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bq2423x timer

Chris Glaser
Guru**** 150830 points
Other Parts Discussed in Thread: BQ24232

bq24232 Dynamic Charge Timer (TMR). We have an 800mAh cell and have two charge modes, 100mA and 500mA. We currently have the TMR resistor set for 5 hours. Does this mean that when we go to 100mA mode we will only charge for 5 hours? This would not completely charge our cell.

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    TI__Guru**** 150830 points

    The timers will be extended if the charge current is reduced.  Reasons for the charge current being reduced include DPPM, thermal regulation, and a low input voltage source.  You will keep your fast charge current set to some value and the timer will be extended proportional to the fraction of that current actually going into the pack.  So, if you have your fast charge current set to 1A and you are operating in USB500 mode, then the Vin-DPM loop will activate and reduce the charge current to around 475 mA.  The timer frequency will go to about half of what it was, resulting in a doubling of charge time.  Like the termination current, you can always add a parallel resistor/FET on the TMR pin to adjust the timer manually between 2 values.

    From the datasheet, page 19: "The charge current limit is adjustable from 25 mA to 500 mA. The valid resistor range is 1.8 kΩ to 36 kΩ. Note that if ICHG is programmed as greater than the input current limit, the battery does not charge at the rate of ICHG, but at the slower rate of IIN(MAX) (minus the load current on the OUT pin, if any). In this case, the charger timers are proportionately slowed down."