LF JFET Input Operational Amplifiers. These are the first monolithic JFET input operational amplifiers to incorporate well matched, high voltage JFETs on the. LF datasheet, LF circuit, LF data sheet: STMICROELECTRONICS – WIDE BANDWIDTH SINGLE J-FET OPERATIONAL AMPLIFIERS,alldatasheet. LF datasheet, LF circuit, LF data sheet: TI – LF/LF/LF/ LF/LF/LF/LF JFET Input Operational Amplifiers,alldatasheet.
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PDIP package Soldering 10 sec. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Unless otherwise specified the absolute maximum negative input voltage is equal to the negative power supply voltage. It is the time required for the error voltage the voltage at the inverting input pin on the amplifier to settle to within 0. The Temperature Coefficient of datashewt adjusted input offset voltage changes only a small amount 0.
Common-mode rejection and open-loop voltage gain are also unaffected by offset adjustment. Due to limited production test time, the input bias currents measured are correlated to junction temperature. In normal operation datasneet junction temperature rises above the ambient temperature as a result of internal power dissipation, Pd.
Use of a heat sink is recommended if input bias current is to be kept to a minimum. Maximum power dissipation is defined by the package characteristics. Operating the part near the maximum power dissipation may cause the part to operate outside specified limits.
Input Bias Current Figure 2. Input Bias Current Figure 3. Input Bias Current Figure 4.
Voltage Swing Figure 5. Supply Current Figure 6. Negative Current Limit Figure 8. Positive Current Limit Figure 9.
LF357 Datasheet PDF
Open-Loop Voltage Gain Figure Gain Bandwidth Figure Normalized Slew Rate Figure Output Impedance Figure Inverter Settling Time Figure Bode Plot Figure Common-Mode Rejection Ratio Figure Power Supply Rejection Ratio Figure Undistorted Output Voltage Swing Figure Equivalent Input Noise Voltage Figure These amplifiers feature low input bias and offset currents, as well as low offset voltage and offset voltage drift, coupled with offset adjust which does not degrade drift or common-mode rejection.
These devices can replace expensive hybrid and module FET operational amplifiers. These JFETs have large reverse breakdown voltages from gate to source and drain eliminating the need for clamps across the inputs.
Therefore large differential input voltages can easily be accommodated without a large increase in input current. The maximum differential input voltage is independent of the supply voltages. However, neither of the input voltages should be allowed to exceed the negative supply as this will cause large currents to flow which can result in a destroyed unit.
In fact, the common-mode voltage can exceed the positive supply by approximately mV independent of supply voltage and over the full operating temperature range. Customers should validate and test their design implementation to confirm system functionality. Exceeding the negative common-mode limit on either input will force the output to a high state, potentially causing a reversal of phase to the output. Exceeding the negative common-mode limit on both inputs will force the amplifier output to a high state.
In neither case does a latch occur since raising the input back within the common-mode range again puts the input stage and thus the amplifier in a normal operating mode.
Exceeding the positive common-mode limit on a single input will not change the phase of the output however, if both inputs exceed the limit, the output of the amplifier will be forced to a high state.
These amplifiers will operate with the common-mode input voltage equal to the positive supply. Precautions should be taken to ensure that the power supply for the integrated circuit never becomes reversed in polarity or that the unit is not inadvertently installed backwards in a socket as an unlimited current surge through the resulting forward diode within the IC could cause fusing of the internal conductors and result in a destroyed unit.
All of the bias currents in these amplifiers are set by FET current sources. The drain currents for the amplifiers are therefore essentially independent of supply voltage. As with most amplifiers, care should be taken with lead dress, component placement and supply decoupling in order to ensure stability. For example, resistors from the output to an input should be placed with the body close to the input to minimize pick-up and maximize the frequency of the feedback pole by minimizing the capacitance from the input to ground.
A feedback pole is created when the feedback around any amplifier is resistive. The parallel resistance and capacitance from the input of the device usually the inverting input to AC ground set the frequency of the pole.
In many instances the frequency of this pole is much greater than the expected 3-dB frequency of the closed loop gain and consequently there is negligible effect on stability margin. However, if the feedback pole is less than approximately six times the expected 3-dB frequency a lead capacitor should be placed from the output to the input of the op amp.
The value of the added capacitor should be such that the RC time constant of this capacitor and the resistance it parallels is greater than or equal to the original feedback pole time constant. Settling Time Test Circuit 8. In particular, use FET to isolate the probe capacitance. Apply a V step function to the input. Use an oscilloscope to probe the circuit as shown in Figure To compensate add C2 such that: Leakage of D2 provided by feedback path through Rf.
TA can be estimated by same considerations as previously but, because of the added — propagation delay in the feedback loop A2 the overshoot is not negligible. Overall system slower than fast sample and hold R1, CC: When one wishes to take advantage of the low input bias current of the LFx5x, typically less than 30 pA, it is essential to have an excellent layout.
Fortunately, the techniques of obtaining low leakages are quite simple. First, the user must not ignore the surface leakage of the PCB, even though it may sometimes appear acceptably low, because under conditions of high humidity or dust or contamination, the surface leakage will be appreciable.
To minimize the effect of any surface leakage, lay out a ring of foil completely surrounding the inputs of the LFx5x and the terminals of capacitors, diodes, conductors, resistors, relay terminals, and so forth, connected to the inputs of the op amp, as in Figure To have a significant effect, guard rings must be placed on both the top and bottom of the PCB.
This PC foil must then be connected to a voltage that is at the same voltage as the amplifier inputs, because no leakage current can flow between two points at the same potential. If a guard ring is used and held close to the potential of the amplifier inputs, it will significantly reduce this leakage current. Inverting Amplifier Figure Typical Connections Of Guard Rings The designer should be aware that when it is inappropriate to lay out a PCB for the sake of just a few circuits, there is another technique which is even better than a guard ring on a PCB: Do not insert the input pin of the amplifier into the board at all, but bend it up in the air and use only air as an insulator.
Air is an excellent insulator. In this case datsheet may have to forego some of the advantages of PCB construction, but the advantages are sometimes well worth the effort of using point-to-point up-in-the-air wiring. Input pins are lifted out of PCB and soldered directly to components. All other pins connected to PCB. Air Wiring Another potential source of leakage that datasheeet be overlooked is the device package. When the LFx5x is manufactured, the device is always handled with conductive finger cots.
This is to assure that salts and skin oils do not cause leakage paths on the surface of the package. We recommend that these same precautions be adhered to, during all phases of inspection, test and assembly.
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Created to foster collaboration among engineers. All other trademarks are the property of their respective owners. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.
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Product device recommended for new designs. TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend dataseet this part in a new design. Device has been ld357 but is not in production. Samples may or may not be available. TI has discontinued the production of the device.
TI’s terms “Lead-Free” or “Pb-Free” mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.
Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.