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BQ24780S: The value of input and charging current sense resistor Rac and Rsr

Silvia Gao
Prodigy 170 points
Part Number: BQ24780S

Hi team,

Can the input and charging current sense resistor RAC and RSR be 5-mΩ when the input and charging currents are both bigger than 8.2A?

Best Regards

Silvia Gao

  • 0
    TI__Mastermind 23330 points

    Hello Silvia,

    There should not be an issue using a 5-mΩ current sense resistor for the BQ24780s, The BQ24780s is designed to use a default sense resistor of 10-mΩ, with this sense resistor value the BQ24780s can provide a maximum charge current of 8.128A. There should not be an issue using a 5-mΩ current sense resistor, however it might be better to choose a battery charger that is reccommneded for higher charging current: Battery Charger

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    TI__Prodigy 170 points

    Hi Christian,

    The customer plans to use 5-mΩ resistor as both charge and input current sense resistor, and he has several questions as below:

    1. For PMON Gain, what does 0 and 1 represent respectively when RAC = RSR = 5-mΩ? Does 0 represent 0.125uA/W and 1 represent 0.5uA/W?

    2. To support hybrid power boost mode, what is the minimum input current need to be set to when RAC = RSR = 5-mΩ? 1536mA*0.5?

    3.How to set charge current register (REG0x14) and input current register (REG0x3F) when RAC = RSR = 5-mΩ? Set value = Target value*0.5?

    4. In the formula that calculates IPMON below, is IBAT and IIN respectively equal to the read back value of register * 2 when RAC = RSR = 5-mΩ?

    5. What will happen if an unreasonable Gain setting causes IPMON exceeding the maximum value in the table? Will IPMON still keep 160uA and the device display an error of 160uA?

    Thanks for your answer!

    Best Regards

    Silvia Gao

  • +1 in reply to Silvia Gao
    TI__Mastermind 23330 points

    Hello Silvia,

    Silvia Gao said:
    For PMON Gain, what does 0 and 1 represent respectively when RAC = RSR = 5-mΩ? Does 0 represent 0.125uA/W and 1 represent 0.5uA/W?

    Yes.

    Silvia Gao said:
    2. To support hybrid power boost mode, what is the minimum input current need to be set to when RAC = RSR = 5-mΩ? 1536mA*0.5?

    3,072mA  it would be double the value if you switched from  RAC = RSR = 10-mΩ to  RAC = RSR = 5-mΩ.

    Silvia Gao said:
    3.How to set charge current register (REG0x14) and input current register (REG0x3F) when RAC = RSR = 5-mΩ? Set value = Target value*0.5?

     It would be double the value if you switched from  RAC = RSR = 10-mΩ to  RAC = RSR = 5-mΩ.

    Silvia Gao said:
    In the formula that calculates IPMON below, is IBAT and IIN respectively equal to the read back value of register * 2 when RAC = RSR = 5-mΩ?

    Yes

    Silvia Gao said:
    What will happen if an unreasonable Gain setting causes IPMON exceeding the maximum value in the table? Will IPMON still keep 160uA and the device display an error of 160uA?

    The BQ24780s is designed to use a default sense resistor of 10-mΩ, We do not have data to provide this information.

    Best Regards,

    Christian.