I would like to build a battery charger with my UC3906 IC. I found a lot of data-sheets, application note, etc. but nothing that comprehensively explain how to choose the values of the resistors. I would expect a "few lines guide" of the form "for a n cells 12V battery, choose R1, R2, etc. such and such." But I found nothing like this. Can someone help? In my case, I have a 6 cells 12V lead acid battery (cells in series apparently, capacity not specified), but it would be nice if the answer be general and valid for any type of lead acid battery.
Look at the spec for the BQ24450. It's the exact same IC, same die - just changed the name for some reason - much better explanations. Also, if you have a problem initially getting the IC into the right state when first powering on (i.e bulk charge ), try putting a 10uf cap or so across the sense resistor that goes to pin 13 (the bottom resistor in the output voltage divider). Or you can put a reset switch across that same resistor - just press the switch after powering on to start the the bulk charge mode. Took me a while to figure that out - the circuit was going directly into the float state - skipping over bulk charge and over voltage. Hope this helps someone!
Thanks a lot for your suggestions! I had the same issue : when power on, the BQ24450 goes to float mode (13.xV). Adding 1uF (I had only such value) across the Rd resistor (from Fig.8) resolve the problem. But adding a switch across the Rd resistor and pressing it, stops the bulk charge mode.