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BQ25792: Battery charge

user6555887
Prodigy 230 points
Part Number: BQ25792

Dear sir:

   When using bq25792 to realize 1-cell battery charging, the following problems appear, please help to confirm the cause，thank you !

1.The charging current of bq25792 is set at 1.5A. When the battery is charged to about 3.1V, the charging current is less than 100mA, and the charging current is unstable. The vsys is only about 3.8V

 The measured waveforms are as follows:

 

2.Replace the 1pcs battery with a voltage of about 4.1V for charging confirmation. The measured waveforms are as follows

VSYS=4.2V,Ibat=260mA

3.Recharge the 3.1v battery and confirm that the charging current can reach 1.5A,VSYS=4.2V,Ibat=1.46A

The above conditions of 2pcs battery are detected, and the register settings are as follows:

  REG00 0x04
  REG01 0x1A4
  REG03 0x96
  REG05 0x2F
  REG06 0x12C
  REG08 0xC3
  REG09 0x05
  REG0A 0x23
  REG0B 0xDC
  REG0D 0xBB
  REG0E 0x39
  REG0F 0x22
  REG10 0x80
  REG13 0x01
  REG14 0x1E
  REG17 0x7A
  REG18 0x14

The circuit diagram is as follows:

Please help to confirm the cause of the defect,Thank you !

  • 0
    TI__Guru*** 143980 points

    Hi Ellie,

    Can you confirm what each of the scope channels are connected to? I assume channel 3 is charge current.  What is your input voltage?

    Are you saying that in (1) that if you connect a 3.1V battery to BAT pin, the current is limited to 100mA but in (3) if you connect a battery then let it discharge to 3.1V, it charges as expected?

    What do the status and fault registers(REG0x1B-0x27)  report during (1) and (3) above?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 230 points

    Dear Jeff：

        The waveform channel is designed as follows:

        Channel1：VSYS     Channel2：Vbat     Channel3：Ibat

       The development board charges the discharged battery(Vbat<2.8V). The charging current is about 150mA at 2.8V ~ 2.99V, less than 100mA

    at 2.99V ~ 3.5V, unmeasured at 3.5V ~ 3.9V, 1A at 3.9V~ 4.1V, 300mA at 4.1V ~ 4.15V and 150mA above 4.15V

      Sometimes the battery voltage is above 3.5V, and the charging current can reach 1.5A after replugging the battery, sometimes not.

       The registers are set as follows:

      REG00 0x04
      REG01 0x1A4
      REG03 0x96
      REG05 0x2F
      REG06 0x12C
      REG08 0xC3
      REG09 0x05
      REG0A 0x23
      REG0B 0xDC
      REG0D 0xBB
      REG0E 0x39
      REG0F 0x22
      REG10 0x80
      REG13 0x01
      REG14 0x1E
      REG17 0x7A
      REG18 0x14
      REG1B 0x0F
      REG1C 0x6A
      REG1D 0x01
      REG1E 0x10
      REG1F 0x00
      REG20 0x00
      REG21 0x00
      REG22 0x00
      REG23 0x00
      REG24 0x00
      REG25 0x00
      REG26 0x00
      REG27 0x00

    Please confirm it,Thank you!

  • 0 in reply to user6555887
    TI__Guru*** 143980 points

    Hi Ellie,

    That status and fault registers look normal.  Is PFM enabled or disabled?  If you toggle PFM bit (REG0x12b4) does that resolve the issue?  If not, if the battery charges slightly, does that fix the issue?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 230 points

    Dear Jeff:

        After register REG12 is set to 0xb4, the battery can stably charge at 1.5A. This problem has been solved. Thank you very much!

    But now there are two problems:

    1. Reg12 is set to 0xb4, the battery is charged after the battery is empty (Vbat < 2.8V), the charging current jumps to 1.5A directly, and there is no precharging process. Reg08 is set to 0xc3, and the threshold voltage from precharging to fast charging is set to 4.2 * 71.4% ≈ 3V. Do we need other settings?

    2. Reg12 is set to 0xb4. When the battery is charged to 4.2V, remove the battery and place it for a period of time. When Vbat < 4.1V, insert the battery again,the battery doesn't charge

    Please confirm the above questions,Thank you very much!

       Best regards,
       Ellie
  • 0 in reply to user6555887
    TI__Guru*** 143980 points

    Hi Ellie,

    Regarding 1, if the resistance from BAT pin to battery is high or the battery has high impedance, then the precharge current may be enough to cause the 2.8V battery to immediately rise to 3.0V.  If you lower the precharge current value or lower the LOWV percentage, precharge should occur.

    Regarding 2, what is the recharge voltage setting in REG0A?  Default setting is 200mV.  If you want recharge at 4.1V, you can set to lower voltage.

    Regard,

    Jeff