TCR (Temperature Coefficient of Resistance)

Temperature coefficient of resistance quantifies how much a resistor's value drifts as its body temperature changes. It is defined as ΔR / (R × ΔT) and expressed in ppm/K. A 100 Ω resistor with ±50 ppm/K TCR will drift by ±0.5 Ω across a 100 °C temperature swing, while a ±5 ppm/K precision part drifts only ±0.05 Ω over the same range. TCR can be positive (resistance rises with temperature, like copper) or negative (resistance falls, like carbon and many semiconductors).

TCR matters wherever a resistor sets a precision ratio: feedback networks in op-amps, gain-setting elements in instrumentation amplifiers, current-sense shunts where 1 ppm/K translates directly to measurement error, voltage references, and ladder networks in DACs. In high-current shunts self-heating drives temperature up by tens of kelvin even within rated power, so a low TCR alloy such as Manganin (≈15 ppm/K) or Zeranin is essential.

For power resistors TCR is less critical (±200 to ±400 ppm/K is normal) because they dissipate rather than measure, but extreme TCR can move a snubber damping resistance or a pre-charge time constant out of spec at hot ambient. Always check both the cold and hot-end resistance values when computing worst-case circuit behaviour.