Constant-On-Time Buck Control for Voltage Droop and DC Accuracy
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Solution Overview
Problem
Conventional switching voltage regulators (VRs) face challenges with high DC accuracy and voltage droops during load transients, leading to sub-optimal power-performance and increased costs due to frequency guard-banding, which affects processor core frequencies and average selling prices.
Innovation Solution
The implementation of a high gain integrator and elimination of minimum off-time in Constant-On Time (COT) buck converters to improve DC accuracy and transient response, allowing the high-side switch to remain turned on beyond a turn-on time if the output voltage remains below a reference, ensuring continuous charging of the output capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional switching voltage regulators are used, then DC accuracy can be maintained, but voltage droops occur during load transients leading to sub-optimal power-performance
Solution Approach 1:
The patent implements a dynamic control mechanism where the buck converter switches between PWM mode and COT mode based on operating conditions. During load transients, the controller dynamically transitions to COT mode which provides faster response and reduced voltage droop, while returning to PWM mode during steady-state to maintain DC accuracy. This dynamic switching resolves the contradiction between maintaining DC precision and preventing voltage droop during transients.
Solution Approach 2:
The patent changes the control parameter from fixed-frequency PWM to variable-frequency COT during transient conditions. By detecting voltage droop and switching to COT mode with extended on-time pulses, the system adjusts the switching parameters dynamically to prioritize transient response over steady-state frequency stability, thereby reducing voltage droop while maintaining overall system performance.
2Reliability
If frequency guard-banding is applied to compensate for DC inaccuracy and voltage droops, then processor core frequency is reduced, but power-performance deteriorates
Solution Approach 1:
The patent employs a feedback mechanism that continuously monitors the output voltage and detects load transient conditions. When voltage droop is detected, the feedback loop triggers a transition to COT mode with extended on-time, automatically compensating for the voltage drop without requiring frequency guard-banding. This real-time feedback correction allows the processor to maintain higher frequencies while ensuring voltage stability.
Solution Approach 2:
The patent implements preliminary detection of voltage droop conditions and proactively extends the on-time pulse before the voltage drops to critical levels. By anticipating and preemptively correcting voltage droop through early detection and extended charging pulses, the system prevents performance degradation without needing to reduce processor frequency as a conservative measure.
3Ease of operation
If minimum off-time is implemented in COT buck converters, then switch control is simplified, but transient response becomes slower
Solution Approach 1:
The patent implements a dynamic off-time mechanism where the minimum off-time constraint is relaxed or eliminated during transient conditions. The controller dynamically adjusts the off-time based on the detected voltage droop severity, allowing extended on-time pulses when needed for fast transient response, while maintaining normal off-time constraints during steady-state operation. This dynamic approach resolves the contradiction between simplified control and fast transient response.
Solution Approach 2:
The patent changes the off-time parameter from a fixed minimum value to a variable parameter that can be extended or eliminated based on transient conditions. By allowing the off-time to become negative or zero during severe transients, the system prioritizes transient response speed over the simplification benefits of fixed minimum off-time, achieving both control simplicity and fast response through adaptive parameter adjustment.
Data Source
AI summary
A one-shot inductor current scheme which includes a controller to generate a signal to control a high-side switch and a low-side switch such that the high-side switch remains turned on beyond a turn-on time if a voltage level on an output supply rail remains below a reference. The scheme reduces the minimum operating voltage Vmin and/or frequency guard-band of the SoCs (system-on-chips).