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BQ77915: OCD Fault is not working

kommu Padmavathi
Prodigy 20 points
Part Number: BQ77915

My application is a basic 5S configuration,  I'm using a 25 mOhm current sense to develop the 60mV @ SRP & SRN. My problem is that OCD fault is not working at 2.4A

  • 0
    TI__Expert 7465 points

    Hi Kommu,

    Can you send me your schematic? Do you know what value the OCD protection is happening at? Also, keep in mind that the tolerance of the resistor will affect the accuracy of the current protection.

  • 0 in reply to Shawn Hinkle
    Prodigy 20 points

    I am using 3.2v 3000mAH batteries * 5 series. I want to verify the over current , according to this resistor at SRP and SRN pin I am getting 60mV but OCD protection is not happening. Correct me if my assumptions or calculation was wrong. If I want to make different OCD protection at different currents what needs to be done..? How to calculate the sense resistor for 1A, 2A, 3A, 5A ocd protections?

  • 0 in reply to kommu Padmavathi
    TI__Expert 7465 points

    Hi Kommu,

    Without seeing your schematic, it will be difficult for me to determine what could be going wrong. I do believe your calculation is correct. Any extra resistance on the board from solder or other components could lead to a different current threshold. However, if you are using BQ7791500, the voltage between SRP and SRN should always be 60mV when the protection trips. Keep in mind, this protection does have delay and the fault must occur for the entire delay for the protection to trip.

    The process for selecting a sense resistor is outlined in section 10.2.2.1 of the datasheet, step 2.