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LM4808

Dual 105mW Headphone Amplifier

General Description

The LM4808is a dual audio power amplifier capable of delivering 105mW per channel of continuous average power into a 16?load with 0.1%(THD+N)from a 5V power supply.Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components using surface mount packaging.Since the LM4808does not require bootstrap capacitors or snub-ber networks,it is optimally suited for low-power portable systems.

The unity-gain stable LM4808can be configured by external gain-setting resistors.

Key Specifications

n THD+N at 1kHz at 105mW continuous average output power into 16?0.1%(typ)n THD+N at 1kHz at 70mW continuous average output power into 32?0.1%(typ)n Output power at 0.1%THD+N at 1kHz into 32?70mW (typ)

Features

n LLP ,MSOP ,and SOP surface mount packaging n Switch on/off click suppression

n Excellent power supply ripple rejection n Unity-gain stable

Minimum external components

Applications

n Headphone Amplifier n Personal Computers

n Portable electronic devices

Typical Application

Boomer ?is a registered trademark of National Semiconductor Corporation.

10127601

*Refer to the Application Information Section for information concerning proper selection of the input and output coupling capacitors.

FIGURE 1.Typical Audio Amplifier Application Circuit

August 2001

LM4808Dual 105mW Headphone Amplifier

?2001National Semiconductor Corporation https://www.wendangku.net/doc/853164854.html,

Connection Diagrams

LLP Package

10127657

Top View

Order Number LM4808LD

See NS Package Number LDA08B

SOP &MSOP Package

10127602

Top View

Order Number LM4808M,LM4808MM See NS Package Number M08A,MUA08A

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Absolute Maximum Ratings

(Note 3)

If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distributors for availability and specifications.Supply Voltage 6.0V

Storage Temperature ?65?C to +150?C Input Voltage

?0.3V to V DD +0.3V

Power Dissipation (Note 4)Internally limited

ESD Susceptibility (Note 5)3500V ESD Susceptibility (Note 6)250V Junction Temperature 150?C

Soldering Information (Note 1)Small Outline Package Vapor Phase (60seconds)215?C Infrared (15seconds)220?C Thermal Resistance

θJC (MSOP)56?C/W θJA (MSOP)210?C/W θJC (SOP)35?C/W θJA (SOP)170?C/W θJC (LLP)15?C/W

θJA (LLP)117?C/W (Note 9)θJA (LLP)

150?C/W (Note 10)

Operating Ratings

Temperature Range T MIN ≤T A ≤T MAX ?40?C ≤T

≤85?C

Supply Voltage

2.0V ≤V DD ≤5.5V

Note 1:See AN-450“Surface Mounting and their Effects on Product Reli-ability”for other methods of soldering surface mount devices.

Electrical Characteristics (Notes 2,3)

The following specifications apply for V DD =5V unless otherwise specified,limits apply to T A =25?C.Symbol

Parameter

Conditions

LM4808

Units (Limits)Typ (Note 7)Limit (Note

V DD Supply Voltage 2.0V (min)5.5

V (max)I DD Supply Current V IN =0V,I O =0A 1.2 3.0mA (max)P tot Total Power Dissipation V IN =0V,I O =0A 616.5mW (max)V OS Input Offset Voltage V IN =0V

1050

mV (max)

Ibias Input Bias Current 10pA V CM Common Mode Voltage 0V 4.3

V G V Open-Loop Voltage Gain R L =5k ?67dB Io Max Output Current THD+N <0.1%

70mA R O Output Resistance 0.1?V O Output Swing

R L =32?,0.1%THD+N,Min .3V R L =32?,0.1%THD+N,Max 4.7PSRR Power Supply Rejection Ratio Cb =1.0μF,Vripple =100mV PP ,

f =100Hz 89dB Crosstalk Channel Separation

R L =32?75dB THD+N

Total Harmonic Distortion +Noise

f =1kHz

R L =16?,

V O =3.5V PP (at 0dB)0.05%66dB R L =32?,

V O =3.5V PP (at 0dB)

0.05%66dB SNR Signal-to-Noise Ratio V O =3.5V pp (at 0dB)105dB f G Unity Gain Frequency Open Loop,R L =5k ? 5.5MHz P o

Output Power

THD+N =0.1%,f =1kHz R L =16?105mW

R L =32?

7060mW THD+N =10%,f =1kHz R L =16?150mW R L =32?

90mW C I

Input Capacitance

LM4808

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Electrical Characteristics (Notes 2,3)

(Continued)

The following specifications apply for V DD

=5V unless otherwise specified,limits apply to T A =25?C.

Symbol

Parameter

Conditions

LM4808

Units

(Limits)Typ (Note 7)Limit (Note

C L Load Capacitance 200

pF SR

Slew Rate

Unity Gain Inverting

V/μs

Electrical Characteristics (Notes 2,3)

The following specifications apply for V DD =3.3V unless otherwise specified,limits apply to T A =25?C.Symbol

Parameter

Conditions

Conditions Units

(Limits)Typ (Note 7)Limit (Note

I DD Supply Current V IN =0V,I O =0A 1.0mA (max)V OS Input Offset Voltage V IN =0V

mV (max)

P o

Output Power

THD+N =0.1%,f =1kHz R L =16?40mW R L =32?

THD+N =10%,f =1kHz R L =16?56mW R L =32?

Electrical Characteristics (Notes 2,3)

The following specifications apply for V DD =2.6V unless otherwise specified,limits apply to T A =25?C.Symbol

Parameter

Conditions

Conditions Units (Limits)Typ (Note 7)Limit (Note

I DD Supply Current V IN =0V,I O =0A 0.9mA (max)V OS Input Offset Voltage V IN =0V

5mV (max)P o

Output Power

THD+N =0.1%,f =1kHz R L =16?20mW R L =32?

16mW THD+N =10%,f =1kHz R L =16?31mW R L =32?

Note 2:All voltages are measured with respect to the ground pin,unless otherwise specified.

Note 3: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 4: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 .For the LM4808,T JMAX =150?C,and the typical junction-to-ambient thermal resistance,when board mounted,is 210?C/W for package MUA08A and 170?C/W for package M08A.Note 5:Human body model,100pF discharged through a 1.5k ?resistor.Note 6:Machine Model,220pF–240pF discharged through all pins.Note 7:Typicals are measured at 25?C and represent the parametric norm.

Note 8:Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).Datasheet min/max specification limits are guaranteed by design,test,or statistical analysis.

Note 9:The given θJA is for an LM4808packaged in an LDA08B with the Exposed-DAP soldered to a printed circuit board copper pad with an area equivalent to that of the Exposed-DAP itself.

Note 10:The given θJA is for an LM4808packaged in an LDA08B with the Exposed-DAP not soldered to any printed circuit board copper.

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External Components Description

(Figure 1)

Components Functional Description

1.R i

The inverting input resistance,along with R f ,set the closed-loop gain.R i ,along with C i ,form a high pass filter with f c =1/(2πR i C i ).

2.C i The input coupling capacitor blocks DC voltage at the amplifier’s input terminals.C i ,along with R i ,create a highpass filter with f C =1/(2πR i C i ).Refer to the section,Selecting Proper External Components ,for an explanation of determining the value of C i .

3.R f The feedback resistance,along with R i ,set closed-loop gain.

4.C S

This is the supply bypass capacitor.It provides power supply filtering.Refer to the Application Information section for proper placement and selection of the supply bypass capacitor.

5.C B

This is the half-supply bypass pin capacitor.It provides half-supply filtering.Refer to the section,

Selecting Proper External Components ,for information concerning proper placement and selection of C B .

6.C O This is the output coupling capacitor.It blocks the DC voltage at the amplifier’s output and forms a high pass filter with R L at f O =1/(2πR L C O )

7.R B

This is the resistor which forms a voltage divider that provides 1/2V DD to the non-inverting input of the amplifier.

Typical Performance Characteristics

THD+N vs Frequency

1012760310127604

THD+N vs Frequency THD+N vs Frequency

1012760510127606

LM4808

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Typical Performance Characteristics

(Continued)

THD+N vs Frequency

1012760710127608

THD+N vs Frequency THD+N vs Frequency

1012760910127610

THD+N vs Frequency THD+N vs Frequency

1012761110127612

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Typical Performance Characteristics

(Continued)

THD+N vs Output Power

1012761310127614

THD+N vs Output Power THD+N vs Output Power

1012761510127616

THD+N vs Output Power THD+N vs Output Power

1012761710127618

LM4808

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Typical Performance Characteristics

(Continued)

THD+N vs Output Power

1012761910127620

THD+N vs Output Power

Output Power vs Load Resistance

10127621

10127622

Output Power vs Load Resistance Output Power vs Load Resistance

1012762310127624

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Typical Performance Characteristics(Continued)

Output Power vs Supply Voltage

Output Power vs

Power Supply 1012762510127626

Output Power vs Power Supply

Clipping Voltage vs

Supply Voltage 1012762710127628

Power Dissipation vs Output Power

Power Dissipation vs

Output Power

1012762910127630

LM4808

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Typical Performance Characteristics

(Continued)

Power Dissipation vs

Output Power

Channel Separation

10127631

10127632

Channel Separation Noise Floor

10127633

10127634

Power Supply Rejection Ratio

Open Loop

Frequency Response

10127635

10127650

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Typical Performance Characteristics

(Continued)

Open Loop

Frequency Response

Open Loop

Frequency Response

1012765110127638

Supply Current vs Supply Voltage Frequency Response vs Output Capacitor Size

10127644

10127645

Frequency Response vs Output Capacitor Size Frequency Response vs Output Capacitor Size

1012764610127647

LM4808

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Typical Performance Characteristics

(Continued)

Typical Application Frequency Response

1012764810127649

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Application Information

EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATION

The LM4808’s exposed-dap(die attach paddle)package (LD)provides a low thermal resistance between the die and the PCB to which the part is mounted and soldered.This allows rapid heat transfer from the die to the surrounding PCB copper traces,ground plane,and surrounding air. The LD package should have its DAP soldered to a copper pad on the PCB.The DAP’s PCB copper pad may be con-nected to a large plane of continuous unbroken copper.This plane forms a thermal mass,heat sink,and radiation area. However,since the LM4808is designed for headphone ap-plications,connecting a copper plane to the DAP’s PCB copper pad is not required.The LM4808’s Power Dissipation vs Output Power Curve in the Typical Performance Char-acteristics shows that the maximum power dissipated is just 45mW per amplifier with a5V power supply and a32?load. Further detailed and specific information concerning PCB layout,fabrication,and mounting an LD(LLP)package is available from National Semiconductor’s Package Engineer-ing Group under application note AN1187.

POWER DISSIPATION

Power dissipation is a major concern when using any power amplifier and must be thoroughly understood to ensure a successful design.Equation1states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and driving a specified output load.

P DMAX=(V DD)2/(2π2R L)(1)

Since the LM4808has two operational amplifiers in one package,the maximum internal power dissipation point is twice that of the number which results from Equation1.Even with the large internal power dissipation,the LM4808does not require heat sinking over a large range of ambient tem-perature.From Equation1,assuming a5V power supply and a32?load,the maximum power dissipation point is40mW per amplifier.Thus the maximum package dissipation point is80mW.The maximum power dissipation point obtained must not be greater than the power dissipation that results from Equation2:

P DMAX=(T JMAX?T A)/θJA(2)

For package MUA08A,θJA=210?C/W.T JMAX=150?C for the LM4808.Depending on the ambient temperature,T A,of the system surroundings,Equation2can be used to find the maximum internal power dissipation supported by the IC packaging.If the result of Equation1is greater than that of Equation2,then either the supply voltage must be de-creased,the load impedance increased or T A reduced.For the typical application of a5V power supply,with a32?load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately133.2?C provided that device operation is around the maximum power dissipation point.Power dissipation is a function of output power and thus,if typical operation is not around the maximum power dissipation point,the ambient temperature may be increased accordingly.Refer to the Typical Perfor-mance Characteristics curves for power dissipation infor-mation for lower output powers.

POWER SUPPLY BYPASSING

As with any power amplifier,proper supply bypassing is

critical for low noise performance and high power supply

rejection.Applications that employ a5V regulator typically

use a10μF in parallel with a0.1μF filter capacitors to stabi-

lize the regulator’s output,reduce noise on the supply line,

and improve the supply’s transient response.However,their

presence does not eliminate the need for a local0.1μF

supply bypass capacitor,C S,connected between the

LM4808’s supply pins and ground.Keep the length of leads

and traces that connect capacitors between the LM4808’s

power supply pin and ground as short as possible.Connect-

ing a1.0μF capacitor,C B,between the IN A(+)/IN B(+)node

and ground improves the internal bias voltage’s stability and

improves the amplifier’s PSRR.The PSRR improvements

increase as the bypass pin capacitor value increases.Too

large,however,increases the amplifier’s turn-on time.The

selection of bypass capacitor values,especially C B,depends

on desired PSRR requirements,click and pop performance

(as explained in the section,Selecting Proper External

Components),system cost,and size constraints.

SELECTING PROPER EXTERNAL COMPONENTS

Optimizing the LM4808’s performance requires properly se-

lecting external components.Though the LM4808operates

well when using external components with wide tolerances,

best performance is achieved by optimizing component val-

ues.

The LM4808is unity-gain stable,giving a designer maximum

design flexibility.The gain should be set to no more than a

given application requires.This allows the amplifier to

achieve minimum THD+N and maximum signal-to-noise ra-

tio.These parameters are compromised as the closed-loop

gain increases.However,low gain demands input signals

with greater voltage swings to achieve maximum output

power.Fortunately,many signal sources such as audio

CODECs have outputs of1V RMS(2.83V P-P).Please refer to

the Audio Power Amplifier Design section for more infor-

mation on selecting the proper gain.

Input and Output Capacitor Value Selection

Amplifying the lowest audio frequencies requires high value

input and output coupling capacitors(C I and C O in Figure1).

A high value capacitor can be expensive and may compro-

mise space efficiency in portable designs.In many cases,

however,the speakers used in portable systems,whether

internal or external,have little ability to reproduce signals

below150Hz.Applications using speakers with this limited

frequency response reap little improvement by using high

value input and output capacitors.

Besides affecting system cost and size,C i has an effect on

the LM4808’s click and pop performance.The magnitude of

the pop is directly proportional to the input capacitor’s size.

Thus,pops can be minimized by selecting an input capacitor

value that is no higher than necessary to meet the desired

?3dB frequency.

As shown in Figure1,the input resistor,R I and the input

capacitor,C I,produce a?3dB high pass filter cutoff fre-

quency that is found using Equation(3).In addition,the

output load R L,and the output capacitor C O,produce a-3db

high pass filter cutoff frequency defined by Equation(4).

f I-3db=1/2πR I C I(3)

f O-3db=1/2πR L C O(4)

LM4808

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Application Information(Continued)

Also,careful consideration must be taken in selecting a

certain type of capacitor to be used in the system.Different

types of capacitors(tantalum,electrolytic,ceramic)have

unique performance characteristics and may affect overall

system performance.

Bypass Capacitor Value

Besides minimizing the input capacitor size,careful consid-

eration should be paid to the value of the bypass capacitor,

C B.Since C B determines how fast the LM4808settles to

quiescent operation,its value is critical when minimizing

turn-on pops.The slower the LM4808’s outputs ramp to their

quiescent DC voltage(nominally1/2V DD),the smaller the

turn-on pop.Choosing C B equal to 1.0μF or larger,will

minimize turn-on pops.As discussed above,choosing C i no

larger than necessary for the desired bandwith helps mini-

mize clicks and pops.

AUDIO POWER AMPLIFIER DESIGN

Design a Dual70mW/32?Audio Amplifier

Given:

Power Output70mW

Load Impedance32?

Input Level1Vrms(max)

Input Impedance20k?

Bandwidth100Hz–20kHz±0.50dB

The design begins by specifying the minimum supply voltage

necessary to obtain the specified output power.One way to

find the minimum supply voltage is to use the Output Power

vs Supply Voltage curve in the Typical Performance Char-

acteristics section.Another way,using Equation(5),is to

calculate the peak output voltage necessary to achieve the

desired output power for a given load impedance.To ac-

count for the amplifier’s dropout voltage,two additional volt-

ages,based on the Dropout Voltage vs Supply Voltage in the

Typical Performance Characteristics curves,must be

added to the result obtained by Equation(5).For a

single-ended application,the result is Equation(6).

(5)

V DD≥(2V OPEAK+(V OD

TOP

+V OD

BOT

))(6)

The Output Power vs Supply Voltage graph for a32?load

indicates a minimum supply voltage of4.8V.This is easily

met by the commonly used5V supply voltage.The additional

voltage creates the benefit of headroom,allowing the

LM4808to produce peak output power in excess of70mW

without clipping or other audible distortion.The choice of

supply voltage must also not create a situation that violates

maximum power dissipation as explained above in the

Power Dissipation section.Remember that the maximum

power dissipation point from Equation(1)must be multiplied

by two since there are two independent amplifiers inside the

package.Once the power dissipation equations have been

addressed,the required gain can be determined from Equa-

tion(7).

(7)

Thus,a minimum gain of1.497allows the LM4808to reach

full output swing and maintain low noise and THD+N perfro-

mance.For this example,let A V=1.5.

The amplifiers overall gain is set using the input(R i)and

feedback(R f)resistors.With the desired input impedance

set at20k?,the feedback resistor is found using Equation

(8).

A V=R f/R i(8)

The value of R f is30k?.

The last step in this design is setting the amplifier’s?3db

frequency bandwidth.To achieve the desired±0.25dB pass

band magnitude variation limit,the low frequency response

must extend to at lease one?fifth the lower bandwidth limit

and the high frequency response must extend to at least five

times the upper bandwidth limit.The gain variation for both

response limits is0.17dB,well within the±0.25dB desired

limit.The results are an

f L=100Hz/5=20Hz(9)

and a

f H=20kHz*5=100kHz(10)

As stated in the External Components section,both R i in

conjunction with C i,and C o with R L,create first order high-

pass filters.Thus to obtain the desired low frequency re-

sponse of100Hz within±0.5dB,both poles must be taken

into consideration.The combination of two single order filters

at the same frequency forms a second order response.This

results in a signal which is down0.34dB at five times away

from the single order filter?3dB point.Thus,a frequency of

20Hz is used in the following equations to ensure that the

response is better than0.5dB down at100Hz.

C i≥1/(2π*20k?*20Hz)=0.397μF;use0.39μF.

C o≥1/(2π*32?*20Hz)=249μF;use330μF.

The high frequency pole is determined by the product of the

desired high frequency pole,f H,and the closed-loop gain,

A V.With a closed-loop gain of1.5and f H=100kHz,the

resulting GBWP=150kHz which is much smaller than the

LM4808’s GBWP of900kHz.This figure displays that if a

designer has a need to design an amplifier with a higher

gain,the LM4808can still be used without running into

bandwidth limitations.

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Demonstration Board Layout

10127639

Recommended SO PC Board Layout:

Top Silkscreen

10127660

Recommended LD PC Board Layout:

Top Silkscreen

10127640

Recommended SOP PC Board Layout:

Top Layer

10127661

Recommended LD PC Board Layout:

Top Layer

10127642

Recommended SOP PC Board Layout:

Bottom Layer

10127662

Recommended LD PC Board Layout:

Bottom Layer

LM4808

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Physical Dimensions

inches (millimeters)

unless otherwise noted

Order Number LM4808LD NS Package Number LDA08B

Order Number LM4808M NS Package Number M08A

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Physical Dimensions

inches (millimeters)unless otherwise noted (Continued)

Order Number LM4808MM NS Package Number MUA08A

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS 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.

National Semiconductor Corporation Americas

Email:support@https://www.wendangku.net/doc/853164854.html,

National Semiconductor Europe

Fax:+49(0)180-5308586Email:europe.support@https://www.wendangku.net/doc/853164854.html,

Deutsch Tel:+49(0)6995086208English Tel:+44(0)8702402171Fran?ais Tel:+33(0)141918790

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Tel:81-3-5639-7560Fax:81-3-5639-7507

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LM4808Dual 105mW Headphone Amplifier

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.