LM1875
www.ti.com
SNAS524A –MAY 2004–REVISED MAY 2004
LM1875 20W Audio Power Amplifier
Check for Samples: LM1875
1FEATURES DESCRIPTION
The LM1875 is a monolithic power amplifier offering
2• Up to 30 Watts Output Power very low distortion and high quality performance for
• AVO Typically 90 dB consumer audio applications.
• Low Distortion: 0.015%, 1 kHz, 20 W The LM1875 delivers 20 watts into a 4Ωor 8Ωload
• Wide Power Bandwidth: 70 kHz on ±25V supplies. Using an 8Ωload and ±30V
• Protection for AC and DC Short Circuits to supplies, over 30 watts of power may be delivered.
The amplifier is designed to operate with a minimum
Ground of external components. Device overload protection
• Thermal Protection with Parole Circuit consists of both internal current limit and thermal
• High Current Capability: 4A shutdown.
• Wide Supply Range 16V-60V The LM1875 design takes advantage of advanced
• Internal Output Protection Diodes circuit techniques and processing to achieve
extremely low distortion levels even at high output
• 94 dB Ripple Rejection power levels. Other outstanding features include high
• Plastic Power Package TO-220 gain, fast slew rate and a wide power bandwidth,
large output voltage swing, high current capability,
APPLICATIONS and a very wide supply range. The amplifier is
• High Performance Audio Systems internally compensated and stable for gains of 10 or
greater.
• Bridge Amplifiers
• Stereo Phonographs
• Servo Amplifiers
• Instrument Systems
Connection Diagram
Figure 1. NDH0005D, KC0005A,
NEB0005E, NEB0005B,
Front View
1Please 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.
2All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 2004, 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.
LM1875
SNAS524A –MAY 2004–REVISED MAY 2004
www.ti.com
Typical Applications
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.
Absolute Maximum Ratings(1)
Supply Voltage 60V
Input Voltage −VEE to VCC
Storage Temperature −65°C to + 150°C
Junction Temperature 150°C
(Soldering, 10 seconds) 260°C
Lead Temperature θJC 3°C
θJA 73°C
(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.
2Submit Documentation Feedback Copyright © 2004, Texas Instruments Incorporated
Product Folder Links: LM1875
LM1875
www.ti.com
SNAS524A –MAY 2004–REVISED MAY 2004
Electrical Characteristics
VCC=+25V, −VEE=−25V, TAMBIENT=25°C, RL=8Ω, AV=20 (26 dB), fo=1 kHz, unless otherwise specified.
Parameter Conditions Typical Tested Limits Units
Supply Current POUT=0W 70 100 mA
Output Power(1) THD=1% 25 W
THD(1) POUT=20W, fo=1 kHz 0.015 %
POUT=20W, fo=20 kHz 0.05 0.4 %
POUT=20W, RL=4Ω, fo=1 kHz 0.022 %
POUT=20W, RL=4Ω, fo=20 kHz 0.07 0.6 %
Offset Voltage ±1 ±15 mV
Input Bias Current ±0.2 ±2 μA
Input Offset Current 0 ±0.5 μA
Gain-Bandwidth Product fo=20 kHz 5.5 MHz
Open Loop Gain DC 90 dB
PSRR VCC, 1 kHz, 1 Vrms 95 52 dB
VEE, 1 kHz, 1 Vrms 83 52 dB
Max Slew Rate 20W, 8Ω, 70 kHz BW 8 V/μs
Current Limit VOUT = VSUPPLY −10V 4 3 A
Equivalent Input Noise Voltage RS=600Ω, CCIR 3 μVrms
(1) Assumes the use of a heat sink having a thermal resistance of 1°C/W and no insulator with an ambient temperature of 25°C. Because
the output limiting circuitry has a negative temperature coefficient, the maximum output power delivered to a 4Ωload may be slightly
reduced when the tab temperature exceeds 55°C.
Typical Applications For Single Supply Operation
Figure 2.
Copyright © 2004, Texas Instruments Incorporated Submit Documentation Feedback 3
Product Folder Links: LM1875
LM1875
SNAS524A –MAY 2004–REVISED MAY 2004
www.ti.com
Typical Performance Characteristics
THD vs Power Output THD vs Frequency
Figure 3. Figure 4.
Power Output vs Supply Supply Current vs Supply
Voltage Voltage
Figure 5. Figure 6.
PSRR vs Frequency Device Dissipation vs Ambient Temperature†
†φINTERFACE = 1°C/W.
See Application Hints.
Figure 7. Figure 8.
4Submit Documentation Feedback Copyright © 2004, Texas Instruments Incorporated
Product Folder Links: LM1875
LM1875
www.ti.com
SNAS524A –MAY 2004–REVISED MAY 2004
Typical Performance Characteristics (continued)
Power Dissipation vs Power Output Power Dissipation vs Power Output
Figure 9. Figure 10.
IOUT vs VOUT-Current Limit/
Safe Operating Area Boundary Open Loop Gain and Phase vs Frequency
Thermal shutdown with infinite heat sink
Thermal shutdown with 1°C/W heat sink
Figure 11. Figure 12.
Input Bias Current vs Supply Voltage
Figure 13.
Copyright © 2004, Texas Instruments Incorporated Submit Documentation Feedback 5
Product Folder Links: LM1875
LM1875
www.ti.com
SNAS524A –MAY 2004–REVISED MAY 2004
APPLICATION HINTS
STABILITY
The LM1875 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 LM1875 can be made to oscillate under certain conditions. These usually involve
printed circuit board layout or output/input coupling.
Proper layout of the printed circuit board is very important. While the LM1875 will be stable when installed in a
board similar to the ones shown in this data sheet, it is sometimes necessary to modify the layout somewhat to
suit the physical requirements of a particular application. When designing a different 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 LM1875 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 LM1875 is no exception. If the output of
the LM1875 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 LM1875. A method commonly employed to protect
amplifiers from low impedances at high frequencies is to couple to the load through a 10Ωresistor in parallel with
a 5 μH inductor.
DISTORTION
The preceding suggestions regarding circuit board grounding techniques will also help to prevent excessive
distortion levels in audio applications. For low THD, it is also necessary to keep the power supply traces and
wires separated from the traces and wires connected to the inputs of the LM1875. This prevents the power
supply currents, which are large and nonlinear, from inductively coupling to the LM1875 inputs. Power supply
wires should be twisted together and separated from the circuit board. Where these wires are soldered to the
board, they should be perpendicular to the plane of the board at least to a distance of a couple of inches. With a
proper physical layout, THD levels at 20 kHz with 10W output to an 8Ωload should be less than 0.05%, and less
than 0.02% at 1 kHz.
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 audio 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 LM1875 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
possibility 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 LM1875, and needn't be added externally when standard reactive loads are driven.
Copyright © 2004, Texas Instruments Incorporated Submit Documentation Feedback 7
Product Folder Links: LM1875
LM1875
SNAS524A –MAY 2004–REVISED MAY 2004
www.ti.com
THERMAL PROTECTION
The LM1875 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 LM1875 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.
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 operation. 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 device.
POWER DISSIPATION AND HEAT SINKING
The LM1875 must always be operated with a heat sink, even when it is not required to drive a load. The
maximum idling current of the device is 100 mA, so that on a 60V power supply an unloaded LM1875 must
dissipate 6W of power. The 54°C/W junction-to-ambient thermal resistance of a TO-220 package would cause
the die temperature to rise 324°C above ambient, so the thermal protection circuitry will shut the amplifier down if
operation without a heat sink is attempted.
In order to determine the appropriate heat sink for a given application, the power dissipation of the LM1875 in
that application must be known. When the load is resistive, the maximum average power that the IC will be
required to dissipate is approximately:
where
• VSis the total power supply voltage across the LM1875
• RLis the load resistance
• PQis 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. The curves of “Power Dissipation vs Power Output” give a better
representation of the behavior of the LM1875 with various power supply voltages and resistive loads. As an
example, if the LM1875 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 LM1875 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. [EM00001]The maximum ambient operating temperature
can be reduced 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.
8Submit Documentation Feedback Copyright © 2004, Texas Instruments Incorporated
Product Folder Links: LM1875
LM1875
www.ti.com
SNAS524A –MAY 2004–REVISED MAY 2004
NOTE
When using a single supply, maximum transfer of heat away from the LM1875 can be
achieved by mounting the device directly to the heat sink (tab is at ground potential); this
avoids the use of a mica or other type insulator.
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 (usually
considered to be a worst-case loudspeaker load) will be roughly that of the same amplifier driving the resistive
part of that load. For example, a loudspeaker 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 4Ω, and the amplifier power dissipation will
roughly follow the curve of power dissipation with a 4Ωload.
Component Layouts
Figure 14. Split Supply
Copyright © 2004, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: LM1875
PACKAGE OPTION ADDENDUM
www.ti.com 9-Mar-2013
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package Qty Eco Plan
(2)
Lead/Ball Finish MSL Peak Temp
(3)
Op Temp (°C) Top-Side Markings
(4)
Samples
LM1875T ACTIVE TO-220 NDH 5 45 TBD Call TI Call TI 0 to 70 LM1875T
LM1875T/LB02 ACTIVE TO-220 NEB 5 45 TBD Call TI Call TI LM1875T
LM1875T/LB03 ACTIVE TO-220 NDH 5 45 TBD Call TI Call TI LM1875T
LM1875T/LB05 ACTIVE TO-220 NEB 5 45 TBD Call TI Call TI LM1875T
LM1875T/LF02 ACTIVE TO-220 NEB 5 45 Green (RoHS
& no Sb/Br) CU SN Level-1-NA-UNLIM LM1875T
LM1875T/LF03 ACTIVE TO-220 NDH 5 45 Green (RoHS
& no Sb/Br) CU SN Level-1-NA-UNLIM LM1875T
LM1875T/LF05 ACTIVE TO-220 NEB 5 45 Green (RoHS
& no Sb/Br) CU SN Level-1-NA-UNLIM LM1875T
LM1875T/NOPB ACTIVE TO-220 NDH 5 45 Green (RoHS
& no Sb/Br) CU SN Level-1-NA-UNLIM 0 to 70 LM1875T
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) Only one of markings shown within the brackets will appear on the physical device.
PACKAGE OPTION ADDENDUM
www.ti.com 9-Mar-2013
Addendum-Page 2
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
MECHANICAL DATA
NDH0005D
www.ti.com
MECHANICAL DATA
NEB0005B
www.ti.com
MECHANICAL DATA
NEB0005E
www.ti.com
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products Applications
Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive
Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications
Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers
DLP® Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps
DSP dsp.ti.com Energy and Lighting www.ti.com/energy
Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial
Interface interface.ti.com Medical www.ti.com/medical
Logic logic.ti.com Security www.ti.com/security
Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense
Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video
RFID www.ti-rfid.com
OMAP Applications Processors www.ti.com/omap TI E2E Community e2e.ti.com
Wireless Connectivity www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2013, Texas Instruments Incorporated
