LF355N - Monolithic JFET Input Operational Amplifier

Overview

The LF355N is a pioneering monolithic JFET input operational amplifier that combines well-matched, high-voltage JFETs with standard bipolar transistors using BI-FET™ technology. This innovative integration delivers exceptional performance characteristics, making it ideal for precision analog applications. The device offers low input bias and offset currents, low offset voltage and drift, while maintaining high slew rate, wide bandwidth, and fast settling time.

As part of the LF155A/LF156A/LF157A series, the LF355N represents a significant advancement in operational amplifier technology, particularly for applications requiring high input impedance and low noise performance. The device features internal offset adjustment that doesn't compromise drift characteristics or common-mode rejection ratio.

Features

• Low input bias current: 30 pA (typical)
• Low input offset current: 3 pA (typical)
• Exceptionally high input impedance: 10¹²Ω (typical)
• Low input offset voltage: 1 mV (typical)
• Low input offset voltage temperature drift: 3 μV/°C (typical)
• Low input noise current: 0.01 pA/√Hz (typical)
• High common-mode rejection ratio: 100 dB (typical)
• Large DC voltage gain: 106 dB (typical)
• High slew rate: 12 V/μs (typical)
• Wide bandwidth: 4 MHz (typical)
• Fast settling time: 2 μs to 0.01% (typical)
• Internal frequency compensation
• Output short-circuit protection
• Low power consumption: 4.5 mA (typical)

Applications

The LF355N's unique combination of features makes it suitable for a wide range of precision analog applications:

• High-impedance instrumentation amplifiers
• Precision integrators
• Sample-and-hold circuits
• Data acquisition systems
• Medical instrumentation
• Photodiode amplifiers
• Low-noise preamplifiers
• Active filters
• Analog-to-digital converter interfaces
• Voltage followers
• Signal conditioning circuits
• Test and measurement equipment

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage: ±18V
• Input Voltage: ±15V
• Differential Input Voltage: ±30V
• Output Short-Circuit Duration: Continuous
• Operating Temperature Range: -55°C to +125°C
• Storage Temperature Range: -65°C to +150°C
• Junction Temperature: 150°C

DC Characteristics (V_S = ±15V, T_A = 25°C)

• Input Offset Voltage: 1 mV (max 5 mV)
• Input Offset Current: 3 pA (max 50 pA)
• Input Bias Current: 30 pA (max 200 pA)
• Input Resistance: 10¹²Ω (min 10¹⁰Ω)
• Large Signal Voltage Gain: 106 dB (min 94 dB)
• Common Mode Rejection Ratio: 100 dB (min 90 dB)
• Supply Voltage Rejection Ratio: 100 dB (min 90 dB)
• Output Voltage Swing: ±13V (min ±12V)

AC Characteristics (V_S = ±15V, T_A = 25°C)

• Slew Rate: 12 V/μs (min 8 V/μs)
• Gain Bandwidth Product: 4 MHz (typical)
• Settling Time to 0.01%: 2 μs (typical)
• Equivalent Input Noise Voltage: 25 nV/√Hz at 1 kHz
• Total Harmonic Distortion: 0.01% at 1 kHz

Package Information

The LF355N is available in multiple package options to suit different application requirements:

8-Pin DIP (Dual Inline Package)

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

8-Pin SOIC (Small Outline Integrated Circuit)

• Package Code: D
• Dimensions: 4.90mm x 3.90mm
• Pin Spacing: 1.27mm
• Lead Material: Copper Alloy
• Finish: Matte Tin
• Operating Temperature: -55°C to +125°C

Pin Configuration

• Pin 1: Offset Null
• Pin 2: Inverting Input
• Pin 3: Non-Inverting Input
• Pin 4: V- (Negative Supply)
• Pin 5: Offset Null
• Pin 6: Output
• Pin 7: V+ (Positive Supply)
• Pin 8: No Connection

Design Considerations

When implementing the LF355N in circuit designs, several important considerations should be noted:

Power Supply Requirements

The LF355N operates from dual power supplies ranging from ±5V to ±18V. For single-supply operation, proper biasing of the input common-mode range is required. Decoupling capacitors (0.1 μF ceramic) should be placed as close as possible to the power supply pins.

Input Protection

While the JFET input stage provides inherent protection against moderate overvoltage conditions, additional protection diodes may be required in harsh environments where input voltages might exceed the supply rails.

Thermal Considerations

The LF355N has a maximum power dissipation of 500 mW at 25°C. In high-temperature environments or high-power applications, proper heat sinking or derating may be necessary.

PCB Layout Guidelines

• Keep input traces short to minimize noise pickup
• Use ground planes to reduce parasitic capacitance
• Separate analog and digital grounds
• Minimize stray capacitance at the summing junction

Performance Graphs

(Note: In an actual datasheet, this section would include graphical representations of key performance parameters)

• Open-Loop Frequency Response
• Input Bias Current vs. Temperature
• Output Voltage Swing vs. Load Resistance
• Slew Rate vs. Supply Voltage
• Common-Mode Rejection vs. Frequency

Alternative Parts

For applications with slightly different requirements, consider these alternative devices:

• LF356: Single operational amplifier with similar characteristics
• LF347: Quad JFET-input operational amplifier
• TL081: Lower-cost JFET-input operational amplifier
• OPA604: High-performance audio operational amplifier