What Is LF347N?
LF347N is a high-speed quad JFET input operational amplifier, integrating four independent op-amp channels for multi-channel analog signal processing. Compared with traditional bipolar input operational amplifiers, LF347N features a JFET input structure with higher input impedance and lower input bias current, reducing signal source loading and making it suitable for weak and high-impedance analog signal applications.
LF347N provides wide bandwidth, high slew rate, and low input offset voltage, enabling fast and stable signal amplification and conditioning.
How Does LF347N Op Amp Work?
LF347N integrates four independent operational amplifier units. Each op amp uses a JFET differential input stage to detect the voltage difference between the two inputs. Its high input impedance reduces input current and minimizes signal loss from high-impedance sources. The differential signal is amplified through the gain stage and delivered by the bipolar output stage to drive external loads.
With external feedback, LF347N uses its high open-loop gain to achieve stable functions such as voltage amplification, filtering, and voltage buffering. Without feedback, it can operate as a voltage comparator. Thanks to its Bi-FET architecture, LF347N offers high slew rate and 4MHz gain bandwidth, making it suitable for medium-frequency analog signal processing. Proper power decoupling and input voltage range design help ensure stable operation in sensor interfaces, audio preamplifiers, and active filter circuits.
LF347N Key Specifications Listed
LF347N technical specifications, attributes, parameters, and other vital data are below.
Parameter | Value |
Part Number | LF347N |
Manufacturer | STMicroelectronics |
Amplifier Type | J-FET |
Packaging | Tube |
Lead Free Status / RoHS Status | Lead free / RoHS Compliant |
Current - Output / Channel | 40mA |
Slew Rate | 16 V/µs |
Current - Supply | 1.4mA |
Current - Input Bias | 20pA |
Number of Circuits | 4 |
Voltage - Input Offset | 3mV |
Mounting Type | Through Hole |
Gain Bandwidth Product | 4MHz |
Voltage - Supply, Single/Dual (±) | 8 V ~ 36 V, ±4 V ~ 18 V |
Operating Temperature | 0°C ~ 70°C |
Supplier Device Package | 14-DIP |
Package | 14-DIP (0.300, 7.62mm) |
Base Part Number | LF347 |
LF347N Internal Architecture Explained
Each channel of the LF347N operational amplifier shares only the power supply pins and contains the following internal functional blocks:
l JFET Differential Input Stage: Provides high input impedance and low input bias current, reducing signal loading and enabling accurate processing of high-impedance sensor signals.
l Intermediate Gain Stage: Provides high voltage amplification and improves signal accuracy through internal compensation circuits to reduce DC offset.
l Level Shift Circuit: Adjusts DC voltage levels between the gain and output stages, expanding output swing and improving signal range.
l Complementary Bipolar Output Stage: Uses a push-pull structure to drive external loads with basic short-circuit protection for improved reliability.
l Bias and Regulation Network: Provides stable operating currents for internal circuits, ensuring consistent performance across different temperatures.
LF347N Pin Configuration
LF347N adopts a standard 14-pin package design. Each op amp channel includes a non-inverting input, inverting input, and output pin. The four independent op amps are assigned to different pins and can perform analog functions such as signal amplification, buffering, and filtering. The V+ (positive supply) and V− (negative supply) pins provide operating power for the device, ensuring proper operation of the internal differential input stage, gain stage, and output stage.
LF347N Features and Benefits
l Low power consumption
l Wide common-mode(up to VCC+) and differential voltage range
l Low input bias and offset current
l Output short-circuit protection
l High input impedance J–FET input stage
l Internal frequency compensation
l Latch-up-free operation
l High slew rate: 16V/µs (typ)
LF347N Application Fields
1. Industrial Control and Automation Systems
LF347N can be used for analog signal acquisition and processing in industrial control equipment, such as PLC input modules, automated inspection systems, and control terminals. Its high input impedance helps reduce sensor signal loss and improves measurement accuracy and system stability.
2. Sensor Signal Conditioning Systems
LF347N is widely used in sensor interface circuits for temperature, pressure, and optical sensors to amplify, filter, and buffer weak analog signals. Its low input bias current reduces measurement errors and makes it suitable for high-impedance sensor applications.
3. Test and Measurement Equipment
With high gain performance and fast response characteristics, LF347N is suitable for test instruments such as oscilloscopes, data acquisition systems, and voltage measurement devices, supporting signal amplification, waveform processing, and precision measurement.
4. Audio and Signal Processing Circuits
LF347N can be applied in audio preamplifiers, active filters, and signal conditioning circuits. Its low-noise analog processing capability helps improve signal quality in audio and communication systems.
5. Medical and Laboratory Equipment
In medical instruments and laboratory systems, LF347N can be used for biological signal acquisition, detection modules, and analysis equipment. It provides stable amplification for low-level analog signals and improves measurement reliability.
LF347N Circuit Functions
This diagram shows the internal circuit of a single LF347N op amp. The JFET differential input stage provides high input impedance and low input bias current, while the constant-current source ensures stable operation. The amplified differential signal passes through the gain stage with RC Miller compensation for improved stability.
After level shifting, the signal reaches the complementary push-pull output stage, which includes current limiting and protection circuits. Powered by Vcc+ and Vcc−, LF347N works with external feedback networks to perform functions such as signal amplification and filtering.
LF347N Package
This part shows the package outlines of the LF347N operational amplifier.
Design Tips
1) LF347N is a JFET-input quad op amp. Use low-leakage PCB materials to reduce leakage current interference on high-impedance input signals.
2) Place a 0.1μF decoupling capacitor close to the Vcc+ and Vcc− pins to suppress power noise and prevent self-oscillation.
3) When using high-value resistors at the non-inverting input, add a balance resistor to reduce DC output offset caused by input bias current.
4) The input signal must stay within the specified common-mode voltage range; otherwise, output distortion may occur.
5) In closed-loop applications, ensure sufficient phase margin. Add a small compensation capacitor in the feedback path if oscillation occurs.
6) For capacitive loads, add a small series isolation resistor to improve phase stability and prevent output oscillation.
7) The four op amp channels operate independently. However, total power dissipation should remain within the device limit.
8) Keep input signal traces away from output and power traces to avoid unwanted coupling and parasitic oscillation.
9) Maintain the operating temperature within the specified range. Input bias current may increase significantly at high temperatures.
10) Do not use the op amp in open-loop mode to directly drive heavy loads. Open-loop operation is mainly for comparator functions, while linear amplification requires negative feedback.
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