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MSP430F5335 drains backup battery in 30 days

Normand Martel77
Prodigy 70 points

I have a portable medical device application where we power the main source with an AA battery.  The 5335 has an RTC with a backup power domain that can be powered by a coin cell on VBAT to hold time while the battery is swapped or the device sits on a shelf.

In this particular implementation, the backup battery is being completely drained in 30 days or less (while the main cell is removed).

Any idea why this is happening?

We've used this cell with the external TI RTC chip and it lasts for over 5 years.

Seems that something is drawing power and I don't understand what.

Thanks in advance.

  • 0
    Guru 11940 points

    Measure the current consumption over time, an associate it with the software functionality causing it. I hardly see a way around that.

    Else, not much information to work with ...

  • 0 in reply to f. m.
    Prodigy 70 points
    The battery is a 3.3 VDC Lithium coin cell connected to VBAT. Since this is the backup domain, the main logic is all turned off. Only the backup domain is operating... i.e. Keeping time, 8 backup registers bytes, and a couple control registers.

    We noticed with new batteries that the unit burns them down to 2.850 VDC in 30 minutes, and then the current falls off to nothing. The batteries then seem to last longer. So, there is something magical about 3.3 VDC and the 2.850 VDC threshold.

    Is there something that needs to be configured inside the supply supervisor or something to ensure only the backup domain is active when the main power source is removed?

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