Anti-latch circuit for low dropout dual supply voltage regulator

Abstract

Efficient very low dropout (i.e., approximately equal to about V.sub.CESAT of the output transistor) dual supply voltage regulator circuits and methods are provided. The voltage regulators are capable of providing very low dropout irrespective of supply sequencing. Traditional supply sequencing problems are overcome by including an anti-latch circuit that monitors the output power supply during power-on. The anti-latch circuit is also coupled to any location in the regulator circuit where the drive current can be inhibited whenever the output power monitor senses that the output power supply is not fully operational. The anti-latch circuit operates to prevent drive current from being supplied to the output transistor unless output power is available so that the substrate of the regulator is not permitted to become forward biased (and thus prevents the establishment of an undesired latch condition).