PCB Trace Temperature Compensation for DCR Current Sensing
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Solution Overview
Problem
Conventional DCR sensing techniques for power supply circuits face inaccuracies in output current sensing due to temperature variations in the inductor's parasitic resistance, requiring additional temperature sensors that increase costs and complexity.
Innovation Solution
A system using a printed circuit board (PCB) metal trace with a similar temperature coefficient to the inductor, allowing for temperature compensation without a discrete temperature sensor, by calibrating the inductor current detection and calibration circuit to accurately detect Over Current Protection (OCP) conditions across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional DCR sensing techniques are used to sense output current, then the power dissipation is reduced compared to sense resistor methods, but the measurement precision deteriorates due to temperature variations in inductor resistance
Solution Approach 1:
The patent creates a copy of the inductor's temperature characteristics using a separate temperature compensation inductor that is physically coupled to the power inductor. This compensation inductor replicates the temperature-dependent resistance changes without carrying the full load current, allowing accurate temperature compensation of the sensing signal while minimizing power dissipation in the sensing path.
Solution Approach 2:
The patent changes the resistance parameter of the sensing path by introducing a temperature compensation mechanism that dynamically adjusts the sensing circuit's reference resistance to match the inductor's resistance at different temperatures. This compensates for temperature-induced resistance changes and maintains measurement accuracy across varying operating conditions.
2Measurement precision
If a temperature sensor is added near the inductor to compensate for resistance variations, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent merges the temperature compensation function with the existing inductor structure by using a second inductor that serves dual purposes: maintaining magnetic coupling for circuit operation and providing temperature sensing capability. This eliminates the need for separate temperature sensors and reduces overall circuit complexity while improving measurement precision.
Solution Approach 2:
The patent enables the inductor structure itself to provide temperature compensation information through the resistance characteristics of the compensation inductor. The system uses its own existing components (the compensation inductor's resistance changes) to automatically compensate for temperature effects, eliminating the need for external temperature sensors or additional complexity.
3Measurement precision
If a sense resistor is placed in the output current path to accurately sense current, then the measurement precision improves, but the power dissipation increases
Solution Approach 1:
The patent creates a parallel sensing path using the compensation inductor's resistance characteristics to copy the current sensing function without requiring a high-value sense resistor in the main current path. This allows accurate current measurement while minimizing power dissipation in the sensing elements.
Solution Approach 2:
The patent introduces the compensation inductor as an intermediary element that mediates between the power inductor and the sensing circuitry. This intermediary provides temperature-compensated resistance information that enables accurate current sensing through DCR methods without requiring a traditional sense resistor, thus reducing power dissipation.
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 accurate OCP detection without a temperature sensor near the inductor, reducing fabrication costs and improving detection accuracy compared to conventional methods.
Implementation Method 1
the inductor is disposed directly above the metal trace when viewed from a top-down perspective... the metal trace has a similar temperature coefficient as a winding of the inductor... the resistance of the metal trace changes proportionally to the resistance of the inductor across a range of temperatures
Implementation Method 2
The inductor current detection and calibration circuit detects the OCP condition, in part, by sensing a voltage across the metal trace via the first and second package terminals... the resistance of the metal trace and the inductor vary proportionally over a range of temperatures
Data Source
AI summary
A system comprises an integrated circuit package, an inductor that is part of a power supply, and a printed circuit board (PCB) having a metal trace disposed directly below the inductor when viewed from a top-down perspective. The integrated circuit package includes a first terminal, a second terminal, and a novel inductor current detection and calibration circuit. The first terminal is coupled to a first end of the metal trace and the second terminal is coupled to a second end of the metal trace. During operation of the power supply, the novel circuit detects an OCP condition whereby an output current of the power supply exceeds an OCP level. The novel circuit detects the OCP condition in part by sensing a voltage across the metal trace. After calibration at room temperature, the novel circuit performs accurate OCP detection over a range of temperatures without using any temperature sensor near inductor.