We are using the TI BQ24103 Lion battery charging chip. I am using it on a test fixture in production that we use to test and condition batteries. It was originally configured with a TTC(time to charge) cap of 0.1 uF. This gives us a maximum charge time of around 4.5 hours.
This work great for our smaller batteries, but now we are trying to use these test fixtures on our larger batteries. These batteries typically take 8-10 hours to charge. The maximum TTC capacitance is .22 uF which gives a charge time of 572 minutes(9.5 hours). I need a maximum charge time of about 12-15 hours which require a capacitance of about .33 uF.
The data sheet even says you can short the pin to ground to disable the charge time limit entirely. By the letter of the datasheet, this capacitance is out of range, but looking at the details of the part, I don’t see any good reason why I can’t use a .33 uF capacitor on the TTC pin.
I don’t want to disable the time limit entirely, but I do want to extend it out around 15 hours. Note, this is for a production test board, not an actual shipping unit, so I am willing to take responsibility for breaking the spec. I just want a little insight into how that particular pin works before I make my decision.
-Paul
