LF356

LF356: Monolithic JFET Input Operational Amplifier

Overview

The LF356 is a pioneering monolithic JFET input operational amplifier that integrates well-matched, high-voltage JFETs with standard bipolar transistors using BI-FET™ technology. This combination delivers superior performance, including low input bias and offset currents, low offset voltage, and minimal offset voltage drift. The LF356 is designed for applications requiring high input impedance, low noise, and wide bandwidth, making it a versatile choice for precision analog circuits.

Key Features

• JFET Input Stage: Provides high input impedance, minimizing loading effects on signal sources.
• Low Input Bias Current: Typically 30 pA, ensuring minimal current draw from input sources.
• Low Offset Voltage: Typically 3 mV, enhancing accuracy in precision applications.
• Low Noise: Input voltage noise of 12 nV/√Hz at 1 kHz, ideal for sensitive signal conditioning.
• Wide Bandwidth: Unity-gain bandwidth of 5 MHz, suitable for high-frequency applications.
• High Slew Rate: 12 V/µs enables fast signal response in dynamic applications.
• BI-FET™ Technology: Combines JFET and bipolar transistors for optimal performance.
• Wide Supply Voltage Range: Operates from ±5V to ±18V, offering flexibility in power supply design.

Applications

The LF356 is widely used in applications requiring high input impedance, low noise, and precision signal processing. Key application areas include:

• Instrumentation Amplifiers: High input impedance and low bias current make it ideal for sensor interfaces.
• Active Filters: Wide bandwidth and low noise support high-performance filter designs.
• Data Acquisition Systems: Precision signal conditioning for analog-to-digital converters.
• Audio Processing: Low noise and distortion enhance audio signal integrity.
• Medical Electronics: Suitable for low-level signal amplification in ECG and EEG systems.
• Test and Measurement Equipment: High accuracy and stability ensure reliable measurements.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LF356 under typical operating conditions (V_CC = ±15V, T_A = 25°C unless otherwise noted):

• Input Offset Voltage: 3 mV (max)
• Input Bias Current: 30 pA (typ)
• Input Offset Current: 3 pA (typ)
• Input Resistance: 10¹² Ω (typ)
• Large-Signal Voltage Gain: 200 V/mV (min)
• Supply Voltage Range: ±5V to ±18V
• Supply Current: 3.6 mA (typ)
• Slew Rate: 12 V/µs (typ)
• Gain Bandwidth Product: 5 MHz (typ)
• Input Voltage Noise: 12 nV/√Hz at 1 kHz

Package Information

The LF356 is available in multiple package options to suit various assembly and thermal requirements. The following packages are commonly offered:

• 8-Pin PDIP (Plastic Dual In-Line Package):
  • Package Code: N
  • Dimensions: 9.81 mm x 6.35 mm
  • Operating Temperature Range: -55°C to +125°C
• 8-Pin SOIC (Small Outline Integrated Circuit):
  • Package Code: D
  • Dimensions: 4.90 mm x 3.91 mm
  • Operating Temperature Range: -55°C to +125°C
• TO-99 Metal Can Package:
  • Package Code: H
  • Dimensions: 9.08 mm diameter
  • Operating Temperature Range: -55°C to +125°C

Advantages of BI-FET™ Technology

The LF356 leverages BI-FET™ technology to combine the benefits of JFET and bipolar transistors. This integration provides:

• High Input Impedance: JFET input stage minimizes loading effects.
• Low Power Consumption: Bipolar output stage ensures efficient power use.
• Improved Linearity: Reduced distortion in signal processing applications.
• Robust Performance: Stable operation across a wide temperature range.

Design Considerations

When designing with the LF356, consider the following guidelines to optimize performance:

• Power Supply Decoupling: Use 0.1 µF ceramic capacitors close to the supply pins to minimize noise.
• Thermal Management: Ensure adequate heat dissipation in high-power applications, especially in the TO-99 package.
• PCB Layout: Minimize parasitic capacitance and inductance by keeping traces short and direct.
• Input Protection: Add clamping diodes if input signals may exceed the supply rails.

Conclusion

The LF356 is a high-performance operational amplifier that excels in applications requiring precision, low noise, and high input impedance. Its BI-FET™ technology and robust electrical characteristics make it a reliable choice for a wide range of analog signal processing tasks. Whether used in instrumentation, audio, or medical electronics, the LF356 delivers consistent performance and versatility.