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LM26480: Reason for nPOR default state being HIGH

Part Number: LM26480

Is there a reason why even before the Enable pins are asserted for both of the bucks, nPOR is high? I.e. Why is nPOR high before t0?

  • Hi Jerome,

    nPOR is an open drain output, which means that it must be pulled high by default so it can then pull active low to indicate a fault event. My guess is that this diagram was drawn the way it is to illustrate the default state of nPOR in relation to EN1 and EN2. The initial state of nPOR must be high so that it is then pulled low when EN1 goes high. The device will then ensure that the supply for Buck2 comes up, otherwise it stays in the low state to indicate a fault. The counter delay indicates the period of time that the nPOR pin "waits" for the Buck2 supply to come up, before ensuring whether to go back high or stay low.

    Best,
    Emily