OP191 Datasheet, PDF (13/20 Pages) Analog Devices – Micropower Single-Supply Rail-to-Rail Input/Output Op Amps

OP191/OP291/OP491
I_IN
2mA
1mA
–10V
–5V
5V
10V
V_IN
–1mA
–2mA
Figure 56. Input Overvoltage Characteristics
This input current is not inherently damaging to the device as
long as it is limited to 5 mA or less. In the case shown, for an
input of 10 V over the supply, the current is limited to 1.8 mA.
If the voltage is large enough to cause more than 5 mA of
current to flow, then an external series resistor should be added.
The size of this resistor is calculated by dividing the maximum
overvoltage by 5 mA and subtracting the internal 5 kΩ resistor.
For example, if the input voltage could reach 100 V, the external
resistor should be (100 V/5 mA) –5 k = 15 kΩ. This resistance
should be placed in series with either or both inputs if they are
subjected to the overvoltages. For more information on general
overvoltage characteristics of amplifiers refer to the 1993 System
Applications Guide, available from the Analog Devices Literature
Center.
Output Voltage Phase Reversal
Some operational amplifiers designed for single-supply
operation exhibit an output voltage phase reversal when their
inputs are driven beyond their useful common-mode range.
Typically for single-supply bipolar op amps, the negative supply
determines the lower limit of their common-mode range. With
these devices, external clamping diodes, with the anode
connected to ground and the cathode to the inputs, prevent
input signal excursions from exceeding the device’s negative
supply (i.e., GND), preventing a condition which could cause
the output voltage to change phase. JFET-input amplifiers may
also exhibit phase reversal, and, if so, a series input resistor is
usually required to prevent it.
The OP191 family is free from reasonable input voltage range
restrictions due to its novel input structure. In fact, the input
signal can exceed the supply voltage by a significant amount
without causing damage to the device. As illustrated in Figure
57, the OP191 family can safely handle a 20 V p-p input signal
on ± 5 V supplies without exhibiting any sign of output voltage
phase reversal or other anomalous behavior. Thus no external
clamping diodes are required.
Overdrive Recovery
The overdrive recovery time of an operational amplifier is the
time required for the output voltage to recover to its linear
region from a saturated condition. This recovery time is
important in applications where the amplifier must recover
quickly after a large transient event, such as a comparator. The
circuit shown in Figure 58 was used to evaluate the OP191
family’s overload recovery time. The OP191 family takes
approximately 8 µs to recover from positive saturation and
approximately 6.5 µs to recover from negative saturation.
V_IN
10V STEP
V_S = ±5V
R1
9kΩ
R2
10kΩ
3
1/2
1
2 ^OP291
R3
10kΩ
V_OUT
Figure 58. Overdrive Recovery Time Test Circuit
V_IN
20Vp-p
+5V
3
8
1/2
1
2 ^OP291
4
–5V
100
90
V_OUT
5µs
5µs
100
90
10
10
0%
0%
20mV
20mV
TIME – 200µs/DIV
Figure 57. Output Voltage Phase Reversal Behavior
TIME – 200µs/DIV
REV. 0
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