Inductor Current Sensing in Constant On-Time Regulators
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Solution Overview
Problem
Measuring output current in buck regulators is complex and inefficient, often requiring costly sense resistors that increase ripple and degrade transient response.
Innovation Solution
A current monitor system that senses inductor current at a predetermined time point during operation of a constant on-time regulator, using processor calculations based on on-time, off-time, and skip periods to determine output current, eliminating the need for sense resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used to measure output current, then current measurement is achieved, but cost and complexity increase
Solution Approach 1:
The patent extracts the current measurement function from the traditional sense resistor approach and implements it through inductor current sensing at specific time points. By measuring inductor current at half the on-time period, the system obtains output current information without requiring external sense resistors, thereby reducing circuit complexity while maintaining measurement capability
Solution Approach 2:
The patent uses the inductor as an intermediary element to obtain output current information. Instead of directly measuring output current through sense resistors, the system measures the inductor current (which is related to output current) at a specific time point, using the inductor as a mediator to achieve indirect but accurate measurement
2Measurement precision
If a sense resistor is used to measure output current, then current measurement is achieved, but power efficiency deteriorates
Solution Approach 1:
The patent removes the sense resistor from the circuit entirely, extracting the measurement function to the controller that samples inductor current at specific time points. This elimination of the sense resistor component directly eliminates the power loss associated with it, improving overall system efficiency while maintaining current measurement capability
3Measurement precision
If a sense resistor is used to measure output current, then current measurement is achieved, but output voltage ripple increases
Solution Approach 1:
The patent extracts the measurement function away from the output path by sensing inductor current rather than placing sense resistors in the output circuit. This removal of sense resistors from the output path eliminates their contribution to output voltage ripple, reducing harmful effects on voltage stability
Solution Approach 2:
The patent uses inductor current sensing as an intermediary measurement approach. By measuring the inductor current (which correlates to output current) rather than directly sensing output current through resistors, the system obtains measurement data without introducing resistive elements that would generate voltage ripple in the output circuit
4Measurement precision
If a sense resistor is used to measure output current, then current measurement is achieved, but transient response degrades
Solution Approach 1:
The patent performs preliminary measurement of inductor current at a specific time point (half the on-time period) during the switching cycle. This timing-based sampling approach provides advance information about current levels without introducing the resistive loading that would degrade transient response, allowing the system to maintain fast transient performance
Data Source
AI summary
A current monitor includes current sense logic and a processor. The current sense logic senses inductor current at a predetermined time point during operation of a constant on-time regulator. The processor determines output current of the constant on-time regulator based on the inductor current sensed at the predetermined time point. The predetermined time point corresponds to half of an on-time period of the constant on-time regulator. The output current may be determined during continuous conduction mode (CCM) or discontinuous conduction mode (DCM). During DCM mode, the processor determines the output current of the constant on-time regulator based on a skip time.