Layout Design for Parallel Use of Kelvin-Structured Resistors

Figure 1: Three Kelvin-structure 4-pin resistors in parallel. (Image source: Shenzhen Milliohm Electronic Co., Ltd)

When three Kelvin-structure 4-pin resistors are used in parallel, routing considerations must prioritize "even current distribution" , "no interference with voltage detection" , and "preservation of the Kelvin structure's characteristics" . The routing principles and steps are as follows:

1. Core Principle: Separate current and voltage paths and maintain symmetry

1. Current Path (I+, I-): Thick, symmetrical, and even current paths carry the main current. These paths should be connected using thick wire or copper. The length and impedance of the current paths of the three resistors should be as consistent as possible to avoid uneven current distribution (overloading a resistor) due to parasitic parameter differences.
2. Voltage Detection Path (V+, V-): Thin, independent, and interference-free voltage paths carry only weak detection signals and should be connected using separate, thin wires. These paths should be strictly connected from the resistor's voltage terminals (V+, V-). Sharing wires with the current paths is prohibited (otherwise, additional resistance will be introduced, undermining the precision advantage of the Kelvin structure).

As shown in the Figure 2, when three resistors are used in parallel, the voltage detection pin of one of the resistors can be used since the voltage pins of the other two resistors are not set to electrical network signals, but are left floating and only connected to the pads for fixing. Because the voltage drop of all resistors in the parallel resistor network is the same, there is a common voltage between the resistors connected in parallel, and this voltage is the same for all parallel-connected components.

Figure 2: Bare Alloy Resistor Series – Kelvin Parallel Layout. (Image source: Shenzhen Milliohm Electronic Co., Ltd)

2. Specific Routing Steps and Details

1. Resistor Layout: Symmetrical and Compact to Reduce Parasitic Parameters

   Place the three Kelvin resistors side by side or in a compact triangle with even spacing. Ensure that each resistor is physically the same distance from the current sink and voltage sensing point to minimize parasitic inductance or resistance variation caused by varying wiring lengths. The resistor pins should be oriented in the same direction (e.g., current terminals facing outward, voltage terminals facing inward) to facilitate centralized routing.

2. Current Path (I+, I-) Routing: Use a busbar or copper patch, with symmetrical branches as much as possible.

   Busbar/Copper Patch Area Design:

   Input (I+): Create a common I+ busbar (recommended copper thickness ≥ 35 μm, width calculated based on total current, e.g., ≥ 5 mm for a total current of 100 A). Connect the I+ terminals of the three resistors to this busbar via branch wires of equal length and width (branch length difference ≤ 1 mm, uniform width).

   Output (I-): Similarly, set up a common I- bus. Connect the I- terminals of the three resistors to this bus via branch wires of equal length and width.

   Avoid current crossing: The current path must be kept away from the voltage detection path to reduce electromagnetic interference (large currents can generate magnetic fields that interfere with voltage signals).

3. Voltage Detection Path (V+, V-) Wiring: Independent leads, directly connected to the detection chip.

Independent leads: Lead the V+ terminal of one of the three resistors through a separate thin wire (e.g., 0.2 mm wide with 18 μm copper thickness, as the current is extremely low). The same applies to the V- terminal of each resistor.

Short and straight: The voltage detection line should be as short as possible to avoid winding and reduce parasitic resistance and noise.

Do not connect the V+ lead of a resistor to the I+ bus (or the I+ terminal of another resistor). It must be strictly connected to the V+ terminal of that resistor. Similarly, connect the V- lead only to its own V- terminal.

Summary

There must be careful consideration to the routing related to three Kelvin-structure 4-pin resistors when they are used in electronic measurements. Following the guidance outlined in this blog will help you avoid some common mistakes and erroneous measurement headaches.