5 Replies Latest reply on Jan 8, 2013 3:59 PM by user_14586677

    Help with Power Supply Design for PSoC Device


       I need help designing a power supply for a portable medical research device that uses PSoC 3. My problem is designing a configuration for multiple voltages with pcb size and power efficiency in mind. I need ~3.3 V, ~ +/- 1.5 V, and +/- 20 V. 




      Below I’ve listed device info and estimated current consumption of both the analog and digital components. 


      Device Info: My device will be worn by small rodents and used to (1) amplify low-voltage and low frequency (< 15 kHz) analog signals, (2) output 100uA@20V constant current pulses, and (3) communicate with PC via BT. This device will be small (2’x2’ double sided pcb) and light weight. Thus, efficiency and pcb footprint are extremely important. Component cost isn’t much of a concern.


      Digital Components:

      1. PSoC 3:  10 mA @ 3.3 V (Supply Range: 1.7 - 5.0 V )
      3. RN-42 Bluetooth Module:  15 mA @ 3.3V (Supply Range: 3.0 - 3.6 V, peak current 50mA)

      Analog Components: All analog components use dual power supplies (+/-). 

      1. Section A:  1mA @ +/- 1.5 V (<1% duty cycle, Supply Range: 1.0 - 3.3 V)
      3. Section B:  2mA @ +/- 20.0 V (1% duty cycle)

      Battery: I was hoping to use a 3.6 V LiPo battery unless there is a more appropriate battery or source voltage.


      Questions: Where and how should I use LDO, switching, or linear regulators together for this application? What’s the best way to get the +/- 20 V? Should I adjust any component supply voltages for higher efficiency? ... etc...?  Any help would be tremendously appreciated.

        • 1. Re: Help with Power Supply Design for PSoC Device

          Some basic thoughts -




          1) Linear regulators generally speaking, lower noise, lower efficiency, most simple,


          layout insensitive (to some degree).


          2) Charge pump regulators noisy, simple.


          3) Buck/Boost noisy, layout sensitive, more efficient, parts count can be higher.


          4) If you have very low level signals linear more forgiving, excellent PSRR, switching topologies more




          5) Set a battery life goal, that then leads you to an allowable efficiency target.


          6) TI, LTC, so many others have design/selection tools that do an excellent job of


          helping with design, selection, even thru thermal considerations. Webench......


          7) Caps, pay attention to actual datasheets, not all caps are equal. Your are especially concerned with ESR


          in switching designs. Also some regulators have a minimum requirement on output cap ESR.


          8) L's, their losses to be looked at vendor to vendor.


          9) Pick synchronous where ever possible (for efficiency, catch diode is a switch, not a diode). If using diodes


          pick fast recovery, schottkys.




          You have a lot of options and tools at vendor websites.




          Regards, Dana.

          • 2. Re: Help with Power Supply Design for PSoC Device

            If you wind up switching, and need low noise for low level, great bulk caps


            are polymers, an order of magnitude better ESR vs F curves over Tanatalum.










            Regards, Dana.

            • 3. Re: Help with Power Supply Design for PSoC Device

              Lastly if you go switching layout very important, google


              "switching regulator layout considerations", there is lots


              of application notes and help on this topic.




              Regards, Dana.

              • 4. Re: Help with Power Supply Design for PSoC Device

                Thanks for all the input dana. 




                Battery life is of great concern. I would prefer to use a linear LDO regulator for simplicity and lower noise, but it's my understanding that a 3.7V LiPo will range from 3.9-2.7V while in use. Thus I couldn't get maxium operating time for my device with a LDO. 




                I'm looking at using TI's TPS63001 buck/boost converter to provide the first stage of power, and to power my digital components (PSoC 3 and BT module). It's fixed at 3.3V, has small footprint (3x3mm QFN10), and only requires one inductor plus filter caps.




                Would this be a good choice for powering the PSoC from a 3.7V LiPo battery ?





                • 5. Re: Help with Power Supply Design for PSoC Device

                  That looks like a good starting point, although there are buck/boost parts


                  out there that have multi outputs, Micrel for one.




                  To develop + 1.5 a zener if thats accurate enough. To get - 1.5 one approach


                  is to use a clk or pwm output and a diode-C network to invert voltage. Like


                  these basic approaches.




                  See attached diode inverters.




                  Rewgards, Dana.