Power Switch Current Sensing With Blanking Slope Correction
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Solution Overview
Problem
Existing current sensing techniques in switching voltage converters, particularly those using the on-state resistance of power switches, face inaccuracies due to noise and ringing artifacts immediately after switch transitions, which become significant at higher switching frequencies, limiting the accuracy of inductor current estimation and leading to overdesign of cooling infrastructure.
Innovation Solution
A current estimation circuit that senses the voltage across the load terminals of a power switch, ignores the noisy portion of the waveform during a blanking interval, estimates the slope of the waveform after the blanking interval, and uses this slope to model and correct the current estimation, providing accurate current estimates without complex compensation or frequent sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If R_DSON-based current sensing is used to estimate inductor current, then power consumption is reduced and accuracy is improved compared to shunt resistors, but measurement precision deteriorates due to ringing and noise artifacts immediately after switch turn-on transition
Solution Approach 1:
The patent extracts only the useful portion of the voltage waveform by implementing a blanking interval that excludes the noisy region immediately after switch turn-on. By ignoring the first portion of the waveform where ringing and ground bounce occur, the circuit obtains clean measurements from the remaining linear portion of the waveform, thus maintaining R_DSON-based sensing benefits while eliminating measurement errors.
Solution Approach 2:
The patent applies preliminary correction by estimating the slope of the voltage waveform during the blanking interval and using this slope to calculate what the voltage should have been at the start of the measurement window. This preliminary estimation allows the circuit to compensate for the excluded noisy portion and achieve accurate current sensing without being affected by the initial ringing artifacts.
2Measurement precision
If a blanking interval is implemented to ignore noisy waveform portion after turn-on transition, then measurement precision is improved by avoiding ringing artifacts, but current estimation accuracy deteriorates because the blanked portion contains useful current information
Solution Approach 1:
The patent employs feedback by using the measured voltage waveform from the non-blanked portion to estimate the slope, then applying this slope information to reconstruct the voltage values that would have been present during the blanking interval. This feedback loop ensures that the current information contained in the blanked portion is recovered through mathematical reconstruction rather than direct measurement.
Solution Approach 2:
The patent introduces slope estimation as an intermediary element that bridges the gap between the blanked noisy portion and the clean measurement portion. By calculating the slope during the valid measurement window and extrapolating it backward, the circuit acts as a mediator to recover the current information that would otherwise be lost in the blanking interval, combining both portions' worth of data without directly measuring the noisy region.
3Productivity
If switching frequency is increased to improve power density and reduce inductor size, then productivity is improved, but measurement precision deteriorates because the blanking interval becomes a larger portion of the switching cycle
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the slope estimation parameters based on the actual waveform characteristics observed during each switching cycle. Rather than using fixed blanking intervals or static slope values, the circuit adapts its measurement and correction parameters to match the specific operating conditions, allowing accurate current sensing across a wide range of switching frequencies while maintaining the benefits of high-frequency operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate current estimation across a wide range of duty cycles and switching frequencies, reducing the need for overdesign and minimizing cooling infrastructure, thereby optimizing power usage and cost in server applications.
Implementation Method 1
R DSON -based current sensing... sense the voltage across one (or both) of the power switches connected to the inductor, and to use the on-state resistance (e.g., R DSON ) of the power switch (or switches) to estimate the current through that switch (or those switches)
Data Source
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AI summary
A current estimation circuit is configured to estimate current within a power switch, e.g., within a switching voltage converter, using a voltage measured across its load terminals and its on-state resistance. Ringing and other transient anomalies associated with a turn-on transition of the power switch are neglected by ignoring the measured voltage across the power switch for a blanking interval after the transition. During the remainder of the conduction interval of the power switch, the measured voltage is sampled to provide first and second samples. Also during this interval, a slope of the measured voltage is estimated and tracked. The estimated slope and the first and second samples are combined to produce an estimate of the current for the entire conduction interval of the power switch, including the blanked interval. The estimated slope is used to correct for inaccuracy introduced by not using measured voltage during the blanking interval.