Current Sense Resistor Selection Guide

1. Construction Technologies

Current sense resistors are available in four main construction types, each with different trade-offs between accuracy, cost, and power handling.

Metal Alloy

The most widely used technology for precision current sensing. A stamped or trimmed metal alloy element is encapsulated in a moulded body with tin-plated terminations. Metal alloy resistors offer the lowest TCR (typically 15–75 ppm/°C), excellent stability, and resistance values from below 1 mΩ up to several hundred mΩ.

Best for: High accuracy, AEC-Q200 applications, wide current range. Stackpole CSS, CSSH, CSSU, CSM, CSNL.

Foil on Ceramic

A resistive foil is bonded to a ceramic substrate and laser-trimmed to the target resistance. Foil technology achieves the lowest TCR of any construction type — values below 10 ppm/°C are achievable — with excellent long-term stability. The ceramic substrate gives excellent power handling per unit area.

Best for: Lowest TCR requirement, tight initial tolerance, high stability. Stackpole CSRF.

Thick Film

A resistive paste is screen-printed onto a ceramic substrate and fired, then laser-trimmed. Thick film resistors are lower cost than metal alloy and cover a wider resistance range (typically 1 mΩ to 10 Ω for current sense). TCR is typically 75–200 ppm/°C.

Best for: Lower cost, moderate accuracy, wider resistance range. Stackpole CSR, CSRN, CSRW.

Thin Film

A resistive layer is sputtered onto a ceramic substrate under vacuum, then patterned and trimmed. Thin film offers tighter initial tolerance and lower TCR than thick film, approaching metal alloy performance at a lower cost point.

Best for: Mid-range accuracy, good TCR, tighter tolerance than thick film. Stackpole CSRT.

2. Understanding TCR

Temperature Coefficient of Resistance (TCR) describes how resistance changes with temperature, expressed in parts per million per degree Celsius (ppm/°C). For a resistor with TCR of 50 ppm/°C, the resistance will shift by 50 ppm for every 1°C change from the reference temperature (typically 25°C).

For a current sense resistor, the total measurement error budget typically includes:

• Initial tolerance — fixed at manufacture (e.g. ±1%)
• TCR error — varies with operating temperature
• Self-heating — the resistor heats under load, causing additional TCR-driven drift
• Long-term drift — resistance change over the product lifetime

TCR Guidance by Application

Application	Typical Temp Range	Recommended TCR
Consumer / low-accuracy	0 to 70°C	<200 ppm/°C
Industrial instrumentation	–40 to 85°C	<75 ppm/°C
Automotive body/chassis	–40 to 125°C	<50 ppm/°C
EV/HEV powertrain	–40 to 150°C	<25 ppm/°C
High-precision measurement	–40 to 85°C	<15 ppm/°C

3. Power Derating

All resistors must be derated above a specified ambient temperature. Below this temperature, the full rated power is available. Above it, the maximum allowable power reduces linearly to zero at the maximum operating temperature.

Derating Calculation

The derating curve is typically linear from the full-power temperature T_rated to the maximum temperature T_max:

Pallowed = Prated × (Tmax − Tambient) / (Tmax − Trated)

Always verify against the specific datasheet, as derating profiles vary between series.

PCB Thermal Management

• Use large copper pours connected to the resistor pads to spread heat
• Place thermal vias under high-power resistors to conduct heat to inner copper layers
• Consider the thermal resistance of the PCB laminate at elevated temperatures
• For chassis-mount power resistors, ensure the mounting surface is flat and use thermal compound if required

4. PCB Layout Principles

2-Terminal (Standard) Layout

For resistances above approximately 10 mΩ, a standard 2-terminal connection is typically adequate. Route the current-carrying traces symmetrically to each pad. Avoid routing voltage sense traces over or near current-carrying conductors.

4-Terminal Kelvin Layout

Below 10 mΩ, trace and via resistance becomes significant relative to the sense resistance. A Kelvin (4-terminal) layout separates the current-carrying path from the voltage measurement path:

• Force terminals (outer): Carry the full load current. Use wide, low-resistance traces.
• Sense terminals (inner): Connected to the voltage measurement circuit. Carry negligible current. Route as a differential pair directly to the ADC or current-sense amplifier.
• The sense taps must connect as close to the resistor body as possible — any resistance between the sense tap and the resistor body appears as measurement error.
• Route sense traces away from high-current conductors to minimise inductive coupling.
• Use matched-length, matched-impedance traces for the differential sense pair.

5. Series Comparison

Series	Construction	Size Range	Min R	Max W	TCR (ppm)	AEC
CSS	Metal alloy	0201–4527	0.2 mΩ	5 W	15	Yes
CSSH	Metal alloy	0805–3637	0.3 mΩ	7 W	15	Yes
CSRF	Foil	0402–2512	1 mΩ	—	50	Partial
CSSK	Metal alloy (Kelvin)	0612, 3637	0.55 mΩ	3 W	—	Yes
CSM	Metal alloy	0603, 2512	1 mΩ	3 W	50	Partial
CSNL	Metal alloy (low L)	1206–2512	0.2 mΩ	3 W	50	Partial
CSR	Thick film	0201–1225	3 mΩ	—	100	No
CSRT	Thin film	0201–2512	10 mΩ	—	50	Yes
HCS	Metal alloy	1206–5930	<0.3 mΩ	10 W	50–300	Yes

6. How to Choose

1. Define the measurement range: What is the maximum current? At what resistance will the sense voltage be usable by your ADC or sense amplifier (typically 50–100 mV full scale)?
2. Calculate required TCR: Based on your operating temperature range and accuracy budget, determine the maximum acceptable TCR.
3. Check power dissipation: At maximum current, P = I² × R. Ensure this is within the derated power rating at your maximum ambient temperature.
4. Select package size: Larger packages handle more power and allow lower resistance values. Automotive applications often require 2512 or larger.
5. Confirm AEC-Q200 if needed: Automotive designs require AEC-Q200 qualification. Check the datasheet qualification matrix carefully, as AEC status varies by package size within a series.
6. Consider layout requirements: Below 10 mΩ, plan for Kelvin routing or choose a Kelvin-terminated part (CSSK).