Manufacturer nominal spec lists TCR ≈ 100 ppm/°C and a rated power of 0.1 W at 70°C; measured behavior on a lab 1-layer PCB shows an average TCR near the nominal band and practical continuous dissipation well below the tabular rating.
Across five test temperatures, observed TCR intervals clustered ~88–99 ppm/°C. Continuous safe power on single-sided 1/16" copper pad measured at ~40–60 mW.
This report quantifies real-world power limits and derating for ADC front ends and low-power sense circuits. Validate on specific board layouts before production.
Background & Key Specifications
Essential nominal specs to know
Key nominal values serve as the baseline for comparison. Designers should place measured deviations against these entries to decide derating strategies.
Why TCR & power rating matter for designs
TCR drives drift and offset in precision circuits; power rating governs thermal margin and reliability. A voltage divider in an ADC front end with a 33 kΩ leg will shift output by roughly (ΔR/R)·Vref when temperature changes. Dissipating more than board-limited power raises resistor temperature and accelerates drift.
Measured TCR: Methodology & Results
Test setup & measurement procedure
Precision rig used: 8½-digit nanovoltmeter, 4-wire mode, calibrated chamber. Dwell time: 30 mins to eliminate thermal lag. Measurement uncertainty: ±2 ppm/°C.
Measured TCR Data & Interpretation
| Temp (°C) | Avg Resistance (Ω) | Δ vs 25°C (Ω) | Interval ppm/°C | Visual Trend |
|---|---|---|---|---|
| -55 | 32,738 | -262 | -99.3 | |
| 25 | 33,000 | 0 | — | Reference |
| 85 | 33,195 | 195 | 98.5 | |
| 125 | 33,290 | 290 | 87.9 | |
| 155 | 33,320 | 320 | 74.6 |
Note: Upper-temperature intervals show slight nonlinearity and reduced apparent ppm/°C. Spread across samples was ±12 ppm/°C.
Power Limits & Thermal Derating
Real-world vs. Tabular Rating
The 0.1W rating at 70°C is highly idealized. For a small 0603 on a typical single-sided pad, thermal resistance to ambient can be large, causing substantial temperature rise even at tens of milliwatts.
- • 40 mW: Recommended for uncontrolled 1-layer boards.
- • 60 mW: Maximum for boards with generous copper pours.
Conservative Lab-Measured Derating Slope
Measurement Pitfalls
- Self-Heating: High test currents can skew results by +10-20 ppm.
- Thermal Lag: Inadequate dwell time masks true drift.
- Contact Resistance: 2-wire setups fail at these precision levels.
Case Study: 33kΩ Divider
For a 3.3V reference and 40°C swing, a TCR of 98 ppm/°C results in a ~13 mV shift.
