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BQ24133: Rac minimum value; Vin, in-rush current protection, Minimum Vin for 2S application

Part Number: BQ24133

Hello Ti Engineers,

I have a number of questions regarding the BQ24133 charging circuit

1. What is the minimum resistance that can be used for Rac? The value of Rac in the datasheet examples are 20mΩ. Since our system has a typical continuous current of 8A (Max). We were considering lowering the Rac to minimize the voltage drop across. Can we go with 10mΩ?

2. Does the BQ24133 have a Input In-Rush Current limit?, If we set IDPM to 8.5A. What would the scenario be if the charger is disabled and system has an inrush current >9A for a few seconds? How does the Charger Circuit behave? will it disable the ACFET and RBFET? If The BQ24133 does not have an in rush charge current protection. Do you have a recommended part for that?

3. What is the minimum input voltage for a 2S Application (max li-ion battery voltage of 8.42V)? Can 9V be used? Does it have a limitation for what fast charge current can be used?



  • HI Daniel,

    Regarding 1, 10mohm can be used. Accuracy of input current at light will be worse than datasheet spec.  Datasheet equations all assume 20mohm.

    Regarding 2, no.  The charger does not care about inrush current unless the peak current exceeds the input current limit.  If that happens, the converters output charge current is reduced, potentially to zero.  The AC and RB FETs stay on.  With input voltage likely dropping, resulting in ACDRV likely dropping a bit, the FETs will naturally "soft start".  I am not aware of an IC that products in-rush after power up, i.e. after the FETs are already on.

    Regarding 3, 9V is perfect.  I don't recommend less than 8.7V.