Datasheet LM4882MX, LM4882MM, LM4882MDC, LM4882M Datasheet (NSC)

LM4882
250mW Audio Power Amplifier with Shutdown Mode

General Description

The LM4882 is a single-ended audio power amplifier ca­pable of delivering 250 mW of continuous average power
into an 8Ω load with 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 LM4882 does not require bootstrap capacitors or
snubber networks, it is optimally suited for low-power por­table systems.

The LM4882 features an externally controlled, low power
consumption shutdown mode which is virtually clickless and
popless, as well as an internal thermal shutdown protection
mechanism.

The unity-gain stable LM4882 can be configured by external
gain-setting resistors.

Key Specifications

n THD+Nat1kHzat250mW

continuous average output
power into 8Ω 1.0%(max)

n Output Power at 1%THD+N

at 1kHz into 4Ω 380mW (typ)

n THD+Nat1kHzat85mW

continuous average output
power into 32Ω 0.1%(typ)

n Shutdown Current 0.7 µA (typ)

Features

n MSOP surface mount packaging
n “Click and Pop” Suppression Circuitry
n Supply voltages from 2.4V–5.5V
n Operating Temperature −40˚C to 85˚C
n Unity-gain stable
n External gain configuration capability
n No bootstrap capacitors, or snubber circuits are

necessary

Applications

n Personal Computers
n Cellular Phones
n General Purpose Audio

Typical Application Connection Diagram

Boomer®is a registered trademark of National Semiconductor Corporation.

DS100030-1

*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

MSOP and SOIC Package

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Top View

Order Number LM4882MM or LM4882M

See NS Package Number MUA08A or M08A

January 1998

LM4882 250mW Audio Power Amplifier with Shutdown Mode

© 1998 National Semiconductor Corporation DS100030 www.national.com

Absolute Maximum Ratings (Note 1)

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

Supply Voltage 6.0 V
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) 2000V

PIn 5 1500V
Junction Temperature 150˚C
Soldering Information

Small Outline Package

Vapor Phase (60 seconds) 215˚C
Infrared (15 seconds) 220˚C

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

Thermal Resistance

θ

JC

(MSOP) 56˚C/W

θ

JA

(MSOP) 210˚C/W

θ

JC

(SOP) 35˚C/W

θ

JA

(SOP) 170˚C/W

Operating Ratings

Temperature Range

T

MIN

≤ TA≤ T

MAX

−40˚C ≤ TA≤ 85˚C

Supply Voltage 2.4V ≤ 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

LM4882

Units

(Limits)

Typical

(Note 5)

Limit

(Note 6)

I

DD

Quiescent Current VIN= 0V, IO= 0A 2 4.0 mA (max)

I

SD

Shutdown Current V

pin1=VDD

0.5 5 µA (max)

V

OS

Offset Voltage VIN= 0V 5 50 mV (max)

P

O

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

R

L

=4Ω 380 mW

R

L

=8Ω 270 250 mW (min)

R

L

=32Ω 95 mW

THD+N=10%;f=1kHz

R

L

=4Ω 480 mW

R

L

=8Ω 325 mW

R

L

=32Ω 125 mW

THD + N Total Harmonic Distortion + Noise R

L

=8Ω,PO= 250 mWrms; 0.5

%

R

L

=32Ω,PO= 85 mWrms; 0.1

%

f=1kHz

PSRR Power Supply Rejection Ratio V

pin3

= 2.5V, V

ripple

= 200 mVrms,

f = 120 Hz

50 dB

Electrical Characteristics (Notes 1, 2)

The following specifications apply for VDD= 3V unless otherwise specified. Limits apply for TA= 25˚C.

Symbol Parameter Conditions

LM4882

Units

(Limits)

Typical

(Note 5)

Limit

(Note 6)

I

DD

Quiescent Current VIN= 0V, IO= 0A 1.2 mA

I

SD

Shutdown Current V

pin1=VDD

0.3 µA

V

OS

Offset Voltage VIN=0V 5 mV

P

O

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

R

L

=8Ω 80 mW

R

L

=32Ω 30 mW

THD+N=10%;f=1kHz

R

L

=8Ω 105 mW

R

L

=32Ω 40 mW

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Electrical Characteristics (Notes 1, 2) (Continued)

The following specifications apply for VDD= 3V unless otherwise specified. Limits apply for TA= 25˚C.

Symbol Parameter Conditions

LM4882

Units

(Limits)

Typical

(Note 5)

Limit

(Note 6)

THD + N Total Harmonic Distortion + Noise R

L

=8Ω,PO= 70 mWrms; 0.25

%

R

L

=32Ω,PO= 30 mWrms; 0.3

%

f=1kHz

PSRR Power Supply Rejection Ratio V

pin3

= 2.5V, V

ripple

= 200 mVrms,

f = 120 Hz

50 dB

Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 2:

Absolute MaximumRatings

indicate limitsbeyondwhichdamage to the device mayoccur.

Operating Ratings

indicate conditionsforwhichthe device is func-

tional, butdonot 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

JMAX

, θJA, and the ambient temperature TA. The maximum

allowable power dissipation is P

DMAX

=(T

JMAX−TA

)/θJA. For the LM4882, T

JMAX

= 150˚C, and the typical junction-to-ambient thermal resistance, when board

mounted, is 210˚C/W for the MUA08A Package and 170˚C/W for the M08A Package.

Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Typicals are measured at 25˚C and represent the parametric norm.
Note 6: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).

External Components Description

(Refer to

Figure 1

)

Components Functional Description

1. R

i

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

i

at fc=1/(2πRiCi).

2. C

i

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

i

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

for an explanation of how to determine the values of C

i

.

3. R

f

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

4. C

S

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 selection of C

B

.

6. C

O

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

L

at fO=1/(2πRLCO).

Typical Performance Characteristics

THD+N vs Frequency

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THD+N vs Frequency

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THD+N vs Frequency

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Typical Performance Characteristics (Continued)

THD+N vs Frequency

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THD+N vs Frequency

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THD+N vs Frequency

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THD+N vs Frequency

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THD+N vs Frequency

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THD+N vs
Output Power

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THD+N vs
Output Power

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THD+N vs
Output Power

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Typical Performance Characteristics (Continued)

THD+N vs
Output Power

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THD+N vs
Output Power

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THD+N vs
Output Power

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THD+N vs
Output Power

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THD+N vs
Output Power

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Output Power vs
Supply Voltage

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Output Power vs
Supply Voltage

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Output Power vs
Supply Voltage

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Typical Performance Characteristics (Continued)

Dropout Voltage vs
Supply Voltage

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Dropout Voltage vs
Supply Voltage

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Power Supply
Rejection Ratio

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Output Power vs
Load Resistance

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Power Dissipation vs
Output Power

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Supply Current vs
Supply Voltage

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Typical Performance Characteristics (Continued)

Open Loop
Frequency Response

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Output Attenuation in
Shutdown Mode

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Noise Floor

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Frequency Response
vs Output Capacitor Size

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Frequency Response
vs Output Capacitor Size

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Frequency Response
vs Input Capacitor Size

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Typical Application
Frequency Response

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Typical Application
Frequency Response

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Power Derating Curve

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Application Information

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the
LM4882 contains a shutdown pin to externally turn off the
amplifier’s bias circuitry. This shutdown features turns the
amplifier off when a logichigh 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 switch­ing the shutdown pin to the V

DD

, the LM4882 supply current
draw will be minimized in idle mode. While the device will be
disabled with shutdown pin voltages less than V

DD

, the idle
current may be greater than the typical value of 0.5 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 externalpull-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
LM4882. 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.

P

DMAX

=(VDD)2/(2π2RL) (1)

Even with this internal power dissipation, the LM4882 does
not require heat sinking over a large range of ambient tem­perature. From Equation 1, assuming a 5V powersupply and
an 4Ω load, the maximum power dissipation point is
316 mW. The maximum power dissipation point obtained
must not be greater than the power dissipation that results
from Equation 2:

P

DMAX

=(T

JMAX−TA

)/θJA(2)

For the LM4882 surface mount package, θ

JA

= 210˚C/W and

T

JMAX

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

A

reduced. For
the typical application of a 5V power supply, with an 4Ω load,
the maximum ambient temperature possible without violating
the maximum junction temperature is approximately 83˚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 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 TypicalPerformance Characteristics 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 LM4882. The selection of bypass capaci­tors, especially C

B

, is thus dependent upon desired low fre­quency PSRR, click and pop performance as explained in
the section, Proper Selection of External Components
section, system cost, and size constraints.

PROPER SELECTION OF EXTERNAL COMPONENTS

Selection of external components when using integrated
power amplifiers is critical to optimize device and system
performance. While the LM4882 is tolerant of external com­ponent combinations, consideration to component values
must be used to maximize overall system quality.

The LM4882 is unity gain stable and this gives a designer
maximum system flexibility. The LM4882 should be used in
low gain configurations to minimize THD+N values, and
maximize the signal to noise ratio. Low gain configuartions
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 considerations is the closed
loop bandwidth of the amplifier. To a large extent, the band­width is dictated by the choice of external components
shown in

Figure 1

. Both the input coupling capacitor, Ci, and

the output coupling capacitor, C

o

, form first order high pass
filters which limit low frequency response. These values
should be chosen based on needed frequency response for
a few distinct reasons.

CLICK AND POP CIRCUITRY

The LM4882 contains circuitry to minimize turn-on and turn­off transients or “clicks and pops.” In this case, turn-on refers
to either power supply turn-on or the device coming out of
shutdown mode. When the device is turning on, the amplifi­ers are internally muted. An internal current source ramps up
the voltage of the bypass pin. Both the inputs and outputs
track the voltage at the bypass pin. The device will remain
muted until the bypass pin has reached its half supply volt­age, 1/2 V

DD

. As soon as the bypass node is stable, the de­vice will become fully operational, where the gain is set by
the external resistors.

Although the bypass pin current source cannot be modified,
the size of C

B

can be changed to alter the device turn-on
time and the level of “clicks and pops.” By increasing the
value of C

B

, the level of turn-on pop can be reduced. How­ever,the tradeoff for using a larger bypass capacitor is an in­crease in turn-on time for the device. There is a linear rela­tionship between the size of C

B

and the turn-on time. Here

are some typical turn-on times for a given C

B

:

C

B

T

ON

0.01 µF 20 ms

0.1 µF 200 ms

0.22 µF 420 ms

0.47 µF 900 ms

In order to eliminate “clicks and pops,” all capacitors must be
discharged before turn-on. Rapid on/off switching of the de-

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Application Information (Continued)

vice or the shutdown function may cause the “click and pop”
circuitry to not operate fully, resulting in increased “click and
pop” noise.

The value of C

i

will also reflect turn-on pops. Clearly, a cer-

tain size for C

i

is needed to couple in low frequencies without
excessive attenuation. But in many cases, the speakers
used in portable systems have little ability to reproduce sig­nals below 100 Hz to 150Hz. Inthis case, using a large input
and output coupling capacitor may not increase system per­formance. In most cases, choosing a small value of C

i

in the

range of 0.1 µF to 0.33 µF, along with C

B

equal to 1.0 µF
should produce a virtually clickless and popless turn-on. In
cases where C

i

is larger than 0.33 µF, it may be advanta-

geous to increase the value of C

B

.Again, it should be under-

stood that increasing the value of C

B

will reduce the “clicks

and pops” at the expense of a longer device turn-on time.

AUDIO POWER AMPLIFIER DESIGN

Design a 250 mW/8Ω Audio Amplifier

Given:
Power Output 250 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. The latter is typically 530mV and can be
found from the graphs in the Typical Performance Charac-
teristics. V

OPEAK

can be determined from Equation 3.

(3)

For 250 mW of output power into an 8Ω load, the required
V

OPEAK

is 2 volts. A minimum supply rail of 4.55V results

from adding 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
LM4882 to reproduce peaks in excess of 300 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.

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

(4)

A

V=Rf/Ri

(5)

From Equation 4, the minimum gain is:

A

V

= 1.4

Since the desired input impedance was 20 kΩ, and with a
gain of 1.4, a value of 28 kΩ is designated for R

f

, assuming
5%tolerance resistors. This combination results in anominal
gain of 1.4. The finaldesign step is to address thebandwidth
requirements which must be stated as a pair of −3 dB fre­quency points. Five times away from a −3 dBpoint is0.17 dB
down from passband response assuming a single pole roll­off. As stated in the External Components section, both R

i

in conjunction with Ci, and Cowith RL, create first order high­pass 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 singleorder 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 ensurethat there­sponse is better than 0.5 dB down at 100 Hz.

C

i

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

C

o

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

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 of 1.4 andfH= 100 kHz, the result­ing GBWP = 140 kHz which is much smaller than the
LM4882 GBWP of 12.5Mhz. This figure displays that if a de­signer has a need to design an amplifier with a higher gain,
the LM4882 can still be used without running into bandwidth
limitations.

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10

Physical Dimensions inches (millimeters) unless otherwise noted

Order Number LM4882

NS Package Number M08A

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

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 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, andwhose fail­ure to perform when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected toresult in a significantinjury
to the user.

2. A critical component in 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, orto affect its safetyor effectiveness.

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Order Number LM4882

NS Package Number MUA08A

LM4882 250mW Audio Power Amplifier with Shutdown Mode

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.