Coupled Inductor Current Sensing via Capacitive Decoupling
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Solution Overview
Problem
In buck converters with coupled inductor configurations, measuring inductor current is complicated due to the shared magnetic fields between inductors, making direct current resistance (DCR) sensing challenging.
Innovation Solution
A current sensing circuit with capacitors between sense nodes is used to ensure that sense voltages are proportional to inductor currents, allowing for accurate peak current monitoring and control in both inductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If coupled inductor configuration is used to reduce component count and improve efficiency, then power conversion efficiency and integration density are improved, but current sensing accuracy and measurement precision deteriorate due to shared magnetic fields interfering with DCR sensing
Solution Approach 1:
The current sensing function is segmented into two independent paths: one path uses DCR sensing for each inductor through its respective sense amplifier, while the other path uses a shared current sense amplifier with capacitive coupling to monitor the combined current. This segmentation allows each sensing path to operate independently without mutual interference, resolving the measurement precision issue while maintaining the efficiency benefits of coupled inductors.
Solution Approach 2:
Capacitors are introduced as intermediary elements between the sense nodes of the coupled inductors. These capacitors couple the sense signals to the current sense amplifier, allowing the sensing of inductor currents without direct electrical connection that would cause interference. The capacitive coupling acts as an intermediary that transfers current information while isolating the magnetic field interference, thus maintaining measurement precision in the coupled inductor configuration.
2Ease of manufacture
If DCR sensing method is used to measure inductor current, then circuit complexity is reduced and ease of manufacture is improved, but measurement precision deteriorates in coupled inductor configurations due to magnetic field coupling
Solution Approach 1:
The sensing system is divided into discrete modular components: individual sense amplifiers for each inductor, a shared current sense amplifier, and coupling capacitors. This modular segmentation maintains ease of manufacture by using standard circuit building blocks while enabling precise current measurement in coupled inductor configurations through their coordinated operation.
Solution Approach 2:
Capacitors are used as intermediary elements to couple the sense nodes to the current sense amplifier. This capacitive coupling mechanism provides accurate current measurement without requiring direct resistive connections that would be affected by magnetic field coupling, thus maintaining measurement precision while keeping the circuit structure relatively simple and manufacturable.
3Device complexity
If coupled inductor configuration is used to minimize component count, then device complexity is reduced and productivity is improved, but difficulty of detecting and measuring increases due to magnetic field interference
Solution Approach 1:
The current sensing function is segmented across multiple independent sensing paths with dedicated sense amplifiers and a shared current sense amplifier. This segmentation approach maintains low device complexity by using standard circuit components while simplifying the detection and measurement process through modular, independent sensing channels that do not interfere with each other despite the coupled inductor configuration.
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
Enables effective current sensing and control in coupled inductor configurations, ensuring that sense voltages are directly proportional to inductor currents, facilitating peak current limiting and control loops.
Implementation Method 1
The inductors of the DC-DC converter, in the coupled conductor configuration, share their respectively generated magnetic fields with one another
Implementation Method 2
The current sensing circuit includes a first capacitor coupled between the first sensing circuit and the second sensing circuit
Data Source
AI summary
A circuit and method for current sensing in DC-DC converters having coupled inductors is disclosed. A DC-DC converter includes a first and second inductors coupled to first and second switching nodes, respectively. The DC-DC converter further includes a current sensing circuit. The current sensing circuit includes a first current sensing circuit coupled to the first switching node and having a first sense node, and further includes a second sensing circuit coupled to the second switching node and having a second sense node. The circuit further includes a first capacitor coupled between the first sensing circuit and the second sensing circuit.