Method for reducing body diode conduction in NMOS synchronous rectifiers
AssigneeAdvanced Analogic Technologies, Inc.
InventorsKevin D'Angelo, Robert Wrathall
Life of this patent
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Abstract
A switching regulator that practices the current invention includes a high-side switch M1 connected between an input voltage and a node LX. A low-side switch is connected between the node LX and ground. An inductor L is connected between LX and an output node (VOUT). A filtering capacitor connects VOUT to ground. The switching regulator has two distinct operational phases. During the first operational phase, the high-side switch is OFF and the low-side switch is ON. During the second operational phase, the high-side switch is ON and the low-side switch acts as a current source. During transitions between the second and first operational phases, the low-side switch is controlled to momentarily decrease the regulated drain-to-source current.
Claims20
A method for operating a switching regulator, the switching regulator comprising a high-side switch and a low-side switch, the method comprising:
- controlling the high-side switch to be substantially depleted during a first operational phase and to be substantially enhanced during a second operational phase;
- controlling the low-side switch to be substantially enhanced during the first operational phase and to provide a regulated drain-to-source current during the second operational phase;
- enabling a current mirror to generate a gate voltage for the low-side switch during the second operational phase;
- using, a drain voltage of a diode-connected N-channel MOSFET as the gate voltage of the low-side switch, a current source supplying the gate and drain of the N-channel MOSFET;
- and
- during transitions between the second and first operational phases, controlling the low-side switch to momentarily decrease the regulated drain-to-source current and providing an AC coupling between a voltage used to drive the high-side switch and the gate of the N-channel MOSEFT to momentarily decrease the low-side voltage.
A switching regulator comprising:
- a high-side switch;
- a low-side switch;
- a high-side driver circuit configured to control the high-side switch to be substantially depleted during a first operational phase and to be substantially enhanced during a second operational phase;
- a low-side driver circuit that controls the low-side switch to be substantially enhanced during the first operational phase and to provide a regulated drain-to-source current during the second operational phase;
- a current mirror that is enabled during the second operational phase to generate a gate voltage for the low-side switch, the current mirror comprising a diode connected N-channel MOSFET having its drain connected to supply the gate voltage of the low-side switch and a current source to supply the gate and drain of the N-channel MOSFET;
- a coupling circuit, that momentarily decreases the regulated drain-to-source current during transitions between the second and first operational phases;
- and
- an AC coupling circuit connected between a voltage used to drive the high-side switch and the gate of the N-channel MOSFET to momentarily decrease the low-side drive voltage during transitions between the second and first operational phases.
Dependencies are inferred from the claim text.