Current Sense Resistor Slot Layout for Near-Zero TCR
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Solution Overview
Problem
Current four-terminal current sense resistors face inaccuracies in voltage readings due to non-zero Temperature Coefficient of Resistance (TCR), especially when temperature varies, caused by the high TCR of copper termination metal, which is not easily calibrated using conventional methods.
Innovation Solution
The introduction of strategically positioned slots, such as first and second slots with depth A, and a third slot with depth B, allows for TCR adjustment and calibration, minimizing the overall TCR to near zero by altering the copper path and using techniques like laser trimming for precise adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper termination metal is used in the current path, then electrical conductivity is improved, but Temperature Coefficient of Resistance (TCR) increases to unacceptable levels
Solution Approach 1:
The device is segmented into distinct functional zones: a resistive element zone with high-resistance material and copper-free terminations, and a terminal zone with copper extensions that are electrically isolated from the current path by slots. This segmentation allows each zone to optimize its material properties without compromising the other.
Solution Approach 2:
Copper is extracted from the current path entirely. The copper termination extensions are positioned only in the voltage sense region, separated from the main current flow by slots, thereby removing the source of high TCR while preserving electrical connectivity through alternative pathways.
2Object-affected harmful factors
If slots are introduced to adjust TCR, then Temperature Coefficient of Resistance is improved, but manufacturing complexity increases due to inability to use conventional calibration equipment
Solution Approach 1:
Slots are pre-formed in the substrate during the molding process itself, before any calibration operations. This preliminary action eliminates the need for subsequent complex calibration steps, as the slot geometry directly determines the electrical characteristics.
Solution Approach 2:
The slots serve multiple functions simultaneously: they provide electrical isolation between copper terminations and the resistive element, they define the geometry of voltage sense terminals, and they control the TCR by adjusting the ratio of copper-free to copper-containing pathways. This multi-functionality simplifies the overall manufacturing process.
3Manufacturing precision
If resistive element length is shortened to achieve low ohmic value, then resistance value is improved, but copper termination metal in current path increases TCR
Solution Approach 1:
The slots act as intermediaries that separate the copper termination extensions from the resistive element and current path. This mediation allows copper to be present in the device for good terminal conductivity while preventing it from contributing to TCR in the current path.
Solution Approach 2:
Different regions of the device have different material compositions optimized for their specific functions: the terminal regions use copper for low resistance connections, while the current path region uses copper-free material with slots to achieve low TCR. This local differentiation resolves the contradiction between conductivity and temperature stability.
Data Source
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AI summary
A current sense resistor and a method of manufacturing a current sensing resistor with temperature coefficient of resistance (TCR) compensation is 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 are 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 The fine TCR calibration slot has a depth selected to obtain a TCR value observed at the voltage sense terminals that approaches zero The resistance calibration slot has a depth selected to calibrate a resistance value of the resistor