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UCC28064A: UCC28064A Reset Mechanism

Bekir Fincan
Prodigy 30 points
Part Number: UCC28064A

Tool/software:

Hi,

I want to reset UCC28064A when it latches due to some kind of faults such as CS-open, TSET -open and short operation, open loop, UVLO, external disable, brownout and redundant overvoltage (HVSEN). Although I know when these fault conditions are removed, the fault is cleared and UCC28064A resumes soft-start state, I would like to learn reset mechanism of UCC28064A, if there is.

Does removing Vcc supply voltage of UCC28064A reset the UCC28064A?

External disable forces UCC28064A to operate at standby mode. Does disabling UCC28064A externally reset the UCC28064A?

Is there any other way to clear faults in the UCC28064A by force?

Best Regards, Bekir.

  • +1
    TI__Mastermind 31130 points

    Hello Bekir, 

    There is one fault latch (for COMP_DSCHG "COMP discharge") in the UCC28064A and the reset for this latch is a signal called DISCH_RST ("discharge reset").  

    The purpose of the fault latch is to completely discharge the voltage on the COMP capacitors in order to restart with a soft-start. 
    Your question caused me to discover that there is an error in the UCC28064A block diagram:  a missing Vcomp signal indicator. 

    The latched COMP_DSCHG signal drives an OR-gate which drives a switch to apply a 2kohm resistance to the internal COMP signal and pull down the COMP voltage. 
    This 2kR pull-down stays applied until Vcomp drops below 20mV.  Once that happens, the DISCH_RST signal goes high and resets the fault latch.  

    You can externally reset the fault latch by grounding the COMP pin so that its voltage < 20mV, then release it.  
    Grounding COMP will also instantly discharge the external compensation capacitor Cp, but if the reset is released too soon the voltage on Cz will not have had a chance to discharge much and there will not be a soft start when switching resumes.  You control the timing of the external reset and by consequence you control how "soft" or "hard" the restart input current will be.

    You can avoid a "hard" restart if you discharge the Cz capacitor with a separate transistor at the same time that you pull COMP to GND.  

    Regards,

    Ulrich