Datasheet OP777, OP727, OP747 (Analog Devices) - 11

OP777/OP727/OP747 Input Over Voltage Protection
When the input of an amplifier is more than a diode drop below
VSY = 15V VIN
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/
VOUT
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
VOLTAGE – 5V/DIV
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-
TIME – 400 s/DIV
sion op amps. Unfortunately, such clamp diodes greatly interfere with many application circuits such as precision rectifiers and Figure 4. No Phase Reversal comparators. The OP777/OP727/OP747 series is free from such
Output Stage
limitations. The CMOS output stage has excellent (and fairly symmetric) output drive and with light loads can actually swing to within 1 mV of both
30V
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
OP777/ V p-p = 32V
operation.
OP727/ OP747
Figure 3a. Unity Gain Follower
3.0 V TO 30V VOUT = 1mV VSY = 15V VIN = 1mV OP777/ VIN OP727/ OP747 VOUT
Figure 5. Follower Circuit
VOLTAGE – 5V/DIV TIME – 400 s/DIV 1.0mV
Figure 3b. Input Voltage Can Exceed the Supply Voltage Without Damage
VOLTAGE – 25mV/DIV Phase Reversal
Many amplifiers misbehave when one or both of the inputs are forced beyond the input common-mode voltage range. Phase
TIME – 10 s/DIV
reversal is typified by the transfer function of the amplifier effectively reversing its transfer polarity. In some cases this can cause lockup in Figure 6. Rail-to-Rail Operation servo systems and may cause permanent damage or nonrecoverable
Output Short Circuit
parameter shifts to the amplifier. Many amplifiers feature compensa- The output of the OP777/OP727/OP747 series amplifier is protected tion circuitry to combat these effects, but some are only effective for from damage against accidental shorts to either supply voltage, the inverting input. Additionally, many of these schemes only work provided that the maximum die temperature is not exceeded on a for a few hundred millivolts or so beyond the supply rails. OP777/ long-term basis (see Absolute Maximum Rating section). Current of OP727/OP747 has a protection circuit against phase reversal up to 30 mA does not cause any damage. when one or both inputs are forced beyond their input common-
A Low-Side Current Monitor
mode voltage range. It is not recommended that the parts be In the design of power supply control circuits, a great deal of design continuously driven more than 3 V beyond the rails. effort is focused on ensuring a pass transistor’s long-term reliability over a wide range of load current conditions. As a result, monitoring REV. D –11– Document Outline GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAMS SIMILAR LOW POWER PRODUCTS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS Typical Performance Characteristics BASIC OPERATION OUTLINE DIMENSIONS ORDERING GUIDE REVISION HISTORY