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BQ25883: Command to turn VSYS off, and other questions about BQ25883 & BQ28Z610

Eduardo Barcellos
Intellectual 420 points
Part Number: BQ25883
Other Parts Discussed in Thread: BQ28Z610, EV2400

Hello,

I have 3 questions:

1) Can the main CPU send an I2C command to the BQ25883 chip to turn off VSYS? I looked at all registers and I found several VSYS status registers, ADC registers to read VSYS voltage, INT flags, and so on, but none to control its on/off status. I'd like to be able to cut the battery supply voltage to the main circuit when the device is connected to a secondary power input.

2) What voltage will I actually get on VSYS? I'm using 2x 18650 battery cells in series at a BQ28Z610, each cell with ~3.7V. Will I get around twice that value on VSYS (7.4V) when the batteries are fully charged? My circuit follows at the end.

3) Do I have all that I need for the EV2400 on connector N1 (below)? I believe all I need is SCL, SDA and GND, but note that my circuit has no pullups on SCL and SDA.

Thanks!

Eduardo

  • 0
    TI__Genius 10385 points

    Eduardo,

    1) Can the main CPU send an I2C command to the BQ25883 chip to turn off VSYS? I looked at all registers and I found several VSYS status registers, ADC registers to read VSYS voltage, INT flags, and so on, but none to control its on/off status. I'd like to be able to cut the battery supply voltage to the main circuit when the device is connected to a secondary power input.

    Unfortunately there is no way to disable the VSYS output. I suggest adding a load switch IC after VSYS to disconnect VSYS as necessary.

    2) What voltage will I actually get on VSYS? I'm using 2x 18650 battery cells in series at a BQ28Z610, each cell with ~3.7V. Will I get around twice that value on VSYS (7.4V) when the batteries are fully charged? My circuit follows at the end.

    Section 8.3.6.1 Narrow VDC Architecture describes this in more detail, but in short expect VSYS_MIN to VBATREG. For an 18650 in a 2S configuration VBATREG is typically 8.4V, but please confirm with your battery pack manufacturer.


    3) Do I have all that I need for the EV2400 on connector N1 (below)? I believe all I need is SCL, SDA and GND, but note that my circuit has no pullups on SCL and SDA.

    On your final design it should be removed as it is not necessary. If you're in very early prototyping, it might be useful to retain it for debug if your MCU software is not ready. According to the BQ25883 and BQ28Z610 datasheets, external pullup on SDA and SCL are required for I2C. Please add them.


    Best Regards,

    Ricardo