6

®

OPA501

CURRENT LIMITS

The OPA501 has independent positive and negative current

I

Amperes and R

creases with increasing temperature—see typical perfor-

mance curves. The current limit resistors conduct the full

amplifier output current. Power dissipation of the current

limit resistors at maximum current is:

The current limit resistors can be chosen from a variety of

types. Most wire-wound types are satisfactory, although

some physically large resistors may have excessive induc-

tance which can cause instability.

SAFE OPERATING AREA

Stress on the output transistor is determined by the output

current and the voltage across the conducting output transis-

tor. The power dissipated by the output transistor is equal to

the product of the output current and the voltage across the

conducting transistor, V

APPLICATIONS INFORMATION

Grounding techniques can greatly affect the performance of

a power op amp. Figure 1 shows grounds connected so that

load current does not flow through signal ground connec-

tions. Power supply and load connections should be physi-

cally separated from the amplifier input and signal connec-

tions.

Power supply connections to the amplifier should be by-

passed with 10

µF tantalum capacitors connected close to the

device pins. The capacitors should be connected to load

ground as shown.

Figure 2, shows the permissible range of voltage and cur-

rent. SOA is reduced at high operating temperature—see

Figure 3.

The safe output current decreases as V

short-circuits are very demanding. A short-circuit to ground

forces the full power supply voltage (positive or negative

side) across the conducting transistor. With V

current limit must be set for 2A to be safe for short-circuit

to ground. For further information on SOA and evaluating

signal and load conditions, consult Applications Bulletin

AB-039.

HEAT SINKING

Most applications require a heat sink to assure that the

maximum junction temperature of 200

°C is not exceeded.

The size of the heat sink required depends on the power

dissipated by the amplifier and ambient temperature condi-

tions. Application Bulletin AB-039 explains how to find

maximum power dissipation for DC, AC, reactive loads, and

other conditions. Applications Bulletin AB-038 shows how

to determine heat sink requirements.

The case of the OPA501 is isolated from all circuitry and can

be fastened directly to a heat sink. This eliminates cumber-

some insulating hardware that degrades thermal perfor-

mance. See Applications Bulletin AB-037 for information

on mounting techniques and procedures.

FIGURE 3. Transistor Safe Operating Area at +125

°C Case

Temperature.

FIGURE 1. Basic Circuit Connections.

FIGURE 2. Transistor Safe Operating Area at +25

°C Case

Temperature.

P

SC

1

2

4

6

10

20

40

60 80

10

4

2

1.0

0.8

0.6

0.4

0.2

0.1

Voltage Across Output Transistor (V)

8

6

100

Maximum

Specified

Current

8

T

T

θ

1ms

0.5ms

Maximum

Specified

Voltage

RM, AM

SM, BM

5ms

DC

Power

Dissipation

Limit

Second

Breakdown

Limit

1

2

4

6

10

20

40

60 80

10

4

2

1.0

0.8

0.6

0.4

0.2

0.1

Voltage Across Output Transistor (V)

8

6

100

Maximum

Specified

Current

8

T

T

θ

0.5ms

1ms

Maximum

Specified

Voltage

RM, AM

SM, BM

5ms

DC

+

(1)

+

(1)

OPA501

R

SC

–

R

SC

+

R

2

R

1

V

IN

V–

V+

G = 1 +

R

2

R

1

NOTE: (1) 10µF Tantalum.

Load

R

0. 65

I

LIMIT

− 0.0437Ω