'LiPo Charge Boost circuit doing funny things
I am hobbyist who’s been working for two years on a project. I’m currently having an issue with my power circuit.
It consists of 3 “families” of parts We have:
- TP4056 - LiPo charge IC
- SDB628 - Boost circuit 2V - 28V input, 5V constant output.
- MIC39301S - Takes 5V and drops it to 3.3V constant.
My MCU needs both 3.3V and 5V.
Now here comes the issues. When the device is only on battery power, the SDB628 gives around 3.62V when I measured. Battery not fully charged. I should see 5V not 3.62V.
When it’s only on USB power (battery disconnected) I get roughly 4.8V on the other side of my diode (all well and good!).
When both the battery and USB is connected, I see almost 8V which is so strange! Logically speaking, 3.62 + 4.8 is around 8V…
I have absolutely no idea why. The 3.3V net works fine as it’s driven by the MIC39301S. My issue is with the 5V net. The idea is obviously to always have 5V no matter the battery voltage (3-4V) or USB cable plugged in or not.
I appreciate any help so that I can learn! Thanks :)
Schematic:
Sources
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