[time-nuts] Motorola Oncore UT+ firmware upgrade & backup power questions

Attila Kinali attila at kinali.ch
Sun Mar 15 05:15:45 EDT 2015

On Sat, 14 Mar 2015 12:56:05 +0100
Mike Cook <michael.cook at sfr.fr> wrote:

> Anyway. Using a CR2032 is OK, at least with my hardware and you get backup for at least 4 years.

A CR2032 is a quite huge coin cell. An NVRAM module does not use much
power once Vcc goes to zero. In todays low power modules it's in the order
of 100nA max specified. You can assume it to be somewhere in the range
of 10nA (probably package leakage limited) and 1uA (something has gone
wrong or very old module). Compare that to the ~240mAh capacity a CR2032
has (terminal voltage at 2.0V). Even assumeing a 1uA current, this will
give you 27 years retention. The limit with coin cells is usually their
self-discharge which is often specified in the 1%/year range, but in
reality gives you a battery lifetime of 10 to 20 years.

			Attila Kinali

< _av500_> phd is easy
< _av500_> getting dsl is hard

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