Hi,
You are free to design what ever you like. You don´t need to use a dedicated controller. You are the designer, you set up the requirements.
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I don´t have the time to draw a schematic, but it should be straight forward.
You will have a voltage regulator for the microcontroller...Maybe it has an ENABLE input, then use this to switch ON/OFF. Or use a P-Ch MOSFET, or a high side switch, or a simple battery protection circuit ... it all depends on your requirement, voltages, currents, timings....
Currently we don´t know much about your design.
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in case if MCU in gets hang then what will happen?
You must not ask, you have to specify it. It´s your job.
You are free to use a software timeout, a hardware timeout, a low battery switch OFF, MCU internal watchdog, an external watchdog, no circuit at all... or any other idea.
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Generally a froum is not meat that others do your job. You have to show the requirements (all at once, not piece by piece). You have to draw sketches, flow charts... and so on.
We will help you to rectify mistakes. We will tell you how to improve your idea.
Klaus