12 Replies Latest reply on Jul 16, 2020 5:46 AM by GaneshD_41

    Can Vbackup be drained during VDDD present?

    MoTa_728816

      Hi,

       

      This question is related the question below

      PSoC 6 Vbackup current

       

      The customer is seriously trying to estimate the backup coin battery life.

      And they asked us if the battery can be drained by P0 during VDDD is present.

       

      At first from the description of 15.3 Power Supply, I thought that only when VDDD voltage goes lower than VBACKUP,  it can happen.

      ================

      VDDBAK_CTL = 0 (Default mode): Selects VDDD when the brownout detector in the system resources is enabled and no brownout situation is detected (see the

      Power Supply and Monitoring chapter on page 129 for more details). Otherwise, it selects the highest supply among VDDD and VBACKUP.

      ================

       

      But seeing the diagram, I noticed the path (red line) exists, which is not controlled by the Backup Power Switch.

      So I lost my confidence. It looks like if some port sync a lot of current, Vbackup can be used to help VDDD.

      001-hilighted.JPG

      Question:

      Is there a case when VDDD presents, but VBACKUP is also consumed?

      Especially when VDDD is not lower than VBACKUP (but current may not be sufficient.)

       

      moto

        • 1. Re: Can Vbackup be drained during VDDD present?
          GaneshD_41

          Hi Moto,

           

          >>"It looks like if some port sync a lot of current, Vbackup can be used to help VDDD."

          --> No. The power supply rails in PSoC 6 are independant to each other. The different power supply rails provide power to different ports.

          The VBACKUP supplies power to only port 0. The port 0 contains the pins for wakeup and WCO. The red line shown in the image is to indicate this connection to Port 0.

           

          supply.PNG

          So, the answer for your question "Is there a case when VDDD presents, but VBACKUP is also consumed?" is No. You can confirm this by one more point mentioned in the same section If a supercapacitor is connected to VBACKUP, the PSoC 6 MCU can charge the supercapacitor while VDDD is available. Supercapacitor charging can be enabled by writing “3C” to the EN_CHARGE_KEY bitfield in the BACKUP_CTL register. Note that this feature is for charging supercapacitors only and cannot safely charge a battery. Do not write this key when VBACKUP is connected to a battery. Battery charging must be handled at the board level using external circuitry.

           

          Hope this clears your query.

           

          Thanks

          Ganesh

          • 2. Re: Can Vbackup be drained during VDDD present?
            MoTa_728816

            Dear Ganesh-san,

             

            Thank you very much for your answer!

             

            >>"It looks like if some port sync a lot of current, Vbackup can be used to help VDDD."

            --> No. The power supply rails in PSoC 6 are independant to each other. The different power supply rails provide power to different ports.

            This is very good news.

            (BTW, sync was typo of "sink")

             

            But would you let me confirm a couple of more things.

            (I know, I may be being picky though)

             

            (1)

            > The VBACKUP supplies power to only port 0.

            > The port 0 contains the pins for wakeup and WCO.

            > The red line shown in the image is to indicate this connection to Port 0.

            Yes, but they can be used for other purposes during the normal power mode.

            And there also be some more pins in the Port 0.

            In case VDDD can not supply enough current, can't there be a case those pins will drain current from VBackup?

            002-port0.JPG

             

            (2) My poor English capability does not allow me to read the following sentence to be the proof.

            It sounds like that by the bit in the BACKUP_CTL register, VBACKUP can be used to charge the external supercapacitor.

            But I can not find any proof that the external source will not be drained.

             

            If a supercapacitor is connected to VBACKUP, the PSoC 6 MCU can charge the supercapacitor while VDDD is available. Supercapacitor charging can be enabled by writing “3C” to the EN_CHARGE_KEY bitfield in the BACKUP_CTL register. Note that this feature is for charging supercapacitors only and cannot safely charge a battery. Do not write this key when VBACKUP is connected to a battery. Battery charging must be handled at the board level using external circuitry.

             

            Best Regards,

            18-Jun-2020

            Motoo Tanaka

            • 3. Re: Can Vbackup be drained during VDDD present?
              GaneshD_41

              Hi Motoo,

               

              >>"1. Yes, but they can be used for other purposes during the normal power mode.

              And there also be some more pins in the Port 0.

              In case VDDD can not supply enough current, can't there be a case those pins will drain current from VBackup?"

               

              --> Assuming that VDDD drops its voltage level in the case where it cannot supply enough current, obviously the VBACKUP should supply the power the port 0 pins.

               

              >>"(2) My poor English capability does not allow me to read the following sentence to be the proof.

              It sounds like that by the bit in the BACKUP_CTL register, VBACKUP can be used to charge the external supercapacitor.

              But I can not find any proof that the external source will not be drained."

               

              --> Sorry. It is not a quantitative proof. I mean to say when VDDD is more than VBACKUP the Back up supply domain can infact back power the super capacitor through VDDD and thus the net charge on the super capacitor increases over time.

               

              To answer your queries with quantitative proof, I need to check into the internal documents and internal team. I will do that. Till then I hope my answers may be little helpful to you

               

              Thanks

              Ganesh

               

               

               

              • 4. Re: Can Vbackup be drained during VDDD present?
                MoTa_728816

                Dear Ganesh-san,

                 

                Thank you very much for your response.

                 

                > --> Assuming that VDDD drops its voltage level in the case where it cannot supply enough current,

                > obviously the VBACKUP should supply the power the port 0 pins.

                 

                So, Can I interpret this that, although it's an extreme situation,

                there can be a case when VDDD presents but the VBACKUP power can be drained by the pins in the Port 0 ?

                 

                > To answer your queries with quantitative proof, I need to check into the internal documents and internal team.

                > I will do that.

                 

                 

                I really appreciate it!

                 

                > Till then I hope my answers may be little helpful to you

                No, it's not a "little", you've been a big help ;-)

                 

                Best Regards,

                18-Jun-2020

                Motoo Tanaka

                • 5. Re: Can Vbackup be drained during VDDD present?
                  MoTa_728816

                  Dear Ganesh-san,

                   

                  We discussed with the customer about information currently we have.

                  According to the customer, except when the system is broken / out of order,

                  there will not be a situation that VDDD is lower or equal to Vbackup.

                   

                  Now, if the condition is as below

                  (1) Both VDDD and Vbackup present

                  (2) VDDD > Vbackup

                  Can we think that Vbackup power will not be consumed?

                   

                  Best Regards,

                  26-Jun-2020

                  Motoo Tanaka

                   

                  • 6. Re: Can Vbackup be drained during VDDD present?
                    GaneshD_41

                    Dear Motoo-san,

                     

                    What you are expecting is correct.

                     

                    The external battery on VBACKUP pin is disconnected from supplying power to the backup domain when VDDD is present (and greater than brown-out level). However, IO seems to be still driven by external backup source.

                     

                    Contrary to what I said before, it is not because “we cannot charge the battery/coin-cell, the coin-cell only should supply current to the PORT 0 pins even when the VDDD is present.” It is because that is how IO cell is designed to work.

                     

                    So, Irrespective of VDDD state – VBACKUP would always be the supply to drive the voltage/signal out of Port 0.

                     

                    Hope this answers your questions.

                     

                    Thanks and regards

                    Ganesh

                    • 7. Re: Can Vbackup be drained during VDDD present?
                      MoTa_728816

                      Dear Ganesh-san,

                       

                      Thank you very much for your answer.

                      It is good to know that ” VBACKUP would always be the supply to drive the voltage/signal out of Port 0”.

                       

                      Now what the customer needs to know is, when the VDDD voltage is higher than BOD,

                      although both the VBACKUP and VDDD will be the supply to the Port 0,

                      can we assume that the power of the coin battery connected to the VBACKUP will not be consumed?

                       

                      In other words, can we assume that the only time the power of coin battery is consumed is when VDDD is not present.

                      (Given that when VDDD is present, it has always higher voltage level than VBackup).

                       

                      Best Regards,

                      15-Jul-2020

                      Motoo Tanaka

                      • 8. Re: Can Vbackup be drained during VDDD present?
                        GaneshD_41

                        Dear Motoo-san,

                         

                        My initial responses were not correct.

                         

                        >>"Can we assume that the power of the coin battery connected to the VBACKUP will not be consumed?"

                        --> No. The VBACKUP source supplies power to the Port 0 pins irrespective of the voltage level on the VDDD. So the coin battery connected to the VBACKUP will be consumed.

                         

                        >>"In other words, can we assume that the only time the power of coin battery is consumed is when VDDD is not present."

                        --> No. The battery source connected to VBACKUP only supplies current to Port 0 pins. Not the VDDD.

                         

                        Thanks

                        Ganesh

                         

                         

                        • 9. Re: Can Vbackup be drained during VDDD present?
                          MoTa_728816

                          Dear Ganesh-san,

                           

                          Although I'm not trying to be difficult, I can not believe that VBACKUP is the only power source for Port 0.

                          Because if it's the case, if the design uses Port 0 for normal operation,

                          the life of the con battery connected to the BACKUP must be very short.

                           

                          How about VDDIO, if VDDIO is also connected and applied same voltage with VDDD, will it be used or not?

                           

                          Best Regards,

                          15-Jul-2020

                          Motoo Tanaka

                          • 10. Re: Can Vbackup be drained during VDDD present?
                            GaneshD_41

                            Dear Motoo-san,

                             

                            Do not confuse with the VBACKUP domain and the power supply to the pins on the Port 0.

                             

                            When VDDD is present (and greater than brown-out level) external coin cell is disconnected from supplying power to the backup domain. But, the external source on VBACKUP pin only supplies power to the Port 0 pins.

                             

                            VDDIOx also supplies the power to only the pins of correspoding ports as shown in the image posted in my first response.

                             

                            So, we can recommend the customers to use other port pins for normal usage. Port 0 pins are dedicated for Wake-up and other actions in backup domain.

                             

                            Thanks

                            Ganesh

                            • 11. Re: Can Vbackup be drained during VDDD present?
                              MoTa_728816

                              Dear Ganesh-san,

                               

                              Thank you very much for your detailed explanation.

                               

                              Although I also came up with an idea using EN_CHARGE_KEY to feed power from VDDD to Port 0,

                              it does not seem to be safe to do so.

                               

                              So I understand that the conclusion is as follows (correct me, if I'm wrong)

                              (1) Power from the coin battery will be consumed if Port 0 is used during the normal activity, even if there is VDDD present.

                              (2) To avoid or minimize the consumption of the coin battery, Port 0 should not be used except for the wake-up trigger.

                               

                              Best Regards,

                              16-Jul-2020

                              Motoo Tanaka

                              • 12. Re: Can Vbackup be drained during VDDD present?
                                GaneshD_41

                                Dear Motoo-san,

                                 

                                >>"Although I also came up with an idea using EN_CHARGE_KEY to feed power from VDDD to Port 0,

                                it does not seem to be safe to do so."

                                --> Yes. If you are using battery, this is not a safe option. This can be considered if you are using a super-cap.

                                 

                                >>"Power from the coin battery will be consumed if Port 0 is used during the normal activity, even if there is VDDD present."

                                --> Yes. You are correct.

                                 

                                >>"To avoid or minimize the consumption of the coin battery, Port 0 should not be used except for the wake-up trigger."

                                --> Yes. You are correct. Since the wake-up pin is interrupt pin, it can be configured as High impedance- digital pin.

                                 

                                Thanks

                                Ganesh

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