Hybrid filter for high slew rate output current application

Abstract

An active linear regulator circuit in parallel with a filter capacitor of a switching voltage regulator injects current to a load only when the switching regulator and capacitor cannot supply adequate current to follow high frequency load transients in a manner which is compatible with adaptive voltage positioning (AVP) requirements. control of current injection and determination of the insufficiency of current from the switching regulator and capacitors is achieved by impedance matching of the linear regulator to the switching regulator. The linear regulator thus operates at relatively low current and duty cycle to limit power dissipation therein. By matching impedances and increasing the bandwidth of the switching regulator, filter capacitor requirements can be reduced to the point of being met entirely by packaging and/or on-die capacitors which may be placed close to or at the point of load to reduce parasitic inductance, as can the linear regulator.