LM394N Ultra-Well-Matched Monolithic NPN Transistor Pair

Overview

The LM394N is a high-precision, junction-isolated monolithic NPN transistor pair designed to provide ultra-well-matched characteristics, offering an order of magnitude improvement in matching over conventional transistor pairs. Manufactured by National Semiconductor, this component is ideal for applications requiring precise logarithmic, squaring, or square-root functions, as well as low-noise amplification and signal processing.

The LM394N is part of a family that includes the LM194, both of which are designed to replace conventional transistor pairs with superior performance. The device guarantees matched parameters over a wide range of collector currents (1 µA to 1 mA), making it versatile for various analog circuit designs.

Features

• Emitter-Base Voltage Matching: Matched to within 50 µV, ensuring high precision in differential applications.
• Offset Voltage Drift: Less than 0.1 µV/°C, providing stable performance over temperature variations.
• Current Gain (h_FE) Matching: Matched to within 2%, critical for balanced amplifier designs.
• Common-Mode Rejection Ratio (CMRR): Greater than 120 dB, minimizing noise and interference in differential circuits.
• Wide Operating Current Range: Guaranteed performance from 1 µA to 1 mA collector current.
• Low Noise: Excellent noise characteristics for sensitive analog signal processing.
• Superior Logging Characteristics: Outperforms conventional transistor pairs in logarithmic applications.
• Plug-in Replacement: Compatible with existing designs using conventional matched pairs.

Applications

The LM394N is suited for a variety of precision analog applications, including:

• Low-Cost Accurate Square Root Circuits: Provides precise square-root functionality for signal processing.
• Low-Cost Accurate Squaring Circuits: Enables accurate squaring of input signals.
• Differential Amplifiers: Ideal for high-precision amplification due to matched characteristics.
• Logarithmic Amplifiers: Superior performance in logarithmic conversion applications.
• Analog Multipliers and Dividers: Used in circuits requiring multiplication or division of signals.
• Voltage References and Current Sources: Provides stable references due to low drift and high matching.

Electrical Characteristics

Absolute Maximum Ratings

• Collector-Base Voltage (V_CB): 40 V
• Collector-Emitter Voltage (V_CE): 40 V
• Emitter-Base Voltage (V_EB): 5 V
• Collector Current (I_C): 50 mA (continuous)
• Total Power Dissipation (P_D): 500 mW at 25°C (derate above 25°C)
• Operating Temperature Range: -55°C to +125°C (military-grade versions available)

Typical Performance Characteristics

• Emitter-Base Voltage Matching (ΔV_BE): 50 µV (max)
• Current Gain Matching (Δh_FE): 2% (max)
• Input Offset Voltage Drift: 0.1 µV/°C (max)
• Common-Mode Rejection Ratio (CMRR): 120 dB (min)
• Noise Voltage (10 Hz to 10 kHz): 1 µV (typ)

Package Information

The LM394N is available in a standard 8-pin DIP (Dual Inline Package) or TO-99 metal can package, providing flexibility for different PCB layouts and thermal requirements.

Package Dimensions (8-Pin DIP)

• Body Length: 9.81 mm (0.386 in)
• Body Width: 6.35 mm (0.250 in)
• Lead Pitch: 2.54 mm (0.100 in)
• Lead Length: 3.3 mm (0.130 in)

Thermal Characteristics

• Thermal Resistance (Junction-to-Ambient): 150°C/W (DIP package)
• Thermal Resistance (Junction-to-Case): 45°C/W (TO-99 package)

Conclusion

The LM394N is a high-performance, ultra-well-matched NPN transistor pair designed for precision analog applications. Its exceptional matching characteristics, low noise, and wide operating range make it an ideal choice for engineers designing logarithmic amplifiers, squaring circuits, and other sensitive analog systems. With its plug-in compatibility and robust packaging options, the LM394N offers a reliable upgrade over conventional transistor pairs.