LM723CHNOPB - NATIONAL SEMICONDUCTOR

LM675

LM675 Power Operational Amplifier

Literature Number: SNOSBP3D

LM675

Power Operational Amplifier

General Description

The LM675 is a monolithic power operational amplifier fea-

turing wide bandwidth and low input offset voltage, making it

equally suitable for AC and DC applications.

The LM675 is capable of delivering output currents in excess

of 3 amps, operating at supply voltages of up to 60V. The

device overload protection consists of both internal current

limiting and thermal shutdown. The amplifier is also internally

compensated for gains of 10 or greater.

Features

n3A current capability

typically 90 dB

n5.5 MHz gain bandwidth product

n8 V/µs slew rate

nWide power bandwidth 70 kHz

n1 mV typical offset voltage

nShort circuit protection

nThermal protection with parole circuit (100% tested)

n16V–60V supply range

nWide common mode range

nInternal output protection diodes

n90 dB ripple rejection

nPlastic power package TO-220

Applications

nHigh performance power op amp

nBridge amplifiers

nMotor speed controls

nServo amplifiers

nInstrument systems

Connection Diagram

TO-220 Power Package (T)

00673901

*The tab is internally connected to pin 3 (−VEE)

Front View

Order Number LM675T

See NS Package T05D

Typical Applications

Non-Inverting Amplifier

00673902

May 1999

LM675 Power Operational Amplifier

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage ±30V

Input Voltage −V

to V

Operating Temperature 0˚C to +70˚C

Storage Temperature −65˚C to +150˚C

Junction Temperature 150˚C

Power Dissipation (Note 2) 30W

Lead Temperature

(Soldering, 10 seconds) 260˚C

ESD rating to be determined.

Electrical Characteristics

=±25V, T

=25˚C unless otherwise specified.

Parameter Conditions Typical Tested Limit Units

Supply Current P

OUT

= 0W 18 50 (max) mA

Input Offset Voltage V

= 0V 1 10 (max) mV

Input Bias Current V

= 0V 0.2 2 (max) µA

Input Offset Current V

= 0V 50 500 (max) nA

Open Loop Gain R

=∞Ω90 70 (min) dB

PSRR ∆V

=±5V 90 70 (min) dB

CMRR V

=±20V 90 70 (min) dB

Output Voltage Swing R

=8Ω±21 ±18 (min) V

Offset Voltage Drift Versus Temperature R

<100 kΩ25 µV/˚C

Offset Voltage Drift Versus Output Power 25 µV/W

Output Power THD = 1%, f

= 1 kHz, R

=8Ω25 20 W

Gain Bandwidth Product f

= 20 kHz, A

VCL

= 1000 5.5 MHz

Max Slew Rate 8 V/µs

Input Common Mode Range ±22 ±20 (min) V

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which

guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit

is given, however, the typical value is a good indication of device performance.

Note 2: Assumes TAequal to 70˚C. For operation at higher tab temperatures, the LM675 must be derated based on a maximum junction temperature of 150˚C.

Typical Applications

Generating a Split Supply From a Single Supply

00673903

VS=±8V →±30V

LM675

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Typical Performance Characteristics

THD vs Power Output

Input Common Mode

Range vs Supply Voltage

00673910 00673911

Supply Current vs

Supply Voltage PSRR vs Frequency

00673912 00673913

Device Dissipation vs

Ambient Temperature†

Current Limit vs

Output Voltage*

00673914

†θINTERFACE = 1˚ C/W

See Application Hints.

00673915

*VS=±25V

LM675

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Typical Performance Characteristics (Continued)

vs Supply Voltage

Output Voltage

Swing vs Supply Voltage

00673916

00673917

LM675

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Schematic Diagram

00673905

LM675

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Application Hints

STABILITY

The LM675 is designed to be stable when operated at a

closed-loop gain of 10 or greater, but, as with any other

high-current amplifier, the LM675 can be made to oscillate

under certain conditions. These usually involve printed cir-

cuit board layout or output/input coupling.

When designing a printed circuit board layout, it is important

to return the load ground, the output compensation ground,

and the low level (feedback and input) grounds to the circuit

board ground point through separate paths. Otherwise, large

currents flowing along a ground conductor will generate

voltages on the conductor which can effectively act as sig-

nals at the input, resulting in high frequency oscillation or

excessive distortion. It is advisable to keep the output com-

pensation components and the 0.1 µF supply decoupling

capacitors as close as possible to the LM675 to reduce the

effects of PCB trace resistance and inductance. For the

same reason, the ground return paths for these components

should be as short as possible.

Occasionally, current in the output leads (which function as

antennas) can be coupled through the air to the amplifier

input, resulting in high-frequency oscillation. This normally

happens when the source impedance is high or the input

leads are long. The problem can be eliminated by placing a

small capacitor (on the order of 50 pF to 500 pF) across the

circuit input.

Most power amplifiers do not drive highly capacitive loads

well, and the LM675 is no exception. If the output of the

LM675 is connected directly to a capacitor with no series

resistance, the square wave response will exhibit ringing if

the capacitance is greater than about 0.1 µF. The amplifier

can typically drive load capacitances up to 2 µF or so without

oscillating, but this is not recommended. If highly capacitive

loads are expected, a resistor (at least 1Ω) should be placed

in series with the output of the LM675. A method commonly

employed to protect amplifiers from low impedances at high

frequencies is to couple to the load through a 10Ωresistor in

parallel witha5µHinductor.

CURRENT LIMIT AND SAFE OPERATING AREA

(SOA) PROTECTION

A power amplifier’s output transistors can be damaged by

excessive applied voltage, current flow, or power dissipation.

The voltage applied to the amplifier is limited by the design of

the external power supply, while the maximum current

passed by the output devices is usually limited by internal

circuitry to some fixed value. Short-term power dissipation is

usually not limited in monolithic operational power amplifiers,

and this can be a problem when driving reactive loads, which

may draw large currents while high voltages appear on the

output transistors. The LM675 not only limits current to

around 4A, but also reduces the value of the limit current

when an output transistor has a high voltage across it.

When driving nonlinear reactive loads such as motors or

loudspeakers with built-in protection relays, there is a possi-

bility that an amplifier output will be connected to a load

whose terminal voltage may attempt to swing beyond the

power supply voltages applied to the amplifier. This can

cause degradation of the output transistors or catastrophic

failure of the whole circuit. The standard protection for this

type of failure mechanism is a pair of diodes connected

between the output of the amplifier and the supply rails.

These are part of the internal circuitry of the LM675, and

needn’t be added externally when standard reactive loads

are driven.

THERMAL PROTECTION

The LM675 has a sophisticated thermal protection scheme

to prevent long-term thermal stress to the device. When the

temperature on the die reaches 170˚C, the LM675 shuts

down. It starts operating again when the die temperature

drops to about 145˚C, but if the temperature again begins to

rise, shutdown will occur at only 150˚C. Therefore, the de-

vice is allowed to heat up to a relatively high temperature if

the fault condition is temporary, but a sustained fault will limit

the maximum die temperature to a lower value. This greatly

reduces the stresses imposed on the IC by thermal cycling,

which in turn improves its reliability under sustained fault

conditions. This circuitry is 100% tested without a heat sink.

Since the die temperature is directly dependent upon the

heat sink, the heat sink should be chosen for thermal resis-

tance low enough that thermal shutdown will not be reached

during normal operaton. Using the best heat sink possible

within the cost and space constraints of the system will

improve the long-term reliability of any power semiconductor.

POWER DISSIPATION AND HEAT SINKING

The LM675 should always be operated with a heat sink,

even though at idle worst case power dissipation will be only

1.8W (30 mA x 60V) which corresponds to a rise in die

temperature of 97˚C above ambient assuming θ

= 54˚C/W

for a TO-220 package. This in itself will not cause the thermal

protection circuitry to shut down the amplifier when operating

at room temperature, but a mere 0.9W of additional power

dissipation will shut the amplifier down since T

will then

increase from 122˚C (97˚C + 25˚C) to 170˚C.

In order to determine the appropriate heat sink for a given

application, the power dissipation of the LM675 in that appli-

cation must be known. When the load is resistive, the maxi-

mum average power that the IC will be required to dissipate

is approximately:

where V

is the total power supply voltage across the

LM675, R

is the load resistance and P

is the quiescent

power dissipation of the amplifier. The above equation is

only an approximation which assumes an “ideal” class B

output stage and constant power dissipation in all other parts

of the circuit. As an example, if the LM675 is operated on a

50V power supply with a resistive load of 8Ω, it can develop

up to 19W of internal power dissipation. If the die tempera-

ture is to remain below 150˚C for ambient temperatures up to

70˚C, the total junction-to-ambient thermal resistance must

be less than

Using θ

= 2˚C/W, the sum of the case-to-heat sink inter-

face thermal resistance and the heat-sink-to-ambient ther-

mal resistance must be less than 2.2˚C/W. The case-to-heat-

sink thermal resistance of the TO-220 package varies with

the mounting method used. A metal-to-metal interface will be

about 1˚C/W if lubricated, and about 1.2˚C/W if dry. If a mica

insulator is used, the thermal resistance will be about

LM675

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Application Hints (Continued)

1.6˚C/W lubricated and 3.4˚C/W dry. For this example, we

assume a lubricated mica insulator between the LM675 and

the heat sink. The heat sink thermal resistance must then be

less than

4.2˚C/W − 2˚C/W − 1.6˚C/W = 0.6˚C/W.

This is a rather large heat sink and may not be practical in

some applications. If a smaller heat sink is required for

reasons of size or cost, there are two alternatives. The

maximum ambient operating temperature can be restricted

to 50˚C (122˚F), resulting in a 1.6˚C/W heat sink, or the heat

sink can be isolated from the chassis so the mica washer is

not needed. This will change the required heat sink to a

1.2˚C/W unit if the case-to-heat-sink interface is lubricated.

The thermal requirements can become more difficult when

an amplifier is driving a reactive load. For a given magnitude

of load impedance, a higher degree of reactance will cause

a higher level of power dissipation within the amplifier. As a

general rule, the power dissipation of an amplifier driving a

60˚ reactive load will be roughly that of the same amplifier

driving the resistive part of that load. For example, some

reactive loads may at some frequency have an impedance

with a magnitude of 8Ωand a phase angle of 60˚. The real

part of this load will then be 8Ωx cos 60˚ or 4Ω, and the

amplifier power dissipation will roughly follow the curve of

power dissipation with a 4Ωload.

Typical Applications

Non-Inverting Unity Gain Operation

00673906

Inverting Unity Gain Operation

00673907

LM675

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Typical Applications (Continued)

Servo Motor Control

00673908

High Current Source/Sink

00673909

IOUT =V

IN x 2.5 amps/volt

i.e. IOUT = 1A when VIN = 400 mV

Trim pot for max ROUT

LM675

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Physical Dimensions inches (millimeters) unless otherwise noted

TO-220 Power Package (T)

Order Number LM675T

NS Package T05D

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves

the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR

CORPORATION. As used herein:

1. Life support devices or systems are devices or systems

which, (a) are intended for surgical implant into the body, or

(b) support or sustain life, and whose failure to perform when

properly used in accordance with instructions for use

provided in the labeling, can be reasonably expected to result

in a significant injury to the user.

2. A critical component is any component of a life support

device or system whose failure to perform can be reasonably

expected to cause the failure of the life support device or

system, or to affect its safety or effectiveness.

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Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned

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www.national.com

LM675 Power Operational Amplifier

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