2 Replies Latest reply on Dec 15, 2016 6:39 AM by MaGa_1759861

    PSOC5LP Boost Convertor in Sleep mode


      I have a few questions to use the boost convertor with sleep mode:


      1) Table 6-4 in the datasheet (001-84933 Rev. *I) indicates "the chip must wake up periodically for boost active-mode refresh". How to define 'periodically'?  Everytime the chip wakes up it uses power so I would like this to be as long a period as possible. Is this simply defined by how much you are willing to allow the VBOOST output to drop due to it being discharged by IBOOST in standby? 


      2) AN77900 section 3.6 indicates that when using with sleep mode on wakeup to refresh the boost convertor you need to set the boost mode to active and to restore the system clocks. Assuming that I only want to refresh the boost convertor on most wake-ups do I really need to restore the high-speed system clocks at all? Can I not simply put the boost convertor back into sleep mode and go directly to sleep again? Do I need to wait a time while the boost it is active? And if so what's the best way to reduce power during that process?


      3) Instead of putting the convertor into sleep mode, if I disable the boost convertor via an API call does VBOOST get actively switched to VBAT (i.e. shorting out the external inductor)? If I re-enable the boost convertor after my RTC wake-up (assuming VBAT stays >1.8V) can I then switch it back on and bring my CPU voltages back up again without issue?


      Would very much appreciate it if anyone knows any detail on this.

        • 1. Re: PSOC5LP Boost Convertor in Sleep mode

          1) Yes, you need to wake the PSoC 5LP and set the boost converter to Active mode to refresh the regulator power supply. There is no specific wake-up time, but not recommended to give large Wake-Up times. CTW (1KHz ILO) will be good enough.


          2) There is no need to wait till boost is active. But, you need to save the clocks before Sleep Mode entry and restore it back once the chip wakes up. Many of the clocks are not ON in Sleep. Hence you need to save them and restore it back after wake-up so that their original configurations are restored.


          3) Yes, theoretically this is possible. Ensure that VBAT > 1.8V. Also, highly recommended that PSoC is in Sleep mode during this time.

          • 2. Re: PSOC5LP Boost Convertor in Sleep mode

            Quick Update re:


            item 3)


            Switching stopping / restarting boost on the fly seems to work well. I do not see how you can do this in sleep mode as the core has to be active to execute the Start and Stop commands .... so I am currently doing it in active mode and not seeing problems.


            Was the recommendation really to issue the start boost command and then immediately afterwards enter sleep? If so what is the reason for this? While the external supply voltage will step the internal core voltage is supplied by the core regulator which should remain steady at 1.8V considering it has a 1uF capacitor on it. Or do I have the wrong end of the stick here?


            2) I implemented 1) & 2) and it worked okay (but a 1KHz wakeup is much too power hungry for my battery). Just to kick the boost and go back to sleep you don't need to restart the system clcoks (which again saves quite a bit of power not having to do this). However approach 3) suits my use case far better from the point of battery life .... I am data logging and only need the higher voltage very periodically to store my results to an SDCard.