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BQ25723: Can BQ25723 charge a 4 cell LiFePO4 battery with more than 10A?

Kazuya Nakai59
Guru 21505 points
Part Number: BQ25723
Other Parts Discussed in Thread: BQ25756E, BQ25720, BQ25730

Hello guys,

One of my customers is considering using BQ25723 to charge 4 cell LiFePO4 battery with more than 10A.

At this moment, they have the following questions.
Could you please give me your reply?

Q1.
According to page 28 of BQ25723 datasheet, MAXIMUM INPUT CURRENT LIMIT (IINDPM) is 10A
when EN_FAST_5MOHM is 0b and RSNS_RAC=1b.

Can BQ25723 charge a 4 cell LiFePO4 Li-Ion battery with more than 10A?

Q2. 
They'd like to use BQ25723 with Vin=12V, Vbat=14V conditions.
How much current can BQ25723 charge the battery as the maximum in these conditions?

Q3.
Could I ask you about different device, BQ25756E on this thread because it is a case for same customer?
If I should ask this on new thread, please let me know.

Can BQ25756E discharge with 12V fixed voltage as Vout?

Q4.
Could you please tell me any TI battery charger device which has the following capabilities?

Charging condition: Vin=12V, Vbat=14V/8A(LiFePO4 Li-Ion battery)
Discharge condition: Vout=12V fixed voltage/1A

Your reply would be much appreciated.

Best regards,
Kazuya.

 

  • 0
    TI__Expert 3335 points

    Hi Kazuya,

    Q1.
    According to page 28 of BQ25723 datasheet, MAXIMUM INPUT CURRENT LIMIT (IINDPM) is 10A
    when EN_FAST_5MOHM is 0b and RSNS_RAC=1b. Can BQ25723 charge a 4 cell LiFePO4 Li-Ion battery with more than 10A?

    - The 10A applies to the input VBUS current. BQ25723 can charge with a maximum 16.2A with 5mOhm sense resistor.

    Q2. 
    They'd like to use BQ25723 with Vin=12V, Vbat=14V conditions.
    How much current can BQ25723 charge the battery as the maximum in these conditions?

    - Assuming the 10A maximum input current, the charge current ideally is 12x10/14 = 8.6A. Because of efficiency loss the actual charge current will be less than that. With that high current, the efficiency is usually more than 90% so you can expect a charge current of 8A.

    Q3.
    Could I ask you about different device, BQ25756E on this thread because it is a case for same customer?
    If I should ask this on new thread, please let me know. Can BQ25756E discharge with 12V fixed voltage as Vout?

    - You should ask this in a new thread.

    Q4.
    Could you please tell me any TI battery charger device which has the following capabilities?

    Charging condition: Vin=12V, Vbat=14V/8A(LiFePO4 Li-Ion battery)
    Discharge condition: Vout=12V fixed voltage/1A

    - BQ25720, BQ25723, BQ25730 are all capable of the charging condition mentioned. They all can discharge with 1A as well.

    However it was not clear what you mean by Vout=12V fixed voltage. If battery is discharged in battery only mode then Vout will not be fixed but rather decreasing. Do you mean discharge battery with adapter present  in supplement mode and Vout fixed at 12V? If that is the case then yes the chargers mentioned can do that. 

    Best Regards,

    Munir

  • 0 in reply to Md Munir Hasan
    Guru 21505 points

    Hi Munir,

    Thank you very much for your reply.

    Also I'm sorry that my explanation for their requirement was not enough.
    Vout means that VBUS voltage.
    They'd like to output fixed 12V/1A at VBUS terminal from 14V battery
    when the battery is under discharging.
    At this moment, they have the following questions.
    Could you give me your reply?

    Q1.
    Can all of BQ25720, BQ25723, BQ2573 output it?

    Q2.
    Can either of these devices can't output fixed 12V/1A at VSYS from 14V battery?

    Q3.
    The customer wants to know how to select external FETs (Q1~Q4).
    Should the customer refer 10.2.2.5 Power MOSFETs Selection in BQ25723 datasheet?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Expert 3335 points

    Hi Kazuya,

    Q1.
    Can all of BQ25720, BQ25723, BQ25730 output it?

    - Yes all the mentioned chargers can output VBUS=12V/1A in OTG mode.

    Q2.
    Can either of these devices can't output fixed 12V/1A at VSYS from 14V battery?

    - All of the devices mentioned can output 12V/1A with 14V battery.

    Q3.
    The customer wants to know how to select external FETs (Q1~Q4).
    Should the customer refer 10.2.2.5 Power MOSFETs Selection in BQ25723 datasheet?

    - Yes refer to that section in the datasheet. You can also look at the EVM schematic and look at the MOSFET part number.

    Best Regards,

    Munir

  • 0 in reply to Md Munir Hasan
    Guru 21505 points

    Hi Munir,

    Thank you for your reply and I'm sorry to be late my response.

    Could I ask you an additional question to make sense?

    Q.
    Can all of these devices output 12V fixed voltage from Vbat to BUS using OTG function,
    when Vbat is higher or lower than 12V, or even just 12V?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Expert 3335 points

    Hi Kazuya,

    Yes. OTG supports buck-boost operation. Hence, they can output 12V with higher or lower battery.

    Best Regards,

    Munir