LiPoly charging with MCP73833

September 19th, 2009 · 14 Comments · misc

For my latest projects I used a lot of single cell lipo batteries. They are really nice. High power density, low self-discharge, no memory effect and they can deliver quite an amount of current.
But lipo battery handling is a bit more complicated as with other rechargeable batteries. You have to take care of under voltage and over charging as that may destroy the battery.

I used the Sparkfun LiPoly charger, based on MAX1555, for some time and it works really well. The only thing I missed was a way to control the current. After some research I decided to try another chip, the Microchip MCP73833.

Features of the MCP73833

Copied from the specs:

High accuracy preset output voltage regulation
Regulated output voltage options
User-programmable charge current up to 1A
Two open-drain Status outputs
Preconditioning and end-of-charge ratio options
Under-voltage lockout
Power Good output

What I like is the ability to adjust the charging current and the status outputs, which should get really useful if integrated into a greater application.

The schematic

The schematic is mostly a copy of the reference design. It has three LEDs, one for power good, one for charging and one for charging complete. All pins of the chip itself are also available on two header rows. The idea was to enable easy integration on a breadboard. Actually I misplaced the rows, so they don’t fit (#fail).

The resistor R4 is used to control the charge current. I used a socket for that, so I am able to adapt the current for different batteries. The 10k resistor results in a charge current of 100 mA.

The result

All components were 0805 SMD parts, despite the MCP73833, which is 10-MSOP. This was my first attempt to do something useful with SMD. I used my brand new hot air reflow station, which turns out to work as expected. Only I had to be very precise at dosing the solder paste. Applying too much had to be removed with solder wick later on.

Issues

The next version should include a jack for a wall adapter. The two header pins are not really useful to connect to a power supply. And of course the two rows of header pins should be aligned correctly to fit on a breadboard.

As a sidenote: as you see, the board has a mini-USB connector to be able to connect the charger to a notebook.
I stronly recommend to use some kind of USB hub to test any newly build USB hardware.
I didn’t. And now I have a burned first prototype of my charger and only one USB port left on my MacBook. Although the OS warned me with “something is sucking too much, port gets shut down”, it wasn’t fast enough. So, you have been warned.

14 responses so far ↓

1 jpc // Sep 19, 2009 at 14:04

Try shutting the computer down and removing the battery for several minutes. It seems that the polymer fuses which protect the USB power lines won’t reset themselves while the voltage is applied.

It fixed my short-circuited iBook G4 USB and suffered-from-220V-on-line-out on a MacBook.

It unfortunately didn’t fix my combo line-in/out port on the new MacBook Pro 13″.
2 Alex // Sep 19, 2009 at 17:24

Thanks for the tip. Unfortunately that hasn’t helped.
3 Armandas // Sep 19, 2009 at 18:52

Why would you want to connect VCC to GND like the BAT jumper does? This just can’t be good
4 Alex // Sep 19, 2009 at 18:57

The jumper should be the battery connector.
5 Armandas // Sep 19, 2009 at 18:58

Sorry, didn’t look properly, that one must be just a battery connector. But what is JP2 used for?
6 Alex // Sep 19, 2009 at 19:08

You can connect a 5V power supply to it if you don’t want to use your USB. That one is to be replaced with a proper jack in the next design.
7 FlorinC // Sep 20, 2009 at 01:57

No need for another jack, you can use a AC-to-USB power supply, like this one:
http://www.dealextreme.com/details.dx/sku.4837
8 Lithium-ion polymer battery charging with the Microchip MCP73833 | ToGadget , The Guide to Gadgets // Oct 17, 2009 at 04:23

[...] LiPoly charging with MCP73833 [...]
9 justDIY // Oct 17, 2009 at 04:46

Alex, Thanks for the info on the MCP73833 – I had been looking for a simple LiPo charger for a while now. Maxim has neat parts but their availability sucks!
10 jrob // Oct 17, 2009 at 19:30

usb connector seems like an afterthought, if you intend to use usb check out another IC like
MAX1555
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4002
with current limiting
11 Tim // Oct 19, 2009 at 07:54

Can you use this ‘online’ – i.e. keep a constant 5v supply either from the incoming power or the battery? I’ve just bought an energy monitor that uses a usb connector for power and realised it has no option for batteries internally which is a shame for carrying it about so I was thinkling something that could act as a backup would be great
12 Alex // Oct 19, 2009 at 17:16

Hm, I’m afraid that won’t work.
13 supriono // Nov 8, 2009 at 00:19

coll MAN, I like it
14 Amazing LiPoly Charger with MCP73833 - CircuitGeek // Nov 18, 2009 at 07:35

[...] All the above features made it’s the perfect component for adjusting the charging current and the status outputs! [source] [...]