AXP209 pin 30 - can we use it?

[jess]

Taken from the manual:

"9.4 Backup Batttery
AXP202 supports backup battery charge and discharge. When no main power (BAT/ACIN/VBUS) is
available, LDO1 will choose the backup battery to support the operation of some circuits, such as the
system real-time clock, etc.
When there is a main power, REG35H[7] can be set to charge the backup battery, whose target voltage
is 3.0V by default (adjustable via REG35H[6:5]) and charge current is 200uA by default ( adjustable via
REG35H[1:0])."

From what I understand we can use that (not-connected so far) pin 30 (BACKUP) for keeping the RTC happy using olimex "tiny" 3.7V 1400mAh LiPo - am I right?

[murerten]

No. If you connect the lipo battery as in the olinuxino board RTC is fed with it if main power is off. That backup battery you are talking about is another optional rtc backup battery like unrechargable 3V lithium cr2032 or a rechargable one.

[jess]

No. If you connect the lipo battery as in the olinuxino board RTC is fed with it if main power is off. That backup battery you are talking about is another optional rtc backup battery like unrechargable 3V lithium cr2032 or a rechargable one.

I should have been a bit more specific - I was thinking of attaching "an additional" small LiPo that will take care of my RTC and keep it alive in case I need to remove/replace my "main" battery. Or perhaps when using it exclusively with 12V AC-DC adapter and without "main" battery yet to power RTC during main power loss.

I can see from tablet schematics that pin 30 is always left NOT connected and wonder why...
At least in one place (related to cube board) another user reported problems when trying to use that pin hence my question here.

[vinzer]

Hi everyone,

Do you know if we may use pin 11 from of AXP209 as a 3.3V power source for the circuits including processor ?
The reason I ask is because according to the specs of the 209 chip this pin is 3.3V output. With the same time in two schematics where A13 is used together with A209 for some reason for 3.3V supply external power regulator is used.
The questions is: why ?

Thank you,
Vlad