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BQ2970: What is the difference between OCD and SCD

SANATH kumar
Prodigy 40 points
Part Number: BQ2970

Hi,

I am little bit confused about OVER DISCHARGE CURRENT and SHORT CIRCUIT detection .

As mentioned in the datasheet OCD and SCD is detected based on V- to VSS voltage , where SCD will consider the hike in 10us .

in my circuit when the OCD is triggered as told the Dout goes low but it will not retain when i decrease the load Current why is it like that ? 

and in SCD when the short is released it will retain the normal state, since both are depend on the V- to VSS voltage , is it proper ?

can you briefly explain the difference between OCD and SCD .

Regards ,

SANATH KUMAR

  • 0
    TI__Mastermind 19000 points

    Hi Sanath,

    The OCD and SCD protections on this device will not recover based on the discharge current decreasing. They will instead recover once the load is removed.

    When the protection triggers and the DSG FET is turned off, V- is pulled up to BAT+ by the load. When the load is removed, V- is pulled down to VSS by the small internal current sink. Once V- drops below ~V_BAT - 1V, the device will recover the protection.

    Regards,

    Max Verboncoeur

  • 0 in reply to Maxwell Verboncoeur
    Prodigy 40 points

    hi max ,

    thank you for the clarification.

    I have another doubt When any fault condition rises any one FET will be turned off right , then circuit will be open then how the protection IC recover from protection?

    and in which point i should  measure the voltage drop of FET?

    how can i determine the temparature of FET?

    Regards,

    Sanath kumar

  • 0 in reply to SANATH kumar
    TI__Mastermind 19000 points

    Hi Sanath,

    In a COV condition (overvoltage) the CHG FET will turn off, however the battery will still be able to discharge through the body diode of the FET in order to recover the protection.

    In a CUV condition (undervoltage) the DSG FET will turn off, and the battery will still be able to charge through the body diode to recover.

    The current protections and recoveries will function as I described before.

    SANATH kumar said:
    and in which point i should  measure the voltage drop of FET?

    Do you mean the gate-source voltage? This can be measured from the COUT/DOUT pins.

    SANATH kumar said:
    how can i determine the temparature of FET?

    This device does not include temperature protections, so you will need an external thermistor near the FETs with its own circuitry to control/read it.

    Regards,

    Max Verboncoeur

  • 0 in reply to Maxwell Verboncoeur
    Prodigy 40 points

    hi max,

    thank you for the information.

    i wanted to check drain to source voltage of MOSFET so through which point i can check?

    Regards,

    Sanathkumar

  • 0 in reply to SANATH kumar
    TI__Mastermind 19000 points

    Hi Sanath,

    If you want to check the voltage drop across both of the FETs then you can measure the voltage between PACK- and BAT-. If you want the voltage drop of a single FET you may need to add a test point to the common drain of the FETs.

    Regards,

    Max Verboncoeur