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BQ25798: shutdown mode vs ship mode

Part Number: BQ25798

Tool/software:

Hi,

I'm using the BQ25798 with shipfets installed.

I place the system in backup mode, so only the battery is present, only the battery is powering the system.

In that situation, I plan to shutdown the system to minimize any Iq from BAT. (It is for storage, we will only re-start placing the adapter on again).

My question (1) is: in that scenario, what is the difference between ship mode vs shutdown mode? The only power source is a battery.

And the question 2: with shipfet installed, where is the correct point of connection of the pin BATP?  (direct to BAT+ or BAT IC pins?).

Thanks in advance.

REGARDS

  • Hi,

    When you say backup mode, are you referring to the operation described in datasheet section 9.3.7.2 "Backup Power Supply Mode"? Ship mode and shutdown mode will not work while the converter is operating in the reverse power direction.

    With regard to question 1:

    • Shutdown mode disables the whole device and turns off the ship FET so that there is minimal quiescent current and can only be exited through an adapter plug-in.
    • Ship mode slows down the system clock to reduce the current drawn from the battery and turns off the external ship FET and the internal BATFET.

    With regard to question 2:

    • The connection point of BATP is to the positive terminal of the battery through a 100 Ohm resistor.

    Let me know if this answers your questions.

    Best regards,
    Michael

  • Hi,

    Could you clarify again....

    You say that when we are powering the board from a battery, (for example, if external power is not available), we couldn't  shutdown to all off.... We plan re-start only when external power becomes available. The idea is to enter into a state of near-zero drain current from the battery when boards are stocked, perhaps for months.

    In short: Can we do the shutdown in backup mode? or we need to do that when powering from an adapter?

    It seems that shutdown or ship mode are not related to the origin of the power source. 

    Looking forward to your answer... Best regards.

  • Hi,

    When the board is only powered by the battery, you can shut down the whole system with shutdown mode. This would be the lowest power option. In this case, the only the BQ25798 will only power back on when there is an adapter plugged in.

    Can we do the shutdown in backup mode? or we need to do that when powering from an adapter?

    I want to make sure I understand this question correctly: are you asking if you can enter shutdown mode while in backup mode to turn everything off? This should work, but backup mode will be turned off after doing so.

    Best,
    Michael

  • Hi again,

    I need to concentrate a little bit more, please.

    In the case of working in backup mode, with no power source, energy is used from the battery, but in reverse mode, the board is powered from PMID, not from VSYS. So is it possible to enter into shutdown in that scenario? 

    If possible: do I need to execute a determinate sequence? or simply apply the correct register value...

    If not possible: Any idea? I need to shutdown to preserve battery when the board is stored.

    The IC is very good, with a lot of integrated functionalities, but that is my pendind task.

    Thanks.

  • Hi,

    In the case of working in backup mode, with no power source, energy is used from the battery, but in reverse mode, the board is powered from PMID, not from VSYS. So is it possible to enter into shutdown in that scenario? 

    I believe the answer to this question is yes. In shutdown, the Ship FET is turned off, blocking the reverse path to both VSYS and PMID. If the I2C write is performed, this will cut power from the battery.

    If possible: do I need to execute a determinate sequence? or simply apply the correct register value...

    There are two relevant I2C configurations for this. Upon turning on the BQ25798, set the bit SFET_PRESENT to let the device know that the ship FET is installed. When entering shutdown mode, write to the register bits SDRV_CTRL to turn off the ship FET and enter shutdown mode.

    Let me know if this fully answers your question.

    Best,
    Michael