1 2 Previous Next 15 Replies Latest reply on Feb 19, 2015 8:10 AM by Madhu Lakshmipathy

    FX3 Power supplies


      I opened a support case about thisabout a week ago on invitation from a Cypress employee, but it has been completely ignored. The employee wrote to me, unsolicited, for help with his app note then said I should raise a case about my questions rather than him answering them as it was not his problem. Here's the case which is being ignored:




      FX3 Power supplies




      I need to know the current requirement of the VBUS pin. The data sheet speaks of a large number of separate supply pins but only mentions two current values without relating these to the voltage names. So there is no way to know how much current is drawn by VBUS. Is it ICC USB? Or is it just a supply for the tranceiver and pullups and therfore much smaller?


      I am making a self powered device. I believe I can supply 5V to VBUS on the FX3, from a supply rail in my device, but only connect it when the host is connecting 5V to the receptacle. This should avoid damage from excessive external supplies.


      I then also have to know what to do with VBATT as I don't have a battery. My best guess is to connect it also to 3.3V or 5V, though I have no idea how to justify this as VBATT is not really explained.


      At any rate this requires me to be able to estimate the power required by these pins.


      The other question I have is whether there is any need or benefit from power supply sequencing?

        • 1. Re: FX3 Power supplies





          We are extremely sorry about the inactivity in the case. Please let us know the case number, I will take a look and take necessary actions.


          Regarding VBAT....




          FX3 can select whether to use VBUS or VBATT to power USB PHY. Generally VBATT is used to power FX3 in case if it is acting as USB Host in OTG mode, where battery voltage can vary to large extend (VBATT supply voltage range 3.2V to 6V).


          If FX3 is acting as USB 3.0 Device mode, you can leave VBATT unconnected or you might want to connect VBATT to 3.3V using 0 ohm resistor(we recommend). You need to use VBUS (4.1 V to 6 V input from USB connector VBUS) to power USB PHY. The pin VBUS connects to the VBUS of USB connector, so its range is from 4.1 V to 6 V.


          VBATT: This is the 3.2 V to 6 V power input for the USB PHY. It can be connected from the battery powered by external battery, or regulated 3.3V powered by the external power management IC. This supply input powers the USB PHY through an internal voltage regulator of FX3. This supply is internally regulated to 3.3 V for the USB PHY.




          Regarding VBUS...


          As I already mentioned VBUS pin of FX3 should be connected to VBUS signal of USB connector.  This is mandatory for the connect/disconnect detection to work properly. 




          Regarding power sequencing...




          There is no Power sequencing requirements for FX3. It can be powered simultaneously (all the supplies).

              Regarding ICC USB....   
               ICC_USB is total current for all internal USB circuitry.    






          • 2. Re: FX3 Power supplies

            OK Thanks. But I still don't know how much current VBUS takes worst case.

            • 3. Re: FX3 Power supplies

               I will check with the design team and get back to you on this.







              • 4. Re: FX3 Power supplies

                Thanks - I  look forward to that.

                • 5. Re: FX3 Power supplies

                  The two current values that are mentioned in the data sheet are as follows:


                  ICC Core: Current through all the 1.2V supplies combined. This includes VDD, AVDD, U3RXVDDQ, U3TXVDDQ.


                  ICC USB: It is the current through the VBUS or VBATT supply that is connected to the FX3.


                  I am not sure if you looking for the current through the VBUS pin connected to the FX3 or you are looking for the whole current that has been taken from the VBUS of the USB host. Please let me know.




                  sai krishna.

                  • 6. Re: FX3 Power supplies



                    In the datasheet of FX3, nothing is specified about I/O operating Current (VIO1-5). Assume that i am using all the 32 datalines.






                    Kasthuri Rangan V

                    • 7. Re: FX3 Power supplies

                      Yes. We are not talking about the I/O power consumption numbers in the data sheet as it will completley depend up on the usage (voltage, duty cycle) and the number of I/Os.




                      sai krishna.

                      • 8. Re: FX3 Power supplies

                        Hi Sai,


                         Thanks for you info.. Am now using 8 databits and 3-4 Control bits as GPIOs at I/O level 3.3V. Can you just say approximate value of input current required.


                        Also, Are all the VIO domains configurable to 2.8V?






                        Kasthuri Rangan V

                        • 9. Re: FX3 Power supplies

                          Current consumption in your case will be around 53mA. This is calculated by assuming that all the 12 I/Os have activity factor of 50, @3.3V.




                          sai krishna.

                          • 10. Re: FX3 Power supplies

                            In a previous post the total current draw of the FX3 was listed as 300 mW. The datasheet for the ICC Core (core & analog) currents shows 200 mA @ 1.2V (which is 240 mW) plus the ICC USB current is shown as 60 mA. If we use 5V as the USB voltage this gives us 300 mW. Now adding the current for the I/O power supplies, the total power level will easily exceed the 300 mW that was posted. Since these circuits draw different currents at different times, can you clarify the maximum power levels that we should expect to see when processing HD Video data?

                            • 11. Re: FX3 Power supplies

                              Is there a calculator available for the I/O supplies for various modes?  Obviously some assumptions will need to be made but can we get some ballparks for 1.8v, 2.5v, and 3.3v operation on 16-bit and 32-bit GPIF with 25% and 50% duty cycle on the data and maybe 12.5% duty cycle on N control signals?

                              • 12. Re: FX3 Power supplies



                                Gayathri said  VBUS pin of FX3 should be connected to VBUS signal of USB connector.  This is mandatory for the


                                connect/disconnect detection to work properly. 




                                I am still confused about FX3 Bus Powered and Self powered,they are quite different from FX2.




                                 In FX2,when we want a Self-Powered design, VBUS pin of USB recepatcle can be used as sense signal or even left it float,


                                all power supplyed by regulators not by VBUS.




                                But now in FX3 As Superspeedy mentioned,if I want a Self-Powered design and do not use battery,should I connect the VBUS pin




                                of FX3 to VBUS pin of USB receptacle or connect to 5V regulator? As Gayathri mentioned,I am afraid that Self-powered of FX3 is




                                not real "Self-powered" because VBUS of USB receptacle always powered VBUS pin of FX3. something else also surprise me that




                                FX3 do not have a "wakeup" pin.And here is a message I got from Cypress Community:


                                The JTAG interface of FX3 does not work if VBATT pin is not connected to a power supply.In bus-power designs,it will be powered


                                via VBUS;in self-powered designs,it needs to be powered via VBATT. Question: in self-powered mode when I want to use JTAG,


                                what voltage should be supplyed to VBATT?




                                Is there any APP Note talk about self-power application of FX3 in detail in CPRESS?




                                Thanks & Regards

                                • 13. Re: FX3 Power supplies

                                   The VBUS pin in a self powered design must be connected to the VBUS input of FX3. This is needed as FX3 needs to know when it was connected to the host i.e it's just a sense pin and the chip doesn't draw power from it. Power is instead drawn from the other source you'd be using.




                                  Regarding VBATT, you can just short this to a 3.3V output.

                                  • 14. Re: FX3 Power supplies



                                    If we don't want to use USB3 port, how to make the port sleeping without any power consumption? 


                                    In previous talking, someone mentioned that the JTAG would not work if no power to Vbat, is it true?



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