What is LF353N Op-Amp : Pin Configuration & Its Working

In 1968, FAIRCHILD introduced a multi-stage amplifier, called an operational amplifier, available in the form of monolithic IC in small size, high reliability, low cost, and less power consumption.  LF353N was developed by Texas instruments. It is a dual JFET op-amp with high input impedance whose inputs are connected through a JFET (high voltage). This article gives a brief description of LF353N Op-Amp, pin configuration, technical specifications, circuit diagram, and applications.

What is LF353N Op-Amp?

The LF353N op-amps are dual JFET input op-amps with an internally trimmed offset voltage. These are high-speed operational amplifiers available at affordable rates in the form of Integrated chips. They can provide a high slew rate and high gain-bandwidth with the application of a low supply current. The matched JFET input devices with high voltage can provide very low offset and input bias currents. These types of op-amps are compatible with the performance upgraded LM1558 and LM358 op-amps.

The LF353N is a JFET dual input operational amplifier designed by Texas Instruments. The op-amp input is connected via a high voltage JFET, making it suitable for low noise, low power, and fast switching audio applications often found in dual power supplies. Since the input op-amp is powered by the JFET, it provides high input impedance and 4 MHz wide bandwidth, with a high slew rate of 13 V / μs.

It also provides low input noise and low bias current, making it suitable for audio amplifier applications. The operational amplifiers are designed for use with ±18 Volts dual supply voltages. When used with a single power supply, the output voltage is limited to 0.7 Volts for low and 1.5 Volts for high. Therefore, operational amplifiers are more commonly used in analogue circuits or audio circuits. The digital equivalent of the LF353N is the Microchip MCP6002.

Pin Configuration/Pin Diagram

LF353N OP-AMP pin configuration/pin diagram is illustrated below. It is an 8-pin operational amplifier IC available in PDIP and SOIC packages.

Pin1 (OUTPUT A): This pin refers to the output terminal of the operational amplifier A.

Pin2 (INV. INPUT A): This pin refers to the inverting input terminal of operational amplifier A.

Pin3 (NON-INV. INPUT A): This pin refers to the non-inverting input terminal of operational amplifier A.

Pin4 (VEE/GND or V-): This pin refers to the common ground connection or the negative power supply.

Pin5 (NON-INV. INPUT B): This pin refers to the non-inverting input terminal of operational amplifier B.

Pin6 (INV INPUT B): This pin refers to the inverting input terminal of operational amplifier B.

Pin7 (OUTPUT B): This pin refers to the output terminal of the operational amplifier B.

Pin8 (VCC Or V+): This pin refers to the positive voltage supply for the chip.

Technical Specifications:

The LF353N OP-AMP Technical specifications are listed below.

• Absolute Maximum Ratings:
• It is an 8-pin JFET Dual op-amp available in PDIP and SOIC packages.
• Power Supply voltage Vcc is ±18V.
• Differential input voltage is ±30V.
• The range of input voltage is ±15V.
• The duration of the output short circuit continues.
• Power dissipation is 500mW.
• The range of operating temperature is 0°C to +70°C.
• The short temperature range is -65°C to +150°C.
• Input noise voltage (25nV√Hz) and noise current (0.01pA/√Hz) is low.
• Input impedance (10¹²Ohms) and slew rate (13V/µS) is high.
• The internal trimmed offset voltage is 10mV.
• Low total harmonic distortion – ≤0.02%.
• The fast setting time to 0.01% is 2µS.

Electrical Specifications:

• Input offset voltage (@Rs=10kOhms, 0°C≤T≤+70°C) is 5mV to 10mV.
• Input offset voltage drift (@Rs=10kOhms, 0°C≤T≤+70°C) is 10µV/ °C.
• Input offset current is 25 to 100pA and 4nA @0°C≤T≤+70°C.
• Input bias current 50-200nA and 8nA @0°C≤T≤+70°C.
• Input resistance is 10¹²Ohms.
• Maximum signal voltage gain @±10V, RL=2kohms is 25-100V/mV and @0°C≤T≤+70°C is 15.
• Output voltage swing @RL = 10kOhms is ±12V to ±13.5V.
• The input voltage range is ±11V to ±15/-12V.
• CMRR (common-mode rejection ratio) @Rs=10Khms is 70-100dB.
• Power supply rejection ratio (PSRR) @Rs=10KOhms is 70-100dB.
• The slew rate is 13V/µS.
• The power supply current is 3.6mA to 6.5mA.
• The Gain-Bandwidth product is 4MHz.
• Channel separation @f=1Hz to 20KHz is 120dB.
• Equivalent input noise voltage @f=1KHz, Rs=100 Ohms is 16 nV/√Hz.
• Equivalent input noise current @f=1KHz is 0.01pA/√Hz.
• Crosstalk attenuation is 120dB.

Alternatives of LF353N Op-Amp are TL074, MCP6002, and LM1558 are the equivalents or alternatives of LF353N Op-Amp.

Circuit Diagram/How to Use:

The LF353N op-amps are mainly used in high-speed integrators, Digital to Analog converters, sample and hold circuits, and many other circuits with high input impedance and low input bias current. These types of devices produce low noise with offset drift voltage. Consider an application circuit diagram of a 3-way crossover network in audio systems to learn how to use the LF353N op-amp IC.

Below is a schematic diagram of an active three-way crossover circuit commonly used in audio amplifier systems. The National Semiconductor LF353N op-amp with 2 JFET inputs and an internally compensated input bias is the heart of the circuit. The IC LF353N offers wide bandwidth, low bias current, and low input drift current thanks to its JFET front-end. The circuit’s operation is very easy and straightforward.

It uses two LF353N chips. The input audio signal is initially buffered by the op-amp IC2a, and the gain during this buffering stage can be adjusted by the POT R7. The audio input buffer is then split into three bands using filters based on op-amps IC2b, IC1a, and IC1b. IC2b handles the bass, IC1a handles the mid frequencies, and IC1b handles the high frequencies. We can use POT R22, R23, and R24 to adjust the bass, midrange, and treble.

Before designing the 3-way crossover network, the following instructions are to be followed.

• To improve the sound quality, assemble the circuit on a good PCB.
• The power of the circuit should be 12 Volts DC supply.
• Mount the LF353N chips on holders.
• The outputs OP1, OP2 & OP3 should be connected to the corresponding multichannel power amplifier stage inputs.

Where to Use/Applications of LF353N Op-Amp:

The applications Of LF353N Op-Amp are listed below

• Used in low noise audio circuits.
• Used in designing high input impedance circuits.
• Used in high-speed integrators.
• Used in hold and sample circuits.
• Fast digital to analog converters.
• Many other types of circuits with low input bias current, input offset voltage, high input impedance, wide bandwidth, and high slew rate.

Please refer to this link to know more about LF353N Op-Amp Datasheet

Thus, the LF353N 8-pin dual JFET op-amps are used in audio circuits with low input bias current, input offset voltage, and high input impedance and produce low noise and offset drift voltage. Here is a question for you, “What are the other types of dual JFET operational amplifiers available in the market?