Power-up initialization circuit that operates robustly over a wide range

Abstract

A power-up initialization circuit includes a transistor that generates a positive leakage current at the onset of a power-up ramp voltage. The positive leakage current drives a first node connected to a latch to a first defined state. The latch drives a complementary second node to a second defined state, complementary to the state of the first node. The latch acts as a keeper that is switchable and allows current flow during power-up but prevents leakage current when the power-up is complete and nodes are set to selected states. A keeper is a circuit element that holds a dynamic circuit to a static behavior. One type of keeper is a latch. Another type of keeper is a MOSFET transistor having a thin channel width and a gate terminal connected to a reference such as a ground or VSS reference. A power-up initialization circuit includes a capacitive switch connected to a power source and connected to a power-up control node, and a current source connected to the power source and connected to an internal node. The current source has a control terminal connected to the power-up control node. The current source sets a state at the internal node according to a signal on the power-up control node. The power-up initialization circuit furthers includes a latch connected to the internal node and connected to a controlled node. The latch sets a state of the controlled node opposite the state of the internal node.