OP181 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
OP181 Datasheet PDF : 16 Pages
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OP181/OP281/OP481
0.2ms
100
100
VOUT 90
90
0V
VIN
10
10
0%
0%
0.1V
Figure 35. Input and Output Signals with VCM < 0 V
Overdrive Recovery Time
The amount of time it takes for an amplifier to recover from
saturation can be an important consideration when using an
amplifier as a comparator or when outputs can be driven to the
supplies. The overdrive recovery time for the OP181 is 50 µs
with the amplifier running from a 3 volt supply and increases
to 100 µs with a 10 volt supply. Figure 36 shows the result of
the OP181 running from a 3 V supply with its output being
overdriven.
VIN 100
SCALE 0.1V 90
0V
VOUT
SCALE 1V
10
0%
0V
0.1V
0.2ms
VS = +3V
AV = +100
Figure 36. Output of the Op Amp Recovering from
Saturation
Capacitive Loading
Most low supply current amplifiers have difficulty driving
capacitive loads due to the higher currents required from the
output stage for such loads. Higher capacitance at the output
will increase the amount of overshoot and ringing in the
amplifier’s step response and could even affect the stability of
the device. However, through careful design of the output stage
and its high phase margin, the OPx81 family can tolerate some
degree of capacitive loading. Figure 37 shows the step response
of an OP181 with a 10 nF capacitor connected at the output.
Notice that the overshoot of the output does not exceed more
than 10% with such a load, even with a supply voltage of only
+3 V.
Figure 37. Ringing and Overshoot of the Output of the
Amplifier
A Micropower Reference Voltage Generator
Many single supply circuits are configured with the circuit
biased to 1/2 of the supply voltage. In these cases, a false-
ground reference can be created by using a voltage divider
buffered by an amplifier. Figure 38 shows the schematic for
such a circuit.
The two 1 MΩ resistors generate the reference voltage while
drawing only 1.5 µA of current from a 3 V supply. A capacitor
connected from the inverting terminal to the output of the op
amp provides compensation to allow for a bypass capacitor to be
connected at the reference output. This bypass capacitor helps
establish an ac ground for the reference output. The entire
reference generator draws less than 5 µA from a 3 V supply
source.
+3V TO +12V
10kΩ
0.022µF
1MΩ
1MΩ
2
7
OP181 6
3
4
1µF
100Ω
1µF
VREF
+1.5V TO +6V
Figure 38. A Micropower Bias Voltage Generator
A Window Comparator
The extremely low power supply current demands of the OPx81
family make it ideal for use in long life battery powered applica-
tions such as a monitoring system. Figure 39 shows a circuit
that uses the OP281 as a window comparator.
REV. 0
–11–
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