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BQ21080: BQ21080

Aykut Çinay
Prodigy 30 points
Part Number: BQ21080

Tool/software:

Hello

I am using BQ21080 in my project. I want to charge my 18650 Li-Po Battery with CC-CV. I set the regulation voltage to 4200 mV and the charge current to 800 mA,

I started the charge cycles. The first constant current cycle started. There is no problem but when the charge cycle is switched to Constant Voltage, the Battery Voltage is not 4.2 V as expected. I am measuring 3.95 V.

What is the problem here. Can you please help me with this?

Best regards

  • 0
    TI__Intellectual 1280 points

    Hello Aykut,

    Could you please verify if the charger is in a regulation mode other than constant voltage (CV), such as thermal, input voltage, or input current regulation? Please check CHG_STAT (REG0x00 bits 6-5) and TS_STAT (REG0x01 bits 4-3).

    Refer to page 11 of the BQ21080 datasheet:

    "Charging is done through the internal battery MOSFET. There are several loops that influence the charge current: constant current loop (CC), constant voltage loop (CV), input current limit, thermal regulation, VDPPM, and VINDPM. During the charging process, all loops are enabled and the one that is dominant takes control."

    Refer to page 22 of the BQ21080:

    "When VHOT < VTS < VWARM, the battery regulation voltage is reduced by 100 mV or 200 mV based on the value programmed in the TS_VRCG_0 bit within the TS_Setting register."

    If TS_STAT is reporting the battery is warm, then charge voltage is being reduced.

    Best regards,

    Alec Lehman

  • 0 in reply to Alec Lehman
    Prodigy 30 points

    My initial setting state is like below.

    RegulationVoltage    (VBATREG_6:0) : 4200 mV

    Battery Charging      (CHG_DIS)         : Battery Charging Enabled 

    Charge Current        (ICHG)                 : 100mA

    PrechargeCurrent    (IPRECHG)          : Precharge is Term 

    Termination Current (ITERM)                : %10 

                                     (VINDPM)             : Disabled

                                     (THERM_REG)    : Disabled

                                     (IBAT_OCP)         : 1500 mA

                                     (BUVLO)              : 3000 

                                     CHG_STATUS_INT_MASK :  Enable

                                     ILIM_INT_MASK                  : Enable

                                    VDPM_INT_MASK                : Disable

                                    TS_INT_MASK                      : Disable

                                    TREG_INT_MASK                 : Disable

                                    BQ21080_INT_MASK            : Disable

                                    PG_INT_MASK                      : Disable

                                   (TS_EN)                                   : Disable

                                   (VLOWV_SEL)                         : Disable

                                   (SAFETY_TIMER)                    : Disable 

                                   (WATCHDOG_SEL)                 : Disable

    input current           (ILIM)                                        : 1100 mA

                                   (EN_PUSH)                              : Disable

                                   (SYS_REG_CTRL)                  :  Regulation_PASS_THROUGH

                                   (SYS_MODE)                          : Source_VIN_VBAT

                                   (VDPPM_DIS)                         : Disable 

    Thermal regulation : OFF

    VVINDPM, VDPPM, and VINDPM : OFF

    If the charging voltage is active in my project, I want to charge 18650 after the first state. First, I charge a low charging current like 100 mA. The charging state is Constant Current as expected. Because the battery voltage level is 3.95 V.

    (If I take the ILIM flag, I reduce the charging current by 10 mA)

    After a while, I want to change the charging current to 800 mA. When I change the charging current, the charging status changes to constant voltage, but the battery voltage level is still 3.95V.

    1. TS_STAT is normal as setup above

    What do you suggest I do in this situation? 

  • 0 in reply to Aykut Çinay
    TI__Intellectual 1280 points

    Hello Aykut,

    Thank you for providing the device settings and confirming that the charging status is reporting constant voltage when your battery is 3.95V.

    Aykut Çinay said:
    After a while, I want to change the charging current to 800 mA. When I change the charging current, the charging status changes to constant voltage, but the battery voltage level is still 3.95V.

    Could you please measure the voltage on the BAT pin of the IC when the charging status is reporting constant voltage? It's possible that the voltage on the BAT pin is significantly higher than the battery voltage. If you're using long cables between your battery and the IC during testing, the IR (voltage) drop across the cables could become significant, especially when you increase the charge current to 800 mA.

    Best regards,

    Alec Lehman