LF357N

LF357N - Monolithic JFET Input Operational Amplifier

Overview

The LF357N is a high-performance monolithic operational amplifier that combines well-matched, high-voltage JFETs with standard bipolar transistors using BI-FET™ technology. This device represents the first generation of operational amplifiers to successfully integrate these technologies on a single chip. The LF357N is designed to deliver exceptional electrical characteristics including low input bias currents, high slew rates, wide bandwidth, and fast settling times, making it suitable for precision applications requiring high-speed signal processing.

Key advantages of the LF357N include its ability to maintain excellent drift characteristics and common-mode rejection even when using offset adjustment. The amplifier's architecture provides superior performance compared to conventional bipolar or FET-input op-amps, particularly in applications requiring high input impedance and low noise.

Features

• Low input bias current: 30 pA (typical)
• Low input offset current: 3 pA (typical)
• Exceptionally high input impedance: 10¹²Ω
• Low input offset voltage: 1 mV (typical)
• Low input offset voltage temperature drift: 3 μV/°C
• Low input noise current: 0.01 pA/√Hz
• High common-mode rejection ratio: 100 dB (typical)
• Large DC voltage gain: 106 dB (typical)
• High slew rate: 50 V/μs (typical)
• Wide bandwidth: 20 MHz (typical)
• Fast settling time: 200 ns to 0.01%
• Internal frequency compensation
• Output short-circuit protection
• Latch-up free operation

Applications

The LF357N's combination of high-speed and precision characteristics makes it suitable for a wide range of demanding applications:

• High-speed sample-and-hold circuits
• Fast integrators and differentiators
• Precision instrumentation amplifiers
• Data acquisition systems
• Active filters with high Q requirements
• Logarithmic amplifiers
• Photodiode and other transducer amplifiers
• Medical instrumentation
• Audio processing equipment
• Analog-to-digital converter interfaces
• Oscilloscope vertical amplifiers
• Function generators

Electrical Characteristics

The following table summarizes the key electrical specifications of the LF357N (V_S = ±15V, T_A = 25°C unless otherwise specified):

Input Characteristics

• Input Offset Voltage: 1 mV (max 5 mV)
• Input Offset Voltage Drift: 3 μV/°C (typical)
• Input Bias Current: 30 pA (typical), 200 pA (max)
• Input Offset Current: 3 pA (typical), 50 pA (max)
• Input Resistance: 10¹²Ω (typical)
• Input Capacitance: 2 pF (typical)
• Input Voltage Range: ±12V (typical)
• Common Mode Rejection Ratio: 100 dB (typical)

Output Characteristics

• Output Voltage Swing: ±12V (typical, R_L = 2kΩ)
• Output Current: ±20 mA (typical)
• Short Circuit Current: ±30 mA (typical)
• Output Resistance: 0.1Ω (typical)

Dynamic Characteristics

• Slew Rate: 50 V/μs (typical)
• Gain Bandwidth Product: 20 MHz (typical)
• Settling Time (to 0.01%): 200 ns (typical)
• Rise Time: 40 ns (typical)
• Overshoot: 5% (typical)

Power Supply Characteristics

• Supply Voltage Range: ±5V to ±18V
• Supply Current: 10 mA (typical), 12 mA (max)
• Power Consumption: 150 mW (typical)
• PSRR (Power Supply Rejection Ratio): 100 dB (typical)

Package Information

The LF357N is available in several industry-standard packages:

8-Pin DIP (Dual Inline Package)

• Package Code: N
• Dimensions: 9.81mm x 6.35mm x 3.3mm
• Pin Pitch: 2.54mm
• Lead Material: Copper Alloy
• Lead Finish: Matte Tin
• Operating Temperature Range: -55°C to +125°C
• Storage Temperature Range: -65°C to +150°C

8-Pin SOIC (Small Outline Integrated Circuit)

• Package Code: D
• Dimensions: 4.9mm x 3.9mm x 1.25mm
• Pin Pitch: 1.27mm
• Lead Material: Copper Alloy
• Lead Finish: Matte Tin
• Operating Temperature Range: -55°C to +125°C

Design Considerations

When implementing the LF357N in circuit designs, several important considerations should be noted:

PCB Layout Guidelines

• Use a ground plane to minimize noise and improve stability
• Keep input traces as short as possible to reduce stray capacitance
• Place bypass capacitors (0.1μF ceramic) close to the power supply pins
• Use shielded cables for high-impedance inputs in noisy environments

Thermal Management

• For continuous operation at maximum ratings, consider heat sinking
• Allow adequate air flow around the device in high-temperature environments
• Monitor junction temperature in precision applications

Stability Considerations

• The LF357N is internally compensated for unity gain stability
• For capacitive loads greater than 100pF, use a small series resistor at the output
• Avoid excessive source resistance at the inputs to prevent oscillation

Conclusion

The LF357N operational amplifier represents a significant advancement in analog signal processing technology, combining the benefits of JFET and bipolar technologies in a single monolithic device. Its exceptional combination of high speed, precision, and versatility makes it an excellent choice for demanding applications across multiple industries. When properly implemented with attention to layout and thermal considerations, the LF357N delivers reliable, high-performance operation in even the most challenging circuit environments.