Choosing Voltage Regulator Lipo Battery

Thread Starter


Joined Sep 8, 2020
I am designing the power input circuit for a microcontroller. The controller operates between 2.1v - 3.6v. For power purposes, I am using a Lipo battery with a range from 2.5v to 4.2v. I am looking to regulate the Lipo battery when in the range 3.6v-4.2v to a fixed 3.6v output. Once the battery starts draining below 3.6v I want the regulator to ideally just pass on the voltage from Lipo since it is now in the supply range of the controller. If someone has worked on something similar and can recommend a chip for regulation. I am currently looking at synchronous dc/dc buck converters. But their datasheets don't usually talk about the operation once the input voltage drops below the fixed output voltage, whether they just pass the voltage or not. The current draw from the battery will be max 50mA.


Joined Jun 29, 2019
If MCU operating voltage range is 2.1 to 3.6 volts then 3.6 volts means maximum voltage you do not want to exceed. Sounds like the MCU-s normal working voltage is 3.3 volts, for this purposes are plenty of LDO regulators available like LD1117-33.
The other thing is protecting Lipo from dropping voltage below 3.6 volts which can ruin your battery.


Joined Sep 10, 2020
Not sure what happen when Vin is below Vout on a buck regulator, but it seems you need a buck-boost regulator for your project.
Check TPS63900 IC


Joined Nov 6, 2012
A LiPo Battery is probably a bad idea.
They have very strict charge and discharge requirements/limitations,
and have a short life expectancy when compared to other available Battery technologies.

You will do permanent damage to a LiPo Cell if you discharge it below ~3V.

LiPo's require a specific dedicated charging system for charging without starting a Chemical Fire.

LiPo's go dead very abruptly,
everything's going fine one minute, then Battery Damage Voltage Crash the next minute.

The only reason to use a LiPo Battery is if you absolutely have to have
the smallest, and/or, lightest weight Battery possible.

Next, you don't really have a "Voltage-Range", you need exactly 3.3V "Regulated", at all times.
If this is a critical application, you need some sort of a warning device,
or an automatic, orderly shut down,
when the input voltage drops below ~3.1V.

In addition to this, even if you have a LDO Switching Regulator,
you need at least twice the required voltage for reliable operation, (minimum 5V).
2- LiPo Cells would be ~7.6V, nominal, and ~6V at "Critical Discharge Level", and would be much safer,
that is, if you just have to run LiPo Batteries.

50ma. ????, or is that the "Quiescent Current" at "Idle" ????
I would be willing to bet that it will pull more than 3-times that under heavy Computing Loads,
and the required Voltage Regulator is not 100% efficient either.