I am having a problem with a BQ24100 charger I would like to some guidance on. On a normal functioning unit the charger turns on and chargers as expected then turns off and decays until the recharge threshold is reached when it turns back on. On some units though we see it looks like the charger is continuously on or on-off-on. Doing a review of the circuit it seems correct. The circuit has been in the field for some time now. The only things I can see are the output inductor is not the ideal inductor. We are using a 4.7uH inductor where the manual says it should be closer to a 10uH. In table 3 It states to select the inductor to give you a Fo of 16Khz although it gives a range of 8k-32khz. Looks like our circuit is about 23khz. How important is it to stay at 16khz and what are the instabilities of running at 23khz? The current capabilities of the inductor are within spec.
We do power other things off the battery while it is being charged but they should not pull that much current and the cell should be able to provide since we don't us any of the circuits if the battery is below 3.5v. I could understand that while in CV mode the circuit could pull enough to deplete the battery below Vrecharge threshold but nothing in the circuit should do that and this is only happening on 10% or less of our production. Once the circuit stops 'oscillating' it seems to go back to normal. Below is a output waveform of a unit that was acting up. I started to probe it with my DMM and before I could get my scope out the problem went way. It seems to a common theme; as soon as we start to probe around and debug it the unit fixes itself. Any ideas?
