∆RCL =

x (T – 25)

–2mV

| ILIM |

(AM, BM, SM)

RCL =

– 0.057

(AP)

RCL =

– 0.02

0.809

| ILIM |

0.813

| ILIM |

OPA541

www.ti.com

SBOS153B – SEPTEMBER 2000 – REVISED JANUARY 2016

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The OPA541 is specified for operation from 8 V to 80 V (±4 V to ±40 V). Specifications apply over the –40°C to

85°C temperature range while the device operates from –40°C to 125°C. Parameters that can exhibit significant

variance with regard to operating voltage or temperature are presented in Typical Characteristics.

8.1.1 Current Limit

Internal current limit circuitry is controlled by a single external resistor, RCL. Output load current flows through this

external resistor. The current limit is activated when the voltage across this resistor is approximately a base-

emitter turnon voltage. The value of the current limit resistor is calculated by Equation 1.

(1)

Because of the internal structure of the OPA541, the actual current limit depends on whether current is positive

or negative. The above RCL gives an average value. For a given RCL, +IOUT will actually be limited at

approximately 10% below the expected level, while –IOUT will be limited approximately 10% above the expected

level.

The current limit value decreases with increasing temperature due to the temperature coefficient of a base-

emitter junction voltage. Similarly, the current limit value increases at low temperatures. Current limit versus

resistor value and temperature effects are shown in Typical Characteristics. Approximate values for RCL at other

temperatures may be calculated by adjusting RCL shown in Equation 2.

(2)

The adjustable current limit can be set to provide protection from short circuits. The safe short-circuit current

depends on power supply voltage. See the discussion on safe operating area in Safe Operating Area to

determine the proper current limit value.

Because the full load current flows through RCL, it must be selected for sufficient power dissipation. For a 5-A

current limit on the TO-3 package, the formula yields an RCL of 0.105 Ω (0.143 Ω on the power plastic package

due to different internal resistances). A continuous 5 A through 0.105

Ω would require an RCL that can dissipate

2.625 W.

Sinusoidal outputs create dissipation according to RMS load current. For the same RCL, AC peaks would still be

limited to 5 A, but RMS current would be 3.5 A, and a current-limiting resistor with a lower power rating could be

used. Some applications (such as voice amplification) are assured of signals with much lower duty cycles,

allowing a current resistor with a low power rating. Wire-wound resistors may be used for RCL. Some wire-wound

resistors, however, have excessive inductance and may cause loop-stability problems. Evaluate circuit

performance with the resistor type planned for production to assure proper circuit operation.

8.1.2 Heat Sinking

Power amplifiers are rated by case temperature, not ambient temperature as with signal operational amplifiers.

Sufficient heat sinking must be provided to keep the case temperature within rated limits for the maximum

ambient temperature and power dissipation. The thermal resistance of the heat sink required may be calculated

by Equation 3.

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