Temperature Sweep Analysis

Temperature Sweep Analysis (Premium) #

Temperature Sweep analysis shows how your circuit performs across a range of temperatures. Essential for designs that must work reliably in varying environmental conditions, from arctic cold to desert heat.

What It Does #

Temperature Sweep:

  1. Sets circuit temperature to multiple points
  2. Recalculates all temperature-dependent parameters
  3. Runs selected analysis at each temperature
  4. Shows how performance varies with temperature

When to Use #

Use Temperature Sweep for:

  • Automotive Circuits: -40°C to +125°C operation
  • Outdoor Equipment: Weather-resistant designs
  • Precision Circuits: Compensating for thermal drift
  • Power Electronics: Thermal derating and protection
  • Military/Aerospace: Extreme environment operation

Temperature Effects on Components #

Resistors #

  • Metal Film: ±50 ppm/°C typical
  • Carbon Film: ±200-500 ppm/°C
  • Wire Wound: ±20 ppm/°C
  • Formula: R(T) = R₀[1 + TC1(T-T₀) + TC2(T-T₀)²]

Capacitors #

  • C0G/NP0: ±30 ppm/°C
  • X7R: ±15% from -55°C to +125°C
  • Y5V: +22% to -82% variation
  • Aluminum Electrolytic: -40% at low temps

Semiconductors #

  • Diode Vf: -2 mV/°C
  • BJT Vbe: -2.1 mV/°C
  • BJT Beta: Increases ~0.5%/°C
  • MOSFET Vth: -2 to -4 mV/°C
  • MOSFET Rds(on): Increases ~0.4%/°C

Inductors #

  • Ferrite Core: -1000 to +4000 ppm/°C
  • Iron Powder: More stable
  • Air Core: Minimal change

Configuration #

Temperature Range #

  • Start Temperature: Minimum (e.g., -40°C)
  • Stop Temperature: Maximum (e.g., +85°C)
  • Step Size: Temperature increment (e.g., 5°C)
  • Reference Temperature: Usually 25°C or 27°C

Analysis Options #

Combine with:

  • DC Operating Point: Bias drift
  • AC Analysis: Frequency response shifts
  • Transient: Timing changes
  • DC Sweep: Threshold variations

Example Circuits #

Voltage Reference Temperature Drift #

* Bandgap reference with compensation
V1 vcc 0 DC 5
R1 vcc n1 10k TC1=50e-6
R2 n1 0 4.7k TC1=50e-6
D1 n1 n2 DMOD
D2 n2 0 DMOD
.MODEL DMOD D IS=1e-14 N=1

.temp -40 25 85
.dc temp -40 85 5

Results show:

  • Uncompensated: 2.5V ±100mV
  • Compensated: 2.5V ±5mV
  • Temperature coefficient: 20 ppm/°C

Op-Amp Offset Drift #

* Precision op-amp circuit
X1 in 0 out vcc vee OPAMP
R1 in 0 100k
R2 out in 100k
VOS n1 in DC 100u ; Input offset

.temp -25 25 75
.op

Typical drift:

  • Standard op-amp: 10 µV/°C
  • Precision op-amp: 0.1 µV/°C
  • Auto-zero: 0.01 µV/°C

Crystal Oscillator Stability #

* 10MHz crystal oscillator
X1 osc CRYSTAL
C1 n1 0 22p TC1=30e-6
C2 n2 0 22p TC1=30e-6
R1 n1 n2 1M

.temp -20 25 70
.ac dec 100 9.99M 10.01M

Frequency drift:

  • AT-cut crystal: ±20 ppm
  • Temperature compensated: ±2 ppm
  • Oven controlled: ±0.1 ppm

Thermal Design Strategies #

Compensation Techniques #

Opposing Temperature Coefficients

  • Combine positive and negative TC components
  • Classic: Diode compensates BJT Vbe
  • Ratio tracking for references

Active Compensation

  • Temperature sensor feedback
  • Microcontroller correction
  • Lookup tables

Physical Matching

  • Keep critical components thermally coupled
  • Use matched arrays
  • Common heatsinks

Component Selection #

Low Drift Components

  • Precision resistors (5-25 ppm/°C)
  • C0G/NP0 capacitors
  • Low TC voltage references
  • Chopper-stabilized op-amps

Temperature Ratings

  • Commercial: 0°C to 70°C
  • Industrial: -40°C to 85°C
  • Automotive: -40°C to 125°C
  • Military: -55°C to 125°C

Interpreting Results #

Linear Temperature Dependence #

  • Straight line on temp plot
  • Single TC1 coefficient
  • Easy to compensate

Nonlinear Behavior #

  • Curved response
  • Needs TC2 or piecewise model
  • Harder to compensate

Thermal Runaway Risk #

  • Positive feedback with temperature
  • Power devices especially vulnerable
  • Add thermal protection

Common Issues and Solutions #

Oscillator Frequency Drift #

Problem: Timing errors accumulate Solution:

  • Use temperature-stable components
  • Add compensation network
  • Consider TCXO/OCXO

Reference Voltage Drift #

Problem: ADC/DAC accuracy degrades Solution:

  • Bandgap references
  • Buried Zener references
  • Ratiometric measurements

Amplifier Gain Drift #

Problem: Calibration shifts Solution:

  • Matched resistor networks
  • Gain set by resistor ratios
  • Software calibration

Power Device Derating #

Problem: Reduced safe operating area Solution:

  • Thermal derating curves
  • Active temperature monitoring
  • Adequate heatsinking

Advanced Analysis #

Self-Heating Effects #

Components heat due to power dissipation:

  • Power resistors
  • Linear regulators
  • Power transistors

Include thermal resistance:

.param Rth=50  ; °C/W
.param Tamb=25 ; Ambient
Tj = Tamb + P*Rth

Thermal Time Constants #

Temperature changes aren’t instant:

  • Small components: milliseconds
  • Power devices: seconds
  • Heatsinks: minutes

Junction Temperature #

For semiconductors:

Tj = Ta + (Rjc + Rcs + Rsa) × P
Where:
- Rjc = Junction to case
- Rcs = Case to sink  
- Rsa = Sink to ambient

Best Practices #

  1. Know Your Environment: Define actual temperature range
  2. Derate Components: Don’t use at limits
  3. Test Extremes: Include margins beyond spec
  4. Consider Gradients: Temperature varies across PCB
  5. Include Self-Heating: High power components
  6. Verify Critical Nodes: Focus on sensitive circuits

Export Options #

Premium features include:

  • Temperature vs. parameter plots
  • CSV data for all temperatures
  • Worst-case identification
  • Thermal coefficient extraction
  • Multi-parameter tracking

See Also #