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Original question:

BQ25672: Always no charging current (CC mode & No Fault)

BQ25672: Abnormal current during battery charging

xu elvis
Prodigy 10 points
Part Number: BQ25672

Tool/software:

Hi TI:

I simply used BQ25672 to charge the battery(2S 18650), And all the configurations use the default settings. When I plugged in the battery to start charging, the following situation occurred:

[ Input Vol: 9.0V ]

Q1. The battery can be charged normally, but the current is relatively low (about 0.7A, the default config is 1A);

Q2. Sometimes, when inserting the battery, the charging current is only 0.25A to 0.45A , And the BQ25672 and Inductance shows obvious signs of overheating (about 40~50℃). And now the SW1/2 is 4.2V;

[ Input Vol: from 6V to 9V (Use a variable power supply) ]

Q3. When the input voltage gradually increased from 6V to 9V, the battery failed to charge properly.

This is my schematic:

This is my layout (Two-Layer):

Register dump for the above three problem points:

Dump registers in Q1:

0x12 0x03 0x48 0x00 0x64 0x4c 0x00 0x9c 0xc3 0x05 0x63 0x00 0xdc 0x4b 0x3d 0xa2 0x85 0x40 0x00 0x21 0x1e 0xaa 0xc0 0x7a 0x54 0x00 0x9c 0x2f 0x8a 0x01 0x00 0x00 0x00 0x00 0xaf 0x92 0x50 0x1c 0x20 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x30 0x00 0x00 0x00 0x00 0x00 0x00 0x23 0x67 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x21

Dump registers in Q2 (Charge current is 0.42A with overheating):

0x12 0x03 0x48 0x00 0x64 0x4c 0x00 0x98 0xc3 0x05 0x63 0x00 0xdc 0x4b 0x3d 0xa2 0x85 0x40 0x00 0x21 0x1e 0xaa 0xc0 0x7a 0x54 0x00 0x98 0x2f 0x6a 0x01 0x00 0x00 0x00 0x01 0xaf 0x92 0x50 0x18 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x30 0x00 0x00 0x00 0x00 0x00 0x00 0x23 0x61 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x21

Dump registers in Q3:

0x12 0x03 0x48 0x00 0x64 0x26 0x00 0x98 0xc3 0x05 0x63 0x00 0xdc 0x4b 0x3d 0xa6 0x85 0x40 0x00 0x21 0x1e 0xaa 0xc0 0x7a 0x54 0x00 0x32 0x27 0x0a 0x01 0x00 0x00 0x00 0x00 0xdf 0x92 0x50 0x18 0x20 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x30 0x00 0x00 0x00 0x00 0x00 0x00 0x11 0xaa 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x21

  • 0
    TI__Guru**** 166626 points

    Hi Elvis,

    BQ25672 is a buck only charger so VBUS >= VREG is required to complete a charge cycle. The PCB layout does not follow the recommended layout per the datasheet = EVM layout.  Frankly, I can't figure out the layout because the pin out does not appear to match the IC. The traces for the high current PMID, SWx, SYS are too thin. 100nF caps on PMID and SYS must be placed on top of the IC to filter switching noise or the charger does not regulate IINDPM or charge current correctly.

    Regarding Q1, the charger is in taper charge (constant voltage regulation) per REG1C[7:5].  The voltage at BAT pin = VREG and the current is naturally tapering down.

    Regarding Q3, the charger has auto set EN_HIZ due to poor source (input voltage dropped below 3.6V during power up).  The charger will attempt to startup again after about 10 minutes.  If this is a solar app and the battery is removed or deeply discharged resulting in pack protector FET opening, SYS may crash.  Please read https://www.ti.com/lit/pdf/sluab26.

    Regarding Q2, the charger is reporting fast charge but that is clearly not the case. When measured on an oscope, do SW1/SW2 have squarish switching pulses?

    Regards,

    Jeff