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BQ40Z60 in embedded device

loic jacquinot18
Prodigy 20 points
Other Parts Discussed in Thread: BQ40Z60

Hi all,

I'd like to use BQ40Z60 as an integrated charger/monitor in an handheld device, so system will always be attached to VSYS.

- Is it possible to charge battery while using the attached system (considering the input has enough power to supply it)

- My battery pack is 2-cell but with a built-in protection and balance circuitry, so there are only 3 pins : +VBAT (7.4V), Temperature, and -VBAT (GND). No pin for cell-1 and cell-2 interconnection. How should I connect my battery pack to the BQ40Z60? Should I short or unconnect unused VCx and TSx pins?

- Do I need to populate Q1 and Q6 (from the EVM Schematic)

- Do I need to remove one or multiple MOSFTs to permit simultaneous charge and system ON?

Thanks a lot for yoyr help.

Regards,

Loic

  • 0
    Intellectual 300 points
    Based on my experience, I ma trying to answer your questions:
    - Yes, bq40z60 can charge the battery while attached the system. But the charging current will be your setting charging current minus the system load current.
    - bq40z60 is for balancing charging purpose, if your battery pack does not have the cell-1/cell-2 interconnection, do not use bq40z60. You can use other battery cheap charge IC, TI has many others avaiable.
    - Looks Q1/Q6 is pre-charge purpose, you need it when battery is over-discharged although for some reason bq40z60's pre-charging function is not really working properly so far. (Except this function, all other features are very good based on my test). It will not cost you too much even you put Q1/Q6 into your schematic.
    - No. Sugget keep the original circcuit whih will save you lot of time for trouble-shooting. I only remove U1 (BQ294700) others are keep unchaged in my schematic.

    Good luck

    Lankor
  • 0 in reply to Lankor Liu99
    Prodigy 230 points
    - Yes, bq40z60 can charge the battery while attached the system. But the charging current will be your setting charging current minus the system load current.

    Ok it's a good point.

    - bq40z60 is for balancing charging purpose, if your battery pack does not have the cell-1/cell-2 interconnection, do not use bq40z60. You can use other battery cheap charge IC, TI has many others avaiable.

    Interresting, it will help in chosing battery (we have both 1-cell and 2-cell packs so we'll probably go to two 1-cell according to this information). We already built a small dual battery charger (for 1-cell packs) but the interresting thing was to have both charger and monitor in a single IC.

    - Looks Q1/Q6 is pre-charge purpose, you need it when battery is over-discharged although for some reason bq40z60's pre-charging function is not really working properly so far. (Except this function, all other features are very good based on my test). It will not cost you too much even you put Q1/Q6 into your schematic.

    Ok I didn't know exactly what was their role, I thought it was to blow the fuse. It's a fact, and they are small enough to be populated.

    - No. Sugget keep the original circcuit whih will save you lot of time for trouble-shooting. I only remove U1 (BQ294700) others are keep unchaged in my schematic.

    Thank you for your answers it was very helpfull, we'll keep the schematic like this (and without U1 too)

    Regards,

    Loic
  • 0 in reply to Loic Jacquinot
    TI__Guru 73830 points
    Loic,
    The pre-charge circuit components are not required and can be omitted from the design. The device can support simultaneous charging and discharging. Current from the charger will first go to the load and then excess current to charge the cells. The gauge was not designed to support configurations where the center taps in the cell stack are not connected to the gauge. Measuring the series resistance of the cells is critical to proper gauging for Impedance Track devices.
    Tom