LM4871
1.1W Audio Power Amplifier with Shutdown Mode
General Description
The LM4871is a bridge-connected audio power amplifier ca-pable of delivering typically 1.1W of continuous average power to an 8Ωload with 0.5%(THD)from a 5V power sup-ply.
Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components.Since the LM4871does not require output coupling capacitors,bootstrap capacitors,or snubber networks,it is optionally suited for low-power portable sys-tems.
The LM4871features an externally controlled,low-power consumption shutdown mode,as well as an internal thermal shutdown protection mechanism.
The unity-gain stable LM4871can be configured by external gain-tting resistors.
Key Specifications
n THD at 1kHz at 1W continuous average output power into 8Ω0.5%(max)n Output power at 10%THD+N at 1kHz into 8Ω 1.5W (typ)n Shutdown Current
0.6µA (typ)
Features
n No output coupling capacitors,bootstrap capacitors,or snubber circuits are necessary n Small Outline or DIP packaging n Unity-gain stable
n External gain configuration capability n Pin compatible with LM4861
Applications
n Portable Computers n Desktop Computers
n Low Voltage Audio Systems
Typical Application Connection Diagram
Boomer ®is a registered trademark of National Semiconductor Corporation.
DS100008-1
FIGURE 1.Typical Audio Amplifier Application Circuit
Small Outline and DIP Package
DS100008-2
Top View
Order Number LM4871M or LM4871N See NS Package Number M08A or N08E
February 2000
LM48711.1W Audio Power Amplifier with Shutdown Mode
开业花篮贺词©2000National Semiconductor Corporation
Absolute Maximum Ratings (Note 2)
If Military/Aerospace specified devices are required,plea contact the National Semiconductor Sales Office/Distributors for availability and specifications.Supply Voltage 6.0V
Supply Temperature −65˚C to +150˚C Input Voltage
−0.3V to V DD to +0.3V
Power Dissipation (Note 3)Internally Limited
ESD Susceptibility (Note 4)5000V ESD Susceptibility (Note 5)250V Junction Temperature 150˚C
Soldering Information Small Outline Package Vapor Pha (60c.)
215˚C Infrared (15c.)
220˚C
See AN-450″Surface Mounting and their Effects on Product Reliability ″for other methods of soldering surface mount devices.θJC (typ)—M08A 35˚C/W θJA (typ)—M08A 140˚C/W θJC (typ)—N08E 37˚C/W θJA (typ)—N08E
107˚C/W
Operating Ratings
Temperature Range T MIN ≤T A ≤T MAX −40˚C ≤T A ≤85˚C Supply Voltage
2.0V ≤V DD ≤5.5V
Electrical Characteristics
写给自己生日的话
(Notes 1,2)
The following specifications apply for V DD
=5V unless otherwi specified.Limits apply for T A =25˚C.
Symbol Parameter
Conditions LM4871
学业水平Units (Limits)Typical Limit (Note 6)
(Note 7)V DD Supply Voltage
2.0V (min)5.5
V (max)I DD Quiescent Power Supply Current V IN =0V,I o =0A 6.510.0mA (max)I SD Shutdown Current V PIN1=V DD 0.62µA (max)V OS Output Offt Voltage V IN =0V
550mV (max)P o Output Power
THD =0.5%(max);f =1kHz 1.10 1.0
W (min)THD+N =10%;f =1kHz 1.5W THD+N Total Harmonic Distortion+Noi P o =1Wrms;A VD =2;20Hz ≤f ≤20kHz
0.25%PSRR
Power Supply Rejection Ratio
V DD =4.9V to 5.1V
65
dB
Note 1:All voltages are measured with respect to the ground pin,unless otherwi specified.
Note 2:Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.Operating Ratings indicate conditions for which the device is func-tional,but do not guarantee specific performance limits.Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guar-antee 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 3:The maximum power dissipation must be derated at elevated temperatures and is dictated by T JMAX ,θJA ,and the ambient temperature T A .The maximum allowable power dissipation is P DMAX =(T JMAX –T A )/θJA or the number given in Absolute Maximum Ratings,whichever is lower.For the LM4871,T JMAX =150˚C.The typical junction-to-ambient thermal resistance is 140˚C/W for package number M08A and is 107˚C/W for package number N08E.Note 4:Human body model,100pF discharged through a 1.5k Ωresistor.Note 5:Machine Model,220pF–240pF discharged through all pins.Note 6:Typicals are measured at 25˚C and reprent the parametric norm.
Note 7:Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
L M 4871
2
External Components Description(Figure1)
Components Functional Description
1.R i Inverting input resistance which ts the clod-loop gain in conjunction with R f.This resistor also forms a
high pass filter with C i at f C=1/(2πR i C i).
2.C i Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals.Also creates a
highpass filter with R i at f c=1/(2πR i C i).Refer to the ction,Proper Selection of External Components,
for an explanation of how to determine the value of C i.
3.R f Feedback resistance which ts the clod-loop gain in conjunction with R i.
4.C S Supply bypass capacitor which provides power supply filtering.Refer to the Power Supply Bypassing
ction for information concerning proper placement and lection of the supply bypass capacitor.
5.C B Bypass pin capacitor which provides half-supply filtering.Refer to the ction,Proper Selection of External
Components,for information concerning proper placement and lection of C B.
Typical Performance Characteristics
THD+N vs Frequency
DS100008-3THD+N vs Frequency
DS100008-4
THD+N vs Frequency
DS100008-5
THD+N vs Output Power
DS100008-6THD+N vs Output Power
DS100008-7
THD+N vs Output Power
DS100008-8
Output Power vs
Supply Voltage
DS100008-9Output Power vs
Supply Voltage
DS100008-10
Output Power vs
Supply Voltage
跑步短裤DS100008-11
LM4871
3
Typical Performance Characteristics
(Continued)
Output Power vs Load Resistance
DS100008-12Power Dissipation vs Output Power
DS100008-13Power Derating Curve
DS100008-14
Clipping Voltage vs Supply Voltage
DS100008-15
Noi Floor十二星座有什么
投影幕
DS100008-16Frequency Respon vs Input Capacitor Size
DS100008-17
Power Supply Rejection Ratio DS100008-18Open Loop
Frequency Respon DS100008-19
Supply Current vs Supply Voltage
DS100008-20
L M 4871
4
Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure1,the LM4871has two operational am-plifiers internally,allowing for a few different amplifier con-figurations.The first amplifier’s gain is externally config-urable,while the cond amplifier is internally fixed in a unity-gain,inverting configuration.The clod-loop gain of the first amplifier is t by lecting the ratio of R f to R i while the cond amplifier’s gain is fixed by the two internal40kΩresistors.Figure1shows that the output of amplifier one rves as the input to amplifier two which results in both am-plifiers producing signals identical in magnitude,but out of pha180˚.Conquently,the differential gain for the IC is
A VD=2*(R f/R i)
By driving the load differentially through outputs Vo1and Vo2,an amplifier configuration commonly referred to as “bridged mode”is established.Bridged mode operation is different from the classical single-ended amplifier configura-tion where one side of its load is connected to ground.
A bridge amplifier design has a few distinct advantages over the single-ended configuration,as it provides differential drive to the load,thus doubling output swing for a specified supply voltage.Four times the output power is possible as compared to a single-ended amplifier under the same condi-tions.This increa in attainable output power assumes that the amplifier is not current limited or clipped.In order to choo an amplifier’s clod-loop gain without causing ex-cessive clipping,plea refer to the Audio Power Amplifier Design ction.
A bridge configuration,such as the one ud in LM4871, also creates a cond advantage over single-ended amplifi-ers.Since the differential outputs,Vo1and Vo2,are biad at half-supply,no net DC voltage exists across the load.This eliminates the need for an output coupling capacitor which is required in a single supply,single-ended amplifier configura-tion.Without an output coupling capacitor,the half-supply bias across the load would result in both incread internal IC power dissipation and also possible loudspeaker damage. POWER DISSIPATION
Power dissipation is a major concern when designing a suc-cessful amplifier,whether the amplifier is bridged or single-ended.A direct conquence of the incread power deliv-ered to the load by a bridge amplifier is an increa in internal power dissipation.Equation1states the maximum power dissipation point for a bridge amplifier operating at a given supply voltage and driving a specified output load.
P DMAX=4*(V DD)2/(2π2R L)(1)
Since the LM4871has two operational amplifiers in one package,the maximum internal power dissipation is4times that of a single-ended ampifier.Even with this substantial in-crea in power dissipation,the LM4871does not require heatsinking under most operating conditions and output loading.From Equation1,assuming a5V power supply and an8Ωload,the maximum power dissipation point is 625mW.The maximum power dissipation point obtained from Equation1must not be greater than the power dissipa-tion that results from Equation2:
P DMAX=(T JMAX–T A)/θJA(2)
For package M08A,θJA=140˚C/W,and for package N08E,θJA=107˚C/W assuming free air operation.T JMAX=150˚C for the LM4871.TheθJA can be decread by using some form of heat sin
king.The resultantθJA will be the summation of theθJC,θCS,andθSA.θJC is the junction to ca of the
package,θCS is the ca to heat sink thermal resistance and
θSA is the heat sink to ambient thermal resistance.By adding
additional copper area around the LM4871,theθJA can be
reduced from its free air value of140˚C/W for package
河北省教育考试网官网
M08A.Depending on the ambient temperature,T A,and the
θJA,Equation2can be ud to find the maximum internal
power dissipation supported by the IC packaging.If the re-
sult of Equation1is greater than that of Equation2,then ei-
ther the supply voltage must be decread,the load imped-
ance incread,theθJA decread,or the ambient
temperature reduced.For the typical application of a5V
power supply,with an8Ωload,and no additional heatsink-
ing,the maximum ambient temperature possible without vio-
lating the maximum junction temperature is approximately
61˚C provided that device operation is around the maximum
power dissipation point and assuming surface mount pack-
aging.Internal power dissipation is a function of output
power.If typical operation is not around the maximum power
dissipation point,the ambient temperature can be incread.
Refer to the Typical Performance Characteristics curves
for power dissipation information for different output powers
and output loading.
POWER SUPPLY BYPASSING
As with any amplifier,proper supply bypassing is critical for
low noi performance and high power supply rejection.The
capacitor location on both the bypass and power supply pins
should be as clo to the device as possible.Typical applica-
tions employ a5V regulator with10µF and a0.1µF bypass
capacitors which aid in supply stability.This does not elimi-
nate the need for bypassing the supply nodes of the
LM4871.The lection of bypass capacitors,especially C B,
is dependent upon PSRR requirements,click and pop per-
formance as explained in the ction,Proper Selection of
External Components,system cost,and size constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in u,the
LM4871contains a shutdown pin to externally turn off the
amplifier’s bias circuitry.This shutdown feature turns the am-
plifier off when a logic high is placed on the shutdown pin.
The trigger point between a logic low and logic high level is
typically half-supply.It is best to switch between ground and
supply to provide maximum device performance.By switch-
ing the shutdown pin to V DD,the LM4871supply current
draw will be minimized in idle mode.While the device will be
disabled with shutdown pin voltages less then V DD,the idle
current may be greater than the typical value of0.6µA.In ei-
ther ca,the shutdown pin should be tied to a definite volt-
age to avoid unwanted state changes.
In many applications,a microcontroller or microprocessor
output is ud to control the shutdown circuitry which pro-
vides a quick,smooth transition into shutdown.Another solu-
tion is to u a single-pole,single-throw switch in conjunction
with an external pull-up resistor.When the switch is clod,
the shutdown pin is connected to ground and enables the
amplifier.If the switch is open,then the external pull-up re-
sistor will disable the LM4871.This scheme guarantees that
the shutdown pin will not float thus preventing unwanted
state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
带兵的人
Proper lection of external components in applications us-
ing integrated power amplifiers is critical to optimize device
and system performance.While the LM4871is tolerant of
LM4871
5
