Datasheet LM4808MM, LM4808M Datasheet (NSC)

LM4808

Dual 105 mW Headphone Amplifier

LM4808 Dual 105 mW Headphone Amplifier

February 2000

General Description

The LM4808 is a dual audio power amplifier capable of deliv­ering 105 mW per channel of continuous average power into
a16Ωload 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 LM4808 does not require bootstrap capacitors or snub­ber networks, it is optimally suited for low-power portable
systems.

The unity-gain stable LM4808 can be configured by external
gain-setting resistors.

Key Specifications

n THD+N at 1 kHz at 105 mW

continuous average output
power into 16Ω 0.1% (max)

n THD+N at 1 kHz at 70 mW

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

n Output power at 0.1% THD+N

at 1 kHz into 32Ω 70 mW (typ)

Features

n SOP and MSOP surface mount packaging
n Switch on/off click suppression
n Excellent power supply ripple rejection
n Unity-gain stable
n Minimum external components

Applications

n Headphone Amplifier
n Personal Computers
n Microphone Preamplifier

Typical Application Connection Diagram

DS101276-1

*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

Boomer®is a registered trademark of National Semiconductor Corporation.

SOP & MSOP Package

DS101276-2

Top View

Order Number LM4808M, LM4808MM

See NS Package Number M08A, MUA08A

© 2000 National Semiconductor Corporation DS101276 www.national.com

Absolute Maximum Ratings (Note 3)

If Military/Aerospace specified devices are required,

LM4808

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
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

DD

+ 0.3V

Infrared (15 seconds) 220˚C

Thermal Resistance

(MSOP) 56˚C/W

θ

JC

(MSOP) 210˚C/W

θ

JA

(SOP) 35˚C/W

θ

JC

(SOP) 170˚C/W

θ

JA

Operating Ratings

Temperature Range

≤ TA≤ T

T

MIN

MAX

Supply Voltage 2.0V ≤ V

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

−40˚C ≤ TA≤ 85˚C

Vapor Phase (60 seconds) 215˚C

Electrical Characteristics (Notes 2, 3)

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

Symbol Parameter Conditions LM4808 Units (Limits)

Typ (Note 7) Limit (Note 8)

V

DD

I

DD

P

tot

V

OS

Ibias Input Bias Current 10 pA
V

CM

G

V

Io Max Output Current THD+N
R

O

V

O

PSRR Power Supply Rejection Ratio Cb = 1.0µF, Vripple = 100mV

Crosstalk Channel Separation R
THD+N Total Harmonic Distortion +

SNR Signal-to-Noise Ratio V
f

G

P

o

C

I

C

L

SR Slew Rate Unity Gain Inverting 3 V/µs

Supply Voltage 2.0 V (min)

5.5 V (max)
Supply Current VIN= 0V, IO= 0A 1.2 3.0 mA (max)
Total Power Dissipation VIN= 0V, IO= 0A 6 16.5 mW (max)
Input Offset Voltage VIN= 0V 10 50 mV (max)

Common Mode Voltage

0V

4.3 V

Open-Loop Voltage Gain RL=5kΩ 67 dB

<

0.1 % 70 mA
Output Resistance 0.1 Ω
Output Swing RL=32Ω, 0.1% THD+N, Min .3

=32Ω, 0.1% THD+N, Max 4.7

R

L

,

PP

89 dB

f = 100Hz

=32Ω 75 dB

L

f=1kHz

Noise

R

=16Ω,

L

=3.5VPP(at 0 dB)

V

O

R

=32Ω,

L

=3.5VPP(at 0 dB)

V

O

= 3.5Vpp(at 0 dB) 105 dB

O

0.05 %
66 dB

0.05 %
66 dB

Unity Gain Frequency Open Loop, RL=5kΩ 5.5 MHz
Output Power THD+N = 0.1%,f=1kHz

R

=16Ω 105 mW

L

R

=32Ω 70 60 mW

L

THD+N = 10%,f=1kHz
R

=16Ω 150 mW

L

R

=32Ω 90 mW

L

Input Capacitance 3 pF
Load Capacitance 200 pF

DD

≤ 5.5V

V

www.national.com 2

Electrical Characteristics (Notes 2, 3)

The following specifications apply for VDD= 3.3V unless otherwise specified, limits apply to TA= 25˚C.

Symbol Parameter Conditions Conditions Units (Limits)

Typ (Note 7) Limit (Note 8)

I

DD

V

OS

P

o

Supply Current VIN= 0V, IO= 0A 1.0 mA (max)
Input Offset Voltage VIN= 0V 7 mV (max)
Output Power THD+N = 0.1%,f=1kHz

R

=16Ω 40 mW

L

R

=32Ω 28 mW

L

THD+N = 10%,f=1kHz
R

=16Ω 56 mW

L

R

=32Ω 38 mW

L

Electrical Characteristics (Notes 2, 3)

The following specifications apply for VDD= 2.6V unless otherwise specified, limits apply to TA= 25˚C.

Symbol Parameter Conditions Conditions Units (Limits)

Typ (Note 7) Limit (Note 8)

I

DD

V

OS

P

o

Note 2: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 3:

tional, but do not guarantee specific performance limits.
antee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is
given, however, the typical value is a good indication of device performance.

Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
allowable power dissipation is P
mounted, is 210˚C/W for the MSOP Package and 107˚C/W for package N08E.

Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 6: Machine Model, 220 pF–240 pF discharged through all pins.
Note 7: Typicals are measured at 25˚C and represent the parametric norm.
Note 8: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).

Supply Current VIN= 0V, IO= 0A 0.9 mA (max)
Input Offset Voltage VIN= 0V 5 mV (max)
Output Power THD+N = 0.1%,f=1kHz

R

=16Ω 20 mW

L

R

=32Ω 16 mW

L

THD+N = 10%,f=1kHz
R

=16Ω 31 mW

L

R

=32Ω 22 mW

L

Absolute Maximum Ratings

indicate limits beyond which damage to the device may occur.

=(T

DMAX

JMAX−TA

Electrical Characteristics

)/θJA. For the LM4808, T

state DC and AC electrical specifications under particular test conditions which guar-

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

JMAX

Operating Ratings

, θJA, and the ambient temperature TA. The maximum

JMAX

indicate conditions for which the device is func-

LM4808

www.national.com3

External Components Description (

LM4808

Compo-

nents

1. R

i

2. C

i

3. R

f

4. C

S

5. C

B

6. C

O

7. R

B

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

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

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

i

Components, for and explanation of how to determine the value of C
Feedback resistance which sets closed-loop gain in conjuction 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.
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
Output coupling capacitor which blocks the DC voltage at the amplifier’s output. Forms a high pass

filter with R

at fO= 1/(2πRLCO)

L

Resistor which forms a voltage divider that provides a half-supply DC voltage to the non-inverting
input of the amplifier.

Typical Performance Characteristics

Figure 1

)

Functional Description

at fc=1/(2πRiCi).

i

.

i

.

B

THD+N vs Frequency

THD+N vs Frequency

DS101276-3

THD+N vs Frequency

THD+N vs Frequency

DS101276-4

THD+N vs Frequency

DS101276-5

THD+N vs Frequency

DS101276-6

www.national.com 4

DS101276-7

DS101276-8

Typical Performance Characteristics (Continued)

LM4808

THD+N vs Frequency

THD+N vs Frequency

DS101276-9

THD+N vs Frequency

THD+N vs Output Power

DS101276-10

THD+N vs Frequency

DS101276-11

THD+N vs Output Power

THD+N vs Output Power

DS101276-12

DS101276-15

THD+N vs Output Power

DS101276-13

DS101276-16

DS101276-14

THD+N vs Output Power

DS101276-17

www.national.com5

Typical Performance Characteristics (Continued)

LM4808

THD+N vs Output Power

THD+N vs Output Power

THD+N vs Output Power

THD+N vs Output Power

Output Power vs
Load Resistance

DS101276-18

DS101276-21

Output Power vs
Load Resistance

Output Power vs
Supply Voltage

DS101276-19

DS101276-22

DS101276-20

Output Power vs
Load Resistance

DS101276-23

Output Power vs
Power Supply

DS101276-24

www.national.com 6

DS101276-25

DS101276-26

Typical Performance Characteristics (Continued)

LM4808

Output Power vs
Power Supply

Power Dissipation vs
Output Power

DS101276-27

Clipping Voltage vs
Supply Voltage

Power Dissipation vs
Output Power

DS101276-28

Power Dissipation vs
Output Power

DS101276-29

Channel Separation

Channel Separation

DS101276-30

DS101276-33

Noise Floor

DS101276-31

DS101276-34

DS101276-32

Power Supply Rejection Ratio

DS101276-35

www.national.com7

Typical Performance Characteristics (Continued)

LM4808

Open Loop
Frequency Response

Open Loop
Frequency Response

Open Loop
Frequency Response

Supply Current vs
Supply Voltage

Frequency Response vs
Output Capacitor Size

DS101276-50

DS101276-44

Frequency Response vs
Output Capacitor Size

Typical Application
Frequency Response

DS101276-51

DS101276-45

DS101276-38

Frequency Response vs
Output Capacitor Size

DS101276-46

Typical Application
Frequency Response

DS101276-47

www.national.com 8

DS101276-48

DS101276-49

Application Information

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

=(VDD)2/(2π2RL) (1)

DMAX

Since the LM4808 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 LM4808 does
not require heat sinking over a large range of ambient tem­perature. From Equation 1, assuming a 5V power supply and
a32Ωload, the maximum power dissipation point is 40 mW
per amplifier. Thus the maximum package dissipation point
is 80 mW. The maximum power dissipation point obtained
must not be greater than the power dissipation that results
from Equation 2:

P

=(T

DMAX

JMAX−TA

For package MUA08A, θ
M08A, θ

= 170˚C/W. T

JA

JMAX

pending on the ambient temperature, T
roundings, 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
tion of a 5V power supply, with a 32Ω load, the maximum
ambient temperature possible without violating the maximum
junction temperature is approximately 131.6˚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 Character-
istics curves for power dissipation information for lower out­put powers.

POWER SUPPLY BYPASSING

As with any power amplifer, 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 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 LM4808. The selection of bypass capaci­tors, especially C

, is thus dependent upon desired low fre-

B

quency 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 LM4808 is tolerant of external com­ponent combinations, consideration to component values
must be used to maximize overall system quality.

The LM4808 is unity gain stable and this gives a designer
maximum system flexibility. The LM4808 should be used in

)/θ

= 210˚C/W, and for package

JA

(2)

JA

= 150˚C for the LM4808. De-

, of the system sur-

A

reduced. For the typical applica-

A

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 considerations is the closed
loop bandwidth of the amplifier. To a large extent, the band­width is dicated by the choice of external components shown
in

Figure 1

put coupling capacitor, C

. Both the input coupling capacitor, Ci, and the out-

, form first order high pass filters

o

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 value input and output capacitors are both expensive
and space consuming for portable designs. Clearly a certain
sized capacitor is needed to couple in low frequencies with­out severe attenuation. But in many cases the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 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 affected by the size of the input coupling capacitor,
C

. A larger input coupling capacitor requires more charge to

i

reach its quiescent DC voltage (nominally 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
value. Bypass capacitor C

is the most critical component to

B

minimize turn on pops since it determines how fast the
LM4808 turns on. The slower the LM4808’s outputs ramp to
their quiescent DC voltage (nominally 1/2 V

), the smaller

DD

the turn on pop. While the device will function properly, (no
oscillations or motorboating), with C

equal to 1 µF, the de-

B

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

equal to 1 µF or larger is recom-

B

mended in all but the most cost sensitive designs.

AUDIO POWER AMPLIFIER DESIGN
Design a Dual 70mW/32Ω Audio Amplifier

Given:
Power Output 70 mW
Load Impedance 32Ω
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 300mV and can be
found from the graphs in the Typical Performance Charac-
teristics. V

can be determined from Equation 3.

OPEAK

(3)

LM4808

www.national.com9

Application Information (Continued)

For 70 mW of output power into a 32Ω load, the required V

LM4808

is 2.12 volts. A minimum supply rail of 2.42V results

PEAK

from adding V

and VOD. Since 5V is a standard supply

OPEAK

voltage in most applications, it is chosen for the supply rail.
Extra supply voltage creates headroom that allows the
LM4808 to reproduce peaks in excess of 70 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. 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 Equation 4.

A

V=Rf/Ri

From Equation 4, the minimum gain is: A

(5)

= 1.26

V

Since the desired input impedance was 20kΩ, and with a
gain of 1.26, a value of 27kΩ is designated for R
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 −3dB point is

0.17dB down from passband response assuming a single
pole roll-off. As stated in the External Components section,
both R

in conjunction with Ci, and Cowith RL, create first or-

i

der highpass filters. Thus to obtain the desired frequency low
response of 100Hz 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 down 0.34dB 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 than 0.5dB down at 100Hz.

C

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

i

C

≥ 1/(2π*32Ω* 20 Hz) = 249µF; use 330µF.

o

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

V

. With a closed-loop gain of 1.35 and fH= 100kHz, the re-

, and the closed-loop gain, A

H

sulting GBWP = 135kHz which is much smaller than the
LM4808 GBWP of 900kHz. This figure displays that if a de­signer has a need to design an amplifier with a higher gain,
the LM4808 can still be used without running into bandwidth
limitations.

, assuming

f

(4)

-

O

www.national.com 10

LM4808

Application Information (Continued)

Silk Screen

DS101276-39

Top Layer

Bottom Layer

DS101276-42

Drill Drawing

DS101276-43

Solder Mask

DS101276-40

DS101276-41

www.national.com11

Physical Dimensions inches (millimeters) unless otherwise noted

LM4808

Order Number LM4808MM

NS Package Number MUA08A

Order Number LM4808M

NS Package Number M08A

www.national.com 12

Notes

LM4808 Dual 105 mW Headphone Amplifier

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.

National Semiconductor
Corporation

Americas
Tel: [phone]
Fax: [phone]
Email: [e-mail]

www.national.com

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.

National Semiconductor
Europe

Fax: [phone]

Email: [e-mail]
Deutsch Tel: [phone]
English Tel: [phone]
Français Tel: [phone]

National Semiconductor
Asia Pacific Customer
Response Group

Tel: [phone]
Fax: [phone]
Email: [e-mail]

National Semiconductor
Japan Ltd.

Tel: [phone]
Fax: [phone]