Single Cell Lithium
Battery Management System

This board can charge a single Lithium cell while also protecting against 5 fault conditions. I use a MCP73831 for charging the battery, and a BQ29707 for providing protection against over voltage, under voltage, over current discharge protection, over current charge protection, and short circuit protection. These features are critical for interfacing a lithium battery with any project.

Version 1 is seen in the above images, while is works perfectly and meets all of my requirements, it has some problems. The biggest problem with V1 is the cost. The majority of the space on the board is occupied by the 3 large MOSFETS that are seen in the images. While those components take up alot of space, they are also very expensive, each costing around $1 - $2 in low quantities. Version 2 is already in the works, and to combat the FET cost issue, I have chosen a dual array package for the N-channel which is significantly smaller and is closer to 60 cents a peice. same for the P-channel but in a single array. Shown below is the bill of materials for Version 1, it shows the cost of each component and the total price for me to manufactur a board.

$2.92 for the two N-Channel MOSFETS and $1.41 for the P-Channel. This means over 50% of the entire boards cost is taken up with those 3 component, including the cost of getting the PCBs made. I am estimating that in Version 2, I will shave 3$ off the cost of these components alone. Version 2 will incorporate more features, like 5 and 3.3 Volt power rails, 4 layer PCB, and more. This will add a significant cost to the board, but it will hopefully improve it aswell.