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BQ25672: Bq40z50

Ayush Pareek
Prodigy 20 points
Part Number: BQ25672
Other Parts Discussed in Thread: BQ40Z50,

Tool/software:

Hi,

We are using BQ25672 for charging a 4 cell litium ion battery which is have bms Bq40z50. 

1. Once our battery get fully depleted it enter into the discharge cut-off. the battery shows 0V in this condition

2. When we connect the battery to the charger, it shows 2.15 V on the terminal and the charge state is trickle charge. 

3. The charger continues to charge the battery in trickle charge state for 1 hour and then switch to "not charging" state.

4. The battery does not recover with 2.15 V and 100 mA current. 

5. Using a bench supply, I found that battery only recover if we give voltage above 12.6 V

My query is, 

1. The data sheet says that voltage during trickle charge is around 2.5 V/ Cell. If I read the register (REG01_Charge_Voltage_Limit Register), it shows value 16.8V detecting the 4S battery. I assume trickle charge voltage should be 2.5 V * 4 = 10 V for 4 cell battery. is this correct ? 

2. As battery only recover by applying > 12.6 V then, is there a way to get a fully depleted battery using the charger chip (bq25672)? Any reference note or suggestion will be helpful

  • 0
    TI__Guru**** 167196 points

    HI Ayush,

    Regarding 1, the BAT pin regulates to 2.5V*4=10V with 100mA trickle charge for 1.5s.  If the battery pack protector does not close in that time, the charger begins a regular charge cycle.  So, after 1.5s, I would expect the output to be a triangular waveform as the BAT pin capacitance reaches regulation, terminates, discharges then repeats.  If that is not happening, you may have some older ICs that were tested incorrectly.  Can you provide the IC top marking and/or the reel information?

    Regarding 2, assuming you do not have the improperly tested ICs I mention above, the pack protector will eventually close after the charger enters the regular charge cycle.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 20 points

    Hi Jeff, thank you for your support on this

    I verified the output on BATP and I can see triangular waveform. 

    My observations are, 

    1. I tested the battery with a bench power supply and found that PACK protection only recovers if I give 12.6V, 100 mA current for more than 2-3 minutes. 

    2. If I give less than 12.6V and 100 mA current the battery does not accept the current. 

    so want to check 

    1. Can we do configuration to bq40z50 via I2C line to enable the charging in this case?

    2. Can we raise trickle charge voltage and time by configuring the charge IC bq25672?

  • 0 in reply to Ayush Pareek
    TI__Guru**** 167196 points

    Hi Ayush,

    Does the triangular waveform peak at slightly above 12.6V?

    Regarding 1, I will send this to TI's gauge team for comment.

    Regarding 2, unfortunately no.  The trickle charge voltage and current values are fixed.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 20 points

    The BQ25672, only give 2.5 V for a dead battery, It never give >2.5 volt. The oscilloscope trace is attached with this mail. 


  • 0 in reply to Ayush Pareek
    TI__Guru**** 167196 points

    Hi Ayush,

    There were some BQ25672 ICs that were improperly tested and cannot exit trickle charge. Please send the IC top markings and/or the reel label and I will investigate.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 20 points

    Hi Jeff, 

    Please find the IC markings in below image

  • +1 in reply to Ayush Pareek
    TI__Guru**** 167196 points

    Hi Ayush,

    This batch of ICs was tested incorrectly.  Approximately 10% of the batch/reel can get stuck trickle charge when no battery or battery with open pack protector is connected. Otherwise the ICs will work normally.  You can return the ICs referencing "stuck in trickle charge".

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 20 points

    Thanks Jeff for your support.