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BQ25898: Case where REG0D register returns to default after USB connection

Yuta Nishie
Genius 3430 points
Part Number: BQ25898

Hi,

The following questions assume that USB is always connected after USB was connected and IC started charging.

1. If VBUS_STAT changes 010→000→010 after charging starts, will the REG0D register return to the Default value? Is it necessary to reconfigure the REG0D at this time?

2. If charging starts and VBUS_STAT is always 010 and PG_STAT changes 1→0→1, will the REG0D register return to the Default value? Is it necessary to reconfigure the REG0D at this time?

3. In addition to the above, please tell me the case where the REG0D register is expected to return to the default value when the USB cable is continuously connected.

Best Regards,

Nishie

  • 0
    TI__Mastermind 24305 points

    Hi Nishie, 

    Please see my comments below. 

    Firstly, please help to provide detailed test conditions for when VBUS_STAT and PG_STAT are changing during charging. These statuses are not expected to change if a valid input source is connected to VBUS. 

    This may not be the case for your system, but an example of when VBUS_STAT and PG_STAT will change is if VBUS voltage drops below battery voltage. In this case the input supply is no longer considered "good."

    If Vbus voltage reduces below the operational minimum threshold when it rises back to normal level the BQ25898 device will identify this as a new adapter plug in and REG0D will be reset. 

    Can you please help to provide the following information. 

    -Is REG0D value changing when PG_STAT changes from 1->0->1? 

    -Please help to provide a waveform showing VBUS and VBAT at the time when VBUS_STAT and PG_STAT change. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Genius 3430 points

    Hi Garrett-san,

    Thank you for your support.

    Garrett Kreger said:
    Firstly, please help to provide detailed test conditions for when VBUS_STAT and PG_STAT are changing during charging.

    ->Which register information does "provide detailed test conditions" refer to? Or is it voltage information? It would be helpful if you could tell me the necessary items.

    Also I will check with the customer about the VBUS and VBAT waveforms.

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    TI__Mastermind 24305 points

    Hi Nishie, 

    Allow me to further clarify below. 

    Yuta Nishie said:
    Which register information does "provide detailed test conditions" refer to? Or is it voltage information? It would be helpful if you could tell me the necessary items.

    My question refers to voltage information. Specifically can customer show VBUS, VBAT, and PG pin signals during time period when they observe VBUS_STAT and PG_STAT change from 1 -> 0 and 0 -> 1. 

    If they are using BQ25898D version IC then there is no PG pin and that signal can be excluded from the waveform. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Genius 3430 points

    Hi Garrett-san,

    Thank you for your detailed explanation. However, as I checked with the customer, it is difficult to obtain the waveform because this inquiry assumes how to process FW.

    Do you know if REG0D will return to the default only based on the contents of the first inquiry? And could you tell me if I need to reconfigure it?

    Garrett Kreger said:
    If Vbus voltage reduces below the operational minimum threshold when it rises back to normal level the BQ25898 device will identify this as a new adapter plug in and REG0D will be reset. 

    Let me check if my understanding is correct regarding your answer.

    ・When VBUS_STAT changes from 010 to 000 to 010 after USB connection and charging starts

    →In this state, if the voltage of the VBUS falls below the minimum operating voltage and the voltage rises to the normal range, the REG0D register returns to the Default value and must be reset. If the VBUS voltage does not fall below the minimum operating voltage, the REG0D register is not reset, and therefore no reset is required.

    ・PG_STAT changes from 1 to 0 to 1 after USB connection and charging starts, while VBUS_STAT is always 010.

    →In this state, if the voltage of the VBUS falls below the minimum operating voltage and the voltage rises to the normal range, the REG0D register returns to the Default value and must be reset. If the VBUS voltage does not fall below the minimum operating voltage, the REG0D register is not reset, and therefore no reset is required.

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 24305 points

    Hi Nishie, 

    Understood, no worries. Your understanding is correct. Anytime VBUS_STAT changes from 010 to 000 to 010 or PG_STAT changes from 1 to 0 to 1 REG0D will reset to default when VBUS rises back to an appropriate level.

    This behavior occurs because the VBUS voltage rise back to normal level event is treated as a new adapter being plugged in, hence REG0D is reset as part of power up as described in section 9.2.3 of the datasheet. 

    If VBUS does not fall below the minimum operating voltage or Vsleep threshold REG0D register should not change and no reset is required. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Genius 3430 points

    Hi Garrett-san,

    Thank you for your reply.

    Is it correct to understand that the VBUS minimum operation voltage is V(VBUS_OP)=3.9V? Section 9.2.3 lists the specs V(VBUS_UVLOZ), V(BAT)+V(SLEEP), and V(VBUSMIN), so I'm confused as to which value to refer.

    Also, is it correct to understand that the register for checking that VBUS is below (above) the minimum operating voltage or V(sleep) threshold is VBUS_ GD?

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 24305 points

    Hi Nishie-san, 

    Please see my comments below. 

    Yuta Nishie said:
    Is it correct to understand that the VBUS minimum operation voltage is V(VBUS_OP)=3.9V?

    Yes 3.9V is VBUS minimum operating voltage for buck converter to function. I also mention VSleep threshold for the following scenario. Battery is fully charged (VBAT = 4.2V) VBUS may drop below VBAT, but not below 3.9V operational minimum. In this scenario PG_STAT still changes from 1 to 0. 

    Yuta Nishie said:
    Also, is it correct to understand that the register for checking that VBUS is below (above) the minimum operating voltage or V(sleep) threshold is VBUS_ GD?

    I recommend checking either PG_STAT or VBUS_GD register bit to determine if VBUS is not at an acceptable voltage level. Both register bits status convey the same information. 

    Best Regards,

    Garrett