LiPo Charger Booster Circuit Problem

Other Hardware General Electronics
1

I used SparkFun's PowerCell (https://www.sparkfun.com/products/11231) in a prototype product and then integrated the circuit onto our main PCB board. It has stopped working after about 4 months of use and I am having a very hard time trying to debug the issue. I just can't find anything wrong. I think there must be something wrong in my component selection or design - because I had weird issues when I first tried the circuit. I quickly had to replace the chip and it seemed to work fine for several months...

-The battery is fine
-The charger part of the circuit works fine
-I have made very few changes to the original circuit
-There is nothing on the boost chip's output
-Voltages on all control inputs look fine
-I am reading 4.2V on my USB 5V line when the circuit is activated... This seems strange
-I have never witnessed the main circuit draw over 400ma and I have tested in peak conditions.

Info on the circuit here: Battery Boost and Charge Circuit - Google Docs
Eagle files: https://drive.google.com/file/d/0ByaeK3RuGeaaMjVkdm9ZMy1CMDg/edit?usp=sharing
https://drive.google.com/file/d/0ByaeK3RuGeaadW1GRHlGUWo0Q2c/edit?usp=sharing
(first real Eagle project ever...)

I would be so appreciative of any advice - this is driving me crazy. Thanks!

2

I can't click the link where I am (No Eagle), but did you do something to the enable/power line to make sure it stays on, or is connected to a switch or something (And it isn't floating)? I've been fiddling with the same circuit, though I've not transferred it to my own PCB yet, and that's one of the things I've noticed about it. Its the one to specifically disable the output of the boost circuit w/o disabling the charger.

3

Yep - the EN pin is pulled high with the 10K resistor when my 3 position switch is in the battery power mode.

Otherwise, the EN line is pulled to the regulator's ground (this connection is made by the name of the net - you can't see it here).

Thanks for the idea though... I did have to fiddle with the EN at first.