High-Side Power FET Gate Sense Circuit for Buck Regulators
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Solution Overview
Problem
Existing sensing circuits for buck regulators are slow and inaccurate due to the delay introduced by level-shifting circuitry when sensing the gate-source voltage of high-side power FETs, which can lead to shoot-through issues.
Innovation Solution
A gate sense circuit that couples the gate sense signal directly to the high-side gate without the need for level shifting, utilizing a switching circuit with MOSFET switches and positive feedback loops to achieve fast and accurate signal propagation, reducing propagation delay to less than 1 ns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If level-shifting circuitry is used to sense the gate-source voltage of the high-side FET, then the sense signal can be brought down to the low-voltage domain for processing, but the propagation delay increases significantly
Solution Approach 1:
The patent introduces an intermediary sense circuit that couples to the gate of the high-side FET and generates a sense signal that directly follows the gate voltage. This intermediary circuit acts as a mediator between the high-side FET gate and the low-side FET control, eliminating the need for slow level-shifting circuitry while maintaining signal accuracy and reducing propagation delay to less than 1 ns.
2Productivity
If the low-side FET is made to turn on earlier to compensate for level-shifting delay, then the dead time is reduced, but the accuracy is compromised and shoot-through may occur
Solution Approach 1:
The patent implements a feedback mechanism where the sense circuit continuously monitors the gate voltage of the high-side FET and provides real-time feedback to the control circuit. This feedback allows the control circuit to accurately determine when the high-side FET turns off, enabling precise timing for low-side FET activation without premature turning on, thus preventing shoot-through while maintaining fast switching.
3Measurement precision
If the sense circuit operates in the high-voltage domain, then the signal accuracy is maintained, but additional level-shifting circuitry is required
Solution Approach 1:
The patent extracts the level-shifting function from the sense circuit by having the sense circuit generate a sense signal that directly follows the gate voltage transitions. The sense circuit takes out the complexity of level-shifting circuitry by using a simplified configuration that couples to the gate and produces a voltage-following signal, eliminating the need for separate level-shifting stages and reducing overall circuit complexity.
Data Source
AI summary
A circuit for sensing gate voltage of a power FET. A switching circuit includes a switching FET having a high voltage rating, its drain coupled to the gate of the power FET, and its source coupled to an output node. A first feedback loop is coupled to the gate of the switching FET to facilitate sensing rising gate voltage. A second feedback loop is coupled to the gate of the switching FET to facilitate sensing falling gate voltage.