LM675 Power Operational Amplifier: Features
LM675 Power Operational Amplifier: Features
LM675 Power Operational Amplifier: Features
1FEATURES
•
2 3A Current Capability
Connection Diagram
• AVO Typically 90 dB
• 5.5 MHz Gain Bandwidth Product
• 8 V/μs Slew Rate
• Wide Power Bandwidth 70 kHz
• 1 mV Typical Offset Voltage
*The tab is internally connected to pin 3
• Short Circuit Protection (−VEE)
• Thermal Protection with Parole Circuit (100% Figure 1. Front View
Tested) TO-220 Power Package (NDH)
• 16V–60V Supply Range See Package Number NDH0005D
• Wide Common Mode Range
• Internal Output Protection Diodes Typical Applications
• 90 dB Ripple Rejection
• Plastic Power Package TO-220
APPLICATIONS
• High Performance Power Op Amp
• Bridge Amplifiers
• Motor Speed Controls
• Servo Amplifiers
• Instrument Systems
DESCRIPTION
The LM675 is a monolithic power operational
amplifier featuring 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. Figure 2. Non-Inverting Amplifier
The amplifier is also internally compensated for gains
of 10 or greater.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2 All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 1999–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
LM675
SNOSBP3E – MAY 1999 – REVISED MARCH 2013 www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
(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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(3) Assumes TA equal to 70°C. For operation at higher tab temperatures, the LM675 must be derated based on a maximum junction
temperature of 150°C.
ELECTRICAL CHARACTERISTICS
VS=±25V, TA=25°C unless otherwise specified.
Parameter Conditions Typical Tested Limit Units
Supply Current POUT = 0W 18 50 (max) mA
Input Offset Voltage VCM = 0V 1 10 (max) mV
Input Bias Current VCM = 0V 0.2 2 (max) μA
Input Offset Current VCM = 0V 50 500 (max) nA
Open Loop Gain RL = ∞Ω 90 70 (min) dB
PSRR ΔVS = ±5V 90 70 (min) dB
CMRR VIN = ±20V 90 70 (min) dB
Output Voltage Swing RL = 8Ω ±21 ±18 (min) V
Offset Voltage Drift Versus Temperature RS < 100 kΩ 25 μV/°C
Offset Voltage Drift Versus Output Power 25 μV/W
Output Power THD = 1%, fO = 1 kHz, RL = 8Ω 25 20 W
Gain Bandwidth Product fO = 20 kHz, AVCL = 1000 5.5 MHz
Max Slew Rate 8 V/μs
Input Common Mode Range ±22 ±20 (min) V
TYPICAL APPLICATIONS
VS = ±8V → ±30V
Figure 4. Figure 5.
Figure 6. Figure 7.
SCHEMATIC DIAGRAM
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 circuit 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 signals at the input, resulting in high frequency oscillation or excessive distortion. It is advisable
to keep the output compensation 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 10Ω resistor in parallel with
a 5 μH inductor.
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 device 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
resistance 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.
where
• VS is the total power supply voltage across the LM675
• RL is the load resistance
• PQ 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 temperature 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 θJC = 2°C/W, the sum of the case-to-heat sink interface thermal resistance and the heat-sink-to-ambient
thermal 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 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. (1)
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 8Ω and a phase angle of 60°. The real part of this load will
then be 8Ω × cos 60° or 4Ω, and the amplifier power dissipation will roughly follow the curve of power dissipation
with a 4Ω load.
Typical Applications
REVISION HISTORY
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MECHANICAL DATA
NDH0005D
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MECHANICAL DATA
NEB0005B
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