OP281GSZ Analog Devices Inc, OP281GSZ Datasheet - Page 11

• Manufacturer Part Number: OP281GSZ
• Description: IC OPAMP GP R-R 105KHZ LP 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of OP281GSZ

• Slew Rate: 0.028 V/µs
• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Gain Bandwidth Product: 105kHz
• Current - Input Bias: 3nA
• Voltage - Input Offset: 100µV
• Current - Supply: 3.3µA
• Current - Output / Channel: 12mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 12 V, ±1.35 V ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Op Amp Type: Low Power
• No. Of Amplifiers: 2
• Bandwidth: 105kHz
• Supply Voltage Range: 2.7V To 12V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Operating Temperature Range: -40°C To
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

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 4 shows the step response of a single
channel 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.
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 refer-
ence can be created by using a voltage divider buffered by an
amplifier. Figure 5 shows the schematic for such a circuit.
The two 1 MW resistors generate the reference voltage while
drawing only 1.5 mA 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
to establish an ac ground for the reference output. The entire
reference generator draws less than 5 mA from a 3 V supply source.
REV. B
Figure 5. Single Channel Configured as a Micropower
Bias Voltage Generator
Figure 4. Ringing and Overshoot of the Output
of the Amplifier
1M
1M
100
0%
90
10
1 F
3
2
OP281
3V TO 12V
8
4
0.022 F
10k
1
100
1 F
1.5V TO 6V
V
REF
–11–
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 6 shows a circuit that
uses the OP281 as a window comparator.
The threshold limits for the window are set by V
vided that V
rail, in this case ground, as long as the input voltage is less than
V
input voltage is higher than V
V
current flowing in either D1 or D2, the base of Q1 will stay at
ground, putting the transistor in cutoff and forcing V
positive supply rail. If the input voltage rises above V
output of A2 stays at ground, but the output of A1 will go to the
positive rail, and D1 will conduct current. This creates a base
voltage that will turn on Q1 and drive V
condition occurs if V
high, and D2 conducting current. Therefore, V
if the input voltage is between V
if the input voltage moves outside of that range.
The R1 and R2 voltage divider sets the upper window voltage,
and the R3 and R4 voltage divider sets the lower voltage for the
window. For the window comparator to function properly, V
must be a greater voltage than V
The 2 kW resistor connects the input voltage to the input terminals
to the op amps. This protects the OP281 from possible excess
current flowing into the input stages of the devices. D1 and D2 are
small-signal switching diodes (1N4446 or equivalent), and Q1
is a 2N2222 or equivalent NPN transistor.
H
L
. Similarly, the output of A2 will stay at ground as long the
Figure 6. Using the OP281 as a Window Comparator
and V
H
V
, the outputs of both op amps will be 0 V. With no
IN
H
2k
> V
R1
R2
R3
R4
3V
3V
L
. The output of A1 will stay at the negative
V
V
H
L
IN
falls below V
A1
A2
3V
3V
V
V
L
H
OP281-A
OP281-B
=
=
L
. As long as V
R3 + R4
D1
D2
R1 + R2
L
L
.
R4
and V
R2
L
OP281/OP481
with A2’s output going
10k
5.1k
H
OUT
, and V
5.1k
IN
low. The same
3V
remains between
OUT
Q1
H
OUT
V
and V
OUT
will be high
OUT
H
will be low
, the
L
to the
, pro-
H