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DS1307 backup battery lifetime?

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happy2005

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Hi,

I've designed a prototype circuit using DS1307 RTC with CR2016 lithium battery.
I want to know that, how long time this battery supplies backup power to the DS1307 without losing RTC data? I would like to be sure, it should be at least 2 years. Because of the current drawed from the battery is very small, I couldn't measure current value. How can I measure (or calculate) the backup time without waiting 2 years?
Any suggestion, books, links are welcome..
 

IanP

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You can not calculate this time. If you had, say, 100Ω resistor connected between Ds1307 and the battery, using very sensitive voltmiter you would be able to measure some µV voltage drop, but this still wouldn't give you any indication about live-time of this battery.
Normally a lithum battery with device such as DS1307 should last for approx. 10 years .. that is the time Maxim-Dallas describes in the case of DS12887 (RTC with built-in battery) ..
 

    happy2005

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froggy

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Why not just consulting the datasheets:

The battery you using has typ. 80mAh capacity.
DS1307 is using 500nA in battery mode (or 800nA if you are using the square wave output)

This gives you:
for 500nA 160000h or 18.2 year
for 800nA 100000h or 11.4 year

the storage time for a lithium battery is usally specified to 10 years, therefore you can say that the battery should last for 10 years (counted from the battery mfg date).

The only thing that you now have to do is to verify by measurement that this is true, for example with a resistor as previous discussed, for example 100k gives you 0.1V/uA a good starting point.

/Froggy
 

    happy2005

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happy2005

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Thank you all. It is good idea. I will try to measure the current with a series resistor. But , i think, the resistor value should be as low as possible, because of the voltage drop and loading effect. Thank you again.
 

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