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INCREASING OUTPUT CURRENT

R

1

R

2

OPA454

OPA454

SLAVE

MASTER

V

IN

R

(1)

10W

S

R

(1)

10W

S

R

L

A1

A2

UNITY-GAIN NONINVERTING

R

1

R

2

OPA454

PNP

TIP30C,MJL21193,

MJE15004,MJL1302A

NPN

TIP29C,MJL21194,

MJE15003,MJL3281

V

IN

+50V

-50V

V

(3)

O

OUT

L

L

=V

I R

-

R

(1)

20W

3

R

0.2W

5

R

0.2W

4

R

L

C

F

-IN

+IN

V+

V-

V

OUT

(2)

I

L

OPA454

SBOS391 – DECEMBER 2007

The OPA454 drives an output current of a few

milliamps to greater than 50mA while maintaining

good op amp

performance.

See

Figure

7

for

open-loop gain versus temperature at various output

current levels.

In applications where the 25mA output current is not

sufficient to drive the required load, the output current

can be increased by connecting two or more

OPA454s in parallel, as Figure 59 shows. Amplifier

A1 is the master amplifier and may be configured in

virtually any op amp circuit. Amplifier A2, the slave, is

configured

as

a

unity-gain

buffer.

Alternatively,

external output transistors can be used to boost

output current. The circuit in Figure 60 is capable of

supplying

output

currents

up

to

1A,

with

the

transistors shown.

Figure 59. Parallel Amplifiers Increase Output

Current Capability

CONFIGURATION

When in the noninverting unity-gain configuration, the

OPA454 has more gain peaking with increasing

positive

common-mode

voltage

and

increasing

temperature. It has less gain peaking with more

negative common-mode voltage. As with all op amps,

gain peaking increases with increasing capacitive

load. A resistor and small capacitor placed in the

feedback path can reduce gain peaking and increase

stability.

(1) Provides current limit for OPA454 and allows the amplifier to drive the load when the output is between +0.7V and –0.7V.

Figure 60. External Output Transistors Boost Output Current Greater Than 1A

Copyright © 2007, Texas Instruments Incorporated

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