OPA541 High Power Monolithic Operational Amplifier
- SBOS153B September 2000 – January 2016 OPA541
  
  PRODUCTION DATA.

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DATA SHEET

OPA541 High Power Monolithic Operational Amplifier

1 Features

Power Supplies to ±40 V
Output Current to 10-A Peak
Programmable Current Limit
Industry-Standard Pinout
FET Input
TO-3 and Low-Cost Power Plastic Packages

2 Applications

Motor Drivers
Servo Amplifiers
Synchro Excitation
Audio Amplifiers
Programmable Power Supplies

3 Description

The OPA541 device is a power-operational amplifier capable of operation from power supplies up to
±40 V, and delivering continuous output currents up to 5 A. Internal current-limit circuitry can be user-programmed with a single external resistor, protecting the amplifier and load from fault conditions. The OPA541 devices fabricated are using a proprietary bipolar and FET process.

The OPA541 uses a single current-limit resistor to set both the positive and negative current limits. Applications currently using hybrid power amplifiers requiring two current-limit resistors do need not to be modified.

The OPA541 is available in an 11-pin power plastic package and an industry-standard 8-pin TO-3 hermetic package. The power plastic pachage has a copper-lead frame to maximize heat transfer. The TO-3 package is isolated from all circuitry, allowing it to be mounted directly to a heat sink without special insulators.

Device Information⁽¹⁾

PART NUMBER	PACKAGE	BODY SIZE (NOM)
OPA541	TO-220 (11)	10.70 mm × 20.02 mm

For all available packages, see the orderable addendum at the end of the data sheet.

Simplified Schematic

4 Revision History

Changes from A Revision (August 2006) to B Revision

Added ESD Ratings table, Thermal Information tables, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section Go
Deleted THERMAL RESISTANCE section from Electrical CharacteristicsGo

5 Pin Configuration and Functions

KV Package

11-Pin TO-220

Top View

Pin Functions

PIN		I/O	DESCRIPTION
NO.	NAME	I/O	DESCRIPTION
1	+In	I	+Input
2	–In	I	-Input
3	–Vs	–	Negative power supply
4	–Vs	–	Negative power supply
5	Output	O	Output
6	NC	–	No internal connection
7	Output	O	Output
8	Current Sense	I	Current sensing input pin
9	NC	–	No internal connection
10	+Vs	–	Positive power supply
11	+Vs	–	Positive power supply

6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted) ⁽¹⁾

		MIN	MAX	UNIT
Supply voltage, +V_Sto –V_S			80	V
Output current		See SOA, Figure 11
Power dissipation, Internal⁽²⁾			125	W
Input voltage, differential			+V_S
Input voltage, common-mode			+V_S
Temperature, pin solder, 10 s			300	°C
Junction temperature⁽²⁾			150	°C
Operating temperature (case)	AP	–40	85	°C
	AM, BM, SM	–55	125
	AP	–25	85
Storage temperature, T_stg	AM, BM, SM	–65	150	°C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) Long term operation at the maximum junction temperature will result in reduced product life. Derate internal power dissipation to achieve high MTTF.

6.2 ESD Ratings

			VALUE	UNIT
V_(ESD)	Electrostatic discharge	Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001⁽¹⁾	±2000	V
V_(ESD)	Electrostatic discharge	Charged-device model (CDM), per JEDEC specification JESD22-C101⁽²⁾	±250	V

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)

		MIN	MAX	UNIT
Supply Voltage (V+ – V–)		10 (±5)	80 (±40)	V
Specified temperature		–40	125	°C

6.4 Thermal Information

THERMAL METRIC⁽¹⁾		OPA541		UNIT
		KV (TO-220)	LMF (TO-3)
		11 PINS	8 PINS
R_θJA	Junction-to-ambient thermal resistance	21.5	—	°C/W
R_θJC(top)	Junction-to-case (top) thermal resistance	17.4	—	°C/W
R_θJB	Junction-to-board thermal resistance	9.2	—	°C/W
ψ_JT	Junction-to-top characterization parameter	1.5	—	°C/W
ψ_JB	Junction-to-board characterization parameter	9.2	—	°C/W
R_θJC(bot)	Junction-to-case (bottom) thermal resistance	0.1	3	°C/W

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report, SPRA953.

6.5 Electrical Characteristics

At T_C= 25°C and V_S = ±35 VDC, unless otherwise noted.

PARAMETER		TEST CONDITIONS		MIN	TYP	MAX	UNIT
INPUT OFFSET VOLTAGE
V_OS	Input offset voltage	Specified temperature range V_S = ±10 V to ±V_MAX	OPA541AM/AP		±2	±10	mV
	Input offset voltage		OPA541BM/SM		±0.1	±1	mV
	vs temperature		OPA541AM/AP		±20	±40	µV/°C
	vs temperature		OPA541BM/SM		±15	±30	µV/°C
	vs supply voltage		OPA541AM/AP, OPA541BM/SM		±2.5	±10	µV/V
	vs power		OPA541AM/AP, OPA541BM/SM		±20	±60	µV/W
I_B	Input bias current				4	50	pA
I_OS	Input offset current				±1	±30	pA
I_OS	Input offset current	Specified temperature range				5	nA
INPUT CHARACTERISTICS
	Common-mode voltage range	Specified temperature range		±(\|V_S\| – 6)	±(\|V_S\| – 3)		V
	Common-mode rejection	V_CM = (\|±V_S\| – 6 V)		95	113		dB
	Input capacitance				5		pF
	Input impedance, DC				1		TΩ
GAIN CHARACTERISTICS
	Open-loop gain at 10 Hz	R_L = 6 Ω		90	97		dB
	Gain-bandwidth product				1.6		MHz
OUTPUT
	Voltage swing	I_O = 5 A, continuous		±(\|V_S\| – 5.5)	±(\|V_S\| – 4.5)		V
		I_O = 2 A		±(\|V_S\| – 4.5)	±(\|V_S\| – 3.6)
		I_O = 0.5 A		±(\|V_S\| – 4)	±(\|V_S\| – 3.2)
	Peak current			9	10		A
AC PERFORMANCE
	Slew rate			6	10		V/µs
	Power bandwidth	R_L = 8 Ω, V_O = 20 Vrms		45	55		kHz
	Settling time to 0.1%	2-V Step			2		µs
	Capacitive load	Specified temperature range, G = 1		3.3			nF
	Capacitive load	Specified temperature range, G > 10				SOA⁽¹⁾	nF
	Phase margin	Specified temperature range, R_L = 8 Ω			40		°C
±V_S	Power supply voltage	Specified temperature range		±10	±30	±35	V
	Quiescent current				20	25	mA
T_CASE	Temperature range	AM, BM, AP		–25		85	°C
T_CASE	Temperature range	OPA541BM/SM		–55		125	°C

(1) SOA is the Safe Operating Area shown in Figure 11.

6.6 Typical Characteristics

At T_A = 25°C, V_S = ±35 VDC, unless otherwise noted.

Figure 1. Input Bias Current vs Temperature

Figure 3. Normalized Quiescent Current vs Total Power Supply Voltage

Figure 5. Voltage Noise Density vs Frequency

Figure 7. Current Limit vs Resistance Limit

Figure 9. Common-Mode Rejection vs Frequency

Figure 2. Open-Loop Gain and Phase vs Frequency

Figure 4. Output Voltage Swing vs Output Current

Figure 6. Total Harmonic Distortion + Noise vs Frequency

Figure 8. Current Limit vs Resistance Limit vs Temperature

Figure 10. Dynamic Response

7 Detailed Description

7.1 Overview

The OPA541 uses a JFET input stage, followed by a main voltage gain stage, and a class A/B high current output stage.

7.2 Functional Block Diagram

OPA541 OPA541_Functional_Block_Diagram_sbos153.gif

7.3 Feature Description

The OPA541 JFET input stage reduces circuit loading and input bias currents. The class A/B high current output stage incorporates temperature compensated biasing to reduce crossover distortion. The output stage also includes a user settable current limit for amplifier and circuit protection.

7.4 Device Functional Modes

The OPA541 has a single functional mode. The OPA541 is operational when the power supply voltage exceeds 10 V (±5 V) and less than 80 V (±40 V).

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, R_CL. 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.

Equation 1. OPA541 sbos153_eq1.gif

Because of the internal structure of the OPA541, the actual current limit depends on whether current is positive or negative. The above R_CL gives an average value. For a given R_CL, +I_OUT will actually be limited at approximately 10% below the expected level, while –I_OUT 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 R_CL at other temperatures may be calculated by adjusting R_CL shown in Equation 2.

Equation 2. OPA541 sbos153_eq2.gif

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 R_CL, it must be selected for sufficient power dissipation. For a 5-A current limit on the TO-3 package, the formula yields an R_CL 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 R_CL that can dissipate 2.625 W.

Sinusoidal outputs create dissipation according to RMS load current. For the same R_CL, 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 R_CL. 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.

Equation 3. OPA541 sbos153_eq3.gif

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 –V_S. The case must be allowed to float, and likely assumes the potential of –V_S. 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 V_S ±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.

Figure 12. Isolating Capacitive Loads

Because one resistor carries the current previously carried by two, the resistor may require a high power rating. Minor adjustments may be required in the resistor value to achieve the same current limit value. Often, however, the change in current limit value when changing models is small compared to its variation over temperature. Many applications can use the same current limit resistor.

8.2 Typical Applications

8.2.1 Clamping Output for EMF-Generating Loads

OPA541 clamping_output_emf_gen_loads_rev.gif

Figure 13. Clamping Output for EMF-Generating Loads

8.2.1.1 Design Requirements

Motor drive with reversal requiring output clamping
20-V motor
1-Ω DC resistance
10-µH inductance
40°C maximum ambient temperature

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Power Supply Requirements

Select the power supply based on the requirement to achieve a ±20-V output with up to a 5-A load. The maximum value for output voltage swing at 5-A is approximately within 4 V of either rail and ±25. These supplies provide sufficient output swing.

8.2.1.2.2 Current Limit and SOA (Safe Operating Area)

Set the current limit to the highest possible value for the application which generally corresponds to a short circuit on the output. In this application this corresponds to 25-V stress on the output device and examination of the SOA (Safe Operating Area) graph in Figure 11 indicates that a 5-A current limit is within the 25°C SOA.

8.2.1.2.3 Heat Sinking

Short circuit conditions at 5 A and 25 V must support 125 W of dissipation up to the 40°C ambient requirements of the application. This indicates the need for a heatsink with a R_θHA < 0.68°C/W, such as an Waekfield-Vette 345 series.

8.2.1.3 Application Curve

The scope trace in Figure 14 depicts a motor reversal of a 20-V motor being driven by an OPA541 powered by ±25 V. This motor has 1 Ω of DC resistance and 10 µH of inductance.

NOTE

At the beginning of the reversal the motor inductance results in an overshoot up to the supply rail. This overshoot is clamped by the external fast recovery diodes. While the current shown exceeds the 5-A current limit, this current is actually flowing in the flyback diodes.

OPA541 OPA541_app_transient_rev3_sbos153.gif

Figure 14. Transient Response

8.2.2 Paralleled Operation, Extended SOA

Parallel operation is often used to increase output current or wattage. However, due to their low output impedance, power operational amplifiers cannot be connected in parallel without modifying the circuits. Figure 15 shows one method of doing this. The upper amplifier is a master, configured as required to satisfy the circuit function, has a small sense resistor inside its feedback loop. The slave amplifier is a unity gain buffer. Thus, the output voltages of the two amplifiers are equal. If the two sense resistors connected to the load are equal, the amplifiers share current equally. More slaves may be added as desired. The additional resistor and capacitor on the slave enhance stability.

Figure 15. Paralleled Operation, Extended SOA

8.2.2.1 Design Requirements

Design requirements for the parallel connection in Figure 15 are shown here. The maximum current available from a single OPA541 cannot exceed 10 A:

Gain from input to output of –10
Current capability of > 15 A
Short to ground on ±15-V supply rails at 25°C case temperature

8.2.3 Programmable Voltage Source

The programmable voltage source of Figure 16 uses the OPA541 as a current-to-voltage converter for a current output DAC (digital-to-analog converter). The diodes clamp any differential input voltages to safe levels for the OPA541. The OPA541 provides the gain to produce the desired output.

Figure 16. Programmable Voltage Source

8.2.3.1 Design Requirements

Design requirements for Figure 16:

Convert 0 to –2-mA current input to 0-V to 50-V output voltage
Current capability of > 2.5 A
Protection of current output DAC during fast slew

8.2.4 16-Bit Programmable Voltage Source

The 16-bit voltage source achieves its precision by using an OPA27 along with precision resistors in a feedback path that provides high overall accuracy.

Figure 17. 16-Bit Programmable Voltage Source

8.2.4.1 Design Requirements

Design requirements for the programmable voltage source shown in Figure 17:

±30-V output programmable to 16-bit resolution
> ±1.5-A current capability
< 500-μV offset at zero output
linearity error less than ±0.0015%
differential linearity error less than ±0.003%