op495gbc Analog Devices, Inc., op495gbc Datasheet - Page 12

• Manufacturer Part Number: op495gbc
• Description: Dual/quad Rail-to-rail Operational Amplifiers
• Manufacturer: Analog Devices, Inc.

OP295/OP495
4 TO 20 mA CURRENT-LOOP TRANSMITTER
Figure 27 shows a self-powered 4 to 20 mA current-loop
transmitter. The entire circuit floats up from the single-supply
(12 V to 36 V) return. The supply current carries the signal
within the 4 to 20 mA range. Thus, the 4 mA establishes the
baseline current budget within which the circuit must operate.
This circuit consumes only 1.4 mA maximum quiescent
current, making 2.6 mA of current available to power additional
signal conditioning circuitry or to power a bridge circuit.
0V + 3V
3 V LOW DROPOUT LINEAR VOLTAGE REGULATOR
Figure 28 shows a simple 3 V voltage regulator design. The
regulator can deliver 50 mA load current while allowing a
0.2 V dropout voltage. The OP295/OP495 rail-to-rail output
swing drives the MJE350 pass transistor without requiring
special drive circuitry. At no load, its output can swing less than
the pass transistor’s base-emitter voltage, turning the device
nearly off. At full load, and at low emitter-collector voltages, the
transistor beta tends to decrease. The additional base current is
easily handled by the OP295/OP495 output.
The amplifier servos the output to a constant voltage, which
feeds a portion of the signal to the error amplifier.
Higher output current, to 100 mA, is achievable at a higher
dropout voltage of 3.8 V.
1.23V
TOTAL POWER DISSIPATION = 1.6mW
V
IN
5V
SPAN ADJ
R1
17.8kΩ
AD589
10-TURN
Figure 26. A 5 V 12-Bit DAC with 0 V to 4.095 Output Swing
3
10kΩ
I
OUT
182kΩ
Figure 27. 4 to 20 mA Current Loop Transmitter
1%
10-TURN
1.21MΩ
GND CLK SRI
DAC8043
100kΩ
V
HP
5082-2800
5V
4
DD
1%
8
CONTROL
NULL ADJ
DIGITAL
7
220pF
100kΩ
2
3
6
V
1%
R
REF
+
–
LD
FB
5
8
4
2
1
+
OP295/
OP495
1/2
5V
6
1
R2
41.2kΩ
R3
5kΩ
3
2
REF02
+
–
GND
–
5V
4
2N1711
220Ω
8
4
100Ω
100Ω
100kΩ
OP295/
OP495
1%
R4
2
V
O
1
=
20mA
4096
4mA
TO
D
(4.096V)
12V
36V
TO
R
100Ω
L
Rev. E | Page 12 of 16
WAVEFORM
Figure 29 shows the regulator’s recovery characteristic when its
output underwent a 20 mA to 50 mA step current change.
LOW DROPOUT, 500 mA VOLTAGE REGULATOR
WITH FOLDBACK CURRENT LIMITING
Adding a second amplifier in the regulation loop, as shown in
Figure 30, provides an output current monitor as well as
foldback current limiting protection.
CONTROL
CURRENT
5V TO 3.2V
6V
STEP
+
–
OUTPUT
V
50mA
20mA
IN
Figure 30. Low Dropout, 500 mA Voltage Regulator
+
100kΩ
Figure 28. 3 V Low Dropout Voltage Regulator
Figure 29. Output Step Load Current Recovery
5%
100
0%
90
IRF9531
10
G
S
2
MJE 350
1N4148
OP295/
OP495
20mV
with Foldback Current Limiting
REF43
D
2V
1/2
OP295/
4
OP495
43kΩ
0.01µF
1000pF
1/2
7
1
1
6
4
8
A2
A1
+
–
+
–
4
8
6
3
2
5
AD589
124kΩ
+
–
RSENSE
1%
2.5V
3
2
45.3kΩ
1%
210kΩ
1%
1/4W
0.1Ω
1.235V
124kΩ
I
I
1%
O
O
205kΩ
1%
45.3kΩ
1%
(NORM) = 0.5A
(MAX) = 1A
44.2kΩ
1%
30.9kΩ
1%
OP295/
OP495
I
L
1/2
< 50mA
+
5V V
100µF
1ms
V
O
O