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BQ24620: BQ24620 Charging cannot reach the set cut-off voltage

ZHONG
Prodigy 20 points
Part Number: BQ24620

Hi

 

Charge the 7S1P LiFePO4 battery pack with BQ24620,set charge end voltage is 25.12V,but when battery pack charging voltage reach 24.2V ,Charging status changes from charging to charging completed;

battery absent   multimeter VBTA = 24.2V,VBAT(pack+) oscillogram:

 

Charging completed  multimeter VBTA = 24.2V ,VBAT(pack+) oscillogram:

 

Charging completed  multimeter VFB= 1.7V ,VFB(pack+) oscillogram:

 

  How can I charge the battery pack to 25.12V

Thanks,

  • 0
    TI__Mastermind 24075 points

    Hi Zhong,

       VFB = 1.8V detects end of charge. What is the status of STAT1, STAT2? What is your input voltage, and how are you detecting end of charge?

  • 0 in reply to Kedar Manishankar
    Prodigy 20 points

    Hi Kedar

      The charging circuit   set charge end voltage VBAT =1.8V*(1+390K/30.1K)=25.12V, Input Voltage is 27V；

        When the system is connected to a 27V power supply and the battery voltage is below 24.2 ，the status pin  STAT is ON(Charge in progress);Once the Vbat is above 24.2V,the status pin STAT is OFF(Charge complete),During this period the PIN of PG always LOW;

        The picture below is the battery waveform measured by oscilloscope at Charge complete; In my opinion, what caused the charge to stop was the VBAT peak voltage reach 25.12V

      How can I solve this problem?

      Regards,

  • 0 in reply to ZHONG
    TI__Mastermind 24075 points

    Hi Zhong,

       When charging is stopped and you think charge is complete, what is the voltage on REGN? Are you measuring real battery voltage once charge is terminated? What is your termination current set to?