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LF442CN Datasheet(PDF) 6 Page - National Semiconductor (TI) |
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LF442CN Datasheet(HTML) 6 Page - National Semiconductor (TI) |
6 / 12 page Pulse Response R L = 10 kΩ,CL = 10 pF (Continued) Application Hints This device is a dual low power op amp with internally trimmed input offset voltages and JFET input devices (BI-FET II). These JFETs have large reverse breakdown volt- ages 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 in- crease in input current. The maximum differential input volt- age is independent of the supply voltages. However, neither of the input voltages should be allowed to exceed the nega- tive supply as this will cause large currents to flow which can result in a destroyed unit. Exceeding the negative common-mode limit on either input will force the output to a high state, potentially causing a re- versal 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 in- puts exceed the limit, the output of the amplifier will be forced to a high state. The amplifiers will operate with a common-mode input volt- age equal to the positive supply; however, the gain band- width and slew rate may be decreased in this condition. When the negative common-mode voltage swings to within 3V of the negative supply, an increase in input offset voltage may occur. Each amplifier is individually biased to allow normal circuit operation with power supplies of ±3.0V. Supply voltages less than these may degrade the common-mode rejection and re- strict the output voltage swing. The amplifiers will drive a 10 k Ω load resistance to ± 10V over the full temperature range. 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. 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 feed- back 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 consequenty there is negligible effect on stability margin. However, if the feed- back pole is less than approximately 6 times the expected 3 dB frequency a lead capacitor should be placed from the out- put to the input of the op amp. The value of the added ca- pacitor should be such that the RC time constant of this ca- pacitor and the resistance it parallels is greater than or equal to the original feedback pole time constant. Large Signal Inverting DS009155-9 Large Signal Non-Inverting DS009155-10 www.national.com 6 |
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