OP295/OP495

Rev. G | Page 12 of 16

1.23V

AD589

3

LD

2

1

3

2

4

1

8

5V

8

47

6

5

5V

5V

DIGITAL

CONTROL

TOTAL POWER DISSIPATION = 1.6mW

R1

17.8kΩ

DAC8043

VDD

RFB

VREF

IOUT

GND CLK SRI

OP295/

OP495

VO =

(4.096V)

D

4096

R4

100kΩ

R2

41.2kΩ

R3

5kΩ

+

–

Figure 27. A 5 V 12-Bit DAC with 0 V to 4.095 V Output Swing

4 mA TO 20 mA CURRENT-LOOP TRANSMITTER

Figure 28 shows a self-powered 4 mA 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 mA 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.

4

REF02

GND

100Ω

220Ω

2N1711

1

8

3

2

4

220pF

SPAN ADJ

NULL ADJ

HP

5082-2800

100kΩ

1%

2

6

5V

+

–

+

–

RL

100Ω

12V

TO

36V

4mA

TO

20mA

100Ω

1%

1/2

OP295/

OP495

100kΩ

10-TURN

1.21MΩ

1%

182kΩ

1%

10kΩ

10-TURN

VIN

0V + 3V

Figure 28. 4 mA to 20 mA Current Loop Transmitter

3 V LOW DROPOUT LINEAR VOLTAGE REGULATOR

Figure 29 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.

VIN

5V TO 3.2V

MJE 350

43kΩ

AD589

1.235V

3

2

4

1

8

1000pF

IL < 50mA

VO

100µF

44.2kΩ

1%

30.9kΩ

1%

1/2

OP295/

OP495

+

–

+

+

Figure 29. 3 V Low Dropout Voltage Regulator

Figure 30 shows the regulator’s recovery characteristic when its

output underwent a 20 mA to 50 mA step current change.

10

100

0%

90

1ms

20mV

2V

50mA

20mA

OUTPUT

STEP

CURRENT

CONTROL

WAVEFORM

Figure 30. 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 31, provides an output current monitor as well as

foldback current limiting protection.

IRF9531

G

6V

REF43

2

4

6

2.5V

A2

A1

1

4

2

3

5

6

7

8

1N4148

IO (NORM) = 0.5A

IO (MAX) = 1A

RSENSE

0.1Ω

1/4W

SD

5V VO

+

–

1/2

OP295/

OP495

1/2

OP295/

OP495

0.01µF

100kΩ

5%

205kΩ

1%

210kΩ

1%

45.3kΩ

1%

45.3kΩ

1%

124kΩ

1%

124kΩ

1%

+

–

+

–

Figure 31. Low Dropout, 500 mA Voltage Regulator

with Foldback Current Limiting