Shared projects

LIR2450 USB Charger v1.2

by chrislabs.
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2 layer board of 1.45x1.87 inches (36.91x47.60 mm).
Shared on February 10th, 2015 09:53.

Github Repo: github.com/cgrossde/LIR2450-USB-Charger

Based on MCP73831. Beware not tested (yet).

There are two charge modes:

  • fast (45mA)
  • slow (25mA)

Max charge current for a coin cell is usually between 80% and two third of it’s capacity. So you could charge a 100mA coin cell with 80mA. I wanted to increase the lifetime of my coin cells and reduced the charge current. If you want to have different currents here is the equation to calculate R_SLOW/R_FAST:

mA = 1000 / R in kΩ

Example: 1000/20kΩ = 50mA

BOM:

  • MCP73831 SOT-23-5
  • 0603 LED Green (~3.1V voltage drop)
  • 0603 LED Orange (~2V voltage drop)
  • 0805 Resistor 200Ω
  • 0805 Resistor 320Ω
  • 0805 Resistor 40kΩ
  • 0805 Resistor 22kΩ
  • 0805 Capacitor 4.7uF
  • CR/LIR2450 Coin cell holder (20mm diameter, 5mm height)
  • (optional) male pin header, jst pin header

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