• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 98 subscribers
  • Views 777 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

C55x how to keep RTC counting while power off except for RTC power.

user1895036
Prodigy 250 points

Is it possible to keep RTC counting while supplying RTC power (CVDD RTC) and clock (RTC_XI).? Other power supply except fot RTC are off.

On the data sheet, only the "RTC only mode" seems to be able to keep RTC counting while power supply except RTC are off.

  • 0
    TI__Mastermind 30140 points

    Hi,

    Yes - the RTC can stay active and counting while most of the rest of the power supplies are turned off. We call it RTC-only mode, and it is the lowest-power idle/sleep mode.

    At a minimum you need CVDDRTC, DVDDRTC, and LDOI to be supplied when in RTC-only mode.

    All other supplies can be turned off, then an RTC alarm or wakeup event can trigger the supplies to turn back on. The processor boots via the bootloader, and resumes operation. State can be preserved with the RTC scratch registers, based on the interrupt type, or by the time of day in the RTC registers. It is easiest to utilize the on-chip LDOs to make wakeup from RTC-only mode easiest (otherwise, must use the wakeup pin as an output to trigger off-chip LDOs or buck converters to resupply the voltage).

    The power estimation spreadsheet has a macro for RTC-only mode that shows these supplies active and their power consumption during RTC-only mode. Download the spreadsheet at this link:  http://processors.wiki.ti.com/index.php/TMS320C5504/05/14/15/32/33/34/35_Power_Consumption_Summary

    Hope this helps,
    Mark

  • 0 in reply to Mark M
    Prodigy 250 points
    Hi Mark-san,

    Sorry for late reply.

    I tried to test the RTC behavior as follows:
    (DSP_LDO_EN = 0)

    1. Set the date/time to RTC (RTC MIL, RTC SEC, ... RTCYRAR). for example 00h00m
    2. Turn off all supply except LDOI(1.8V), DVDDRTC(1.8V), CVDDRTC(1.1V).
    # CVDD, DVDDIO, DVDDEMIF, VDDA_ANA are off (0V)
    3. Wait for an hour.
    4. Supply all powers for CVDD, DVDDIO, DVDDEMIF, VDDA_ANA again, and negate RESET, C5505 reboot again.
    5. The date/time from RTC has updated. (01h00m)

    It seems that the RTC keeps counting the date/time with supplying only LDOI, DVDDRTC, CVDDRTC.

    If the above behavior correct?

    # We did not modify BG_PD and LDO_PD of RTCPMGT register.
  • 0 in reply to user1895036
    TI__Mastermind 30140 points

    Hi,

    The behavior you have described is expected of the RTC with the non-required power rails turned off.

    Are you not using the on-chip LDOs in your system? You would have had to disable the LDO with BG_PD or LDO_PD to get them to turn off.

    One additional feature you have not utilized is the ability of the RTC to re-enable the other rails after an RTC alarm or interrupt. The on-chip LDOs can automatically turn on after such an alarm or interrupt, and the wakeup pin can be used as an output to enable the DVDDIO, DVDDEMIF rails (for example to enable a DC-DC converter or a load switch).

    Regards,
    Mark

  • 0 in reply to Mark M
    Prodigy 250 points
    Hi Mark,
    Thank you for reply.

    I'm using C5505 in my system. I do not use BG_PD and LDO_PD bit on RTCPMGT register.
    Once I set PG_PD and LDO_PD, the system turns off the power, and C5505 does not restart by negating RESET.
    (My system also asserts RESET(RESET to Low) when turning off the power supply except LDOI, DVDDRTC, CVDDRTC.)