High-Precision PCB Design Essential: Exploring the Principles and Layout Essentials of Four-Wire Kelvin Connection-Shenzhen Chengchi Circuit Technology Co., Ltd.

High-Precision PCB Design Essential: Exploring the Principles and Layout Essentials of Four-Wire Kelvin Connection

Time：2026-01-03 Views：1

In PCB design, the four-wire power interface combined with Kelvin connection (also known as four-terminal connection) is a core technique for achieving high-precision power supply or current/voltage measurement. Its primary purpose is to eliminate voltage errors caused by wire resistance and contact resistance, especially in scenarios requiring high power supply accuracy (such as precision sensors, ADC/DAC, high-power modules, etc.).

01 The Relationship Between Four-Wire Power Interface and Kelvin Connection

The four wires of a four-wire power interface are divided into two groups:

● Force Lines: 2 wires responsible for transmitting the main current (I). Since wires have resistance (R), a voltage drop (V = I × R) occurs.

● Sense Lines: 2 wires used only to detect the actual voltage across the load (V_load). Ideally, the current is ≈ 0, so their own voltage drop is negligible.

The essence of a Kelvin connection is to physically separate the force lines and sense lines in the wiring, allowing the sense lines to directly "sense" the true voltage at the load end, rather than at the power supply output or somewhere along the wiring, thus enabling precise power supply or measurement.

The figure below illustrates the principle of a Kelvin connection. The core purpose of using this method is to eliminate the impact of wire resistance (R_l) on the power supply module's detection, thereby achieving high-precision power supply.

02 How to Implement Kelvin Connection in PCB Layout

Taking "supplying power to a load (e.g., a precision module)" as an example, a four-wire interface is typically defined as: V+ (force positive), V- (force negative), VS+ (sense positive), VS- (sense negative). Specific steps are as follows:

Interface Pin Definition and Connection Target

● Force Lines (V+, V-): Directly connect the power supply output to the load's power input, responsible for delivering the operating current (trace width must be designed based on the maximum current to meet current-carrying requirements).

● Sense Lines (VS+, VS-): One end connects to the power supply's "voltage feedback terminal" (if the power supply supports remote sensing), and the other end must be connected directly to the load's power pins (not to a point midway along the force lines), to detect the actual voltage the load receives.

Core Wiring Principles

Strictly separate force lines and sense lines:

● They must not share copper pours or be routed closely in parallel (to avoid electromagnetic coupling interfering with the sense signal).

● Sense lines should be routed as separate thin traces (since the current is extremely small, the trace width can be much narrower than that of the force lines), and the path should be as short and direct as possible.

For example: Force lines use thick traces (e.g., 2mm wide for a 10A current), while sense lines use thin traces (e.g., 0.2mm wide, carrying only μA-level sense current).

Sense line connection points must be "close to the load":

● VS+ must be connected directly to the load's VCC pin pad, and VS- directly to the load's GND pin pad (not to the V+, V- pads of the force lines).

● Reason: If the sense point is far from the load, the sense line will include the voltage drop across the wire resistance from the end of the force line to the load, causing errors in the sensed value.

Avoid introducing noise into sense lines:

● Sense lines carry weak voltage signals (used for feedback regulation) and should be kept away from high-frequency signal lines, power inductors/transformers, and other noise sources.

● If they are long, consider adding small capacitors (e.g., 100pF) in parallel at both ends of the sense lines to filter out noise.

Closed-Loop Cooperation with the Power Supply (if supported)

If the power supply has "Remote Sense" functionality (e.g., precision linear power supplies, Sense pins of DC-DC modules), the following connections are required:

● Power supply's Sense+ connects to the four-wire interface's VS+

● Power supply's Sense- connects to the four-wire interface's VS-

● Power supply's Output+ connects to V+, and Output- connects to V-

In this case, the power supply automatically adjusts its output based on the difference between VS+ and VS- (i.e., the actual voltage at the load), compensating for the voltage drop across the force lines to ensure the voltage at the load is precisely equal to the set value.

Grounding Handling (for single-ended loads)

If the load is a single-ended circuit (requiring only a single power supply, e.g., VCC and GND), the V- and VS- of the four-wire system typically share a common ground, but note:

● The connection point for VS- must be the load's "local GND" (not the power supply's GND or the force line's GND).

● The GND of the force line (V-) and the GND of the sense line (VS-) converge at the load end to avoid forming ground loops.

03 Application Scenarios and Advantages

● High-Precision Power Supply: For example, supplying power to a 16-bit or higher ADC, where the reference voltage/operating voltage error must be < 1mV. Kelvin connection eliminates wire voltage drop (even a 0.1Ω wire with 1A current has a 0.1V drop, far exceeding the allowable error range).

● Precise Current Measurement: When using a four-wire system to measure current (e.g., connecting a sense resistor in series with the force line and measuring the voltage across it with sense lines), the Kelvin connection eliminates the impact of contact resistance on the measurement.

04 Common Mistakes and How to Avoid Them

The core of the Kelvin connection in a four-wire power interface is "ensuring the sense lines go directly to the load, physically isolated from the force lines." Through careful PCB layout design, the impact of wire resistance can be minimized, enabling precise power supply or measurement.

❌ Routing sense lines parallel to force lines: May introduce electromagnetic interference, causing fluctuations in the sensed voltage.

❌ Placing sense points far from the load: For example, connecting VS+ to the power supply output instead of the load end defeats the purpose of compensation.

❌ Sense lines being too thin or too long: Excessive length introduces wire resistance (even with small current, errors can accumulate), and being too thin may lead to poor contact due to oxidation.

05 Examples of Common Four-Wire Output Ports

In our ATX7006A test system, several power supply modules and signal generation modules such as AWG22, DPS, and DRS can be configured for either four-wire or two-wire port output.

Four-Wire Output Port in AWG22

Four-Wire Output Port in DRS

Four-Wire Output Port in DPS