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TM4C123GH6PGE: Hibernate real time clock coin cell battery life

Srinu Vakada
Intellectual 770 points
Part Number: TM4C123GH6PGE

Hello everyone,

                Thanks to gave suggestions to my previous posts.

Now i am using Tiva (TM4C123GH6PGE) Hibernate for real time clock. I am using CR2032 Lithium coin cell for powering up the Vbat pin and we are using the 1k resistor before the VBAT pin of microcontroller.

Here

1) I want to know about how much time battery will continuously power up my RTC module. I request you to please suggest me.

2) Is there any solution to power up my hibernate RTC upto five years continuously .

I am requesting you to please suggest me above two.

Thanks,

Regards,

Srinu.V.

  • 0
    Guru 117850 points

    Could you not (more quickly & expansively) assist yourself - via the following:

    • the MCU's 'typical' current draw - while 'hibernating' - should appear w/in the MCU's detailed specifications.    (very rear of MCU Manual)    Have you checked?
    • the CR2032 should list its output 'power over time' rating.    Your comparing that (battery) listing - versus your MCU's expected  (total time) w/in 'hibernation' - (reasonably) reveals battery 'life.'

    Coin cells are (just) one option for 'Battery Back-Up.'    Larger cells - especially Lithium - far exceed the energy available from a coin cell.   'You' have investigated such fact - have you not?

    Beyond 'larger' cells - your use of 'Rechargable Cells' - (properly & periodically recharged) - may (even) enable a relatively small cell - to satisfy your 'hibernate' requirement.

    Your note of 'hibernate for up to five years' is (somewhat) unusual - and if 'Power to Recharge' is NOT available - there may be 'No escape' from a physically LARGE cell (or battery pack.)

    It is 'suggested' that (some) investigatory burden falls upon you - you alone 'know' all of the gory details...   (and such investigation - most always - BEST benefits the investigator!)

  • 0 in reply to cb1_mobile
    Intellectual 770 points
    Thanks for your suggestion sir,


    I found that battery capacity of CR2032 is 230mah and hibernate current (I_HIB_RTC) at 85 degree Celsius is 1.69 micro amperes.

    I took a 2 micro amperes as drain current of hibernate RTC.

    According to that values i calculated the lifetime of CR2032 battery is 230mah / 0.002ma = 115000 hours ---> 14 years

    I request you to please suggest me, is there anything wrong in the above calculations. And please suggest me, is it (CR2032) capable to supply the voltage to the hibernate up to 5 years.




    Thanks,
    Regards,
    Srinu.V.
  • 0 in reply to Srinu Vakada
    Guru 117850 points

    Good for you - as feared - few rose to your aid ... your 'Self Investigation' (appears) to have added (much) to your  understanding & capability.

    I must ask:

    • are you sure that (other) current draws - beyond your MCU alone - are 'guaranteed' NOT to occur - during 'MCU's Hibernate?'      (it is doubtful that any 'Power Source Switch-Over circuit' - performs 'energy-free' - is that not so?)     The normal/customary such 'Switch-Over Circuit' detects the absence of 'Primary Power' - and then draws from your 'back-up/Hibernate Source' - along w/the MCU.    (I don't know nor use your MCU - you must check to see how your implementation 'manages' the 'Power Source Switch-Over.')
    • it is expected that  'battery vendors' may specify their battery capacity differently.    Have you checked to see if the data you've acquired 'overlaps' that of several battery vendors?
    • might your calculation  'miss or diminish'  the fact - that as the coin-cell degrades - so too the voltage?     And depending upon your battery's 'knee' - while it still may have 'energy' - the  voltage output  (may)  fall 'too low' - to support the MCU!     (i.e. the 'MCU's demanded minimum voltage'  - may exceed the voltage output - of a 'diminishing' (yet far from exhausted) coin-cell.'     That's troubling - is it not?

    Earlier - the presence of (other) power sources (beyond the 'Hibernate Source Battery'  was queried.     Should the 'hibernate battery' be tasked w/Solely powering the  'OPERATING MCU' - Battery Exhaustion will occur far more quickly!     This factor has not been properly addressed - in my opinion.

    If this task was my firm's (task) - we would employ a rechargeable Li-Ion cell - and suitable 'Normal Operating Power Source' - which 'periodically & properly' - insures that the Li-Ion cell 'maintains full charge.'   (which - by the way - they are quite capable of doing - w/out  intervention - provided there (really) are no current drains being imposed...)

    You are to be commended for progressing from a 'simple' (passive) questioner - to a reasonable 'investigator.'      That skill (almost) guarantees 'fall-out benefits' - to many (perhaps ALL) areas of your work & life...