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LM20323, LM20333, LM20343 Current Limit Behavior


Please tell me how the current limit functions.

In the datasheets, it is merely mentioned that some reference voltage decrement and resulting foldback will occur (shown below).

I want some more detail, because it is a critical informatin for an automotive customer. Especially, what voltage the reference decrements and how much the frequency folds back.


Oguri (TIJ FAE for automotive)

From the Datasheet: For each sequential over-current event, the reference voltage is decremented and PWM pulses are skipped resulting in a current limit that does not aggressively fold back for brief overcurrent events, while at the same time providing frequency and voltage foldback protection during hard short circuit conditions.

  • Hello Oguri-san,

    The current limit scheme will skip 1 pulse out of 16 for every sequential current limit event.  So, after a single current limit is detected on the high-side FET, the switching frequency goes to 15/16 of Fsw.  If a current limit is detected on the next high-side pulse, it then goes to 14/16 of Fsw.  If 16 repeditive current limit signals are detected, then the switching frequency scales back to 1/16*Fsw.

    The same is true for the feedback voltage.  For every sequential current limit event, the feedback voltage is scaled back by 1/16.  After 16 sequential events, the final feedback voltage is 1/16*0.8, nominally.

    Hope this helps.

    Mike Hartshorne