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OP727AR-REEL7 Datasheet(PDF) 11 Page - Analog Devices |
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OP727AR-REEL7 Datasheet(HTML) 11 Page - Analog Devices |
11 / 16 page REV. OP777/OP727/OP747 –11– Input Over Voltage Protection When the input of an amplifier is more than a diode drop below VEE, or above V CC, large currents will flow from the substrate (V–) or the positive supply (V+), respectively, to the input pins which can destroy the device. In the case of OP777/OP727/ OP747, differential voltages equal to the supply voltage will not cause any problem (see Figure 3). OP777/OP727/OP747 has built- in 500 Ω internal current limiting resistors, in series with the inputs, to minimize the chances of damage. It is a good practice to keep the current flowing into the inputs below 5 mA. In this con- text it should also be noted that the high breakdown of the input transistors removes the necessity for clamp diodes between the inputs of the amplifier, a feature that is mandatory on many preci- sion op amps. Unfortunately, such clamp diodes greatly interfere with many application circuits such as precision rectifiers and comparators. The OP777/OP727/OP747 series is free from such limitations. 30V V p-p = 32V OP777/ OP727/ OP747 Figure 3a. Unity Gain Follower TIME – 400 s/DIV VSY = 15V VIN VOUT Figure 3b. Input Voltage Can Exceed the Supply Voltage Without Damage Phase Reversal Many amplifiers misbehave when one or both of the inputs are forced beyond the input common-mode voltage range. Phase reversal is typified by the transfer function of the amplifier effectively reversing its transfer polarity. In some cases this can cause lockup in servo systems and may cause permanent damage or nonrecoverable parameter shifts to the amplifier. Many amplifiers feature compensa- tion circuitry to combat these effects, but some are only effective for the inverting input. Additionally, many of these schemes only work for a few hundred millivolts or so beyond the supply rails. OP777/ OP727/OP747 has a protection circuit against phase reversal when one or both inputs are forced beyond their input common- mode voltage range. It is not recommended that the parts be continuously driven more than 3 V beyond the rails. TIME – 400 s/DIV VSY = 15V VIN VOUT Figure 4. No Phase Reversal Output Stage The CMOS output stage has excellent (and fairly symmetric) output drive and with light loads can actually swing to within 1 mV of both supply rails. This is considerably better than similar amplifiers featuring (so-called) rail-to-rail bipolar output stages. OP777/ OP727/OP747 is stable in the voltage follower configuration and responds to signals as low as 1 mV above ground in single supply operation. V TO 30V VIN = 1mV OP777/ OP727/ OP747 VOUT = 1mV Figure 5. Follower Circuit TIME – 10 s/DIV 1.0mV Figure 6. Rail-to-Rail Operation Output Short Circuit The output of the OP777/OP727/OP747 series amplifier is protected from damage against accidental shorts to either supply voltage, provided that the maximum die temperature is not exceeded on a long-term basis (see Absolute Maximum Rating section). Current of up to 30 mA does not cause any damage. A Low-Side Current Monitor In the design of power supply control circuits, a great deal of design effort is focused on ensuring a pass transistor’s long-term reliability over a wide range of load current conditions. As a result, monitoring D 3.0 |
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