LM335 Precision Temperature Sensor Technical Summary

Overview

The LM335 series represents a family of precision integrated circuit temperature sensors that operate as 2-terminal zeners. These devices provide a breakdown voltage that is directly proportional to absolute temperature, exhibiting a linear scale factor of 10 mV/°K. Designed for easy calibration and high accuracy, the LM335 finds extensive use in temperature measurement and compensation applications across various industries.

The sensor maintains excellent performance across a wide operating current range (400 μA to 5 mA) with minimal change in characteristics, thanks to its low dynamic impedance of less than 1Ω. When properly calibrated at 25°C, the device typically demonstrates less than 1°C error over a 100°C temperature range, making it suitable for precision applications.

Key Features

• Directly calibrated in Kelvin for absolute temperature measurement
• High initial accuracy of 1°C (available in selected versions)
• Wide operating current range: 400 μA to 5 mA
• Low dynamic impedance: <1Ω ensures stable operation
• Simple two-terminal zener operation
• Easy calibration through single-point adjustment
• Extended temperature measurement capability with 200°C overrange
• Available in multiple package options for different application requirements
• Cost-effective solution for precision temperature sensing

Applications

The LM335 temperature sensor is versatile and finds use in numerous applications across various industries:

Industrial Applications

• Process control systems
• Temperature monitoring in industrial equipment
• Environmental chambers and thermal testing
• HVAC system controls

Consumer Electronics

• Thermal protection circuits
• Battery temperature monitoring
• Home appliance temperature control

Automotive Systems

• Engine temperature monitoring
• Cabin climate control systems
• Transmission temperature sensing

Medical Equipment

• Patient monitoring devices
• Laboratory equipment temperature control
• Medical storage temperature monitoring

Scientific and Research

• Precision temperature measurement instruments
• Thermal analysis equipment
• Environmental monitoring systems

Electrical Characteristics

Absolute Maximum Ratings

• Reverse current: 15 mA
• Forward current: 10 mA
• Operating temperature range:
  • LM135: -55°C to +150°C
  • LM235: -40°C to +125°C
  • LM335: -40°C to +100°C
• Storage temperature range: -60°C to +150°C

Typical Electrical Characteristics (TA = 25°C unless otherwise noted)

• Temperature coefficient: 10 mV/K (nominal)
• Calibrated output voltage at 25°C: 2.982V ± specified tolerance
• Dynamic impedance: <1Ω (400 μA to 5 mA)
• Long-term stability: ±0.2°C (typical over 1000 hours)
• Nonlinearity error: ±0.3°C (typical over 100°C range)
• Calibration error at 25°C: ±1°C (for standard accuracy versions)

Package Information

Available Package Options

• TO-92 Plastic Package (Package Number Z03A)
  • Order Numbers: LM335Z, LM335AZ
  • Compact, through-hole package
  • Ideal for general-purpose applications
• SO-8 Surface Mount Package (Package Number M08A)
  • Order Numbers: LM335M, LM335AM
  • Suitable for automated assembly processes
  • Space-constrained applications
• TO-46 Metal Can Package (Package Number H03H)
  • Order Numbers: LM135H, LM135H-MIL, LM235H, LM335H, LM135AH, LM235AH, LM335AH
  • Note: Case is connected to negative pin
  • Hermetically sealed for harsh environments
  • Military-spec versions available

Package Dimensions and Characteristics

Each package option has specific dimensional and thermal characteristics:

TO-92 Package

• Body dimensions: 4.7mm x 3.7mm x 4.7mm (typical)
• Lead spacing: 2.54mm (standard)
• Thermal resistance: 160°C/W (junction to ambient)

SO-8 Package

• Body dimensions: 4.9mm x 3.9mm x 1.75mm
• Lead pitch: 1.27mm
• Thermal resistance: 155°C/W (junction to ambient)

TO-46 Package

• Body diameter: 4.7mm (typical)
• Height: 5.2mm (including leads)
• Thermal resistance: 100°C/W (junction to ambient)

Design Considerations

Calibration Procedure

The LM335 can be easily calibrated for improved accuracy:

1. Adjust the current through the device to 1mA (typical)
2. Measure the output voltage at a known temperature (preferably 25°C)
3. Compare with expected 2.982V output
4. Add a series trimmer resistor if adjustment is needed

Noise Reduction

For applications requiring high precision:

• Add a 0.1μF bypass capacitor close to the sensor
• Use shielded cables for long sensor leads
• Implement averaging in software for noisy environments

Thermal Considerations

• Minimize self-heating by operating at lower currents
• Ensure proper thermal coupling to measured environment
• Consider thermal mass effects for rapidly changing temperatures

Ordering Information

The LM335 is available in several variants with different accuracy grades and temperature ranges:

• Standard accuracy versions (designated without "A")
• Higher accuracy versions (designated with "A")
• Military-grade versions available for harsh environments
• Consult manufacturer datasheet for complete ordering codes