Rustic Engineering

Many things happen since the last post, but now this blog won new projects. First one is a USB Single Cell LiPoly Charger. I have many Lithium Polymer Batteries for my projects and charge them maybe a tricky borring if you don’t have the correct charger.

Really, this batteries needs a specific charger, and may explode if you use other type of charger.

So, we start to find the correct circuit for my DIY charger. After some Google research I find the MAX1811 IC. I’ts a single-cell lithium battery charger that can be powered directly from a USB or from an external supply up to 6.5V. Use a SO-8 Package, easy to solder and can be sampled at Maxim.

It’s only need a feel external components to work. Above you see the schematics and PCB of my version 1:

After the PCB fabrication, solder and wiring, this is the charger working:

Some things about the charger and the MAX1811:

• The SO-8 Package can handle 1.4 Watts.
• You can select between 4.1v and 4.2v battery regulation point.
• You can select between 100ma and 500ma current drain from USB.
• There’s a open drain pin (pin_8) for signaling end of charge condition (2.5V < VBATT < BATT Regulation Voltage). Normal charging resumes when the battery voltage exceeds 2.5V.
• A internal thermal loop limits the MAX1811 die temperature to
  +135°C by reducing the charging current as necessary.

Now that i saw my circuit work, I’m design it to be a USB stick. After some mistakes and bad design, this is the final version: