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BQ25731: About IDCHG_TH2 and OTG output

Tsukui Yusuke
Guru 21930 points
Part Number: BQ25731


Hi,

We are checking the OTG output of BQ25731.
When the output current exceeds IDCHG_TH2, the OTG output drops.
Let me ask you a question about IDCHG_TH2.

What kind of protection does BQ25731 provide if IDCHG_TH2 is exceeded?
In the data sheet, I could only confirm the operation that triggers / PROCHOT.
Does the protection that turns off the OTG output work?

Best regards,
Yusuke

  • 0
    TI__Mastermind 34595 points

    Hi, Yusuke,

    IDCHG_TH1 and IDCHG_TH2 are two level battery discharge current limit, which trigger PROCHOT if enabled.

    The BATOC is especially designed to protect the charger during OTG. 

    9.3.21.6 Battery Discharge Overcurrent Protection (BATOC)
    The charger monitors the battery discharge current to provide the battery overcurrent protection (BATOC)
    through voltage across SRN and SRP. BATOC can be enabled by configuring EN_BATOC=1b. BATOC threshold
    is selected either 133% of IDCHG_TH2 or 200% IDCHG_TH2 through BATOC_VTH bit. The threshold is also
    clamped between 100 mV and 360 mV SRN-SRP cross voltage.
    When discharge current is higher than the threshold after 250-μs deglitch time, BATOC fault is triggered, status
    bit Fault BATOC is set accordingly. Converter shuts down when BATOC is asserted to disable OTG operation
    and reduce discharge current.
    BATOC is not a latch fault, therefore after BATOC fault is removed, with 250-ms relax time, converter resume
    switching automatically. But status bit Fault BATOC is only cleared by host read.

    Regards,

    Tiger 

  • 0 in reply to Tiger Zhou
    Guru 21930 points

    Hi, Tiger,

    Thank you for your support.
    We checked "20h Fault BATOC” .
    However, Fault BATOC bit was 0.

    When checking the operation, the OTG voltage has dropped according to the IDCHG_TH2 set value.
    The output is reduced triggered by the IDCHG_TH2 threshold instead of the BATOC threshold.
    Is there a protection function using IDCHG_TH2 threshold?

    Best regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 34595 points

    Could you share the whole register map? How about OTG_Current? Did you hit the OTG current limit?

  • 0 in reply to Tiger Zhou
    Guru 21930 points

    Hi Tiger,

    Thank you for your response.
    Changing the IDCHG_TH2(IDCHG_TH1) setting eliminates the OTG voltage drop.
    Register map of OTG output settings is as follows.
    Are there any possible factors?

    05/04h 　
    03/02h 　
    07/06h 1740h
    09/08h 3C00h
    0B/0Ah 　
    0F/0Eh
    21/20h 　
    23/22h 　
    01/00h 631Bh
    31/30h B300h
    33/32h 00BAh
    35/34h 1434ｈ
    3D/3Ch 0040h
    37/36h 0A81h
    39/38h 0D00h
    3B/3Ah 2040h
    3F/3Eh 　

    Best regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 34595 points

    Another possibility is to exceed the OTG current limit. 

  • 0 in reply to Tiger Zhou
    Guru 21930 points

    Hi Tiger,

    I checked the operation on the evaluation board.
    Could you check the attached file?

    BQ25731 waveform 20211105.pdf

    ”Drop of OTG Voltage” was confirmed near "DCHG_TH2: 125% IDCHG_VTH1".
    What kind of protection does BQ25731 do near DCHG_TH2?
    And Please tell me the threshold accuracy of "DCHG_TH2: 125% IDCHG_VTH1".

    Best regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    Guru 21930 points

    Hi,

    I would appreciate it if you would update me on this matter.
    And Can you see the PDF file I attached?
    Please let me know if you need any other documents.

    Best regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 34595 points

    If IDCHG_TH2 is exceeded, it reduces the OTG voltage to protect the battery. The IDCHG_TH2 is pretty accurate, within -4% ~ +3% range. 

  • 0 in reply to Tiger Zhou
    Guru 21930 points

    Hi Tiger,

    Thank you for your reply.
    >it reduces the OTG voltage to protect the battery.
    There is no explanation in the data sheet for the above operation.
    In the background, customers want to know more about how to limit current and OTG voltage drop operation details.
    Does BQ25731 perform protective operation when IDCHG_TH2 is exceeded?

    Best regards,
    Yusuke

  • +1 in reply to Tsukui Yusuke
    TI__Mastermind 34595 points

    Just set the IDCHG_TH2 to limit the discharge current. The BATOC will kick in if IDCHG_TH2 is exceeded.