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BQ24072EVM: Charger never terminates

PATRICK OHARA
Genius 3205 points
Part Number: BQ24072EVM


Hello,

I'm using the bq24072EVM to charge a 500mAh 3.7V Li-ion battery. This is a iPod replacement battery that we intend to use in a handheld instrument. As I approach 4.2V and sub 10mA current draw, I expect that the charger will terminate the charging process. It doesn't. Also, if the temperature increases on the battery, the internal thermistor should terminate charging. I used a lighter under the battery to be sure it got hot enough. The increased temperature did not terminate charging. Please explain the charging termination process and how my implementation may be wrong. I've included the setup description below for reference.

The input of the EVM is connected to a Keithley 2281-20-6 Precision DC Supply & Battery Simulator and is delivering 5.25VDC in power supply mode. I'm measuring the current sourced or sunk to the battery via a Keithley DMM6500 6 1/2 digit multimeter configured to measure in circuit (series) current. I have a 10 ohm 50W power resistor connected to the output as a load. The pins on the EVM are connected as follows: JMP1 RES->TMR, JMP2 TD/OFF/TERM -> VSS, JMP3 CE->VSS, JMP4 EN2->VSS, JMP5 EN1->HI.

You can see from the screen capture from the DMM6500 that the current drops substantially. Unfortunately D1 is still illuminated indicating that charging is still occurring.

Thank you,

Patrick

  • 0
    TI__Mastermind 21590 points

    Hello,

    Based on the settings you described, the device is in USB500 mode. With the 10ohm resistor on OUT, that's about 440mA load. With the input current limited to 500mA and a load of 440mA, the device will most likely be in DPPM mode where termination is disabled. Try setting EN2 high and EN1 low to place the device in ILIM mode. 

    For the thermistor, charge will only stop when the TS voltage is above 2.1V or below 0.3V

  • 0 in reply to Raheem
    Genius 3205 points

    Hello Raheem,

    Thank you for your quick response.

    I drained the battery so that it would require charging. I set up the EVM as you suggested - EN1 low & EN2 high. The battery charged, and as before, when it reached ~9 -10mA it turned off supplying just 1.4mA to the battery. Unfortunately D1, the LED that indicates charging was still on. I expect to be able to use CHG as logic input to my CC2640r2 to indicate that charging has completed. Do you have any other suggestions?

    Thanks again for your help,

    Patrick

  • 0 in reply to PATRICK OHARA
    TI__Mastermind 21590 points

    Hello,

    /CHG only reflects the charge status on the first charge cycle. You'll have to toggle the /CE pin to restart the charge cycle and get proper /CHG status.

  • 0 in reply to Raheem
    Genius 3205 points

    Hello Raheem,

    With 5.25 VDC connected to Vin, and no load connected, the battery is sinking about 0.15 A in recharge mode. I pull /CE high for a few seconds and then return /CE low. The battery is sinking 0.12 A and declining. It continues to reduce the current draw to ~10 mA and then drops to ~1.5 mA where it stays pretty constant. D2 /CRG stays high, the LED is still Green. Is there something else that may be causing D2 not to turn off when charging is complete?

    Thanks,

    Patrick

  • 0 in reply to PATRICK OHARA
    TI__Mastermind 21590 points

    Hello Patrick,

    Can you double check to make sure TD is not high. 

    If the device is not in VINDPM  or DPPM mode or thermal regulation, termination should be enabled. 

  • 0 in reply to Raheem
    Genius 3205 points

    Hello Raheem,

    Thanks for hanging in there with me. TD is low 0.00 VDC and TS is 0.55VDC. Other states are: EN1 is low, EN2 is high, CE is low, TMR is RES, PWRGOOD is High, CHG is High, and the battery is sinking 1.5 mA.

    Any other thoughts?

    Patrick

  • 0 in reply to PATRICK OHARA
    TI__Mastermind 21590 points

    Patrick,

    WHen VIN is absent, how much current is pulled from the battery?

  • 0 in reply to Raheem
    Genius 3205 points

    Hi Raheem,

    With the 10 ohm 50 W resistor as a load and VIN 0 V, the battery is pulling .3596 A. With no load the battery draws 3.5 microamps.

    Having let the battery drain for a while the charging limits (set by EN1 & EN2) are working again. During our previous conversations, the battery was at or very near full charge. This may have been why I wasn't seeing the correct behavior from the charger as it didn't require the higher current so it looked the same. However this doesn't explain my original problem that was that the logic level for full charge isn't changing, even after power cycling.

    Don't know if this helps,

    Patrick

  • 0 in reply to PATRICK OHARA
    TI__Mastermind 21590 points

    Hello,

    Can you track look at /CHG on a scope instead of the LED?

    Also can you try using a sourcemeter instead of a real battery.

  • 0 in reply to Raheem
    Genius 3205 points

    Hello Raheem,

    The following four screen shots are of scope probe on CHG  with VIN @ 5.25 VDC with header jumper disconnected, VIN @ 5.25 VDC with header jumper connected, VIN at 0.01 VDC with header jumper disconnected, AC coupled @ 5.25 VDC with header jumper disconnected. I've tried this measurement with both the battery that we intend to use (iPod replacement) and a Keithley 2281S-20-6 operated in battery simulator mode and basic power supply mode.

  • 0
    Genius 3205 points

    After a lot of mucking around, it turns out that I did not have the R10 potentiometer set correctly. The TI top assembly drawing shown below has TP15 labelled as the middle pin on JMP2. However the schematic, also shown below, shows the potentiometer connected to the top pin on JMP2. After adjusting the potentiometer to the correct value (3.0 Kohm) the evaluation board works as expected and terminates correctly.