Can I directly connect L6824D battery charger output to MCU VBat?

[Levan]

Hi all,

I'm interested in utilizing a solar cell as the power source for my MCU project. To achieve this, I've implemented a power harvester that, in turn, employs the L6924D battery charger to efficiently charge a lithium battery. I'm seeking guidance on how to connect the MCU to this power source. Should I directly connect VBat and VDD to the battery, or should I incorporate an LDO circuit by connecting VDD to the LDO and VBat to the battery? Your advice on the preferred approach would be greatly appreciated.

Thanks in advance

[Peter BENSCH · Accepted solution]

Well, it depends on the end-of-charge voltage of the lithium battery, which, except for LiFePO4, is usually 4.1-4.3V, which is definitely too high for VBAT (if you mean VBAT of the STM32) and VDD. Even the typical 3.6V of LiFePO4 can deviate slightly upwards, which can also leave the permissible operating range of the STM32.

If you only have one battery to supply VDD and VBAT and this may also be 3.3V each, there is no point in separating them anyway and you could connect both together to the LDO, which generates the desired voltage from the lithium battery. If you have strict battery life requirements, the LDO should perhaps be an ultra-low quiescent current LDO such as e.g. the STLQ020 or STLQ015.

Hope that helps?

Good luck!
/Peter

[Levan]

Thank you!