Total dose degradation of low-dropout voltage regulators

A low dropout voltage regulator that uses a lateral pnp transistor as a pass transistor in the output stage is evaluated for total dose degradation. Degradation occurs from two different mechanisms, one involving gradual degradation due to changes in internal reference voltage resulting in small changes in output voltage saturation characteristics; and the other causing the output voltage to fall to nearly zero because of gain degradation in the lateral pnp output transistor. Additionally, wide variability was observed between two different lots of devices, produced approximately 18 months apart. This illustrates the importance of lot-sample testing when these highly sensitive devices are considered for use in space.