Battery charge / throughput solution recommendation

Dear MPS,

I want to design a circuit that can handle the following three scenarios:

Scenario 1:
Both an input source and an load are present. The load will be powered from the input source. When the input source can deliver enough current, the backup battery will be charged as well, but this is not an priority.

Scenario 2:
An input source is present, however no load is present. The backup battery will be charged.

Scenario 3:
No input source is present. The load will be fed from the backup battery.

The input voltage will be in the range of 3 -12V, the output voltage has to be 5V (USB). A single cell backup battery will be present. The output current has to be at max 2A, the input current will be at least 100mA and at max 3.
Is there an IC that can handle all of this? Or would I need both an battery charger and a buckboost converter in front of it?
Thank you for your time.

Hello Arthur,

Welcome to the MPS Technical Forum! I’ll start looking into possible solutions for your application, but first I have a few questions about your application. I understand your output load specs are 5V/2A. Can you also please specify your charge voltage, charge current, and battery chemistry? This will help in finding the best design for you.

Hi Bryan,

I want a 1s3p li-ion battery to be connected. This battery pack will consist out of 3 18650 li-ion cells in parallel. As the input current can be as low as 100 mA and as high as 2000 mA, the maximum charge current will be a bit less than 2000 mA. Because of the 1s3p battery, the charge voltage will be at maximum 4.2V.
I hope you can help me finding a solution^

Hi Arthur,
Have you looked at the MP2636? I think it is the closest to what you want.
The only limitation is the transition time between your modes 1 & 2 (load supplied from Vin) to mode 3 (load supplied from battery), which is not instantaneous.

Hi Nico,
This chip indeed looks like it can do the job. I also found the MP2731, which can handle a bit higher input voltage and a few other features which, after looking at them, are really nice.

Hi Arthur,
Yes, except that with the MP2731 the System Output is equal to the battery voltage: it cannot be 5V.
In Boost mode it can provide 5V with the USB On-The-Go (OTG) mode, but it is on its input pin, not the system output: this is different from what you described in your 3 scenarii.