LF347N - Quad JFET Input Operational Amplifier

Overview

The LF347N is a high-performance, low-cost quad JFET input operational amplifier featuring BI-FET II™ technology. This device combines the benefits of JFET input transistors with bipolar output stages to deliver superior performance characteristics. The LF347N is designed for applications requiring high input impedance, low input bias currents, and fast dynamic response. Its internally trimmed input offset voltage ensures precision performance without requiring external adjustments.

This amplifier is pin-compatible with the standard LM148, allowing for easy upgrades in existing designs that use the LM148 or LF124. The LF347N operates over a wide supply voltage range while maintaining low power consumption, making it suitable for both battery-powered and line-operated applications.

Key Features

• Internally Trimmed Offset Voltage: 5 mV maximum ensures precision performance
• Low Input Bias Current: JFET input stage provides typically 50 pA
• High Input Impedance: 10^12 Ω typical
• Wide Gain Bandwidth Product: 4 MHz typical
• Fast Slew Rate: 13 V/µs typical
• Low Supply Current: 3.6 mA per amplifier typical
• Wide Supply Voltage Range: ±5V to ±18V
• Low Noise: 25 nV/√Hz typical at 1 kHz
• Pin-Compatible with LM148: Easy upgrade path for existing designs
• High Output Drive: ±20 mA output current capability

Applications

The LF347N is suitable for a wide range of analog signal processing applications, including:

• High-impedance sensor amplifiers
• Active filters
• Sample-and-hold circuits
• Logarithmic amplifiers
• Precision integrators
• Data acquisition systems
• Medical instrumentation
• Audio preamplifiers
• Test and measurement equipment
• Industrial control systems

Electrical Characteristics

All specifications are given for V_S = ±15V and T_A = 25°C unless otherwise noted.

Input Characteristics

• Input Offset Voltage: 5 mV (max)
• Input Bias Current: 50 pA (typ), 200 pA (max)
• Input Offset Current: 25 pA (typ), 100 pA (max)
• Input Resistance: 10¹² Ω (typ)
• Input Capacitance: 4 pF (typ)
• Input Voltage Range: ±11.5 V (min)

Output Characteristics

• Output Voltage Swing: ±13.5 V (min) into 10 kΩ
• Output Current: ±20 mA (min)
• Short-Circuit Current: 30 mA (typ)
• Output Resistance: 50 Ω (typ)

Dynamic Characteristics

• Gain Bandwidth Product: 4 MHz (typ)
• Slew Rate: 13 V/µs (typ)
• Settling Time (0.1%): 2 µs (typ) for 10 V step
• Equivalent Input Noise Voltage: 25 nV/√Hz at 1 kHz

Power Supply Characteristics

• Supply Voltage Range: ±5V to ±18V
• Supply Current (per amplifier): 3.6 mA (typ), 5.2 mA (max)
• Power Supply Rejection Ratio: 100 dB (typ)

Package Information

The LF347N is available in the following package options:

14-Pin PDIP (Plastic Dual In-line Package)

• Package Code: N
• Dimensions: 19.3 mm x 6.35 mm
• Pin Spacing: 2.54 mm
• Operating Temperature Range: 0°C to +70°C
• Moisture Sensitivity Level (MSL): 1

14-Pin SOIC (Small Outline Integrated Circuit)

• Package Code: D
• Dimensions: 8.65 mm x 3.9 mm
• Pin Spacing: 1.27 mm
• Operating Temperature Range: -40°C to +85°C
• Moisture Sensitivity Level (MSL): 1

Pin Configuration

The LF347N features four independent operational amplifiers in a 14-pin package with the following pinout:

• Pin 1: Output A
• Pin 2: Inverting Input A
• Pin 3: Non-Inverting Input A
• Pin 4: V+
• Pin 5: Non-Inverting Input B
• Pin 6: Inverting Input B
• Pin 7: Output B
• Pin 8: Output C
• Pin 9: Inverting Input C
• Pin 10: Non-Inverting Input C
• Pin 11: V-
• Pin 12: Non-Inverting Input D
• Pin 13: Inverting Input D
• Pin 14: Output D

Design Considerations

Power Supply Decoupling

For optimal performance, it is recommended to use 0.1 µF ceramic capacitors placed as close as possible to the power supply pins (V+ and V-). For applications with long power supply leads or high noise environments, additional 10 µF electrolytic capacitors may be beneficial.

PCB Layout Guidelines

• Keep input traces as short as possible to minimize stray capacitance
• Route output traces away from input traces to prevent feedback
• Use ground planes to minimize noise pickup
• For high-frequency applications, consider using surface mount components to minimize lead inductance

Thermal Considerations

While the LF347N has relatively low power consumption, in high-temperature environments or when driving heavy loads, thermal management should be considered. For the DIP package, increasing copper area around the package can help dissipate heat. For the SOIC package, thermal vias to an internal ground plane may be beneficial.

Reliability and Quality

The LF347N is manufactured using high-reliability processes and undergoes rigorous testing to ensure consistent performance. Key reliability characteristics include:

• ESD Protection: 2000V Human Body Model
• Operating Life: 100,000 hours MTBF
• Qualification: Industrial temperature range available
• RoHS Compliant: Yes

Ordering Information

The LF347N is available in various package and quantity options:

• LF347N: 14-Pin PDIP, tube