LM329 Precision Reference - Technical Summary

Overview

The LM329 is a precision, temperature-compensated 6.9V zener reference diode designed for applications requiring high stability and low dynamic impedance. Unlike traditional zener diodes, the LM329 incorporates active circuitry to buffer the internal zener, enabling consistent performance across a wide operating current range of 0.5 mA to 15 mA. This monolithic silicon chip offers superior noise performance, long-term stability, and a low temperature coefficient, making it ideal for precision voltage reference applications.

Key advantages of the LM329 include its low dynamic impedance (0.8Ω) and excellent temperature stability (0.01%/°C). Additionally, its subsurface zener construction minimizes noise and drift, ensuring reliable performance in critical circuits. The device is available in a cost-effective TO-92 package, making it suitable for both commercial and industrial applications.

Features

• Wide Operating Current Range: 0.6 mA to 15 mA
• Low Dynamic Impedance: 0.8Ω at any operating current
• Temperature Stability: 0.01%/°C temperature coefficient
• Low Noise: 7μV wideband noise for precision applications
• Initial Tolerance: 5% voltage accuracy
• Exceptional Long-Term Stability: 0.002% drift over time
• Cost-Effective: Economical solution for precision voltage references
• Subsurface Zener Construction: Reduces noise and improves stability

Applications

The LM329 is designed for use in precision analog circuits where a stable voltage reference is critical. Its performance characteristics make it suitable for a variety of applications, including:

• Voltage References: Provides a stable 6.9V reference for analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and voltage regulators.
• Test and Measurement Equipment: Ensures accuracy in multimeters, oscilloscopes, and calibration instruments.
• Industrial Control Systems: Used in process control and automation systems where voltage stability is essential.
• Power Supplies: Acts as a precision reference for linear and switching power supplies.
• Medical Electronics: Provides reliable voltage references in diagnostic and monitoring equipment.
• Communication Systems: Ensures signal integrity in RF and baseband circuits.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM329 under typical operating conditions (unless otherwise noted):

Absolute Maximum Ratings

• Operating Current Range: 0.5 mA to 15 mA
• Maximum Power Dissipation: 500 mW (TO-92 package)
• Storage Temperature Range: -65°C to +150°C
• Junction Temperature: +150°C

Typical Performance Characteristics

• Reference Voltage (V_REF): 6.9V ±5%
• Dynamic Impedance (Z_ZT): 0.8Ω (0.6 mA to 15 mA)
• Temperature Coefficient (TC): 0.01%/°C (specified variants)
• Noise Voltage (10 Hz to 10 kHz): 7μV (typical)
• Long-Term Stability: 0.002% over 1000 hours

Package Information

The LM329 is available in a standard TO-92 plastic package, which is widely used for low-power semiconductor devices. The package offers a compact footprint and ease of assembly, making it suitable for prototyping and production environments.

TO-92 Package Details

• Package Type: TO-92 (3-pin)
• Pin Configuration:
  • Pin 1: Anode (Input/Reference)
  • Pin 2: Cathode (Ground)
  • Pin 3: No Connection (NC)
• Dimensions: 4.95 mm (L) x 3.94 mm (W) x 4.95 mm (H)
• Weight: Approximately 0.35 grams
• Ordering Part Number: LM329DZ

Thermal Considerations

For optimal performance, the LM329 should be operated within its specified temperature range. Proper PCB layout and heat dissipation techniques should be employed to minimize thermal drift in high-precision applications.

Typical Applications Circuit

The LM329 can be easily integrated into a variety of circuits. Below is a simple reference voltage circuit example:

Basic Voltage Reference Circuit

• Input Voltage (V_IN): 9V to 15V
• Current-Limiting Resistor (R_LIMIT): Calculated based on desired operating current (e.g., 1.2kΩ for 1 mA).
• Output Voltage (V_OUT): 6.9V ±5%

For noise-sensitive applications, a bypass capacitor (e.g., 0.1μF ceramic) can be added across the LM329 to further reduce output noise.

Conclusion

The LM329 is a versatile and reliable precision voltage reference that offers exceptional performance across a wide range of operating conditions. Its low dynamic impedance, excellent temperature stability, and long-term reliability make it an ideal choice for demanding applications in industrial, medical, and communication systems. With its cost-effective TO-92 packaging, the LM329 provides engineers with a high-performance solution for precision analog design.