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battery controller won't change STAT2 line

Tim Woodward
Prodigy 30 points
Other Parts Discussed in Thread: BQ24105

8831.Battery Controller Schematic.pdf

I am using a BQ24105 controller as shown in the attached schematic. (R71&R73 have been changed to 14.7K; R83 has been changed to 1.8K).

I am never seeing STAT2 change state to ON, even when the current reaches the termination current. When the current does drop to that point, the controller goes into an odd oscillation between termination current and close to zero (600mA and 30uA) at about a 3s duty cycle. Not sure if these two issues are related. I wouldn't care if it was doing the oscillation but I can't ever get indication that charge is complete, since STAT2 never goes to ON.

  • 0
    TI__Mastermind 31120 points

    From you description it sounds like the charger is going in and out of charge.  A typical issue is if there is too much line resistance to the battery or the battery has too much resistance.  In this case the charger will terminate and the voltage will drop due to the drop in voltage across the resistance and the battery will start a new charge.  I am surprise that you don't see the STAT2 pin cycle.

    With a scope, check the battery voltage at the BAT pin and see if this is jumping from 4.2 to 4.1V.

    If you remove the battery, what is its DC voltage.  Most cells relax about 50mV so you should see the cell at 4.15V if it is full.  Take the measurement about 2 minutes after removing from charger.

    If you send waveforms of STAT1/2, VBAT, ISET1/2 and TS.  Maybe I can see something.

  • 0 in reply to Charles Mauney
    Prodigy 30 points

    We took an BQ24105 EVM, brand new out of the box, and connected it to our battery. It would still not indicate charge completion at 133mA. Then we added the recommended capacitor across the battery output in case our leads were too long/inductive. They were only about 2ft long, 22ga wire, so we didn't think so but we wanted to check. Still wouldn't indicate charge completion. Then we tried tying TTC high. That worked. Now STAT1 and STAT2 change state to indicate the change from charge in progress to charge complete. However, we don't have a timer any longer. Is this to be expected? Does TTC have to be tied high in order to get the STAT lines to indicate charge completion?

  • 0 in reply to Tim Woodward
    TI__Mastermind 31120 points

    You may need more capacitance on the BAT connection, on the EVM.

    Also remove the 2 feet of cable and connect the battery directly to the charger to see if you can get it working in that condition.

    Also measure the battery impedance. put a 0.2C load on the battery and then a 0.4C load and measure the voltage change from the two cases and the current change from the two conditions.  Apply the load for 1 second and read the voltage and current and then remove the load.  Apply the second load for 1 second and read the voltage and current and remove the load.  Take the difference of the voltage readings divided by the difference in the current readings.

    Do the measurements with and without the long leads.