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BQ77915: charging 8s li-ion cells

Chileam Bohnen
Prodigy 30 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ77905

Hi,

For a new product we are interested in a charger IC via an USB 3.0, with two BQ77915 circuits for balancing.
The 8 li-ion cells are in series discharged, in a separate current paths configuration.

We seek for advice how to charge the 8 li-ion cells in a separate current path configuration and could the cells be charged in 2x 4 cells in series?

Best Regards,

Chileam

  • 0
    TI__Guru 54715 points
    Hi Chileam,
    The bq77915 will not know the current path, it will respond to its inputs with the CHG and DSG outputs. You can use these to control your current path circuit.
    The bq77905 Separate Current Paths application note www.ti.com/.../slua772 may be helpful.
    To charge the 4 cell groups separately, if you use isolated chargers your cells might remain stacked. You may have to isolate the upper CHG from the CTRC of the lower so that a charge fault could not re-enable the bottom battery.
    If you break the stack you should break the other connections as the voltage limits on the pins do not allow voltage reversal.
  • 0 in reply to WM5295
    Prodigy 30 points

    Ok, I have done some homework. In the attachment is the schematic of a high-level design. 

    In the design are 3 ground plains for simultaneously charging of 2x 4 Series cells.

    Still i got some questions;

    - Are the charger IC's necessary? Could't the VBUS, directly at 20V, be connected?

     - For the project we have an USB-C 60W adaptor for charching, how do we sellect the higher voltage of 20V output by a multi level adaptor?

    regards,

    Chileam

    Li-ion 2 x 4S charging.pdf

  • 0 in reply to Chileam Bohnen
    TI__Guru 54715 points
    Hi Chileam,
    Generally a charger is required to provide the required voltage and current with appropriate control. Sometimes that is built into a power supply intended for use as a charger. A general purpose interface would not seem to be that.
    You should likely consult the specifications for the USB-C standard.
  • 0 in reply to WM5295
    Prodigy 30 points

    Hi,

    We have concluded to design an application specific charger/adapter for USB-C.

    Thanks for the support,

    Chileam