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BQ25895: Charge termination with system load on

Andrew5821
Genius 4565 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQ27510-G3

We have our BQ25895 set to terminate at 256mA.  I noticed it was still charging at ~140mA with the system on.  I then turned the system off and it immediately terminated.  I found this strange.  Any explanation as to why this would be happening?

  • 0
    TI__Guru 57781 points

    Hi,

    Referring to p22 on the d/s,

    If the charger device is in DPM regulation or thermal regulation during charging, the charging current can be less than the programmed value. In this case, termination is temporarily disabled and the charging safety timer is counted at half the clock rate.

    Please check if the device was under DPM or thermal regulation when the system load applied.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Genius 4565 points

    Here are the registers both while charging and after I would expect charge termination.  I see it in neither one of those states.  

    In The Middle of Charging

    BQ25895 Reg00 = 0x5c
    BQ25895 Reg01 = 0x5
    BQ25895 Reg02 = 0x3d
    BQ25895 Reg03 = 0x3a
    BQ25895 Reg04 = 0x30
    BQ25895 Reg05 = 0x13
    BQ25895 Reg06 = 0x5e
    BQ25895 Reg07 = 0x8d
    BQ25895 Reg08 = 0x2
    BQ25895 Reg09 = 0x44
    BQ25895 Reg0A = 0x93
    BQ25895 Reg0B = 0x96
    BQ25895 Reg0C = 0x80
    BQ25895 Reg0D = 0x58
    BQ25895 Reg0E = 0x0
    BQ25895 Reg0F = 0x0
    BQ25895 Reg10 = 0x0
    BQ25895 Reg11 = 0xe2
    BQ25895 Reg12 = 0x0
    BQ25895 Reg13 = 0x1c
    BQ25895 Reg14 = 0x79

    Charge current is 180mA as reported by BQ27510-G3 (Should be terminate by now 256mA +/-20% = 204.8mA)

    BQ25895 Reg00 = 0x5c
    BQ25895 Reg01 = 0x5
    BQ25895 Reg02 = 0x3d
    BQ25895 Reg03 = 0x3a
    BQ25895 Reg04 = 0x30
    BQ25895 Reg05 = 0x13
    BQ25895 Reg06 = 0x5e
    BQ25895 Reg07 = 0x8d
    BQ25895 Reg08 = 0x2
    BQ25895 Reg09 = 0x44
    BQ25895 Reg0A = 0x93
    BQ25895 Reg0B = 0x96
    BQ25895 Reg0C = 0x0
    BQ25895 Reg0D = 0x58
    BQ25895 Reg0E = 0x0
    BQ25895 Reg0F = 0x0
    BQ25895 Reg10 = 0x0
    BQ25895 Reg11 = 0xe2
    BQ25895 Reg12 = 0x0
    BQ25895 Reg13 = 0x1c
    BQ25895 Reg14 = 0x79

  • 0 in reply to Ning T
    Genius 4565 points

    I'm at 78mA and still no charge termination:

    BQ25895 Reg00 = 0x5c
    BQ25895 Reg01 = 0x5
    BQ25895 Reg02 = 0x3d
    BQ25895 Reg03 = 0x3a
    BQ25895 Reg04 = 0x30
    BQ25895 Reg05 = 0x13
    BQ25895 Reg06 = 0x5e
    BQ25895 Reg07 = 0x8d
    BQ25895 Reg08 = 0x2
    BQ25895 Reg09 = 0x44
    BQ25895 Reg0A = 0x93
    BQ25895 Reg0B = 0x96
    BQ25895 Reg0C = 0x0
    BQ25895 Reg0D = 0x58
    BQ25895 Reg0E = 0x0
    BQ25895 Reg0F = 0x0
    BQ25895 Reg10 = 0x0
    BQ25895 Reg11 = 0xe2
    BQ25895 Reg12 = 0x0
    BQ25895 Reg13 = 0x1c
    BQ25895 Reg14 = 0x79

  • 0 in reply to Andrew5821
    Genius 4565 points

    This did end up terminating at 64mA, which I find rather strange considering the programmed settings.

  • 0 in reply to Andrew5821
    TI__Guru 57781 points

    Hi,

    Referring to 8.2.8 Battery Monitor on the d/s, Could you please read ADC values (REG0E, REG0F, REG10, REG11, REG12) during your test and let us know?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Genius 4565 points

    I did, they are posted above

  • 0 in reply to Andrew5821
    TI__Guru 57781 points

    Hi,

    Only REG0D has value, what about other registers?

    BQ25895 Reg0C = 0x0
    BQ25895 Reg0D = 0x58
    BQ25895 Reg0E = 0x0
    BQ25895 Reg0F = 0x0
    BQ25895 Reg10 = 0x0

    Referring to 8.2.8 Battery Monitor, The device includes a battery monitor to provide measurements of VBUS voltage, battery voltage, system voltage, thermistor ratio, and charging current, and charging current based on the device modes of operation. The measurements are reported in Battery Monitor Registers (REG0E-REG12). The battery monitor can be configured as two conversion modes by using CONV_RATE bit: one-shot conversion (default) and 1 second continuous conversion. For one-shot conversion (CONV_RATE = 0), the CONV_START bit can be set to start the conversion. During the conversion, the CONV_START is set and it is cleared by the device when conversion is completed. The conversion result is ready after tCONV (maximum 1 second). For continuous conversion (CONV_RATE = 1), the CONV_RATE bit can be set to initiate the conversion. During active conversion, the CONV_START is set to indicate conversion is in progress. The battery monitor provides conversion result every 1 second automatically. The battery monitor exits continuous conversion mode when CONV_RATE is cleared.

    Thanks,

    Ning.