Inductor Current Detection Circuit for Switch Ringing Accuracy
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Solution Overview
Problem
Existing current detection circuits in DC-DC converters face accuracy issues due to switch ringing during the turn-on period of high-side transistors, leading to less accurate inductor current detection compared to low-side transistors.
Innovation Solution
A current detection circuit that detects only the current flowing through the low-side transistor, using a processing circuit with a capacitor to output a cycle detecting current based on terminal voltage, increasing the voltage with a constant current during the high-side transistor's turn-on period, and varying it with the low-side detecting current during the low-side transistor's turn-on period, determining the constant current magnitude based on terminal voltage levels at specific time points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current detection is performed during the turn-on period of the high-side transistor, then inductor current detection coverage is improved, but measurement precision deteriorates due to switch ringing
Solution Approach 1:
The patent segments the detection process into two distinct parts: (1) using the first detection circuit to detect low-side transistor current during its turn-on period, and (2) using the processing circuit to generate cycle detecting current during the high-side transistor's turn-on period. This segmentation allows each circuit to operate in its optimal condition, avoiding the switch ringing interference that affects high-side detection while maintaining comprehensive current detection coverage.
Solution Approach 2:
The processing circuit acts as an intermediary that generates the cycle detecting current based on terminal voltage from the first capacitor. This intermediary mechanism translates the low-side current detection results into a comprehensive cycle detecting current that represents the entire switching cycle, including periods when the high-side transistor is on, without directly measuring during the problematic high-side turn-on period.
2Measurement precision
If only low-side transistor current is detected, then measurement precision is improved, but detection coverage deteriorates
Solution Approach 1:
The patent changes the parameter being detected from direct high-side transistor current to cycle detecting current generated from terminal voltage. By changing from direct current measurement during high-side turn-on (which suffers from ringing) to voltage-based cycle detection (which is accurate), the system maintains precision while the processing circuit ensures comprehensive cycle coverage is achieved.
Solution Approach 2:
The processing circuit creates a copy or representation of the complete switching cycle current waveform by generating cycle detecting current based on terminal voltage measurements taken during the low-side transistor's turn-on period. This copied signal represents the entire cycle including the high-side conduction period, achieving comprehensive coverage without direct measurement during problematic periods.
3Measurement precision
If terminal voltage is increased with constant current during high-side turn-on, then cycle detecting current accuracy is improved, but energy consumption increases
Solution Approach 1:
The constant current charging of the first capacitor is performed periodically only during the high-side transistor's turn-on period, which is a specific phase of the switching cycle. This periodic action ensures accurate cycle detecting current generation when needed (during high-side conduction) while minimizing energy consumption by not continuously charging the capacitor throughout the entire operating cycle.
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
Improves the accuracy of inductor current detection by matching the slope of the cycle detecting current with the actual inductor current, enhancing the precision of inductor current measurement.
Implementation Method 1
a first capacitor having a first end coupled to the ground and configured to perform an operation during a first and a second switch cycle, the operation including outputting a cycle detecting current based on a terminal voltage established at a second end of the first capacitor; increasing the terminal voltage established on the first capacitor by applying a constant current during a first period of the first switch cycle
Data Source
AI summary
A current detection circuit includes a processing circuit used to operate during each switch cycle which includes a first period and a second period. A cycle detecting current is provided based on the terminal voltage established on a first end of a capacitor. The terminal voltage established on the first end of the capacitor is increased during the first period using a constant current. The terminal voltage established on the first end of the capacitor varies with a low-side detecting current during the second period.