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BQ25798：Ship FET

Mulin Chou
Prodigy 145 points
Part Number: BQ25798
Other Parts Discussed in Thread: TPS25751

Tool/software:

Hi,

I will use EEPROM to control TPS25751 & BQ25798 function, No HOST/MCU.

I want to add ship FET to reduce the consumption, My question is,

(1)when the input source is present, Ship FET ON.

(2)when the input source is not present, Ship FET OFF.

I want to know, EEPROM used, the ship FET will work?

tks.
Mulin

  • 0
    TI__Guru**** 160321 points

    HI Mulin,

    The shipFET is on as long as V(BAT) is greater than 3.0V typical. Input voltage applied or not only determines if the host can write the I2C bits to enter ship mode (I2C available) or shutdown mode (no I2C, lowest Iq).

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 145 points

    sorry I don't get it,
    My application, EEPROM to control TPS25751 & BQ25798 function, No HOST/MCU.
    1. When it into ship mode (ship FET OFF).
    2. When it leave ship mode (ship FET ON).

    tks.
    mulin

  • 0 in reply to Mulin Chou
    TI__Guru**** 160321 points

    Hi Mulin,

    The only way to use the SDRV pin to enter/exit ship mode is for an I2C primary to write to the ship mode register after input voltage is removed.  I don't think EEPROM can do that.  So, I recommend that you do not use SDRV to drive an NFET shipFET.  Instead, I recommend a PFET shipFET that is pulled up to battery with 1Mohm resistor and pulled down by NFET that you can control with a switch.  This PFET would completely disconnect the battery from charger, including BATP pin.  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 145 points

    Dear Jeff,

    could you please drawing simple schematic to '' PFET shipFET that is pulled up to battery with 1Mohm resistor and pulled down by NFET that you can control with a switch.''

    And who can to control ''NFET that you can control with a switch''? SDRV?

    Regards,
    Mulin

  • 0 in reply to Mulin Chou
    TI__Guru**** 160321 points

    Hi Mulin,

    I am confused.  Do you have a way to write to the I2C registers?  SDRV only turns off if the charger receives an I2C write into ship mode or shutdown mode.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 145 points

    Hi,

    I am HW RD, 

    I use TI EEPROM+TPS25751+BQ25798 GUI solution, so I need know What are the limitations of HW application?

    tks.

    Mulin