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C6748 RTC Current consumption

llsmberly
Prodigy 330 points
Other Parts Discussed in Thread: BQ24640

What is the current consumption in RTC-mode of operation? 

  • 0
    TI__Mastermind 24340 points

    Here are some approximate numbers that Tommy got of RTC current at room temperature.  RTC current did not vary significantly between RUN and STOP modes:

    Current consumption on RTC with the core powered up to 1.2V was in the 175-177uA range.

    Current consumption on RTC with the core powered down to  0V was in the 12-14uA range.

     

    Clarification for the two sets of numbers:

    • The RTC power consumption is higher when the core supply (includes PLL supply) is powered up versus powered down.  The RTC module receives an active bus clock when the core is powered up so this will introduce extra switching activity and increase power draw.  Both numbers need to be comprehended if RTC will be powered by a battery.

      With a super-cap that is continuously charged while core is powered up, the increased power draw should be a lesser concern.

  • 0 in reply to Mariana
    Expert 2585 points

    How would you suggest connecting a super-cap to the RTC power pin?  We are interested in having the RTC "battery backed" for a couple of hours (long enough to survive most power outages).

    - Dean

  • 0 in reply to Dean Hofstetter
    TI__Guru 64440 points

    Generically, I would say "hook it up", but clearly there is more to it than that.  Especially from the perspective of a charging circuit for the super cap.  The BQ24640 is such a charging device and has an EVM for testing this out with terminals for the system load.