Current Sense Resistor Slot Layout for Near-Zero TCR
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Solution Overview
Problem
Current four-terminal current sense resistors with low ohmic values and high stability face challenges due to their non-zero Temperature Coefficient of Resistance (TCR), which leads to inaccurate voltage readings when temperature varies.
Innovation Solution
The solution involves a resistor configuration with a resistive strip between conductive strips, featuring a pair of rough TCR calibration slots and a fine TCR calibration slot to adjust the TCR to near zero, along with a resistance calibration slot for precise resistance value calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper termination metal is used in the current path to connect the resistive element to terminals, then the electrical connectivity and current carrying capability are improved, but the Temperature Coefficient of Resistance (TCR) increases significantly due to copper's high TCR of 3900 ppm/°C
Solution Approach 1:
The patent extracts the copper termination metal from the current path by using a four-terminal configuration where voltage sense terminals make direct contact with the resistive element ends, bypassing the copper terminations for the voltage measurement path. This separates the high-current copper connections from the precision voltage sensing path.
Solution Approach 2:
The patent introduces an intermediary approach by using the resistive element itself as the connection medium between the voltage sense terminals and the external circuit, eliminating the need for copper terminations in the voltage sensing path and thus removing the source of high TCR.
2Manufacturing precision
If the length of the resistive element is shortened to achieve low ohmic value, then the resistance value decreases, but the proportion of copper termination metal in the current path increases, driving the overall TCR to 800 ppm/°C or greater
Solution Approach 1:
The patent segments the electrical connections into two distinct paths: a high-current path through copper terminations and a voltage sensing path through the resistive element itself. This segmentation allows the resistive element to serve dual purposes as both the resistance element and the voltage sensing conductor, eliminating copper from the sensing path.
Solution Approach 2:
The resistive element is given multiple functions: it serves as the primary resistance element, the voltage sensing conductor, and the connection medium between the external circuit and the measurement points. This multi-functionality eliminates the need for separate copper terminations in the voltage path.
3Ease of manufacture
If conventional four-terminal resistor configuration is used with slots between terminals, then the structure is simple and easy to manufacture, but the TCR cannot be effectively compensated and remains in the 800 ppm/°C range
Solution Approach 1:
The patent moves the voltage sense terminals from a planar arrangement to a three-dimensional configuration where they contact the ends of the resistive element directly, creating a vertical or depth-dimensional separation between the voltage sensing path and the copper termination structures.
Data Source
AI summary
A current sense resistor and a method of manufacturing a current sensing resistor with temperature coefficient of resistance (TCR) compensation are disclosed. The resistor has a resistive strip disposed between two conductive strips. A pair of main terminals and a pair of voltage sense terminals are formed in the conductive strips. A pair of rough TCR calibration slots is located between the main terminals and the voltage sense terminals, each of the rough TCR calibration slots have a depth selected to obtain a negative starting TCR value observed at the voltage sense terminals. A fine TCR calibration slot is formed between the pair of voltage sense terminals.