4. Re: WaveDAC8 open load Behavior?
                user_14586677

                Here is a Wavedac feeding a  2.7 K R, range set to 2.040 mA. The R value will

                   

                force the Idac out of regulation as you can see in attached pic.

                   

                 

                   

                You can see the Idac in the WaveDAC craps out at ~ 3.6 V, note Vdda was 4.5V in this

                   

                case so that was a complience of ~ .9 V, not taking into account all other errors. ~ spec

                   

                of the PSOC 5LP

                   

                 

                   

                Regards, Dana.

                • 5. Re: WaveDAC8 open load Behavior?
                  neal.o'hara

                  Thank you for all the help, that was what I needed determine!

                  • 6. Re: WaveDAC8 open load Behavior?
                    user_14586677

                    Glad to be of assistance.

                       

                     

                       

                    Regards, Dana.