Synchronous Buck Regulator Current Sensing via MOSFET RDS(ON)
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Solution Overview
Problem
Current voltage regulators in information handling systems face challenges in achieving high accuracy for inductor current sensing due to low signal-to-noise ratio and manufacturing tolerances, which increases costs and complexity, especially in meeting stringent accuracy targets for next-generation servers.
Innovation Solution
A synchronous buck voltage regulator with a controller that measures inductor current during low-side switch ON state and synthesizes values during high-side switch ON state to generate a complete inductor current signal, reducing the need for complex high-precision amplifiers and improving signal fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional DCR-based sensing scheme is used, then cost is reduced and manufacturing is easier, but measurement precision and reliability deteriorate due to low signal-to-noise ratio and manufacturing tolerances
Solution Approach 1:
The patent segments the inductor current sensing into two distinct phases: during HS FET ON time, the controller synthesizes current values using voltage measurements and known inductance; during LS FET ON time, the controller measures actual current through the low-side switch. This segmentation allows each phase to use the most appropriate measurement method, improving overall accuracy without requiring high-precision amplifiers across the entire sensing path.
Solution Approach 2:
The patent introduces an intermediary approach by using the LS FET as a natural current sense element during its ON time. The LS FET's known on-resistance serves as an intermediary sensing element that converts current into a measurable voltage drop, eliminating the need for separate high-precision current sense amplifiers while maintaining measurement accuracy.
2Reliability
If DCR-based sensing is implemented, then initial cost is lower, but ongoing reliability deteriorates due to thermal compensation issues and inductor tolerance variations
Solution Approach 1:
The patent implements feedback by continuously monitoring the actual current during LS FET ON time and using this information to validate and adjust the synthesized current values during HS FET ON time. This closed-loop approach compensates for variations in inductor tolerance and thermal effects, improving sensing reliability without requiring expensive high-precision components.
Solution Approach 2:
The system uses its own operational characteristics to its advantage by leveraging the LS FET's natural presence and known parameters as the sensing element. The controller utilizes the voltage drop across the LS FET during its ON time as a self-provided sensing opportunity, eliminating the need for external sense resistors or complex sensing circuitry that would be susceptible to thermal and tolerance issues.
3Measurement precision
If complete inductor current measurement is attempted during both HS and LS switch states, then measurement coverage is improved, but device complexity and noise susceptibility increase
Solution Approach 1:
The patent employs periodic action by alternating between synthesis during HS FET ON time and direct measurement during LS FET ON time in a regular switching pattern. This periodic approach ensures continuous current information is available throughout the switching cycle while using the quieter, more reliable measurement method during the LS FET ON period when noise is lower.
Solution Approach 2:
The controller performs preliminary synthesis of current values during HS FET ON time based on voltage measurements and known circuit parameters. This preliminary action provides an estimate that is then refined or validated during the subsequent LS FET ON time when actual current measurement is performed, ensuring continuous accurate current information without requiring simultaneous complex measurement circuitry.
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 enhances accuracy and reliability of inductor current sensing while reducing costs and complexity, effectively addressing the limitations of traditional DCR-based sensing schemes.
Implementation Method 1
Voltage regulation based on current sensing in MOSFET drain-to-source resistance in on-state RDS(ON)
Data Source
AI summary
A direct current (DC) power supply system performs a method of delivering electrical energy by a synchronous buck voltage regulator (VR) coupled to an information handling resource of an information handling system by switching between a high side (HS) control switch and a low side (LS) synchronous switch to regulate a direct current (DC) output voltage (VOUT) generated from an input voltage (VIN). Inductor current (IMON) values of the voltage regulator are measured during LS synchronous switch ON state. IMON values of the voltage regulator are synthesized during HS power switch ON state. A complete inductor current signal is generated that combines the measured and synthesized IMON values.