Yesterday, I submitted the Version 1 of the power board to the factory for PCB fabrication. Although it will still take a few days before I receive the actual board, I’ve already started working on the adjustments and design for Version 2.
Admittedly, jumping into Version 2 at this stage is a bit hasty, especially since I haven’t yet confirmed whether the charging, protection, and boost converter sections of the previous design can work together reliably.
However, considering the missing ESD/TVS protection and the shortcomings in the LED indicator design in Version 1, I figured it would be better to start preparing rather than wait idly.
In the initial design, there didn’t include TVS protection for the Type-C connector, since I wanted to quickly verify the core functions. But today, I’ve added that section — it’s actually quite simple, requiring only a single TVS diode.
To make hand soldering easier, I avoided the commonly used ESDA25P35-1U1M due to its packaging being unfriendly for manual soldering. Instead, I chose the SMF5.0CA, which has a large enough footprint to make hand soldering more convenient.
As for the LED indicators, they’re relatively more complex. That’s because the charging chip I’m using, the MCP73831-2, only provides a single STAT pin. The typical application diagram from the datasheet shows only one indicator LED. Fortunately, this pin can output three different states — LOW, HIGH, and HIGH-Z — which makes it feasible to drive two indicator LEDs.
In the modified circuit, I’ve used a bi-color LED package (one housing both red and green LEDs), along with a logic gate circuit. This allows the red LED to light up during charging, and the green LED to light up once charging is complete.
I won’t be show the related schematics for now, as I prefer to wait until I receive and test the Version 1 board. After identifying any issues and making the necessary adjustments and improvements, I will then release the complete Version 2 circuit for the button cell charging section.