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BQ25730: The battery charger design issue for BQ25730

Part Number: BQ25730
Other Parts Discussed in Thread: BQ34Z100-R2, BQ34Z100EVM

Hi,

We use the BQ25730 for battery charge and BQ34Z100-R2 for gas gauge,

Now, we have below issue for the reference design:

1. We use the 18650 lithium battery, we refer to the BQ25730EVM and BQ34Z100EVM, we have no idea how to connect the BAT- and PACK-, the BQ25730 has no PACK- pin;

2. Can we fixed the CELL_BATPRESZ if we have the same series connection of battery, thanks?

  • Hi Zhang,

    1. BQ25730 EVM charges battery with +ve terminal of battery connected to VBAT and -ve terminal of the battery connected to PGND. It is not clear from the diagram what are the functions of BAT+, BAT- and PACK-. My assumption is that PACK- is the pin from battery monitoring circuit internal to the battery pack. However, in this case I would also expect there to be a PACK+ pin which does not seem to be there. If there were a PACK+ pin, then you could connect the PACK+ to VBAT and PACK- to PGND. We need more information of the functions of the pins. Please refer to the datasheet of the battery to see if BAT- and PACK- can be shorted. 

    2. Can you clarify what your question is on CELL_BATPRESZ?

    Best Regards,

    Munir

  • Hi, Md,

    These pictures are screenshot from the EVM( BQ25730EVM and BQ34Z100EVM), we wants to know how to design the BQ25730 and BQ34Z100-R2 output,

    and we have no idea the relevance among the BAT+/ BAT-/ PACK-, the battery only 4 series and we only have the BAT+ and BAT- line.

    The CELL_BATPRESZ is the selection pin for 1- to 5- cell battery setting, so if we can only 4 series that we can design same as below(only reserve the R42 and remove the R24/ R41/ R20/ R21 and JP3, is it right?

  • HI Zhang,

    I thought the screenshot is from the battery datasheet. So please ignore the comment I made earlier. You need to connect battery +ve and -ve terminals to BAT+ and BAT- respectively. Then you will connect VBAT (from EVM) to BAT+ and PGND (from EVM) to PACK-. However, our recommendation is to use a battery protector IC on the path from VBAT to BAT+ because our charger assumes that there is a battery protector IC on the battery pack. So, with the battery protection IC it will look like this.

     

    For CELL_BATPRESZ, yes you need to keep R42 for 4S design.

  • Hi Md,

    This for your professional comment for this issue, but we have only the BAT+ and BAT-, so how to connect the pack-, and I have no idea what is the pack-, 

    so please check if we can connect the PACK- and BAT- together, thanks.

  • Hi Zhang,

    I already described where to connect PACK- with a diagram in the previous reply. Let me know if that diagram is not visible to you. And NO, you cannot connect PACK- and BAT- together. 

    The  bq34z100EVM user guide also describes how to connect PACK- in section 2.3.

    Best Regards,

    Munir

  • Hi Md,

    Can you kindly review our schematic diagram and please check if the BAT+/ BAT-/ PACK-  is right or not, thanks.

    ext-bat_sch_rc3_20231201a.pdf

  • Hi Zhang,

    Here is the schematic that shows how the battery connects to gauge and charger. It is recommended to add battery protection FETs in order to protect the bare cells.

    I can only review the charger part of the schematic which looks ok . For the gauge schematic you need to have it reviewed by the BQ34Z100-R2 support team because you may need to separate the grounds for the gauge and the charger.

    Best Regards,

    Munir

  • Hi MD,

    Pleaes advise how to identify the power on( Adapter insertion) signal from BQ25730, thanks.

  • Hi Zhang,

    You can identify a valid adapter insertion by reading the register 21h 7th bit.

    Best Regards,

    Munir