LF351 Single Operational Amplifier

LF351 is a high speed JFET input operational amplifier. The slew rate here is rapid and bandwidth gain product is quite high too. This high product of gain and bandwidth along with a fast slew rate is at the cost of low value of supply current of value 1.8 mA. The slew rate can be as high as 13 V/µs. Input offset voltage compensation is provided internally in LF351. The input bias and offset currents are very low because of JFET input devices where voltage is well matched. The typical value of input bias current is 50 pA. The bandwidth is around 4 MHz. LF351 is analogous to conventional LM741 OP-AMP with same pin configurations and the same procedure for offset adjustment of OP-AMP. This IC is therefore upgraded alternative of conventional LM741.

LF351 Pinout Details

LF351 is available as an 8-pin IC. in DIP8 and SO-8 packages.  Its pinout diagram is shown as:

LF351 pinout diagram

Pin configuration diagram for both DIP8 and SO-8 packages is same except the 2D dimension diagram. You can check the datasheet given at the end for further information.

Pin Configuration Details

PINSDetails
1 (BALANCE)This pin is for balancing and offset adjustment
2 ( Inverting Input)This pin is for applying inverting input voltage
3 ( Non-inverting Input)This pin is for applying non-inverting input voltage
4 (V-)This pin is for connecting negative end of DC supply voltage
5 ( BALANCE)This pin is for balancing and adjusting
6 ( OUTPUT)This pin is for obtaining output
7 ( V+)This pin is for connecting positive end of DC supply voltage
8 (NOT CONNECTED-NC)This pin is for nothing i.e. it is not connected

Alternative options for an op-amp

LM324NTE922LM709LM201, LM311

LF351 Electrical Features and Specifications

The operational features of LF351 are shown as:

ParametersLM 351
Input offset voltage (mV)10
Input bias current (pA)50-200
Input Offset Current (pA)25-100
Average temperature co-efficient of the input voltage (µV/°C)10
Large signal voltage gain (V/mV)100
Input Resistance (Ω)10^12
Output voltage swing (V)±13.5
Input common mode voltage range (V)+15
Common mode rejection ratio (dB)100
Supply voltage rejection ratio (dB)100
Supply current (mA)3.5
Slew Rate (V/µs)13
Gain bandwidth product (MHz)4
Equivalent input noise voltage (nV/√Hz)25
Equivalent input noise current (pA/√Hz)0.01
1/f Noise corner (Hz)50
Total harmonic distortion Av=10 (%)0.02
Settling time to 0.01% (µs)2
Lead temperature-Metal Can (°C)300
Lead temperature-DIP (°C)260
Differential input voltage (V)±30
Operating temperature range (°C)0-70
Supply voltage (V)±18

Where to use LF351 high Impedance Amplifier?

LF351 avoids the use of clamps at the input as it is JFET based and JFETs have a high reverse break down voltages from gate to source and drain. This makes the imposition of input differential voltages up to ±30V. These input voltages are recommended to keep lower than the negative supply voltage. If the common mode input voltage is kept equal to the positive supply voltage, the slew rate along with gain bandwidth will be compromised. Care should be taken in order to avoid reverse polarity of the supply voltage which will effectively make the whole IC faulty.

How to use a JFET input operational amplifier? 

In order to use LF351, supply voltage is applied in such a way that its negative end is connected to pin no. 4 while positive to the pin no. 7. Inverting input is connected to pin no. 2 and non-inverting at pin no. 3. Pin no 1 and 5 are utilized for offset or balancing. Pin no 8 is kept unused. A simplified schematic of LF351 is shown as:

LF351 Examples

One of the simplest application LF351 IC is a high input impedance inverting amplifier, which is shown as:

LF351 high input impedance inverting amplifier

Another example of LF351 is to indicate or limit the supply current.

supply current limiter example

This example circuit generates a square wave of 0.5Hz at the output terminal. Connect +15 volt with pin 7 and -15 volts with pin 4. Based on the selected resistor and capacitor values, we can change output frequency.  The forumla for frequency is given by : FOSC = 1 / 2RFCF

 

LF351 sqauare wave generator

 

LF351 Applications

The applications of LF351 are:

  • Ultra low duty cycle pulse generator
  • Long time integrator
  • Ultra high duty cycle pulse generator
  • Supply current indictor or limiter
  • Inverting voltage amplifier
  • Non-inverting voltage amplifier
  • Unity follower
  • instrumentation amplifier
  • square wave generator
  • voltage comparator
  • Power supplies
  • oscillators
  • half wave rectifiers

2D Diagram

If you are using this operational amplifier IC in your next project, you will need a 2D dimension diagram to design a PCB. This picture shows a 2D dimension diagram for the DIP8 package. For a 2D diagram of SO-8 package, you can download datasheet provided at the end of article.

2D diagram

DOWNLOAD LF351 DATASHEET

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