How it works
A current-sense resistor intentionally inserts a small resistance into the current path. The resulting voltage follows Ohm's law and can be read by a sense amplifier. Lower resistance reduces wasted power but also reduces the signal available to the amplifier, making offset and unwanted connection resistance more important. Metal strip or foil is a common construction direction, although current sensing is a function rather than one material technology. Kelvin connections separate the high-current terminals from the voltage-sensing points so shared copper and contact drops do not dominate the reading. Element heating and thermal gradients still require attention.
The element may be a printed film, a deposited thin film, a metal alloy strip or a wire. Material and geometry set resistance.
Parameters that matter
- Resistance and tolerance
- The intended sensing resistance and initial uncertainty; keep units explicit to avoid thousandfold errors. (mΩ or µΩ; %)
- Rated current and power
- Both current/termination limits and thermal dissipation conditions must be satisfied. (A; W)
- TCR
- Temperature-related resistance change; confirm whether the specification includes terminal contributions. (ppm/°C)
- Connection geometry
- The recommended current and sense pad layout and calibration points. (two/four terminals; mm)
- Thermal EMF and parasitic inductance
- Temperature-gradient voltage and dynamic-current error; important when the desired sense voltage is small. (µV/°C; nH where supplied)
A worked selection example
Illustrative calculation · not a product guarantee
Measuring up to 10 A with a 50 mV target
Assume a 10 A maximum and a desired 50 mV full-scale drop. Compare against a hypothetical 0.5 mΩ unwanted shared connection resistance.
- Required shunt R = 0.050 / 10 = 0.005 Ω = 5 mΩ.
- At 10 A, heat P = I²R = 100 × 0.005 = 0.5 W.
- A shared 0.5 mΩ connection would add 10% of the shunt resistance and 5 mV at full current.
- Use an appropriate Kelvin layout, then choose power margin from actual board temperature and the manufacturer's derating—not a blanket multiplier.
A nominal 1% shunt cannot rescue a layout that adds 10% uncontrolled series resistance.
Where it fits
Suitable starting points
- Power supply and motor current measurement
- Battery and protection sensing with the correct common-mode design
- Energy measurement after a complete error and temperature assessment
Where to take extra care
- Using only the catalogue wattage without current/terminal limits
- Two-wire sensing that includes uncontrolled high-current copper
- Assuming a shunt's tolerance equals the complete measurement accuracy
Series directions to investigate
Compare two-terminal metal-element chips with dedicated four-terminal Kelvin parts. Fenghua MF/AMF are publicly listed metal current-sense families; verify the terminal arrangement of the exact candidate rather than assuming every MF is four-terminal.
What Chinese suppliers can offer
Where the opportunity lies
Fenghua publishes MF metal alloy and AMF automotive current-sense directions. These provide concrete mainland candidates to compare by resistance, temperature behaviour and mounting.
What still needs evidence
Milliohm parts make terminal geometry and heat flow part of the measurement. An apparent footprint match is insufficient; qualify the real PCB and sense routing, with production-lot evidence.
Questions for the supplier
- 01
Where are the defined sense points, and what PCB footprint is recommended?
- 02
What continuous current and pulse current apply at our mounting temperature?
- 03
Does the TCR include the terminations, and what thermal EMF data is available?
- 04
Can you provide resistance-versus-temperature and load-life data for the exact mΩ value?
Technical references
These references support the principles and catalogue directions discussed here. Public documentation is a different evidence level from a supplier reply, a lot document or an independent test. This guide does not claim those later stages have been completed.
- 1. Metal CSR catalogue
- 2. MF Alloy Chip Fixed Resistors, revision 17.0
- 3. WSMS5515 Power Metal Strip Resistors
- 4. Dale Surface-Mount Resistors
These guides explain selection principles. Final decisions require the current datasheet for the exact ordering code, operating conditions and appropriate application testing.