I am using a BQ24172 in a design, for a 3 series cell pack. The problem I am having is the Fast Charge safety Timer doesnt seem to be operational. I have a .047uF to ground on the TTC pin, which should be a 263 minute (4 hr 23 minutes), but i have run this from 9:10am to 3:50pm (present) and it is still in CC mode at the charge rate I set the ckt up to.
To test the thing I have a DC voltage source which only has a current source capability set to 11.1V, I also have a low value load resistor wired through a Ammeter so that the Ammeter reads negative current when the charger output is supplying current to the load, and positive current when the voltage source is supplying the current. With the voltage source set at 11.1V, the charger IC overrides the DC source, and supplies 12.4V @~ 551 mills. I would have expected the chip to go into fault at around 1:30pm, but no...its still charging away. The pin is at 1.246V, which is also where it is when you cycle the Charger supply off and back on. Anyone know the problem here?
Thanks in Advance
Charlie