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BQ25798: PROG pin etc.

Yoshinobu Kagawa
Expert 2030 points
Part Number: BQ25798


1. Please advise if there is a safety issue if the PROG pin is open or shorted to GND.

2. Is there a BQ25798 datasheet eratta?

3. Allowable inrush current when batteries are installed.
    When the battery is installed, an inrush current flows through the BATFET body diode to the SYS terminal. Please advise its allowable current.
    
4. Examples of shutdown mode and shipping mode applications.
    If you have any specific examples (usage distinctions) for Shutdown mode and Shipping mode, please let us know.

Regards,
Kagawa

  • 0
    TI__Guru**** 169466 points

    HI Kagawa,

    Regarding 1, if PROG is left floating, CELLS, SYSMIN and BATREG registers are set to 4S.  If PROG is shorted to GND, CELLS, SYSMIN and BATREG registers are set to 1S.

    Regarding 2, no.

    Regarding 3, yes.

    Regarding 4, ship and shutdown, with lowers Iq into BATP and BAT, are used when the end product is expected to be packaged with battery attached and stored on a shelf or shipped to another location.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2030 points

    Hi Jeff-san,

    3. Allowable inrush current when batteries are installed.
        When the battery is installed, an inrush current flows through the BATFET body diode to the SYS terminal. Please advise its allowable current.

        The reason for this is to make sure that there is no problem with the body diode, which currently flows about 10.4A, 200us.
        Please advise its allowable current.


        

    Regards,
    Kagawa

  • 0 in reply to Yoshinobu Kagawa
    TI__Guru**** 169466 points

    Hi Kagawa,

    The abs max is 10A for 1s so 10.4A for 200us is okay.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2030 points

    Hi Jeff-san,

    When Charge Voltage is set to 7.2V and Charge Current to 1000mA, the current value increases about 30~40mA during CC charging.
    Can you please explain the reason for this? Is the charge current being fine-tuned according to efficiency and battery voltage?
    Charging is done at the following setting values.





    Regards,
    Kagawa

  • 0 in reply to Yoshinobu Kagawa
    TI__Mastermind 41615 points

    Hi Kagawa-san,

    Is there a system load? Can you report all of the registers settings at this time? Is the charger in DPM and then not in DPM?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Expert 2030 points

    Hi Michael-san,

    The BQ25798EVM evaluation board is not loaded because nothing is connected to the SYSTEM pin.
    Comparing the registers before and after the charge current increases, the VSYSMIN status register changes, which seems to be related to the VSYSMIN pin.
    Is the IC designed to suppress the charging current when the battery voltage is below VSYSMIN?
    Or is the charging current designed to be a few percent higher when the battery has a voltage above VSYSMIN?
    Attached below are the register values before and after the charging current increases.

    1. before charge current increase (at cursor A on the data logger)




    2. after charge current increase (at cursor B on the data logger)




    Regards,
    Kagawa

  • 0 in reply to Yoshinobu Kagawa
    TI__Mastermind 41615 points

    Hi Kagawa-san,

    Please see the following from Section 9.3.8.1, "When the battery voltage is below the minimum system voltage setting, the BATFET operates in linear mode (LDO mode), and the system is regulated at around 200 mV above the minimum system voltage setting. As the battery voltage rises above the minimum system voltage, the BATFET is fully on and the voltage difference between the system and battery is the RDS(ON) of the BATFET multiplied by the charging current."

    The difference here is the BATFET being in LDO mode vs fully on.

    Regards,

    Mike Emanuel