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BQ27Z746: maximum allowed current sense resistor

Jayden Li
Expert 4535 points

Part Number: BQ27Z746

Tool/software:

Hi team,

My customer want to understand if they want to select 100mohm current sense resistor, is it allowed? What is the risk?

According to DS, the maximum allowed resistor is 20mohm.

Thanks!

Jayden Li

  • 0
    TI__Mastermind 48325 points

    Hello Jayden,

    If you can refer to the application note below to changing the external Rsns resistor from the outside values.

    Enhanced Resolution Gauging for Low Current Applications Using Scaling:
    Enhanced Resolution Gauging for Low Current Applications Using Scaling

    Thank you,
    Alan 

  • 0 in reply to Alan Frias
    TI__Expert 4535 points

    Hi Alan,

    Thanks for your feedback!

    I have couple of more questions about different operation modes, could you help comment them 1 by 1 as well? Many thanks in advance!

    1：If the battery is in the ‘SHIP’ mode and gets inserted into the device (the charger is not plugged into the device), my understanding that the battery may wake up, if the device leakage current (120uA - ?) produces voltage across the battery sense resistor > IWAKE and, if IWAKE is enabled.

    2：If the battery is in the ‘SHELF’ mode and gets inserted into the device (the charger is not plugged into the device), my understanding that the battery will not wake up.

    3：In order to wake up the battery from ‘SLEEP’ mode, the device needs to be powered up or the charger needs to be connected – basically the exit from ‘SLEEP” is when the battery senses a current in any direction, which is > SleepCurrent.

    4：In order to wake up the battery from ‘SHIP’ mode, a command must be sent to the battery or the battery needs to sense a current in any direction, which produces voltage across the sense resistor > IWAKE, if IWAKE is enabled. 

    5：In order to wake up the battery from ‘SHELF’ mode, either a command must be sent to the battery or the battery needs to sense a charge voltage. We do not use the ENAB pin on BQ27Z746. Actually, it needs to be pulled low in the schematic.

    Br.

    Jayden Li