National Semiconductor LM4880 Technical data

September 2004

LM4880
Dual 250 mW Audio Power Amplifier with Shutdown
Mode

General Description

The LM4880 is a dual audio power amplifier capable of
delivering typically 250mW per channel of continuous aver­age power to an 8Ω load with 0.1% THD+N using 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 LM4880 does not require bootstrap capacitors or
snubber networks, it is optimally suited for low-power por­table systems.

The LM4880 features an externally controlled, low-power
consumption shutdown mode, as well as an internal thermal
shutdown protection mechanism.

The unity-gain stable LM4880 can be configured by external
gain-setting resistors.

Key Specifications

n THD+N at 1kHz at 200mW continuous average output

power into 8Ω: 0.1% (max)

n THD+N at 1kHz at 85mW continuous average output

power into 32Ω: 0.1% (typ)

n Output power at 10% THD+N at 1kHz into 8Ω:

325mW (typ)

n Shutdown current: 0.7µA (typ)
n 2.7V to 5.5V supply voltage range

Features

n No bootstrap capacitors or snubber circuits are

necessary

n Small Outline (SO) and DIP packaging
n Unity-gain stable
n External gain configuration capability

Applications

n Headphone Amplifier
n Personal Computers
n CD-ROM Players

LM4880 Boomer Audio Power Amplifier Series Dual 250 mW Audio Power Amplifier with

Shutdown Mode

Connection Diagram

Small Outline and

DIP Packages

01234302

Top View

Order Number LM4880M or LM4880N

See NS Package Number M08A for SO

or NS Package Number N08E for DIP

Boomer®is a registered trademark of National Semiconductor Corporation.

© 2004 National Semiconductor Corporation DS012343 www.national.com

Typical Application

LM4880

*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

01234301

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Absolute Maximum Ratings (Note 2)

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

+

See AN-450 “Surface Mounting and their Effects on
Product Reliability” for other methods of soldering surface
mount devices.

Thermal Resistance

θ

(DIP) 37˚C/W

JC

θ

(DIP) 107˚C/W

JA

θ

(SO) 35˚C/W

JC

θ

(SO) 170˚C/W

JA

Power Dissipation (Note 3) Internally limited

ESD Susceptibility (Note 4) 2000V

Operating Ratings

ESD Susceptibility (Note 5) 200V

Junction Temperature 150˚C

Soldering Information

Small Outline Package

Vapor Phase (60 sec.)
Infrared (15 sec.)

215˚C
220˚C

Temperature Range

T

MIN≤TA≤TMAX

−40˚C≤TA≤+85˚C

Supply Voltage 2.7V≤V

DD

≤5.5V

Electrical Characteristics (Notes 1, 2)

The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25˚C.

Symbol Parameter Conditions LM4880 Units

Typical Limit

(Note 6) (Note 7)

V

DD

Supply Voltage 2.7 V (min)

5.5 V (max)

I

DD

I

SD

V

OS

P

O

Quiescent Power Supply Current VIN=0V, IO=0A 3.6 6.0 mA

Shutdown Current V

PIN5=VDD

0.7 5 µA (max)

Output Offset Voltage VIN=0V 5 50 mV

Output Power THD=0.1% (max); f=1 kHz;

R

=8Ω 250 200 mW

L

=32Ω 85 mW

R

L

THD+N=10%; f=1 kHz

R

=8Ω 325 mW

L

R

=32Ω 110 mW

L

THD+N Total Harmonic Distortion+Noise R

=8Ω,PO=200 mW; 0.03 %

L

R

=32Ω,PO=75 mW; 0.02 %

L

f=1 kHz

PSRR Power Supply Rejection Ratio C

Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.

Note 2: Absolute Maximum Ratings indicate limits beyond which damage 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

= 1.0 µF,

B

=200 mVrms, f = 100 Hz

V

RIPPLE

50 dB

(Limits)

(max)

(max)

(min)

Automatic Shutdown Circuit

LM4880

Automatic Switching Circuit

01234303

FIGURE 2. Automatic Shutdown Circuit

FIGURE 3. Automatic Switching Circuit

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01234304

External Components Description (Figure 1)

Components Functional Description

1. R

2. C

i

i

Inverting input resistance which sets the closed-loop gain in conjunction with RF. This resistor
also forms a high pass filter with C

at fc= 1/(2πRiCi).

i

Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also
creates a high pass filter with R

at fc= 1/(2πRiCi). Refer to the section, Proper Selection of

i

External Components, for an explanation of how to determine the value of C

3. R

4. C

F

S

Feedback resistance which sets closed-loop gain in conjunction with Ri.

Supply bypass capacitor which provides power supply filtering. Refer to the Application
Information section for proper placement and selection of the supply bypass capacitor.

5. C

B

Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper
Selection of External Components, for information concerning proper placement and

.

B

at fo= 1/(2πRLCo).

L

6. C

selection of C

o

Output coupling capacitor which blocks the DC voltage at the amplifier’s output. Forms a high
pass filter with R

Typical Performance Characteristics

THD+NvsOutput Power THD+NvsOutput Power

LM4880

.

i

01234305 01234306

THD+NvsOutput Power THD+NvsOutput Power

01234307 01234308

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Typical Performance Characteristics (Continued)

LM4880

THD+NvsOutput Power THD+NvsOutput Power

01234309 01234310

THD+NvsFrequency THD+NvsFrequency

01234311

THD+NvsFrequency THD+NvsFrequency

01234313 01234314

01234312

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Typical Performance Characteristics (Continued)

LM4880

Output Power vs
Load Resistance

Output Power vs

Supply Voltage

Output Power vs
Load Resistance

01234315 01234316

Output Power vs

Supply Voltage

Output Power vs

Supply Voltage

01234317

01234319

01234318

Clipping Voltage vs

Supply Voltage

01234320

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Typical Performance Characteristics (Continued)

LM4880

Clipping Voltage vs

Supply Voltage

Channel Separation

Power Dissipation vs

Output Power

01234321 01234322

Output Attenuation in

Shutdown Mode

Noise Floor

01234323

01234324

Power Supply

Rejection Ratio

01234325 01234326

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Typical Performance Characteristics (Continued)

LM4880

Open Loop

Frequency Response

Frequency Response vs

Output Capacitor Size

01234327

Supply Current vs

Supply Voltage

01234328

Frequency Response vs

Output Capacitor Size

Frequency Response vs

Input Capacitor Size

01234329 01234330

Typical Application

Frequency Response

01234331 01234332

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Typical Performance Characteristics (Continued)

LM4880

Typical Application

Frequency Response Power Derating Curve

Application Information

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the
LM4880 contains a shutdown pin to externally turn off the
amplifier’s bias circuitry. This shutdown feature turns the
amplifier 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
the supply to provide maximum device performance. By
switching the shutdown pin to V
rent draw will be minimized in idle mode. While the device
will be disabled with shutdown pin voltages less than V
the idle current may be greater than the typical value of 0.7
µA. In either case, the shutdown pin should be tied to a
definite voltage because leaving the pin floating may result in
an unwanted shutdown condition.

In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry which pro­vides a quick, smooth transition into shutdown. Another so­lution is to use a single-pole, single-throw switch in conjunc­tion with an external pull-up resistor. When the switch is
closed, the shutdown pin is connected to ground and en­ables the amplifier. If the switch is open, then the external
pull-up resistor will disable the LM4880. This scheme guar­antees that the shutdown pin will not float which will prevent
unwanted state changes.

POWER DISSIPATION

Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. Equation (1) states the maximum power
dissipation point for a single-ended amplifier operating at a
given supply voltage and driving a specified output load.

=(VDD)2/(2π2RL) (1)

P

DMAX

Since the LM4880 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation (1).
Even with the large internal power dissipation, the LM4880
does not require heat sinking over a large range of ambient
temperatures. From Equation (1), assuming a 5V power
supply and an 8Ω load, the maximum power dissipation
point is 158 mW per amplifier. Thus the maximum package

, the LM4880 supply cur-

DD

01234333

01234334

dissipation point is 317 mW. The maximum power dissipa­tion point obtained must not be greater than the power
dissipation that results from Equation (2):

=(T

P

DMAX

For the LM4880 surface mount package, θ

= 150˚C. Depending on the ambient temperature, TA,

T

JMAX

JMAX-TA

)/θ

JA

JA

(2)

= 170˚ C/W and

of the system surroundings, Equation (2) can be used to find
the maximum internal power dissipation supported by the IC
packaging. If the result of Equation (1) is greater than that of
Equation (2), then either the supply voltage must be de­creased, the load impedance increased, or the ambient tem­perature reduced. For the typical application of a 5V power

,

DD

supply, with an 8Ω load, the maximum ambient temperature
possible without violating the maximum junction temperature
is approximately 96˚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 Performance Characteristics
curves for power dissipation information 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. The capacitor location on both the bypass and
power supply pins should be as close to the device as
possible. As displayed in the Typical Performance Charac-
teristics section, the effect of a larger half supply bypass
capacitor is improved low frequency PSRR due to increased
half-supply stability. Typical applications employ a 5V regu­lator with 10 µF and a 0.1 µF bypass capacitors which aid in
supply stability, but do not eliminate the need for bypassing
the supply nodes of the LM4880. The selection of bypass
capacitors, especially C

, is thus dependant upon desired

B

low frequency PSRR, click and pop performance as ex­plained in the section, Proper Selection of External Com-

ponents section, system cost, and size constraints.

AUTOMATIC SHUTDOWN CIRCUIT

As shown in Figure 2, the LM4880 can be set up to auto­matically shutdown when a load is not connected. This cir­cuit is based upon a single control pin common in many
headphone jacks. This control pin forms a normally closed

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Application Information (Continued)

switch with one of the output pins. The output of this circuit
(the voltage on pin 5 of the LM4880) has two states based
on the state of the switch. When the switch is open, signify­ing that headphones are inserted, the LM4880 should be
enabled. When the switch is closed, the LM4880 should be
off to minimize power consumption.

The operation of this circuit is rather simple. With the switch
closed, R
gate voltage of less than 5 mV. This gate voltage keeps the
NMOS inverter off and R
LM4880 to the supply voltage. This places the LM4880 in
shutdown mode which reduces the supply current to 0.7 µA
typically. When the switch is open, the opposite condition is
produced. Resistor R
which turns on the inverter and produces a logic low signal
on the shutdown pin of the LM4880. This state enables the
LM4880 and places the amplifier in its normal mode of
operation.

This type of circuit is clearly valuable in portable products
where battery life is critical, but is also benefical for power
conscious designs such as “Green PC’s”.

AUTOMATIC SWITCHING CIRCUIT

A circuit closely related to the Automatic Shutdown Circuit
is the Automatic Switching Circuit of Figure 3. The Auto-
matic Switching Circuit utilizes both the input and output of
the NMOS inverter to toggle the states of two different audio
power amplifiers. The LM4880 is used to drive stereo single
ended loads, while the LM4861 drives bridged internal
speakers.

In this application, the LM4880 and LM4861 are never on at
the same time. When the switch inside the headphone jack
is open, the LM4880 is enabled and the LM4861 is disabled
since the NMOS inverter is on. If a headphone jack is not
present, it is assumed that the internal speakers should be
on and thus the voltage on the LM4861 shutdown pin is low
and the voltage at the LM4880 pin is high. This results in the
LM4880 being shutdown and the LM4861 being enabled.

Only one channel of this circuit is shown in Figure 3 to keep
the drawing simple but the typical application would a
LM4880 driving a stereo external headphone jack and two
LM4861’s driving the internal stereo speakers. If only one
internal speaker is required, a single LM4861 can be used as
a summer to mix the left and right inputs into a single mono
channel.

PROPER SELECTION OF EXTERNAL COMPONENTS

Selection of external components when using integrated
power amplifiers is critical to optimize device and system
performance. While the LM4880 is tolerant of external com­ponent combinations, care must be exercised when choos­ing component values.

The LM4880 is unity-gain stable which gives a designer
maximum system flexibility. The LM4880 should be used in
low gain configurations to minimize THD + N values, and
maximize the signal to noise ratio. Low gain configurations
require large input signals to obtain a given output power.
Input signals equal to or greater than 1 Vrms are available
from sources such as audio codecs. Please refer to the
section, Audio Power Amplifier Design, for a more com­plete explanation of proper gain selection.

Besides gain, one of the major design considerations is the
closed-loop bandwidth of the amplifier. To a large extent, the

and Roform a resistor divider which produces a

p

pulls the shutdown pin of the

sd

pulls the gate of the NMOS high

p

bandwidth is dictated by the choice of external components
shown in Figure 1. Both the input coupling capacitor, C
the output coupling capacitor, C

, form first order high pass

o

, and

i

filters which limit low frequency response. These values
should be chosen based on needed frequency response for
a few distinct reasons.

Selection of Input and Output Capacitor Size

Large input and output capacitors are both expensive and
space hungry for portable designs. Clearly a certain sized
capacitor is needed to couple in low frequencies without
severe attenuation. But in many cases the transducers used
in portable systems, whether internal or external, have little
ability to reproduce signals below 100 Hz– 150 Hz. Thus
using large input and output capacitors may not increase
system performance.

In addition to system cost and size, click and pop perfor­mance is effected by the size of the input coupling capacitor,

. A larger input coupling capacitor requires more charge to

C

i

reach its quiescent DC voltage (normally 1/2 V

DD

.) This
charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the
capacitor size based on necessary low frequency response,
turn-on pops can be minimized.

Besides minimizing the input and output capacitor sizes,
careful consideration should be paid to the bypass capacitor
size. The bypass capacitor, C

, is the most critical compo-

B

nent to minimize turn-on pops since it determines how fast
the LM4880 turns on. The slower the LM4880’s outputs ramp
to their quiescent DC voltage (nominally 1/2 V
smaller the turn-on pop. Choosing C
with a small value of C

(in the range of 0.1 µF to 0.39 µF),

i

equal to 1.0 µF along

B

DD

), the

should produce a virtually clickless and popless shutdown
function. While the device will function properly, (no oscilla­tions or motorboating), with C

equal to 0.1 µF, the device

B

will be much more susceptible to turn-on clicks and pops.
Thus, a value of C

equal to 1.0 µF or larger is recom-

B

mended in all but the most cost sensitive designs.

AUDIO POWER AMPLIFIER DESIGN

Design a Dual 200 mW/8Ω Audio Amplifier

Given:

Power Output: 200 mWrms Load Impedance: 8Ω
Input Level: 1 Vrms (max) Input Impedance: 20 kΩ
Bandwidth: 100 Hz–20 kHz

±

0.50 dB

A designer must first determine the needed supply rail to
obtain the specified output power. Calculating the required
supply rail involves knowing two parameters, V

opeak

and also
the dropout voltage. As shown in the Typical Performance
Curves, the dropout voltage is typically 0.5V. V

opeak

can be

determined from Equation (3).

(3)

For 200 mW of output power into an 8Ω load, the required

is 1.79V. Since this is a single supply application, the

V

opeak

minimum supply voltage is twice the sum of V

opeak

and Vod.
Since 5V is a standard supply voltage in most applications, it
is chosen for the supply rail. Extra supply voltage creates
headroom that allows the LM4880 to reproduce peaks in
excess of 200 mW without clipping the signal. At this time,
the designer must make sure that the power supply choice
along with the output impedance does not violate the condi­tions explained in the Power Dissipation section. Remem-

LM4880

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Application Information (Continued)

ber that the maximum power dissipation value from Equation

LM4880

(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 Equation (4).

A

=−RF/R

V

From Equation (4), the minimum gain is:: A
Since the desired input impedance was 20 kΩ, and with a

gain of −1.26, a value of 27 kΩ is designated for R
ing 5% tolerance resistors. This combination results in a
nominal gain of −1.35. The final design step is to address the
bandwidth requirements which must be stated as a pair of

−3 dB frequency points. Five times away from a −3 dB point
is 0.17 dB down from passband response assuming a single
pole roll-off. As stated in the External Components section,

i

V

= −1.26

, assum-

f

(4)
(5)

both R

in conjunction with Ci, and Cowith RL, create first

i

order high pass filters. Thus to obtain the desired frequency

±

low response of 100 Hz within

0.5 dB, 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 down 0.34 dB at five times
away from the single order filter −3 dB point. Thus, a fre­quency of 20 Hz is used in the following equations to ensure
that the response if better than 0.5 dB down at 100 Hz.

≥ 1/(2π*20kΩ*20Hz) = 0.397 µF; use 0.39 µF

C

i

≥ 1/(2π*8Ω*20Hz) = 995 µF; use 1000 µF

C

o

The high frequency pole is determined by the product of the
desired high frequency pole, f

. With a closed-loop gain magnitude of 1.35 and fH= 100

A

V

, and the closed-loop gain,

H

kHz, the resulting GBWP = 135 kHz which is much smaller
than the LM4880 GBWP of 12.5 MHz. This figure displays
that if a designer has a need top design an amplifier with a
higher gain, the LM4880 can still be used without running
into bandwidth limitations.

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Application Information (Continued)

LM4880 MDA MWA DUAL 250 MW AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE

LM4880

Die Layout (B - Step)

Die/Wafer Characteristics

Fabrication Attributes General Die Information

Physical Die Identification LM4880B Bond Pad Opening Size (min) 86µm x 86µm

Die Step B Bond Pad Metalization ALUMINUM

Physical Attributes Passivation NITRIDE

Wafer Diameter 150mm Back Side Metal Bare Back

Dise Size (Drawn) 952µm x 1283µm

37mils x 51mils

Thickness 254µm Nominal

Min Pitch 117µm Nominal

Special Assembly Requirements:

Note: Actual die size is rounded to the nearest micron.

Die Bond Pad Coordinate Locations (B - Step)

(Referenced to die center, coordinates in µm) NC = No Connection

SIGNAL NAME PAD# NUMBER

BYPASS 1 -322 523 86 x 86

GND 2 -359 259 86 x 188

NC 3 -359 5 86 x 86

GND 4 -359 -259 86 x 188

SHUTDOWN 5 -323 -523 86 x 86

INPUT B 6 -109 -523 86 x 86

OUTPUT B 7 8 -523 86 x 86

VDD 8 358 -78 86 x 188

GND 9 358 141 86 x 188

OUTPUT A 10 359 406 86 x 86

INPUT A 11 323 523 86 x 86

NC 12 8 523 86 x 86

NC 13 -109 523 86 x 86

X/Y COORDINATES PAD SIZE

XYX Y

01234337

Back Side Connection GND

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Application Information (Continued)

LM4880

IN U.S.A

Tel #: 1 877 Dial Die 1 877 342 5343

Fax: [phone]

IN EUROPE

Tel: [phone] / 1495

Fax: [phone]

IN ASIA PACIFIC

Tel: [phone]

IN JAPAN

Tel: [phone]

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Physical Dimensions inches (millimeters) unless otherwise noted

LM4880

8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC

Order Number LM4880M

NS Package Number M08A

8-Lead (0.300" Wide) Molded Dual-In-Line Package

Order Number LM4880N

NS Package Number N08E

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Shutdown Mode

Notes

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

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.

labeling, can be reasonably expected to result in a
significant injury to the user.

BANNED SUBSTANCE COMPLIANCE

National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification

LM4880 Boomer Audio Power Amplifier Series Dual 250 mW Audio Power Amplifier with

(CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2.

National Semiconductor
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Support Center

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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.

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