Slope Compensation Offset Cancellation in Current-Mode Regulators
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Solution Overview
Problem
Slope compensation in switching regulators complicates over-current protection and load current tracking by introducing a difference between the error signal and inductor current, making it difficult to determine the appropriate limit for the error signal for accurate protection and tracking.
Innovation Solution
The embodiments sample the slope signal when the inductor current reaches a peak or valley command and add it as an offset to the control loop to cancel the effect of slope compensation, ensuring the error signal accurately represents the inductor current, thereby enabling more precise over-current protection and load current tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If slope compensation is added to the control loop, then converter stability is improved, but the error signal deviates from the inductor current, reducing measurement precision
Solution Approach 1:
The patent segments the control loop into two separate paths: one path processes the error signal through the error amplifier for stability control, while the other path directly senses the inductor current through the sense circuit for accurate current measurement. This segmentation allows slope compensation to be applied only where needed for stability without corrupting the current measurement signal.
Solution Approach 2:
The patent extracts the current measurement function from the error signal path by introducing a separate sense circuit that directly measures the inductor current. This extracted measurement path remains free from slope compensation effects, while the error amplifier path can independently apply slope compensation for stability without affecting measurement accuracy.
2Reliability
If slope compensation is applied, then peak current mode control reliability is improved, but over-current protection accuracy deteriorates
Solution Approach 1:
The patent segments the control functions by routing the inductor current measurement through a dedicated sense circuit that feeds directly to the comparator for over-current protection decisions. This separate measurement path ensures that over-current protection accuracy is maintained independent of slope compensation applied in the error amplifier path.
Solution Approach 2:
The sense circuit acts as an intermediary between the inductor and the comparator, providing an accurate representation of the inductor current to the comparator without being affected by slope compensation. This intermediary path preserves measurement precision while allowing slope compensation to improve reliability in the main control loop.
3Stability of the object's composition
If slope compensation signal is added to the error amplifier output, then valley mode control stability is improved, but load current tracking precision deteriorates
Solution Approach 1:
The patent segments the control paths so that the sense circuit provides an uncompromised measurement of the inductor current for load current tracking, while the error amplifier independently applies slope compensation for stability. This segmentation ensures that load current tracking precision is maintained through the direct sense path while stability is improved through slope compensation in the error amplifier path.
Data Source
AI summary
A converter includes an inductor and a transistor. A sense circuit couples to the transistor. The sense circuit generates a sense signal responsive to a current through the first transistor. A comparator has first and second comparator inputs and a comparator output. The comparator output controls a signal to the transistor's control input. An error amplifier has an error amplifier input and an error amplifier output coupled to the first comparator input. A slope compensation circuit couples to at least one of the error amplifier output or the sense circuit and generates a slope signal. A peak detection sample/hold (PK-S/H) tracks the slope signal and, responsive to the transistor being turned off, samples the slope signal and provides the sampled slope signal on its output. The PK-S/H output couples to whichever of the error amplifier or sense circuit to which the slope compensation circuit is not coupled.