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bq24278

leo14
Intellectual 350 points
Other Parts Discussed in Thread: BQ24278

Hi,

I want to charge my li-ion battery with bq24278 without system connection. As I asked earlier, you told me that SW, SYS, and BOOT components should be still connected, and left BGATE unconnected. In this case, then, should these 3 pins be still connected to VBAT? If it is so, what should I do with the MOSFET? If it is not, what should I connect the inductor? In addition, is there a special grounding requirement between AGND and PGND? 

Thanks.

  • 0
    TI__Guru*** 148885 points
    You will need the buck power stage (inductor, boost capacitor and minimum output capacitor on SYS). The inductor connects to the SYS minimum recommended capacitance. The MOSFET is not necessary and the BGATE pin can be left floating. The input capacitor grounds, SYS capacitor grounds and battery ground should tied to PGND. The grounds for the other external components should be tied to AGND. PGND and AGND should be connected at one point close to the IC. If you will be removing and replacing the battery with input power connected, you will need to toggle the CD pin immediately after reconnecting the battery.
  • 0 in reply to Jeff F
    Intellectual 350 points

    Is the battery ground is just "battery ground" or ground of BAT pin and NTC?

  • 0 in reply to leo14
    TI__Guru*** 148885 points
    The battery typical has three connections: bat+, bat-(ground) and NTC. The bat-(ground) will be the ground for the NTC as well.
  • 0 in reply to Jeff F
    Intellectual 350 points

    Is there any application note or information about how BQ24278 works in the absence of both system load and Li-Ion battery?

  • 0 in reply to leo14
    TI__Guru*** 148885 points

    The buck converter regulates theSYS rail to V(SYSREGFETOFF) = 4.33V typical per the elec spec table.

  • 0 in reply to Jeff F
    Intellectual 350 points

    Here is my schematic for the chip:

    When no battery is connected and CD and CE/ is pulled high, D19&D20 leds are ON, Vsys=1.7V, and draws current less than 1mA. When CD is connected to ground, LEDs become off and Vsys=0V. Do you think that is there any problem with the design? Separete ground planes are formed as described in the datasheet and your suggestion and supply ground is connected to PGND directly.