This project was mainly a way for me to learn Altium Designer. It started out with me just messing around, but slowly a nice looking board started to emerge. So, I sent the design off to Gold Phoenix and got back 90 boards. It’s a charger for a single CR2450 (LIR2450 to be exact) coin cell. CR normally applies to primary cells (non-rechargeable). I’m guessing LIR stands for Lithium Ion Rechargeable. I bought a few of these cells from SparkFun a while back, but never really used them because I didn’t have a convenient way to charge them. Sparkfun sells a single-cell lithium charger based of the MAX1555 IC, but that chip has been hard to source lately. Regardless, its charging current is too high for this 110 mAH cell, and their board requires another daughterboard to hold the coin cell.
This board is based around the MCP73832, which contains all the logic and active devices to charge a single lithium ion/polymer cell. It has multiple charge modes, including constant current which does the bulk of charging. R3 sets the constant current. I chose a resistance of 20k ohms, to get a constant current of 50 mA; that’s about the max charging current one should charge a 110 mAH battery at.
Right now I’m only selling bare-boards, $5 each including shipping in North America. If there’s enough interest, I’ll sell fully populated boards. Email me to purchase one.
Post edited. Someone reminded me to post the Bill of Materials (BOM).