A20 battery backuped RTC

[confucij]

Hi there!
I've suffering of lack of documentation about RTC battery charging. What type of batteries it support - LiOn, LiPo, NiCd or what? The only mention about charger I found is in FEX guide:

pmu_backupen: 1 to enable RTC/backup battery charging

I'm planing to use 3V Lithium coin battery will it be OK?

[LubOlimex]

Hey there,

There are two battery options for A20-SOM which are provided by the power management unit. The one implemented in A20-SOM-EVB is the 3.3V Li-Po battery option with battery recharge that can keep the board fully powered. The range of batteries compatible with the A20-SOM-EVB's on-board connection that we sell are available in this sub-part of the web-site: https://www.olimex.com/Products/Power/

The second option is just keeping the RTC alive - connect a battery between 2.5V and 3.1V to pin 6 of GPIO-6 connector of A20-SOM which is signal AXP_BACKUP BACKUP. The characteristics of this second battery can be found on page 7 of the datasheet of AXP209 (search for bakcup battery in the table). The datasheet is here: http://dl.linux-sunxi.org/AXP/AXP209_Datasheet_v1.0en.pdf

You can have both Li-Po battery (keeping the board fully operational) and coin battery (keeping only RTC) options working simultaneously for extra safety.

Best regards,
Lub/OLIMEX