10

®

OPA445

R

1

R

2

OPA445

OPA445

“SLAVE”

“MASTER”

V

IN

R

S

(1)

10

Ω

R

S

(1)

10

Ω

R

L

NOTE: (1) R

S

resistors minimize the circulating

current that will always flow between the two devices

due to V

INCREASING OUTPUT CURRENT

In those applications where the 15mA of output current is

not sufficient to drive the required load, output current can

be increased by connecting two or more OPA445s in parallel

as shown in Figure 7. Amplifier A1 is the “master” amplifier

and may be configured in virtually an 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 8 is capable of

supplying output currents up to 1A.

INPUT PROTECTION

The inputs of conventional FET-input op amps should be

protected against destructive currents that can flow when

input FET gate-to-substrate isolation diodes are forward-

biased. This can occur if the input voltage exceeds the power

is easily accomplished with a resistor in series with the

input. Care should be taken because the resistance in series

with the input capacitance may affect stability. Many input

signals are inherently current-limited, therefore, a limiting

resistor may not be required.

FIGURE 7. Parallel Amplifiers Increase Output Current

Capability.

R

1

R

2

OPA445

TIP30C

TIP29C

V

IN

+45V

–45V

V

O

R

3

(1)

100

Ω

NOTE: (1) Provides current limit for OPA445 and allows the amplifier to

drive the load when the output is between 0.7V and –0.7V.

R

4

0.2

Ω

R

4

0.2

Ω

LOAD

C

F

FIGURE 8. External Output Transistors Boost Output Current up to 1 Amp.