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MSP430F5635: Battery Backup System with coin cell battery

daniolip
Intellectual 320 points
Part Number: MSP430F5635

Hi,

I'm planning to use the "backup battery system" provided on MSP430F5635 to maintain the RTC state when my main power is off. The document is pretty straight forward regarding such capabilities.

My question lies in using such system with a non-rechargeable coin cell battery such CR1220 or CR2032. I know the system charger can be turned off, but what reverse current can I expect to be applied on my battery?

I don't have any numbers, but some research I did implies that any reverse current on such batteries is harmful and can result in catastrophic results. Some documents says 1uA is fine, but others says that any current resulting in 3% charge of total capacity in any given time can have bad results.

What is TI recommendation on such matter? Can I safely connect any coin cell on Vbat pin and expect to work reliably?

  • 0
    TI__Genius 13975 points
    Hello,

    Many customers have successfully implemented their battery backup system with a non-rechargeable coin cell battery with no issues, given that the charging circuit is disabled. That is essentially what the system is meant for. As a precaution if you are worried about any small amounts of reverse current, you can place a small inline resistor in series with the battery but this is not a requirement.

    Best regards,

    Matt
  • 0 in reply to Matt Calvo
    Intellectual 320 points

    Hello,

    Even though the system was design for such, I still have no numbers to back me up about the safety of such system if asked by my CTO. However I accept your answer since my research points that I will have no problems with my battery given that the reverse current is not beyond 1uA.

    Anyway, thanks for the support and quick response.

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