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BQ25180: OTP programming

Part Number: BQ25180
Other Parts Discussed in Thread: BQ25185

Tool/software:

Hi, we have the same issue described in this thread: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1215688/bq25180-is-it-possible-to-change-reset-default-register-values

Is it possible to change the reset values in the BQ25180? For LiFePO4 applications for example, VBATREG defaulted to 7b0001010 (i.e. 3.6v)

Thanks

  • Hello Brian,

    I just sent you a friend request, please accept so we can have a temporary private message session.

    Best regards,

    Alec Lehman

  • Hello Brian,

    I recommend using BQ25185 for your LiFePO4 application. It's a 1A, standalone (RC-settable) linear charger with power path. The battery regulation voltage can be set to 3.6V with a resistor.

    Here is the BQ25185 product page: https://www.ti.com/product/BQ25185

    Please let me know if you have any questions.

    Best regards,

    Alec Lehman

  • Hello Alec, unfortunately the lack of I2C interface in the BQ25185 makes it particularly inconvenient for our application - which is why we would like to use the BQ25180 iff we can access OTP.

    Kind regards,

    Brian

  • Hello Brian,

    There should not be any issues caused by the POR register values when using LiFePO4 with BQ25180. When VIN is inserted and VBAT is below BUVLO, the battery will start charging at the pre-charge current. Then, the register settings can be configured as needed.

    Could you please let me know if you have any other concerns with using LiFePO4 with BQ25180?

    Best regards,

    Alec Lehman

  • Hi Alec, my primary concern is the scenario of a failure in the I2C bus or downstream device: With LiFePO4 cells VBATREG should be 3.6v, but the BQ25180 reset value is 4.2v (i.e. LiPo's upper cutoff), so if the device fails to set the required configuration after a restart it seems that there is a risk of overcharging with this chemistry, am I missing something?

    Thanks very much,

    Brian

  • Hello Brian,

    I believe the following situations expand upon your concerns of overcharging a LiFePO4 cell when the BQ25180 registers are default:

    1. A LiFePO4 cell whose voltage is below the BUVLO threshold (default 3V). The battery will pre-charge at 2mA until VBAT > BUVLO. Then, the battery will fast charge at 10mA until VBAT approaches VBATREG (default 4.2V), which is above 3.6V. The BQ25180 has a fast charge safety timer (default 6 hours) which will stop charging and send an interrupt if the device is in fast charge mode for longer than the fast charge safety timer duration. The pre-charge safety timer is 25% of the fast charge safety timer (so, default 1.5 hours). Depending on the capacity of the LiFePO4 cells you are using, and given that VBAT is ~2V in this instance, it is likely that the pre-charge safety timer will expire before the battery is able to charge up above the BUVLO threshold. In this case, the battery would not enter fast charge, but even if it did, it is still unlikely that it would charge beyond 3.6V before the fast charge safety timer expired. Again, this all depends on the capacity of your cells. Additionally, the device will only be able to start when an adapter is present, assuming that VBAT < VBATPOR (typically 3.21V).
    2. A LiFePO4 cell whose voltage is close to 3.6V. In this case, the battery will fast charge at 10mA towards the VBATREG (default 4.2V) target. However, the device can be powered up in battery only mode, since VBAT (ex. 3.5V) > VBATPOR (typically 3.21V). If an adapter is present, it seems the concern is that the battery will charge beyond 3.6V, since the device will not enter CV charging until VBAT approaches 4.2V.

    In each of these cases, the assumptions are that an adapter is always present and the firmware is unable to set any of the registers. In case 2, a battery protector IC could be used to disconnect the battery from the charger to protect the battery from charging beyond 3.6V. I believe that these situations are the worst-case scenarios when using LiFePO4 cells with BQ25180, but they are only problematic if (1) an adapter is always present, (2) the firmware absolutely cannot communicate with the device, and (3) a battery protector IC is not being used.

    Could you please clarify if you are concerned about the case where your firmware will absolutely not be able to communicate with BQ25180? Is there another case you are thinking about that is not described here?

    Best regards,

    Alec Lehman

  • Hi,

    That's correct: the concern is when the firmware is absolutely unable to communicate with the BQ25180 and when the battery is charged or nearly charged, as you describe in point number 2.

    Is there a way we could change the default VBATREG to avoid overcharging LiFePO4 cells?

    Kind regards,

    Brian

  • Hello Brian,

    That's correct: the concern is when the firmware is absolutely unable to communicate with the BQ25180 and when the battery is charged or nearly charged, as you describe in point number 2.

    In this case, the solution that I recommend is to include a battery protector IC in your design to protect the battery from overvoltage.

    Here is TI's portfolio of battery protector ICs: Battery protectors | TI.com

    Is there a way we could change the default VBATREG to avoid overcharging LiFePO4 cells?

    Unfortunately, we cannot change the default VBATREG at this time.

    Best regards,

    Alec Lehman