LM675Power Operational AmplifierGeneral DescriptionThe LM675 is a monolithic power operational amplifier fea-turing wide bandwidth and low input offset voltage, making itequally suitable for AC and DC applications.The LM675 is capable of delivering output currents in excessof 3 amps, operating at supply voltages of up to 60V. Thedevice overload protection consists of both internal currentlimiting and thermal shutdown. The amplifier is also internallycompensated for gains of 10 or greater.

Featuresn 3A current capabilityn AVO typically 90 dBn 5.5 MHz gain bandwidth productn 8 V/s slew raten Wide power bandwidth 70 kHz

n 1 mV typical offset voltagen Short circuit protectionn Thermal protection with parole circuit (100% tested)n 16V60V supply rangen Wide common mode rangen Internal output protection diodesn 90 dB ripple rejectionn Plastic power package TO-220

Applicationsn High performance power op ampn Bridge amplifiersn Motor speed controlsn Servo amplifiersn Instrument systems

Connection DiagramTO-220 Power Package (T)

00673901*The tab is internally connected to pin 3 (VEE)

Front ViewOrder Number LM675TSee NS Package T05D

Typical ApplicationsNon-Inverting Amplifier

00673902

May 1999LM

675Pow

erOperationalAmplifier

2004 National Semiconductor Corporation DS006739 www.national.com

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 30VInput Voltage VEE to VCCOperating Temperature 0C to +70C

Storage Temperature 65C to +150CJunction Temperature 150CPower Dissipation (Note 2) 30WLead Temperature

(Soldering, 10 seconds) 260CESD rating to be determined.

Electrical CharacteristicsVS=25V, TA=25C unless otherwise specified.

Parameter Conditions Typical Tested Limit UnitsSupply Current POUT = 0W 18 50 (max) mAInput Offset Voltage VCM = 0V 1 10 (max) mVInput Bias Current VCM = 0V 0.2 2 (max) AInput Offset Current VCM = 0V 50 500 (max) nAOpen Loop Gain RL = 90 70 (min) dBPSRR VS = 5V 90 70 (min) dBCMRR VIN = 20V 90 70 (min) dBOutput Voltage Swing RL = 8 21 18 (min) VOffset Voltage Drift Versus Temperature RS < 100 k 25 V/COffset Voltage Drift Versus Output Power 25 V/WOutput Power THD = 1%, fO = 1 kHz, RL = 8 25 20 WGain Bandwidth Product fO = 20 kHz, AVCL = 1000 5.5 MHzMax Slew Rate 8 V/sInput 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 isfunctional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions whichguarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limitis given, however, the typical value is a good indication of device performance.Note 2: Assumes TA equal to 70C. For operation at higher tab temperatures, the LM675 must be derated based on a maximum junction temperature of 150C.

Typical ApplicationsGenerating a Split Supply From a Single Supply

00673903VS = 8V 30V

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Typical Performance Characteristics

THD vs Power OutputInput Common Mode

Range vs Supply Voltage

00673910 00673911

Supply Current vsSupply Voltage PSRR vs Frequency

00673912 00673913

Device Dissipation vsAmbient Temperature

Current Limit vsOutput Voltage*

00673914 INTERFACE = 1 C/WSee Application Hints.

00673915*VS = 25V

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Typical Performance Characteristics (Continued)

IB vs Supply VoltageOutput Voltage

Swing vs Supply Voltage

00673916

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Application HintsSTABILITYThe LM675 is designed to be stable when operated at aclosed-loop gain of 10 or greater, but, as with any otherhigh-current amplifier, the LM675 can be made to oscillateunder certain conditions. These usually involve printed cir-cuit board layout or output/input coupling.When designing a printed circuit board layout, it is importantto return the load ground, the output compensation ground,and the low level (feedback and input) grounds to the circuitboard ground point through separate paths. Otherwise, largecurrents flowing along a ground conductor will generatevoltages on the conductor which can effectively act as sig-nals at the input, resulting in high frequency oscillation orexcessive distortion. It is advisable to keep the output com-pensation components and the 0.1 F supply decouplingcapacitors as close as possible to the LM675 to reduce theeffects of PCB trace resistance and inductance. For thesame reason, the ground return paths for these componentsshould be as short as possible.Occasionally, current in the output leads (which function asantennas) can be coupled through the air to the amplifierinput, resulting in high-frequency oscillation. This normallyhappens when the source impedance is high or the inputleads are long. The problem can be eliminated by placing asmall capacitor (on the order of 50 pF to 500 pF) across thecircuit input.Most power amplifiers do not drive highly capacitive loadswell, and the LM675 is no exception. If the output of theLM675 is connected directly to a capacitor with no seriesresistance, the square wave response will exhibit ringing ifthe capacitance is greater than about 0.1 F. The amplifiercan typically drive load capacitances up to 2 F or so withoutoscillating, but this is not recommended. If highly capacitiveloads are expected, a resistor (at least 1) should be placedin series with the output of the LM675. A method commonlyemployed to protect amplifiers from low impedances at highfrequencies is to couple to the load through a 10 resistor inparallel with a 5 H inductor.

CURRENT LIMIT AND SAFE OPERATING AREA(SOA) PROTECTIONA power amplifiers output transistors can be damaged byexcessive applied voltage, current flow, or power dissipation.The voltage applied to the amplifier is limited by the design ofthe external power supply, while the maximum currentpassed by the output devices is usually limited by internalcircuitry to some fixed value. Short-term power dissipation isusually not limited in monolithic operational power amplifiers,and this can be a problem when driving reactive loads, whichmay draw large currents while high voltages appear on theoutput transistors. The LM675 not only limits current toaround 4A, but also reduces the value of the limit currentwhen an output transistor has a high voltage across it.When driving nonlinear reactive loads such as motors orloudspeakers with built-in protection relays, there is a possi-bility that an amplifier output will be connected to a loadwhose terminal voltage may attempt to swing beyond thepower supply voltages applied to the amplifier. This cancause degradation of the output transistors or catastrophicfailure of the whole circuit. The standard protection for thistype of failure mechanism is a pair of diodes connectedbetween the output of the amplifier and the supply rails.

These are part of the internal circuitry of the LM675, andneednt be added externally when standard reactive loadsare driven.

THERMAL PROTECTIONThe LM675 has a sophisticated thermal protection schemeto prevent long-term thermal stress to the device. When thetemperature on the die reaches 170C, the LM675 shutsdown. It starts operating again when the die temperaturedrops to about 145C, but if the temperature again begins torise, shutdown will occur at only 150C. Therefore, the de-vice is allowed to heat up to a relatively high temperature ifthe fault condition is temporary, but a sustained fault will limitthe maximum die temperature to a lower value. This greatlyreduces the stresses imposed on the IC by thermal cycling,which in turn improves its reliability under sustained faultconditions. This circuitry is 100% tested without a heat sink.Since the die temperature is directly dependent upon theheat sink, the heat sink should be chosen for thermal resis-tance low enough that thermal shutdown will not be reachedduring normal operaton. Using the best heat sink possiblewithin the cost and space constraints of the system willimprove the long-term reliability of any power semiconductor.

POWER DISSIPATION AND HEAT SINKINGThe LM675 should always be operated with a heat sink,even though at idle worst case power dissipation will be only1.8W (30 mA x 60V) which corresponds to a rise in dietemperature of 97C above ambient assuming jA = 54C/Wfor a TO-220 package. This in itself will not cause the thermalprotection circuitry to shut down the amplifier when operatingat room temperature, but a mere 0.9W of additional powerdissipation will shut the amplifier down since TJ will thenincrease from 122C (97C + 25C) to 170C.In order to determine the appropriate heat sink for a givenapplication, 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 dissipateis approximately:

where VS is the total power supply voltage across theLM675, RL is the load resistance and PQ is the quiescentpower dissipation of the amplifier. The above equation isonly an approximation which assumes an ideal class Boutput stage and constant power dissipation in all other partsof the circuit. As an example, if the LM675 is operated on a50V power supply with a resistive load of 8, it can developup to 19W of internal power dissipation. If the die tempera-ture is to remain below 150C for ambient temperatures up to70C, the total junction-to-ambient thermal resistance mustbe less than

Using JC = 2C/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 2.2C/W. The case-to-heat-sink thermal resistance of the TO-220 package varies withthe mounting method used. A metal-to-metal interface will beabout 1C/W if lubricated, and about 1.2C/W if dry. If a micainsulator is used, the thermal resistance will be about

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Application Hints (Continued)1.6C/W lubricated and 3.4C/W dry. For this example, weassume a lubricated mica insulator between the LM675 andthe heat sink. The heat sink thermal resistance must then beless than

4.2C/W 2C/W 1.6C/W = 0.6C/W.This is a rather large heat sink and may not be practical insome applications. If a smaller heat sink is required forreasons of size or cost, there are two alternatives. Themaximum ambient operating temperature can be restrictedto 50C (122F), resulting in a 1.6C/W heat sink, or the heatsink can be isolated from the chassis so the mica washer isnot needed. This will change the required heat sink to a1.2C/W unit if the case-to-heat-sink interface is lubricated.

The thermal requirements can become more difficult whenan amplifier is driving a reactive load. For a given magnitudeof load impedance, a higher degree of reactance will causea higher level of power dissipation within the amplifier. As ageneral rule, the power dissipation of an amplifier driving a60 reactive load will be roughly that of the same amplifierdriving the resistive part of that load. For example, somereactive loads may at some frequency have an impedancewith a magnitude of 8 and a phase angle of 60. The realpart of this load will then be 8 x cos 60 or 4, and theamplifier power dissipation will roughly follow the curve ofpower dissipation with a 4 load.

Typical ApplicationsNon-Inverting Unity Gain Operation

00673906

Inverting Unity Gain Operation

00673907

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Typical Applications (Continued)Servo Motor Control

00673908

High Current Source/Sink

00673909IOUT = VIN x 2.5 amps/volti.e. IOUT = 1A when VIN = 400 mVTrim pot for max ROUT

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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 reservesthe 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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which, (a) are intended for surgical implant into the body, or(b) support or sustain life, and whose failure to perform whenproperly used in accordance with instructions for useprovided in the labeling, can be reasonably expected to resultin a significant injury to the user.

2. A critical component is any component of a life supportdevice or system whose failure to perform can be reasonablyexpected to cause the failure of the life support device orsystem, or to affect its safety or effectiveness.

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LM675

PowerOperationalAm

plifier

LM675General DescriptionFeaturesApplicationsConnection DiagramTypical ApplicationsAbsolute Maximum RatingsElectrical Characteristics Typical ApplicationsTypical Performance CharacteristicsSchematic DiagramApplication HintsSTABILITYCURRENT LIMIT AND SAFE OPERATING AREA (SOA) PROTECTIONTHERMAL PROTECTIONPOWER DISSIPATION AND HEAT SINKING

Typical ApplicationsPhysical Dimensions