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BQ25306: BQ25306 - it doesn't charge battery

Satawat Kaeokrajang
Prodigy 10 points
Part Number: BQ25306

Hi everyone,

I have question about BQ25306 for 2 cell battery charger. I designed circuit diagram, I totally followed datasheet of BQ25306 for the typical application (a standalone charger without power path) but it didn't charge my battery (Li-Ion 2 cells with BMS) when I tested on my layout PCB (Input from power supply 13 Vdc). I checked voltage at output terminal, it was only about  7.2 V and then it had dropped to 6.8 V. Can everyone help me please? Thank you so much

  • 0
    TI__Mastermind 49631 points

    Hi,

    What are VBUS (voltage at VBUS pin), IVBUS, VBAT (voltage at BAT pin), IBAT, VFB, VREGN, VTS?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 10 points

    I've checked charger PCB and now it works. It charges my battery but output isn't stable. (I have set IBAT = 1 A) 

    When I used VBUS= 12 V, VBAT = 7.75 V, IBAT=0.02 A

                        VBUS = 11 V, VBAT = 7.89 V, IBAT=0.827 A

                        VBUS = 10 V, VBAT = 8.08 V, IBAT=0.916 A 

                        VBUS = 9 V, VBAT = 8.21 V, IBAT=0.524 A

                        VBUS = 8 V, VBAT = 7.54 V ,it doesn't charge.

                         Below 8 V, it doesn't charge.

    ***At that moment my battery was about 7.76 V***

    It doesn't make sense why I dropped VBUS, VBAT increased until VBUS=9 V or this is normal operating.

  • 0 in reply to Satawat Kaeokrajang
    TI__Mastermind 49631 points

    Hello,

    Are you using real battery or battery simulator for the tests?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 10 points

    Hello,

    I'm using real battery for the test.

    Thank you,

    Satawat

  • 0 in reply to Satawat Kaeokrajang
    TI__Mastermind 49631 points

    Hi Satawat,

    Did you test on different real batteries with different units and boards? Are the charging behaviors on several boards similar or not?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 10 points

    Hi Ning,

    I've tested on different printed PCBs with the same circuit, the charging behaviors were pretty similar.

    PCB1 

    Without battery, when I used VBUS = 13 V, VBAT = 6.48 V (LED ON)

                                                  VBUS = 12 V, VBAT = 7.59 V (LED ON)

                                                  VBUS = 11 V, VBAT = 7.64 V (LED ON)

                                                  VBUS = 10 V, VBAT = 8.30 V (LED blinking)

                                                  VBUS = 9 V, VBAT = 8.30 V (LED blinking)

                                                  VBUS = 8 V, VBAT = 7.57 V (LED ON)

    with battery, it works only with VBUS = 12V, 11V, 10V, 9V and IBAT = 0.753 A, 0.825 A, 0.919 A, and 0.510 A respectively

    PCB2 

    Without battery, when I used VBUS = 13 V, VBAT = 5.63 V (LED ON)

                                                  VBUS = 12 V, VBAT = 5.78 V (LED ON)

                                                  VBUS = 11 V, VBAT = 6.34 V (LED ON)

                                                  VBUS = 10 V, VBAT = 8.30 V (LED blinking)

                                                  VBUS = 9 V, VBAT = 8.27 V (LED blinking)

                                                  VBUS = 8 V, VBAT = 7.51 V (LED ON)

    with battery, it works only with VBUS = 11V, 10V, 9V and IBAT =  0.840 A, 0.938 A, and 0.365 A respectively

    it seems that it works quite well with VBUS = 10V.

  • 0 in reply to Satawat Kaeokrajang
    TI__Mastermind 49631 points

    Hello,

    We will check and get back to you.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    TI__Mastermind 49631 points

    Hello,

    Is VBUS measured at the VBUS pin and the VBAT measured at the BAT pin?

    Thanks,

    Ning.