Bug #1044

Choose a new rtc backup battery

Added by Kevin Woo over 4 years ago. Updated over 4 years ago.

Status:FixedStart date:01/22/2010
Priority:NormalDue date:
Assignee:Kevin Woo% Done:

0%

Category:Scoutfly
Target version:Development

Description

We need to run on 1.8V

History

#2 Updated by Kevin Woo over 4 years ago

Wikipedia says that the typical capacity is 25mAh with our current draw of 5uA. This leads to about 208 days of running only on the battery. There is also a self discharge of .1mA. This may dramatically lessen the lifetime of the battery.

Alternatively we can use: http://www.allspectrum.com/store/product_info.php?cPath=76_156&products_id=1589&osCsid=f6ab02f15e80a8597fbd2cce9064f1fe&sdesc=CR1220+3.0V+Lithium+Button+Cell+Battery%2C+38mAh%2C+%281pcs%2Fbl%29+%3D%3DSHIPS+GROUND+ONLY%3D%3D+Model+%23+CR1220-BP1

This is a 1220 but has a capacity of 36mAh which gives us 316 days. It costs $0.99 each.

#3 Updated by Kevin Woo over 4 years ago

Using 2 diode drops. Schottky and standard diode -> .3 + .7 in the worst case leads to 2V which is a little dangerous. Common case will be .8 + .4 which leads to exactly 1.8V.

Diode:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=641-1002-1-ND

#4 Updated by Kevin Woo over 4 years ago

  • Status changed from Assigned to Fixed

We're going with the CR1220. Added to both BOMs

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