Current‑sense resistor is a low‑value precision power resistor for current sampling. It converts current signal into measurable voltage drop via ohm's law, widely used in power supply, battery management, motor drive and over‑current protection circuits.
Working Principle
When load current flows through the low‑resistance body, a voltage drop is generated across two terminals. The system amplifies this tiny voltage signal to calculate real‑time loop current. Accurate current measurement relies on stable resistance value and low temperature drift under power‑on heating.
Main Classification
According to structure, it includes metal alloy shunt resistor, thick‑film chip sense resistor and four‑terminal Kelvin type. Package covers through‑hole shunt and multiple SMD sizes. Products are divided into general‑purpose type and high‑precision low‑TCR type for different measurement accuracy requirements.
Key Electrical Parameters
Nominal resistance value is usually below 1Ω for high‑current sampling. Power rating defines maximum sustainable power dissipation. Resistance tolerance represents initial accuracy. TCR temperature coefficient reflects resistance variation with temperature. Thermal resistance, maximum working current and overload capability are critical reliability indicators. Kelvin version pays attention to terminal resistance elimination effect.
Circuit Design Guidelines
Select proper resistance value to balance signal amplitude and power consumption loss. Reserve sufficient power derating margin under continuous working condition. Prefer Kelvin four‑terminal connection for high‑precision sampling to avoid lead resistance interference. Configure filter circuit at post‑stage amplifier input to suppress switching noise. Do not exceed rated power under peak current impact.
PCB Layout Suggestions
For Kelvin current‑sense resistor, separate power current path and sampling signal traces strictly. Sampling traces shall directly connect to resistor sensing pads instead of main power copper. Keep sampling traces short and away from high‑noise switching loops. Widen power copper area for heat dissipation. Follow datasheet pad layout to prevent uneven thermal stress.
Common Failure Modes
Resistance drift out of specification caused by long‑term overload heating. Open‑circuit burnout occurs under excessive over‑current impact. Inaccurate sampling result arises from wrong two‑terminal wiring method or poor soldering. Thermal stress leads to crack inside resistive body. Solder joint aging brings extra contact resistance and measurement error.
Market Application Trend
High‑power compact SMD current‑sense resistors meet miniaturization demand of power modules. Ultra‑low TCR alloy resistors reduce system calibration requirement. Four‑terminal chip products gradually replace discrete through‑hole shunt in mass‑produced hardware.
