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BQ24072: BQ24072:Changing the RISET value and its impact

Naveen Kumar
Prodigy 50 points
Part Number: BQ24072
Other Parts Discussed in Thread: BQ25185

Tool/software:

We are currently using the BQ24072RGTR charger IC in our design. At present, we have configured the RISET pin with a 7.5 kΩ resistor, which sets the charging current to approximately 118 mA.

To address thermal concerns in our application, we are considering increasing the RISET resistor value to reduce the charging current and thereby lower heat generation. We would appreciate your support on the following points:

  1. Maximum RISET Value

    • What is the maximum allowable value for the RISET resistor to ensure proper functionality of the IC while minimizing the charging current?

  2. Proposed Change to 15 kΩ RISET

    • We are currently planning to use a 15 kΩ resistor at RISET, which corresponds to a charging current of approximately 50 mA. Can you confirm if this value is acceptable and within the supported range?

  3. TMR Pulldown Resistor Adjustment

    • We understand that reducing the charging current will increase the charging time. Given that we are using a 47 kΩ pulldown resistor on the TMR pin, would this value still be suitable when using a 15 kΩ RISET resistor?

    • If not, what TMR pulldown resistor value do you recommend to ensure proper charge termination timing at the reduced current?

  4. Impact on Other Pins or Parameters

    • Are there any other configuration pins or parameters that would need to be adjusted as a result of increasing the RISET resistor value?


      Please provide your thoughts on this.

  • 0
    TI__Genius 9215 points

    Hello,

    1. The valid range for the RISET resistor is 590Ω (1.5A) to 8.9kΩ (100mA).

    2. The minimum programmable fast charge current is 100mA, as specified by ICHG in the Electrical Characteristics table.

    3. A 47kΩ resistor on the TMR pin sets the fast charge safety timer to about 6.25 hours. The total charge time depends on the battery capacity, the fast charge current, and the termination current threshold.

    4. I wouldn't recommend setting the charge current outside of the values guaranteed by the BQ2407x datasheet. Have you looked at the BQ25185? It's a newer standalone (resistor-programmable) linear charger that supports charge currents from 5mA to 1A.

    https://www.ti.com/product/BQ25185

    Best regards,

    Alec