Startup circuit for an LDO

摘要

A startup circuit in an LDO includes an operational amplifier having an inverting terminal and a non-inverting terminal and an output node. The non-inverting terminal receives a reference voltage. The startup circuit further includes a feedback capacitor coupled between an output node and the inverting terminal and a current source coupled between the inverting terminal and ground such that the current source and the feedback capacitor together control rate of change of an output voltage of the operational amplifier. A comparator is used to stop the rate of change of output voltage after the output voltage reaches a desired value.

主权项

1. A startup circuit for limiting inrush current in a regulator having a capacitance at an output comprising:
an operational amplifier having an inverting terminal and a non-inverting terminal, the non-inverting terminal receiving a reference voltage; a feedback capacitor connected to an output node of the operational amplifier and coupled to the inverting terminal; and a current source connected to the inverting terminal and coupled to ground such that the current source and the feedback capacitor together control rate of change of an output voltage of the operational amplifier to charge the capacitance at the output, wherein the feedback capacitor is pre-charged to the reference voltage before activating the operational amplifier and wherein the high voltage terminal of the pre-charged feedback capacitor is coupled to the inverting terminal of the operational amplifier and the low voltage terminal of the pre-charged feedback capacitor is coupled to the output node.