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Original question:

BQ25730: About LiFePO4 charger IC

BQ25730: About changing charging conditions corresponding to LiFePO4

Tsukui Yusuke
Guru 21930 points
Part Number: BQ25730
Other Parts Discussed in Thread: BQ25731

Hi,

I was introduced to the LiFePO4 charger in the thread below.
Customers are considering BQ25730 and BQ25731.
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/991992/bq25730-about-lifepo4-charger-ic/3669692#3669692

Customer wants to change the VSYSOVP and VSYS_MIN settings to accommodate the LiFePO4 charging conditions.
Is there a way to change the settings?

And customer wants to charge 3.8A when the battery voltage is 10V@4cell.
However, the data sheet contains the following:


Could you tell me how to set up for a 3.2V LiFePO4 battery?

・Input voltage :8-12V
・4 series cell (LiFePO4)
・Battery voltage :3.2V×4=12.8V (Customer want to precharge from 10V or less)
・Charge current :≒4A (3800mAh / 1C)

Best Regards,
Yusuke

  • 0
    TI__Genius 11385 points

    Hi Yusuku-san,

    SYSOVP is a set parameter and cannot be changed. Please see the below EC table for BQ25730 (pg 15 of datasheet). 



    To change VSYS_MIN, you can write to register 0x0D/0x0C (page 80 of BQ25730 datasheet).

    The screenshot you attached is just the pre-charge current clamp. Once the IC goes out of the pre-charge stage, you can change the charge current via register 0x03/0x02 (pg 49 of datasheet). For pre-charge to fast charge transition of 2S and above, here is the EC for your reference.

    If charging LiFePO4 is needed, you can adjust the IC parameters for your application. Some important registers to look at are ChargeVoltage (0x05/0x04), ChargeCurrent(0x03/0x02), and VSYS_MIN(0x0D/0x0C).

    I would strongly recommend getting an EVM to evaluate.

    https://www.ti.com/tool/BQ25730EVM 

    Thanks,

    Peng

    *If my answer solves your question, please press "This Resolved My Issue" on the thread.   

  • 0 in reply to Pengzhao Zhu
    Guru 21930 points

    Hi Peng-san,

    Thank you for your support.

    Let me clarify my understanding as follows about Ppre-charge to fast charge:
    Setting VSYS_MIN to 9600mV will start fast charge if the 4-cell LiFePO4 voltage is 10V.

    I am concerned that the final voltage is 2.5V per cell.

    Best Regards,
    Yusuke

  • +1 in reply to Tsukui Yusuke
    TI__Genius 11385 points

    Hi Yusuke-san,

    That is correct. For example, if I set the cell setting to 3S and VSYS_MIN to 9600 mV, the charger will be in fast charge mode when the battery voltage hits 9600 mV. In fast charge mode, the charge current is set by the ChargeCurrent(0x03/0x02) register.

    In my opinion, 2.5V per cell is very low as it corresponds to a deeply discharged LiFePO4 battery. However, that won't be the final voltage of the full battery system. You can change the max charge voltage through register 0x05/0x04 to raise the final charge voltage of the battery system. It is recommended to follow the battery manufacturer's recommendations for these parameters.

    Thanks and I hope this helps,

    Peng

    *If my answer solves your question, please press "This Resolved My Issue" on the thread.