Datasheet LM4861 Datasheet (National Semiconductor)

LM4861

1.1W Audio Power Amplifier with Shutdown Mode

LM4861 1.1W Audio Power Amplifier with Shutdown Mode

February 2003

General Description

The LM4861 is a bridge-connected audio power amplifier
capable of delivering 1.1W of continuous average power to
an 8Ω load with 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 LM4861 does not require output coupling capacitors,
bootstrap capacitors, or snubber networks, it is optimally
suited for low-power portable systems.

The LM4861 features an externally controlled, low-power
consumption shutdown mode, as well as an internal thermal
shutdown protection mechanism.

The unity-gain stable LM4861 can be configured by external
gain-setting resistors for differential gains of up to 10 without
the use of external compensation components. Higher gains
may be achieved with suitable compensation.

Connection Diagram

Key Specifications

j

THD+N for 1kHz at 1W continuous

average output power into 8Ω 1.0% (max)

j

Output power at 10% THD+N

at 1kHz into 8Ω

j

Shutdown Current 0.6µA (typ)

1.5W (typ)

Features

n No output coupling capacitors, bootstrap capacitors, or

snubber circuits are necessary

n Small Outline (SO) packaging
n Compatible with PC power supplies
n Thermal shutdown protection circuitry
n Unity-gain stable
n External gain configuration capability

Applications

n Personal computers
n Portable consumer products
n Self-powered speakers
n Toys and games

See NS Package Number M08A

Boomer®is a registered trademark of National Semiconductor Corporation.

Small Outline Package

01198602

Top View

Order Number LM4861M

© 2003 National Semiconductor Corporation DS011986 www.national.com

Typical Application

LM4861

FIGURE 1. Typical Audio Amplifier Application Circuit

01198601

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LM4861

Absolute Maximum Ratings (Note 2)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/

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

mount devices.

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 3) Internally limited

ESD Susceptibility (Note 4) 3000V

ESD Susceptibility (Note 5) 250V

Junction Temperature 150˚C

Soldering Information

Small Outline Package

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

215˚C
220˚C

+

Operating Ratings

Temperature Range

T

≤ TA≤ T

MIN

Supply Voltage 2.0V ≤ V

Thermal Resistance

θ

(typ) —M08A 35˚C/W

JC

θ

(typ) — M08A 140˚C/W

JA

θ

(typ) — N08E 37˚C/W

JC

θ

(typ) — N08E 107˚C/W

JA

MAX

−40˚C ≤ TA≤
+85˚C

≤ 5.5V

DD

Electrical Characteristics (Note 1) (Note 2)

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

LM4861

Symbol Parameter Conditions

Typical Limit

(Note 6) (Note 7)

V

DD

Supply Voltage 2.0 V (min)

5.5 V (max)

I

DD

I

SD

V

OS

P

O

THD+N Total Harmonic Distortion + Noise P

PSRR Power Supply Rejection Ratio V

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 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 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
allowable power dissipation is P
and the typical junction-to-ambient thermal resistance, when board mounted, is 140˚C/W.

Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor.

Note 5: Machine Model, 220pF– 240pF discharged through all pins.

Note 6: Typicals are measured at 25˚C and represent the parametric norm.

Note 7: Limits are guaranteed to Nationai’s AOQL (Average Outgoing Quality Level).

Note 8: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.

Quiescent Power Supply Current VIN= 0V, IO= 0A (Note 8) 6.5 10.0 mA (max)

Shutdown Current V

pin1=VDD

0.6 10.0 µA (max)

Output Offset Voltage VIN= 0V 5.0 50.0 mV (max)

Output Power THD = 1% (max);f=1kHz 1.1 1.0 W(min)

= 1Wrms; 20 Hz ≤ f ≤ 20 kHz 0.72 %

O

= 4.9V to 5.1V 65 dB

DD

, θJA, and the ambient temperature TA. The maximum

DMAX

=(T

)/θJAor the number given in theAbsolute Maximum Ratings, whichever is lower. For the LM4861, T

JMAX−TA

JMAX

Units

(Limits)

= 150˚C,

JMAX

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High Gain Application Circuit

LM4861

01198603

FIGURE 2. Audio Ampiifier with AVD=20

Single Ended Application Circuit

*CSand CBsize depend on specific application requirements and constraints. Typical vaiues of CSand CBare 0.1 µF.

**Pin 1 should be connected to V

***These components create a “dummy” load for pin 8 for stability purposes.

to disable the amplifier or to GND to enable the amplifier. This pin should not be left floating.

DD

FIGURE 3. Single-Ended Amplifier with AV=−1

01198604

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External Components Description

(Figures 1, 2)

Components Functional Description

1. R

2. C

3. R

4. C

i

i

f

S

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/(2π RiCi).

i

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

at fC=1/(2π RiCi).

i

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 supply bypass capacitor.

5. C

B

Bypass pin capacitor which provides half supply filtering. Refer to the Application Information section
for proper placement and selection of bypass capacitor.

(Note 9) Cfin conjunction with Rfcreates a low-pass filter which bandwidth limits the amplifier and prevents

6. C

f

possible high frequency oscillation bursts. f

Note 9: Optional component dependent upon specific design requirements. Refer to the Application Information section for more information.

=1/(2π RfCf)

C

Typical Performance Characteristics

THD+N vs Frequency THD+N vs Frequency

LM4861

01198605 01198606

THD+N vs Frequency THD+N vs Output Power

01198607 01198609

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Typical Performance Characteristics (Continued)

LM4861

THD+N vs Output Power

Output Power vs

Supply Voltage

01198610

Output Power vs
Load Resistance

01198617

Power Dissipation vs

Output Power

Noise Floor vs Frequency

01198618

01198614

01198616

Supply Current Distribution

vs Temperature

01198615

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Typical Performance Characteristics (Continued)

Supply Current vs

Supply Voltage Power Derating Curve

LM4861

Power Supply

Rejection Ratio

01198612

01198613

Open Loop

Frequency Response

01198620 01198619

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Application Information

LM4861

BRIDGE CONFIGURATION EXPLANATION

As shown in Figure 1 , the LM4861 has two operational
amplifiers internally, allowing for a few different amplifier
configurations. The first amplifier’s gain is externally config­urable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of
the first amplifier is set by selecting the ratio of R
the second amplifier’s gain is fixed by the two internal 40kΩ
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both
amplifiers producing signals identical in magnitude, but out
of phase 180˚. Consequently, the differential gain for the IC
is:

=2*(Rf/ Ri)

A

vd

By driving the load differentially through outputs V

, an amplifier configuration commonly referred to as

V

O2

“bridged mode” is established. Bridged mode operation is
different from the classical single-ended amplifier configura­tion 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. Consequently, four times the output power is
possible as compared to a single-ended amplifier under the
same conditions. This increase in attainable output power
assumes that the amplifier is not current limited or clipped. In
order to choose an amplifier’s closed-loop gain without caus­ing excessive clipping which will damage high frequency
transducers used in loudspeaker systems, please refer to
the Audio Power Amplifier Design section.

A bridge configuration, such as the one used in Boomer
Audio Power Amplifiers, also creates a second advantage
over single-ended amplifiers. Since the differential outputs,

and VO2, are biased at half-supply, no net DC voltage

V

O1

exists across the load. This eliminates the need for an output
coupling capacitor which is required in a single supply,
single-ended amplifier configuration. Without an output cou­pling capacitor in a single supply, single-ended amplifier, the
half-supply bias across the load would result in both in­creased internal IC power dissipation and also permanent
loudspeaker damage. An output coupling capacitor forms a
high pass filter with the load requiring that a large value such
as 470µF be used with an 8Ω load to preserve low frequency
response. This combination does not produce a flat re­sponse down to 20Hz, but does offer a compromise between
printed circuit board size and system cost, versus low fre­quency response.

POWER DISSIPATION

Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power
delivered to the load by a bridge amplifier is an increase in
internal power dissipation. Equation 1 states the maximum
power dissipation point for a bridge amplifier operating at a
given supply voltage and driving a specified output load.

= 4*(VDD)2/(2π2RL) (1)

P

DMAX

Since the LM4861 has two operational amplifiers in one
package, the maximum internal power dissipation is 4 times
that of a single-ended amplifier. Even with this substantial
increase in power dissipation, the LM4861 does not require
heatsinking. From Equation 1, assuming a 5V power supply
and an 8Ω load, the maximum power dissipation point is

to Riwhile

f

O1

and

625mW.The maximum power dissipation point obtained from
Equation 1 must not be greater than the power dissipation
that results from Equation 2:

P

=(T

DMAX

JMAX−TA

For the LM4861 surface mount package, θ

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

T

JMAX

)/θ

JA

= 140˚C/W and

JA

(2)

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 or the load impedance increased. For the typical
application of a 5V power supply, with an 8Ω load, the
maximum ambient temperature possible without violating the
maximum junction temperature is approximately 62.5˚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 can
be increased. Refer to the Typical Performance Charac-
teristics 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 THD+N due to in­creased half-supply stability. Typical applications employ a
5V regulator with 10µF and a 0.1µF bypass capacitors which
aid in supply stability, but do not eliminate the need for
bypassing the supply nodes of the LM4861. The selection of
bypass capacitors, especially C

, is thus dependant upon

B

desired low frequency THD+N, system cost, and size con­straints.

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the
LM4861 contains a shutdown pin to externally turn off the
amplifier’s bias circuitry. The shutdown feature turns the
amplifier off when a logic high is placed on the shutdown pin.
Upon going into shutdown, the output is immediately discon­nected from the speaker. Atypical quiescent current of 0.6µA
results when the supply voltage is applied to the shutdown
pin. 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 that
when closed, is connected to ground and enables the am­plifier. If the switch is open, then a soft pull-up resistor of
47kΩ will disable the LM4861. There are no soft pull-down
resistors inside the LM4861, so a definite shutdown pin
voltage must be applied externally, or the internal logic gate
will be left floating which could disable the amplifier unex­pectedly.

HIGHER GAIN AUDIO AMPLIFIER

The LM4861 is unity-gain stable and requires no external
components besides gain-setting resistors, an input coupling
capacitor, and proper supply bypassing in the typical appli­cation. However, if a closed-loop differential gain of greater
than 10 is required, a feedback capacitor may be needed, as
shown in Figure 2, to bandwidth limit the amplifier. This
feedback capacitor creates a low pass filter that eliminates

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Application Information (Continued)

possible high frequency oscillations. Care should be taken
when calculating the −3dB frequency in that an incorrect
combination of R
typical combination of feedback resistor and capacitor that
will not produce audio band high frequency rolloff is R
100kΩ and C
point of approximately 320kHz. Once the differential gain of
the amplifier has been calculated, a choice of R

can then be calculated from the formula stated in the

and C

f

External Components Description section.

VOICE-BAND AUDIO AMPLIFIER

Many applications, such as telephony, only require a voice­band frequency response. Such an application usually re­quires a flat frequency response from 300Hz to 3.5kHz. By
adjusting the component values of Figure 2, this common
application requirement can be implemented. The combina­tion of R

and Ciform a highpass filter while Rfand Cfform a

i

lowpass filter. Using the typical voice-band frequency range,
with a passband differential gain of approximately 100, the
following values of R
tions stated in the External Components Description sec­tion.

= 10kΩ,Rf= 510k ,Ci= 0.22µF, and Cf= 15pF

R

i

Five times away from a −3dB point is 0.17dB down from the
flatband response. With this selection of components, the
resulting −3dB points, f
spectively, resulting in a flatband frequency response of
better than
the passband. If a steeper rolloff is required, other common
bandpass filtering techniques can be used to achieve higher
order filters.

SINGLE-ENDED AUDIO AMPLIFIER

Although the typical application for the LM4861 is a bridged
monoaural amp, it can also be used to drive a load single­endedly in applications, such as PC cards, which require that
one side of the load is tied to ground. Figure 3 shows a
common single-ended application, where V
drive the speaker. This output is coupled through a 470µF
capacitor, which blocks the half-supply DC bias that exists in
all single-supply amplifier configurations. This capacitor,
designated C
highpass filter. The −3dB point of this high pass filter is
1/(2πR

LCO

product of R
cies to the load. When driving an 8Ω load, and if a full audio
spectrum reproduction is required, C
470µF. V

O2

a 0.1 µF capacitor to a 2kΩ load to prevent instability. While
such an instability will not affect the waveform of V
good design practice to load the second output.

and Cfwill cause rolloff before 20kHz. A

f

= 5pF. These components result in a −3dB

f

f

, and Cffollow from the equa-

i,Ci,Rf

and fH, are 72Hz and 20kHz, re-

L

±

0.25dB with a rolloff of 6dB/octave outside of

O1

in Figure 3, in conjunction with RL, forms a

O

f

will result,

is used to

), so care should be taken to make sure that the

and COis large enough to pass low frequen-

L

should be at least

O

, the output that is not used, is connected through

,itis

O1

LM4861

AUDIO POWER AMPLIFIER DESIGN

Design a 1W / 8Ω Audio Amplifier

Given:

Power Output 1 Wrms

=

Load Impedance 8Ω

Input Level 1 Vrms

Input Impedance 20 kΩ

Bandwidth 100 Hz– 20 kHz

±

0.25 dB

A designer must first determine the needed supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graph in the Typical Per-
formance Characteristics section, the supply rail can be
easily found. A second way to determine the minimum sup­ply rail is to calculate the required V

using Equation 3

opeak

and add the dropout voltage. Using this method, the mini­mum supply voltage would be (V

opeak+VOD

, where VODis

typically 0.6V.

(3)

For 1W of output power into an 8Ω load, the required V

opeak

is 4.0V. A minumum supply rail of 4.6V results from adding

and Vod. But 4.6V is not a standard voltage that exists

V

opeak

in many applications and for this reason, a supply rail of 5V
is designated. Extra supply voltage creates dynamic head­room that allows the LM4861 to reproduce peaks in excess
of 1Wwithout 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.

Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa­tion 4.

(4)

R

f/Ri=AVD

From equation 4, the minimum A

/ 2 (5)

is 2.83: Avd=3

vd

Since the desired input impedance was 20kΩ, and with a A
of 3, a ratio of 1:1.5 of Rfto Riresults in an allocation of Ri=
20kΩ,R

= 30kΩ. The final design step is to address the

f

bandwidth requirements which must be stated as a pair of

−3dB frequency points. Five times away from a −3db point is

0.17dB down from passband response which is better than

±

the required

0.25dB specified. This fact results in a low and
high frequency pole of 20Hz and 100kHz respectively. As
stated in the External Components section, R
tion with C

create a highpass filter.

i

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

C

i

in conjunc-

i

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

= 2 and fH= 100kHz, the resulting GBWP =

vd

, and the differential gain,Avd.

H

100kHz which is much smaller than the LM4861 GBWP of
4MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4861 can still be used without running into bandwidth
problems.

vd

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LM4861 MDA MWA

1.1W Audio Power Amplifier with Shutdown Mode

LM4861

Die Layout (B - Step)

01198626

DIE/WAFER CHARACTERISTICS

Fabrication Attributes General Die Information

Physical Die Identification LM4861B Bond Pad Opening Size (min) 83µm x 83µm

Die Step B Bond Pad Metalization ALUMINUM

Physical Attributes Passivation VOM NITRIDE

Wafer Diameter 150mm Back Side Metal BARE BACK

Dise Size (Drawn) 1372µm x 2032µm

54.0mils x 80.0mils

Thickness 406µm Nominal

Min Pitch 108µm 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, N.U. = Not Used

SIGNAL NAME PAD# NUMBER

SHUTDOWN 1 -425 710 83 x 83

BYPASS 2 -445 499 83 x 83

NC 3 -445 -34 83 x 170

NC 4 -445 -383 83 x 83

INPUT + 5 -445 -492 83 x 83

INPUT - 6 -352 -710 83 x 83

GND 7 -243 -710 83 x 83

Vo1 8 -91 -710 170 x 83

GND 9 445 -574 83 x 170

VDD 10 445 -2 83 x 170

NC 11 445 387 83 x 83

GND 12 445 633 83 x 170

Vo2 13 -63 710 170 x 83

GND 14 -215 710 83 x 83

X/Y COORDINATES PAD SIZE

XYX Y

Back Side Connection GND

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LM4861 MDA MWA

1.1W Audio Power Amplifier with Shutdown Mode

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]

LM4861

(Continued)

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Physical Dimensions inches (millimeters)

unless otherwise noted

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

Order Number LM4861

NS Package Number M08A

LM4861 1.1W Audio Power Amplifier with Shutdown Mode

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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.

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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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