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Original question:

BQ21080: BQ21080

BQ21080: VDPPM issue occurred

Lumina Gui
Genius 3435 points
Part Number: BQ21080

Tool/software:

Dear TI Engineer,

In our smart galsses project, we found that when increasing the load (enable the WiFi function) will cause VSYS to lose power. The application diagram is as follows:

We measured the waveform when this problem occurred, the red line represents VBUS, the yellow line represents VBUS current, and the blue line represents VSYS output from the charging IC.

We read the value of each register when the problem occurred and found that the FLAG0 Register displayed VDPPM fault detected.

The register setting is as below:

charger_bq21080_dump_regs Reg[ 0] = 0x61
charger_bq21080_dump_regs Reg[ 1] = 0x00
charger_bq21080_dump_regs Reg[ 2] = 0xa0
charger_bq21080_dump_regs Reg[ 3] = 0x5f
charger_bq21080_dump_regs Reg[ 4] = 0xc3
charger_bq21080_dump_regs Reg[ 5] = 0x50
charger_bq21080_dump_regs Reg[ 6] = 0x97
charger_bq21080_dump_regs Reg[ 7] = 0x04
charger_bq21080_dump_regs Reg[ 8] = 0x8f
charger_bq21080_dump_regs Reg[ 9] = 0x09
charger_bq21080_dump_regs Reg[ a] = 0x00
charger_bq21080_dump_regs Reg[ b] = 0xcf
charger_bq21080_dump_regs Reg[ c] = 0xc0

Do you have any better suggestions to solve this problem?

Best Regards,

  • 0
    TI__Expert 6260 points

    Hello Lumina,

    Thanks for reaching out. I'll review your question and follow up with you on Monday (5/12).

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Genius 3435 points

    Hi Alec,

    Supplementary description of the problem as below:

    1) This problem only occurs when the battery level is above 80%, and it does not occur when the battery level is low. Removing the battery also not have this problem;

    2) When VDPPM fault detected, re plugging and unplugging the adapter can solve this problem;

    3) When VDPPM fault is detected, the maximum load current measured from the Vin input can reach 700mA;

    4) We also tried to disable the VDPPM (bit VDPPM_DIS =1), this problem still exists;

    5) We also tried to set SYS_REG_CTRL_2:0=001h, this problem still exists;

    Thanks,

    Kind Regards

  • 0 in reply to Lumina Gui
    TI__Expert 6260 points

    Hello Lumina,

    Thanks for the information.

    I noticed from your register logs that REG0x02=0xA0, which indicates both a TS fault and a VDPPM fault were detected.

    • Could you please share the BQ21080 portion of your schematic?

    From your waveform capture, it looks like VSYS falls below the 1.6V SYS short threshold, which disables the input FET. Once VSYS rises above the 1.6V threshold, the input FET is reenabled, but the SYS load pulls it down again, causing the cycle to repeat. Is this the problem you are seeing?

    • Could you please share another waveform capture of the issue with VBAT included?
    • Does VSYS fall at the moment the load increases?

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Genius 3435 points

    Hello Alec,

    Thanks a lot for your reply, and now we have encountered a new issue with VDPPM abnormality. That is, when the camera's recording function is turned on during charging, bq21080 will continue to report interruptions. 

    The log information we obtained is as follows:

    Is there any suggestion for this problem?

    Thanks,

    Kind Regards

  • 0 in reply to Lumina Gui
    TI__Expert 6260 points

    Hello Lumina,

    Thanks for the update. The continuous interrupts suggest that something is repeatedly triggering them. Since the VDPPM flag is the only one being set, it's likely the device is repeatedly entering and exiting VDPPM. This behavior may be related to the previous issue you observed when enabling the WiFi function. Is that issue still occurring?

    Could you please provide waveforms showing VBUS, VBAT, IBUS, and IBAT during the camera recording enable and WiFi load enable?

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Genius 3435 points

    Hi Alec,

    The schematic is as below:

    Set to VSYS follow battery voltage mode. When the battery voltage is low and the charging current is high, Vin will be pulled to around 4.1V. As the charging current decreases, Vin will rise, but it will occasionally trigger continuous interruptions when fully charged.

    At the same time, we found that when VDPPM is disabled, interruptions are 100% to occur, but after enable it, the interruptions will becomes a probability happens.

    The waveform is as below:

    Thanks,

    Best Regards,

  • 0 in reply to Lumina Gui
    TI__Expert 6260 points

    Hello Lumina,

    Thanks for the update. I'll review this and follow up with you by end of day.

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    TI__Expert 6260 points

    Hello Lumina,

    Thanks for sharing the waveform.

    It looks like the problem is that VIN is too low during charging. This could be caused by too much voltage drop (IR drop) between the input source and the VIN pin of the BQ21080. When VIN falls below the sleep threshold, the charger considers power "not good" and stops pulling current from the input.

    The sleep threshold, VSLEEP, is 72mV typical. If VIN drops below VBAT + VSLEEP, the charger considers VIN power to be not good, and it stops pulling current from the input. An interrupt is generated when power good status changes.

    At the start of the waveform, VIN and VBAT are both about 4.4V, and VSYS is slightly higher than VBAT - this is expected in battery tracking mode, where VSYS = VBAT + 225mV (typical).

    Just before the first interrupt pulse, the charger likely enters sleep mode. VIN rises to around 5V because no current is being pulled. At the same time, VSYS falls to battery voltage.

    Before the third interrupt pulse, VSYS rises again to its normal level, but VIN drops back to 4.4V and crosses the sleep threshold, so charging stops again.

    This matches your observation that the issue only happens when the battery is nearly full. When VBAT is close to VIN, current that's pulled from the input likely pulls VIN below the sleep threshold.

    To confirm this is the root cause, I recommend testing with a higher input voltage or setting SYSREG to Passthrough mode, which connects VIN directly to VSYS and gives more headroom between VIN and VBAT.

    Let me know if the issue goes away when VIN is higher.

    Best regards,

    Alec