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BQ25798: BQ25798 Working

Chintan Mevada
Prodigy 90 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQSTUDIO, USB2ANY, EV2400, TPS25751

Tool/software:

1. If i Put 24V adapter and connect 1 Cell So What is my Output of BAT, SYS and PMID.

2. If I disconnect adapter and I have battery of 4.2V then its possible to get 5V at PMID and SYS Pin.

3. If I not connect battery and give 24V input then what is output of PMID and SYS.

4. What I set Voltage on SYS pin.

  • 0
    TI__Guru**** 166136 points

    Hi Chintan,

    Regarding 1, with default 1S, V(BAT) = voltage of battery, V(PMID)=24V, V(SYS)=higher of MINSYS (3.5V default) or battery voltage+~200mV.

    Regarding 2, no.  With backup mode implementing quick turn on reverse/OTG/source mode, V(PMID) can be 5V but V(SYS)=V(BAT).

    Regarding 3, V(PMID)=24V and if charge is enabled but not battery attached, V(SYS) has a triangle wave going between VREG (4.2V default) and MINSYS (3.5V) default.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 90 points

    Hi Jeff,

    Regarding 1, Okay.

    Regarding 2, How PMIC set 5V at PMID pin It could be set 3.3V or We will set manually 5V at PMID pin. How PMIC Know that I need Buck or Boost.

    Regarding 3, If VBAT = 4.2V then I set 3.3V at SYS pin

    4. What happen if VBAT <= 3.5V after that PMIC set 5V at PMID pin.

    5. How the Path will mange at Backup Mode and In backup Mode VBUS work as input or output.

    6. How we can set ICHRG and VSYSMIN and VREG througu I2C.

  • 0 in reply to Chintan Mevada
    Prodigy 90 points

    7. If i connect differential pair then i can connect directly with Computer.

  • 0 in reply to Chintan Mevada
    TI__Guru**** 166136 points

    Hi Chintan,

    Regarding 2, after VBUS is removed if EN_BACKUP bit = 1, the charger automatically changes the converter's operating direction to reverse/OTG/source (from forward/charge/sink) so that the battery can provide a regulated voltage at PMID.  The lowest regulated voltage at PMID is 2.8V in the OTG regulation voltage register.

    Regarding 3 and 4, the converter is a 4 switch buck boost.  It auto switches from buck to boost and vice versa.

    Regarding 5, in backup mode, external power to VBUS cannot be applied.  If using backup mode, the expectation is that the system load is at PMID, not SYS, and that the PMID load needs a minimum, uninterrupted supply.

    Regarding 6, ICHG is set in REG0x03-0x04 and MINSYS (SYSMIN) is set in register 0x0D.

    Regarding 7, a differential pair for I2C SCL and SDA lines is not required but you will need a host processor to communicate via I2C. TI offers the EV2400 with BQSTUDIO downloadable software or USB2ANY with online TI Charger GUI to help with prototyping on the EVM.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 90 points

    Hi Jeff,

    Regarding 7, A differential pair is not for I2C it is for USB D+/D-. So, If i Connect USB Type C VBUS and D+/D- pin on PMIC and connect direct with Computer then it can be supported or not.

    Please give me reference of USB Type C to PMIC connection Schematic. So, I can complete my project. 

  • 0 in reply to Chintan Mevada
    TI__Guru**** 166136 points

    Hi Chintan,

    USB-C requires CC1/2 communicating output power levels.  It only uses D+/D- for data transmission so connecting USB-C D+/D- to 798 D+/D- does not help.  You will need a separate USB-C IC like TPS25751 to communicate with the USB-C port.  I recommend taking a look at https://www.ti.com/tool/USB-PD-CHG-EVM-01.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 90 points

    Hi Jeff,

    Thanks for your suggestion and reply so, I can resolved my issue and doubts.

    Regards,

    Chintan