ED has been shelling out a few interesting articles lately, one of them written by Mr. Schweber on protection mechanisms relevant to ASICs. (please bear with any potential corrigendum in this post as my timekeeper has imposed a strict limit of 10 mins. for this leisure writing activity - in spite of the heaps of tasks accrued on my to-do list, my fingers can't just keep still when there are thoughts racing through my mind in reaction to a worthwhile article especially when it's from ED or SemiWiki) The author of said article from ED uses an allusion to insurance as an opening gambit to readers, then proceeds to elaborate the discussion's significance. It is superseded by a moderately exhaustive account of OCP, UVLO, OVP, and thermal shutdown ( more information available from the original article :

If you have finished perusing the article, there is one subtle phenomenon I would like to bring up. It was left unmentioned maybe because it occurs in the time domain but I think it plays a crucial role especially in systems riddled with vexing noise transients (i.e. ASICs deployed in locations with high-power operating machinery near its periphery).

Let us take a closer look again at how UVLO was described. It indeed protects the circuit from catastrophic damage when the input voltage falls below a certain threshold by turning the ASIC off. This threshold is guarded by hysteresis to avoid repeated on/off operation of the device. However, what happens if the voltage falls below, say 100mV of the threshold for a mere 100┬Ás only (a convex transient)?

Is it still excusable for the ASIC under question to turn itself off?

If the chip were exposed to an inconveniently noisy but reasonable environment, it'll be operating less frequently. A drop of 100mV from the threshold may not spell immediate disaster for the IC in question, so such chips would have an additional lenient feature that allows it to overlook such transients. Hence, even if a pulse that partially drops the input voltage below UVLO threshold were to occur, it will only trigger UVLO after a certain amount of time.

This, of course, does not apply to OCP or OVP as destruction would be instantaneous.