How can I design a back-up battery management circuit

Hi, I am recently assigned to a project which is highly related to power management. The problem is simply like this: There is a circuit that already works but it is wanted to work on some areas constantly have power line down issues. So, I need to design a power management circuit that will always work with or without power line. When power goes down, management system must switch automatically to battery mode, and when it comes back it should automatically start to charge battery. So bottom line, microcontroller must always work without any data loses.

Since I got the project, I have been researching for power management chips on digikey, so far I found lots of chips however I am not sure they are what I am looking for.

https://www.digikey.com/product-search/en/integrated-circuits-ics/pmic-supervisors/2556197

https://www.digikey.com/product-sea...s-ics/pmic-battery-management/2556336?stock=1

The main circuit works on 3.3 V standart VDD and current consumption is max 33 mA.

For instance, this is what I am inspecting most: **broken link removed**

What I am not clear about is this can drive both main circuit and charge the battery at the same time. And also when power line is down, can it companse instant voltage peak and do not cause to data lose. If anyone can help me I would be very appreciated. Thanks.

You can put some back-up capacitors to increase the circuit working time out of external energy source.

With the battery, supply a low power comparator (its current consumption actually depends of your need) with a battery supplied reference, say 3V, being the compared voltage one generated by the external power supply.

The comparator will ever compare the internal supply reference with the external. When the external voltage is not enough (find a value) it must switch from the external supply to the battery. You could achieve that with inverted mosfet transistors for instance, when one is turned on the other is not and there will not be current between both different supplies.

Hi Alper,

I would consider using something like this, nothing wrong with the part you have chosen. But the linear data sheets has more information to help with your issues/concerns.

http://cds.linear.com/docs/en/datasheet/4079f.pdf

This is a new product that linear have release in their battery management line, this should be able to maintain battery charging and runs itself (depending on the length of down time) easily. What voltage you set the circuit to switch in will have a effect on the instant voltage but the transient response of the FB should compensate fast enough so the line doesn't drop out.