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LiFePo4 Charger array

I don't suppose someone could tell me if I'm on the right track here?  I'm no EE, having a hack's grasp of circuits, just doing this to keep from idle hands.  Anyway, I've designed a LiFePo4 charging circuit with the hope to add it to 6 LiFe batteries--trying to make a battery pack I can just plug in for my little guy.  Anyways, I have no idea if I'm close--don't suppose someone could look it over before I try to etch it?

I'm using this IC:


Trying to charge this battery:


BRD_LiFePo4_Charger_Single_to_Chain_3.2_SMD_--_Finished.pdf20.81 KB
LiFePo4_Charger_Single_to_Chain_3.2_SMD_--_Finished.pdf23.57 KB

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I am not familiar with these batteries except for what I read in the two links you gave.  But this is what I see from that. According to the battery data sheet, the standard charge current should be 100 mA.  The chip is only specified down to 130 mA using a 10K prog resistor.  You have a 1.5K in the schematic, which would give a 700 mA charge current.  The max charge current for the batteries is listed as 600 mA, but that will probably shorten the life.  I would recommend changing the prog resistor to 10K and increasing the input capacitor from 4.7 uF to about 25 uF since you are powering 6 chargers.  It wasn't clear if that is critical or not.  Also, you don't specify on your schematic what input power you are applying.  According to the app note for the chip, it should be between 4.15 and 5.8 volts and it needs to be able to provide 6 times the charge current, or about 1 amp.  Other than that it looks ok to me, keeping in mind I am only going on the information provided.

You, sir, are awesome.  Like I said, I'm pure hack.  I've been looking at it so long I'm not seeing simple stuff.  I also noticed I have no heat-slug connection for the DFNs.  I didn't put the input voltage because I didn't know what I needed.  I figured I could decide that later--when someone told me how to keep from blowing myself up.


Two follow ups:

First, am I correct in thinking I can wire these to batteries in parallel (with a nominal resistor between) and make myself a single connection chargable battery pack?

Second, without circuit solving math, do you know if I could change the cap and resistor to make it an array of 9?

Again, I cannot tell you how appreciative I am.  I'm learning lots, um, I think.


You cannot charge more than one cell in series.  Each cell has to be connected to one charger chip and they all have to be connected in parallel with a common ground, as shown in your schematic.  You can have as many of those as you want;  nine is no problem.  As long as your power source can handle the current.  Microchip makes a similar chip (the 223?) for charging two cells in series.  

I didn't look at your PCB layout but as you mentioned it will need heatsinking.  Following the example layout in the app note is probably a good idea.  It will definitely need a good heat-conducting connection from chip to board/heat sink.  Soldering it by hand will be a royal pain.  Google can help you find ways of doing that effectively.  Good luck.

The links you gave to the IC and the battery are both broken.