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BQ25756: The minimum charging current is limited to 400mA?

GIEDI WANG
Prodigy 20 points
Part Number: BQ25756
Other Parts Discussed in Thread: TPS25751

Dear sir,

While looking for a USB-PD Extended Power Range (EPR) bidirectional converter 10S lithium battery charging solution, I stumbled upon TI’s “BQ25756” solution. I have some questions about this:

1. The input voltage range is shown as 5V / 9V by , the output voltage is 30-42V, and the charging current is 650mA. Is 27W suitable for this IC design?

2. The input voltage range is shown as 5 to 15V, the output voltage is 30-42V, and the charging current is 250mA. Is 12W suitable for this IC design?

3. Study 2. ICHG_REG register bits (host software control), describe "To set the maximum charge current using the ICHG_REG register bits, write to the ICHG_REG register bits.
The charge current limit range is from 400 mA to 20,000 mA with 50 mA/step. The default ICHG_REG is set to
maximum code, allowing ICHG pin to limit the current in hardware"
In 8.3.4.1.1 Charge Current Programming (ICHG pin and ICHG_REG)), page 24 of data sheet.
The minimum charging current is limited to 400mA? How to set it to 250mA?

Best Regards,

Giedi Wang

  • 0
    TI__Mastermind 20120 points

    Hello Giedi,

    Thanks for working with this charger.

    1. Yes, the charger will work for this application.

    2. For the 250 mA charging current, is that a limitation of the battery or the input supply?

    3. For USB-EPR, I recommend using IAC_DPM to limit the charge current. The IAC_DPM setting will keep the charger from drawing to much power from the input. To use this, you'll need to set the IAC_DPM setting to the maximum current of the USB contract.

    Also for working with USB-PD EPR with the BQ25756 EVM, I recommend changing the input sense resistor to 5mΩ instead of 2mΩ.

    We have also released the TPS25751. This IC will manage USB SPR contracts as well as control the BQ25756. We have a reference design for both ICs together here: https://www.ti.com/tool/PMP41083

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 20 points

    Hi Ethan,

    Thanks for your reply.

    2. The 250 mA charging current that a limitation of the battery.

    3.The charge current limit range is from 400 mA to 20,000 mA with 50 mA/step. The default ICHG_REG is set to

       maximum code, allowing ICHG pin to limit the current in hardware" , is that set up input charge current ?

       My design structure is the same as PM41083.

       Study the PMP41083 that Ichg (A) changes with input power. How to set the constant current 250 mA for the 10S battery.

    Best Regards,

    Giedi Wang

  • 0 in reply to GIEDI WANG
    Prodigy 20 points

    Hi Ethan,

    Re-study the data sheet and confirm PMP41083.I know the design function that is limited the PD power to control the charger current of battery, right?

    The default ICHG_REG is set the charge current limit range is from 400 mA to 20,000 mA with 50 mA/step. If the charge current limit is set up

    400mA,the charger current of battery can't over 400mA.

    Best Regards,

    Giedi Wang

  • 0 in reply to GIEDI WANG
    TI__Mastermind 20120 points

    Hello Giedi,

    You can adjust the resistor on the ICHG pin to reduce the current to 250 mA. The charger will work in buck mode and boost mode, but not buck-boost mode when operating below 400mA.

    Best Regards,
    Ethan Galloway