OP293FS-REEL7 Analog Devices Inc, OP293FS-REEL7 Datasheet - Page 12

• Manufacturer Part Number: OP293FS-REEL7
• Description: IC,Operational Amplifier,DUAL,BIPOLAR,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of OP293FS-REEL7

• Rohs Status: RoHS non-compliant
• Design Resources: 4 mA-to-20 mA Loop-Powered Temperature Monitor Using ADuC7060/1 (CN0145)
• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.015 V/µs
• Gain Bandwidth Product: 35kHz
• Current - Input Bias: 20nA
• Voltage - Input Offset: 250µV
• Current - Supply: 30µA
• Current - Output / Channel: 25mA
• Voltage - Supply, Single/dual (±): 1.7 V ~ 36 V, ±0.85 V ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• -3db Bandwidth: -
• Other names: OP293FS-REEL7; OP293FS-REEL7TR

OP193/OP293/OP493
A Single-Supply Instrumentation Amplifier
Designing a true single-supply instrumentation amplifier with
zero-input and zero-output operation requires special care.
The traditional configuration, shown in Figure 9, depends upon
amplifier A1’s output being at 0 V when the applied common-
mode input voltage is at 0 V. Any error at the output is multiplied
by the gain of A2. In addition, current flows through resistor R3
as A2’s output voltage increases. A1’s output must remain at 0 V
while sinking the current through R3, or a gain error will result.
With a maximum output voltage of 4 V, the current through R3
is only 2 µA, but this will still produce an appreciable error.
One solution to this problem is to use a pull-down resistor. For
example, if R3 = 20 kΩ, then the pull-down resistor must be
less than 400 Ω. However, the pull-down resistor appears as a
fixed load when a common-mode voltage is applied. With a 4 V
common-mode voltage, the additional load current will be 10 mA,
which is unacceptable in a low power application.
Figure 10 shows a better solution. A1’s sink current is provided
by a pair of N-channel FET transistors, configured as a current
mirror. With the values shown, sink current of Q2 is about
340 µA. Thus, with a common-mode voltage of 4 V, the addi-
tional load current is limited to 340 µA versus 10 mA with a
400 Ω resistor.
–IN
+IN
20k
R1
REF-43BZ
V
V
TEMP
GND
OUT
V
I N
1/2 OP293
1.98M
A1
2
6
4
3
R2
5V
R1 10k
V+
V–
ALL RESISTORS 1/4W, 5% UNLESS OTHERWISE NOTED
I
SINK
20k
R3
1.98M
1/2 OP293
R4
2
3
A2
1/2 OP293
5V
V+
V–
8
4
1
V
OUT
R3
100k
V
TEMP
1k
R2
5k
R5
ZERO
TRIM
R4
20k
A Low-Power, Temperature to 4–20 mA Transmitter
A simple temperature to 4–20 mA transmitter is shown in Fig-
ure 11. After calibration, this transmitter is accurate to ± 0.5°C
over the –50°C to +150°C temperature range. The transmitter
operates from 8 V to 40 V with supply rejection better than
3 ppm/V. One half of the OP293 is used to buffer the V
pin, while the other half regulates the output current to satisfy
the current summation at its noninverting input:
The change in output current with temperature is the derivative
of the transfer function:
V
SET
–IN
+IN
I
OUT
3k
R6
6
5
1/2 OP293
20k
+
R1
V
TEMP
SPAN TRIM
5k
R7
1/2 OP293
R2 R10
∆
1.98M
7
A1
∆
×
I
VN2222
R2
OUT
T
5V
(
×
R6
R9
100k
V+
V–
Q1
=
1%, 1/2 W
+
1k
5V
R8
∆
R7
10k
100
V
R10
∆
TEMP
T
)
R2 R10
2N1711
−
I
R
1N4002
OUT
V
LOAD
(
×
20k
Q2
R6
SET
R3



+
R2
8V TO 40V
R7
1/2 OP293
R2 R10
V+
1.98M
A2
+
5V
)
R4
R6
×
V+
V–
+
R7
TEMP
V



OUT