REV. B

–8–

OP295/OP495

Table I. Single Supply Low Noise Preamp Performance

R1

270

Ω

1.0 k

Ω

R3, R4

200

Ω

910

Ω

3.15 nV/

√Hz

8.6 nV/

√Hz

4.2 nV/

√Hz

10.2 nV/

√Hz

4.0 mA

1.3 mA

11

µA3 µA

Bandwidth

1 kHz

1 kHz

Closed-Loop Gain

1000

1000

Driving Heavy Loads

The OP295/OP495 is well suited to drive loads by using a

power transistor, Darlington or FET to increase the current to

the load. The ability to swing to either rail can assure that the

device is turned on hard. This results in more power to the load

and an increase in efficiency over using standard op amps with

their limited output swing. Driving power FETs is also possible

with the OP295/OP495 because of its ability to drive capacitive

loads of several hundred picofarads without oscillating.

Without the addition of external transistors the OP295/OP495

can drive loads in excess of

± 15 mA with ± 15 or +30 volt

supplies. This drive capability is somewhat decreased at lower

supply voltages. At

±5 volt supplies the drive current is ±11 mA.

Driving motors or actuators in two directions in a single supply

application is often accomplished using an “H” bridge. The

principle is demonstrated in Figure 3a. From a single +5 volt

supply this driver is capable of driving loads from 0.8 V to 4.2 V

in both directions. Figure 3b shows the voltages at the inverting

and noninverting outputs of the driver. There is a small crossover

glitch that is frequency dependent and would not cause problems

5k

10k

1.67V

10k

10k

2N2222

2N2222

OUTPUTS

2N2907

2N2907

+5V

0

≤ V

Figure 3a. “H” Bridge

10

90

100

0%

2V

2V

1ms

Figure 3b. “H” Bridge Outputs

unless this was a low distortion application such as audio. If this

is used to drive inductive loads, be sure to add diode clamps to

protect the bridge from inductive kickback.

Direct Access Arrangement

OP295/OP495 can be used in a single supply Direct Access Ar-

rangement (DAA) as is shown an in Figure 4. This figure shows

a portion of a typical DM capable of operating from a single

+5 volt supply and it may also work on +3 volt supplies with

minor modifications. Amplifiers A2 and A3 are configured so

that the transmit signal TXA is inverted by A2 and is not in-

verted by A3. This arrangement drives the transformer differen-

tially so that the drive to the transformer is effectively doubled

over a single amplifier arrangement. This application takes ad-

vantage of the OP295/OP495’s ability to drive capacitive loads,

and to save power in single supply applications.

2.5V REF

A3

20k

Ω

20k

Ω

750pF

20k

Ω

22.1k

Ω

0.1

µF

475

Ω

3.3k

Ω

0.0047

µF

0.1

µF

0.033

µF

A2

A1

20k

Ω

20k

Ω

37.4k

Ω

390pF

RXA

TXA

OP295/

OP495

OP295/

OP495

OP295/

OP495

1:1

Figure 4. Direct Access Arrangement

A Single Supply Instrumentation Amplifier

The OP295/OP495 can be configured as a single supply instru-

equal to

V

+

2

put common-mode voltage range includes ground and the out-

put swings to both rails.

V+

V

IN

V

REF

1

R1

100k

R2

20k

R3

20k

R4

100k

V

O

V

V

5 +

200k

R

G

(

)

R

G

3

2

8

7

4

5

6

1/2

OP295/

OP495

1/2

OP295/

OP495

Figure 5. Single Supply Instrumentation Amplifier

absolute value as well as temperature coefficient to maximize