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Like almost aiiic power regulator.s, the LX8585/85A regulators are equipped with Safe Operating Area (SOA) protection. The SOA circuit limit.s the regulator'.s maximum output current to progre.s- .sively lower value.s as the input-to-output voltage difference increa.se.s. By limiting the maximum output current, the SOA circuit keep.s the amount of power that i.s dis.sipated in the regulator it.self within safe limit.s for all values of input-to-output voltage within the operating range of the regulator. The LX8585/85A SOA protection .sy.stem is cle.signed to be able to supply .some output current for all value.s of input-to-output voltage, up to the device breakdown voltage. Under some condition.s, a correctly operating SOA circuit may prevent a power .supply .sy.stem from returning to regulated operation after removal of an intermittent .short circuit at the output of the regulator. Thi.s i.s a normal mode of operation which can be .seen in mo.st .similar product.s, including older device.s .such as 7800 .serie.s regulators. It is mo.st likely to occur when the power sy.stem input voltage i.s relatively high and the load impedance i.s relatively low. When the power .sy.stem i.s .started "cold", both the input and output voltage.s are very clo.se to zero. The output voltage clo.sely follows the rising input voltage, and the input-to-output voltage difference i.s .small. The SOA circuit therefore permits the regulator to supply large amount.s of current a.s needed to develop the de.signed voltage level at the regulator output. Now consider the ca.se where the regulator is .supplying regulated voltage to a resistive load under .steady state condition.s. A moderate input-to-output voltage appear.s acro.s.s the regulator but the voltage difference is small enough that the SOA circuitry allow.s .sufficient current to flow through the regulator to develop the designed output voltage acro.s.s the load resistance. If the output re.si.stor i.s .short- circuited to ground, the input-to-output voltage difference acro.ss the regulator .suddenly become.s larger by the amount of voltage that had appeared acro.s.s the load resi.stor. The SOA circuit reads the increased input-to-output voltage, and cut.s back the amount ofcurrent thatit will permit the regulator to supply to its output terminal. When the short circuit acro.ss the output re.sistor i.s removed, all the regulator output current will again flow through the output re.sistor. The maximum current that the regulator can .supply to the re.si.stor will be limited by the SOA circuit, based on the large input-to-output voltage acros.s the regulator at the time the .short circuit i.s removed from the output.
