OP295_06 Datasheet, PDF (12/16 Pages) Analog Devices – Dual/Quad Rail-to-Rail Operational Amplifiers

OP295/OP495
5V
R1
17.8kΩ
1.23V
3
I_OUT
5V
8
V_DD
R_FB ²
1
DAC8043 ^VREF
AD589
GND CLK SRI LD
4 765
5V
3₊ ⁸
D
V_O = ₄₀₉₆ (4.096V)
1
2 – _{4 OP295/}
OP495
DIGITAL
CONTROL
TOTAL POWER DISSIPATION = 1.6mW
R2
41.2kΩ
R3
5kΩ
R4
100kΩ
Figure 26. A 5 V 12-Bit DAC with 0 V to 4.095 Output Swing
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.
NULL ADJ
SPAN ADJ
100kΩ
10-TURN
V_IN
0V + 3V
10kΩ
1.21MΩ
10-TURN
1%
182kΩ
1%
3₊
2–
6 ^REF02 2
+
GND
4
5V
100Ω
–
8
220Ω
1
4 1/2
OP295/
OP495
2N1711
220pF
HP
100kΩ
5082-2800 ^1%
100Ω
1%
12V
TO
36V
4mA
TO
20mA
R_L
100Ω
Figure 27. 4 to 20 mA Current Loop Transmitter
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.
+
V_IN
5V TO 3.2V
MJE 350
1
1000pF
43kΩ
8 ₊₃
4 ^–2
AD589
I_L < 50mA
44.2kΩ
1%
V_O
+
100µF
30.9kΩ
1%
1/2
OP295/
OP495
1.235V
Figure 28. 3 V Low Dropout Voltage Regulator
Figure 29 shows the regulator’s recovery characteristic when its
output underwent a 20 mA to 50 mA step current change.
2V
100
50mA ₉₀
STEP
CURRENT
CONTROL
WAVEFORM
20mA
OUTPUT
10
0%
20mV
1ms
Figure 29. Output Step Load Current Recovery
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.
IRF9531
SD
+
6V
G
–
RSENSE
0.1Ω
I_O (NORM) = 0.5A
I_O (MAX) = 1A
1/4W
5V V_O
210kΩ 205kΩ
1%
1%
1N4148
8 ₊5
7 A2
100kΩ
5%
1/2 ^{– 6}
OP295/
OP495
0.01µF
45.3kΩ 45.3kΩ
1%
1%
1
1/2
OP295/
OP495
+3
A1 124kΩ
1%
4 –2
124kΩ
1%
REF43
2.5V
2
6
4
Figure 30. Low Dropout, 500 mA Voltage Regulator
with Foldback Current Limiting
Rev. E | Page 12 of 16