Voltage clamp circuit

摘要

A clamping circuit for clamping a circuit node during an initial circuit powerup interval includes a switching circuit and a switching control circuit. The switching circuit is an N-MOSFET with its drain and source terminals connected to circuit ground and the subject node sought to be clamped, respectively, and its gate terminal connected to the switching control circuit. The switching control circuit includes a number of N-MOSFETs which are interconnected in such a manner as to receive the power supply voltage and generate a switching signal which turns the switching circuit N-MOSFET on during an initial circuit powerup interval to clamp the subject node and then off after the power supply has reached a preselected minimum value. Upon initial circuit powerup, the switching control circuit self-triggers itself to turn the switching circuit on and clamp the subject node at ground potential. After the power supply has reached a preselected minimum value, the switching control circuit self-triggers itself again to turn the switching circuit off and thereby release the subject node from any clamping action. This clamping circuit is useful for temporarily clamping a VBB pad driven by a charge pump for back-biasing an integrated circuit substrate to prevent circuit latchup during initial circuit powerup.