Precise and robust enable control circuitry for LDO voltage regulators

Abstract

This paper presents novel circuit solutions for two issues related to the Enable control of low-dropout (LDO) voltage regulators: setting precise voltage thresholds for the ON/OFF states of the LDO and ensuring that in the OFF state the LDO output is not affected by fast variations of the supply voltage. First, an Enable circuit with hysteresis and temperature compensated thresholds is described: the accuracy of its threshold voltages - including their low temperature coefficients - are predicted by analytical analysis and validated by measurements performed on a silicon implementation. Second, a simple yet effective comparator is proposed, able to significantly reduce the effect the supply voltage variations have on the output voltage when the regulator is in OFF state. Simulation results show that, when the supply voltage varies from 0 to 28V in 28μs, the overshoot of the output voltage is reduced from 5.5V to under 200mV, that is by a factor of 35.