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LM5022: LM5022 current limit question

Dane Zhang
Expert 7795 points
Part Number: LM5022

Hi team,

In application where VIN=12V, VOUT=53.5V. And set the current limit according to formula below to 2.33A.

when both the input and output current exceed this overcurrent point, the phenomenon is that the output voltage decreases as the current increases, but it is still above 35V. Judging from the phenomenon, it seems that overcurrent is not triggered.

Does the setting of the overcurrent point not follow this formula? Or is the form of overcurrent protection not shutting down the MOS?

  • 0
    TI__Mastermind 19595 points

    Hello Dane,
    Thanks for reaching out to us via e2e.

    Opposite to our newer devices, the LM5022 does not provide such type of an overcurrent protection which would turn-off the FET for longer / for more than the remainder of the current cycle.

    The current LIMIT is meant to be the threshold for the cycle-by-cycle peak current mode control loop. It will determine at which peak current the FET has to be turned off during a regular cycle.

    The second comparator for the so-called OVERCURRENT detection will only get triggered when e.g. the inductor is shorted, so that there will we a very high current already at the beginning of a cycle.
    Nevertheless, this is also just a cycle-by-cycle over current protection function, so the FET will again turn-on at the beginning of the next cycle.

    There is no hiccup mode or anything similar implemented in the LM5022.

    You have to calculate the components of the power stage in a way that the current limit will leave some margin over the expected peak inductor current at maximum load, taking losses and tolerances into account.
    If the load will try to draw more current, it will get limited, but not completely turned off.

    Best regards
    Harry