Lion 3.7 V battery charger

[cllunlu]

Hi,

I wanna add battery for internal rtc and when power get off, device will run until battery charge off. So I have to add chargable lion battery in schematic. Anyone can help to adding battery and charging part. I use pic18f66j65 microcontroller.

Thanks you

 

[D.A.(Tony)Stewart]

I believe all RTC application notes show how to use a supercap or primary Lithium battery e.g. 3.0V for battery backup.
Using a secondary 3.7V LiPo can also be done.

 

[andre_luis]

Despite being obvious, it is important remember to set a regulated voltage reference for the A/D converter used to monitor Battery, smaller than the shutdown voltage of the core.

 

[doraemon]

Hello!

Just for info, I used the following implementation (see picture).
I didn't use a battery, but a capacitor.
Its capacity is 0.2F, and it could run a clock for more than a week.
Advantages: no battery charge circuit needed. A resistor and a diode is enough.
Exteremly small, less than 2mm high. 6mm in diameter.
NB: It was made by Panasonic, but they stopped or will stop the production.
There are alternative at Digikey. Look for "supercap".
NB: in this case, diode wasn't even needed. I was using a RTC1390 from Maxim.
This chip manages the charge by itself.

 

[cllunlu]

Thanks everyone,
I wanna know how to charge lipo rechargeable battery 3.7V which energizer when energy get off in circuit.