Running STM32U083 directly from Li-SOCL2 battery

Magvel · ‎2025-11-24

I am using STM32U083 MCU in a project that runs on a 3.6v Li-SOCL2 lithium thionyl chloride battery (OC voltage 3.65V / Nominal voltage at 1mA 3.6V).

Currently I have used a LDO of 2.5v to power the MCU, but I was thinking if we can eliminate the LDO and directly power the MCU from the battery.

Going through the datasheet I have found that the recommended input supply voltage is 1.55v-3.6v, and max is 4.0v, I have seen a mass produced device using the same battery directly on a STM32L053 MCU. I am expecting the same might be possible with U083 as well.

Please suggest if this is okay or is there can be any potential issues that can happen.

Ozone · ‎2025-11-24

> Going through the datasheet I have found that the recommended input supply voltage is 1.55v-3.6v, and max is 4.0v, I have seen a mass produced device using the same battery directly on a STM32L053 MCU. I am expecting the same might be possible with U083 as well.

You might be right, and the short period above the 3.6V rating does not damage the MCU.

However, I think you need to consider the other end of the discharge curve.
When the battery voltage drops below the brown-out limit, your device will be dead - until the battery is replaced.
With some battery management system, you could avoid that, and schedule some actions before charge runs out.

Obviously this is not a point many mass products deem worthwile.

View solution in original post

Ozone · ‎2025-11-24

> Going through the datasheet I have found that the recommended input supply voltage is 1.55v-3.6v, and max is 4.0v, I have seen a mass produced device using the same battery directly on a STM32L053 MCU. I am expecting the same might be possible with U083 as well.

You might be right, and the short period above the 3.6V rating does not damage the MCU.

However, I think you need to consider the other end of the discharge curve.
When the battery voltage drops below the brown-out limit, your device will be dead - until the battery is replaced.
With some battery management system, you could avoid that, and schedule some actions before charge runs out.

Obviously this is not a point many mass products deem worthwile.

Andrew Neil · ‎2025-11-25

@Magvel wrote:
max is 4.0v

As your screenshot shows, that is the Absolute Maximum - that's not a guaranteed operating voltage.

@Magvel wrote:
I have seen a mass produced device using the same battery directly on a STM32L053 MCU.

As you know, many mass produced devices prioritise low cost against reliability, etc.

They're taking a gamble - do you want to take same gamble?

Are you aiming at the same market - where minimum cost trumps all else?

Sure, you'll probably get away with it, most of the time - is that sufficient for you?

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

Magvel · ‎2025-11-25

Hi @Andrew Neil, the product is competing in the same low cost market, but I didn't wanted to gamble so I asked here in the community, as I have mentioned even though the absolute max is 4.0V our system absolute max is 3.6v-3.7v in normal operation it will never exceed 3.6v, which is just at the corner of operating voltage(3.6v) given in datasheet. So I was doubtful if we can use the MCU in such a corner condition safely. I believe it is perfectly safe as the absolute maximum is around 4.0v as confirmed by @Ozone.

I will anyway test and validate the product working thoroughly before taking a final call.