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Original question:

BQ77905: Is it possible to order a factory programmed IC with OT discharge cutoff at 60 degrees C, OV at 4.2V and UV at 3...

BQ77905: BQ77905 enter Charge or Discharger state when the SPR/SRN are shorted?

Harry Xu
Prodigy 40 points
Part Number: BQ77905
Other Parts Discussed in Thread: INA381

I just inherent a BMS design using BQ775905.   The battery pack use 0.1mR shunt so the over current protection can not be used directly on the BQ77905.   The previous designer decided to short out the SPR SRN pins so to disable the over current protection.   Will BQ77905 OV, UV, OT still work?   What state -- Charge or Discharge -- BQ77905 will enter when SPR/SRN pins are shorted.  My understand is that the protection level are different under charge and discharge.  

Since a very low shunt resistor is used, can a current sense amplifier be used to amplify the shunt signal?  

What is the maximum current draw from AVDD?  How is the regulation of the AVDD 3V?  Can it be used to power a shunt amplifier like INA381?    

  • +1
    TI__Mastermind 42060 points

    Hello Harry,

    OV/UV and normal OT protections should work just fine. However, you must keep in mind OTC and OTD, these will turn off either the CHG or DSG FET at higher temperatures. If the SRN/SRP pins are shorted, the body diode in this scenario would not work. Additionally, any recovery mechanisms that use current would not work. 

    I would recommend to read all of Section 8.3.2 Fault Operation of the datasheet. See how each protection and its recovery is affected by not having current detection. The device would not be able to tell if the part is in charge or discharge if the pins are shorted together.

    This could possibly be done. However, it must be kept in mind that you would need a current sense amplifier that is able to provide a positive and negative signal in order for our device to detect the difference between charge and discharge currents.

    AVDD is not recommended to be used with any external circuitry. This is solely used for the internals of the IC. 

    Best Regards,

    Luis Hernandez Salomon