10

1

0.1

1

10

100

|V – V

| (V)

S

OUT

T = +25°C

T = +85°C

C

C

AP, AM

BM, SM

T

C = +125°C

“M” Package only

θHS =

TCASE – TAMBIENT

PD (max)

OPA541

SBOS153B – SEPTEMBER 2000 – REVISED JANUARY 2016

www.ti.com

Application Information (continued)

(3)

Commercially available heat sinks often specify their thermal resistance. These ratings are often suspect,

however, because they depend greatly on the mounting environment and air flow conditions. Actual thermal

performance should be verified by measuring the case temperature under the required load and environmental

conditions.

No insulating hardware is required when using the TO-3 package. Because mica and other similar insulators

typically add approximately 0.7°C/W thermal resistance, their elimination significantly improves thermal

performance. See Related Documentation for further details on heat sinking. On the power plastic package, the

metal tab may have a high or low impedance connection to –VS. The case must be allowed to float, and likely

assumes the potential of –VS. Current must not be conducted through the case.

8.1.3 Safe Operating Area

The safe operating area (SOA) plot provides comprehensive information on the power-handling abilities of the

OPA541. The SOA shows the allowable output current as a function of the voltage across the conducting output

transistor (see Figure 11). This voltage is equal to the power supply voltage minus the output voltage. For

example, as the amplifier output swings near the positive power supply voltage, the voltage across the output

transistor decreases and the device can safely provide large output currents demanded by the load. Short circuit

protection requires evaluation of the SOA. When the amplifier output is shorted to ground, the full power supply

voltage is impressed across the conducting output transistor. The current limit must be set to a value which is

safe for the power supply voltage used. For instance, with VS ±35 V, a short to ground would force 35 V across

the conducting power transistor. A current limit of 1.8 A would be safe.

Figure 11. Safe Operating Area

Reactive or EMF-generating loads such as DC motors can present difficult SOA requirements. With a purely

reactive load, output voltage and load current are 90° out of phase. Thus, peak output current occurs when the

output voltage is zero and the voltage across the conducting transistor is equal to the full power supply voltage.

See Related Documentation for further information on evaluating SOA.

8.1.4 Replacing Hybrid Power Amplifiers

The OPA541 can be used in applications currently using various hybrid power amplifiers, including the OPA501,

OPA511, OPA512, and 3573. Of course, the application must be evaluated to assure that the output capability

and other performance attributes of the OPA541 meet the necessary requirements. These hybrid power

amplifiers use two current limit resistors to independently set the positive and negative current limit value.

Because the OPA541 uses only one current limit resistor to set both the positive and negative current limit, only

one resistor such as Figure 12 need be installed. If installed, the resistor connected to pin 2 (TO-3 package) is

superfluous, but is does no harm.

10

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