Datasheet LM4818M Datasheet (NSC)

LM4818

350mW Audio Power Amplifier with Shutdown Mode

LM4818 350mW Audio Power Amplifier with Shutdown Mode

April 2002

General Description

The LM4818 is a mono bridged power amplifier that is ca­pable of delivering 350mW
or 300mW
THD+N from a 5V power supply.

The LM4818 Boomer audio power amplifier is designed
specifically to provide high quality output power and mini­mize PCB area with surface mount packaging and a minimal
amount of external components. Since the LM4818 doesnot
require output coupling capacitors, bootstrap capacitors or
snubber networks, it is optimally suited for low-power por­table applications.

The closed loop response of the unity-gain stable LM4818
can be configured using external gain-setting resistors. The
device is available in SO package type to suit various appli­cations.

output power into an 8Ω load with 10%

RMS

output power into a 16Ω load

RMS

Typical Application

Key Specifications

n THD+N at 1kHz, 350mW continuous average output

power into 16Ω 10% (max)

n THD+N at 1kHz, 300mW continuous average output

power into 8Ω 10% (max)

n Shutdown Current 0.7µA (typ)

Features

n SOP surface mount packaging.
n Switch on/off click suppression.
n Unity-gain stable.
n Minimum external components.

Applications

n General purpose audio
n Portable electronic devices
n Information Appliances (IA)

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FIGURE 1. Typical Audio Amplifier Application Circuit

Boomer®is a registered trademark of National Semiconductor Corporation.

© 2002 National Semiconductor Corporation DS200389 www.national.com

Connection Diagrams

LM4818

Small Outline (SO) Package

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Top View

Order Number LM4818M

See NS Package Number M08A

SO Marking

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Top View

XY - Date Code

TT - Die Traceability

Bottom 2 lines - Part Number

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LM4818

Absolute Maximum Ratings (Notes 2, 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
Power Dissipation (P

) (Note 4) Internally Limited

D

DD

+0.3V

Operating Ratings (Notes 2, 3)

ESD Susceptibility (Note 5) 2.5kV
ESD Susceptibility (Note 6) 200V
Junction Temperature (T

) 150˚C

J

Soldering Information (Note 1)

Electrical Characteristics VDD=5V(Notes 2, 3)

The following specifications apply for V

Symbol Parameter Conditions

I

DD

I

SD

I

SDIH

I

SDIL

V
P

OS

O

Quiescent Power Supply Current VIN= 0V, Io= 0A 1.5 3.0 mA (max)
Shutdown Current V
Shutdown Voltage Input High 4.0 V (min)
Shutdown Voltage Input Low 1.0 V (max)
Output Offset Voltage VIN= 0V 5 50 mV (max)

Output Power

THD+N Total Harmonic Distortion + Noise P

= 5V, RL=16Ωunless otherwise stated. Limits apply for TA= 25˚C.

DD

PIN1=VDD

THD = 10%, f

THD = 10%, f

= 270mW

O

(Note 10) 1.0 5.0 µA (max)

= 1kHz 350 mW

IN

= 1kHz, RL=8Ω 300 mW

IN
RMS,AVD

1kHz

Small Outline Package

Vapor Phase (60 seconds) 215˚C

Infrared (15 seconds) 220˚C

Thermal Resistance

θ

(SOP) 35˚C/W

JC

θ

(SOP) 170˚C/W

JA

Temperature Range

T

MIN

≤ TA≤ T

MAX

−40˚C ≤ TA≤ 85˚C

Supply Voltage 2.0V ≤ V

LM4818

Typical Limit

(Note 7) (Notes 8, 9)

=2,fIN=

1%

≤ 5.5V

CC

Units

(Limits)

Electrical Characteristics VDD=3V(Notes 2, 3)

The following specifications apply for V

Symbol Parameter Conditions

I

DD

I

SD

I

SDIH

I

SDIL

V
P

OS

O

Quiescent Power Supply Current VIN= 0V, Io= 0A 1.0 3.0 mA (max)
Shutdown Current V
Shutdown Voltage Input High 2.4 V (min)
Shutdown Voltage Input Low 0.6 V (max)
Output Offset Voltage VIN= 0V 5 50 mV

Output Power

THD+N Total Harmonic Distortion + Noise P

= 3V and RL=16Ωload unless otherwise stated. Limits apply to TA= 25˚C.

DD

PIN1=VDD

THD = 10%, f
THD = 10%, f

= 80mW

O

(Note 10) 0.7 5.0 µA (max)

= 1kHz 110 mW

IN

= 1kHz, RL=8Ω 90 mW

IN

RMS,AVD

1kHz

=2,fIN=

LM4818

Typical Limit

(Note 7) (Notes 8, 9)

Units

(Limits)

1%

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Electrical Characteristics VDD=3V(Notes 2, 3)

The following specifications apply for V

LM4818

25˚C. (Continued)

Note 1: See AN-450 ’Surface Mounting and their Effects on Product Reliability’ for other methods of soldering surface mount devices.
Note 2: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 3:

Absolute Maximum Ratings

functional, but do not guarantee specific performance limits.
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’s 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 170˚C/W for the SOP package.

Note 5: Human body model, 100pF discharged through a 1.5 kΩ resistor.
Note 6: Machine Model, 220pF–240pF capacitor is discharged through all pins.
Note 7: Typical specifications are specified at 25˚C and represent the parametric norm.
Note 8: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 9: Datasheet min/max specification limits are guaranteed by designs, test, or statistical analysis.
Note 10: The Shutdown pin (pin 1) should be driven as close as possible to V

indicate limits beyond which damage to the device may occur.

=(T

DMAX

JMAX–TA

= 3V and RL=16Ωload unless otherwise stated. Limits apply to TA=

DD

Electrical Characteristics

)/θJA. For the LM4818, T

state DC and AC electrical specifications under particular test conditions which

= 150˚C and the typical junction-to-ambient thermal resistance (θJA) when board

JMAX

for minimum current in Shutdown Mode.

DD

Operating Ratings

, θJA, and the ambient temperature TA. The maximum

JMAX

indicate conditions for which the device is

External Components Description (

Figure 1

)

Components Functional Description

1. R

2. C

3. R

4. C

Combined with Rf, this inverting input resistor sets the closed-loop gain. Rialso forms a high pass filter with

i

i

f

S

at fc= 1/(2πRiCi).

C

i

This input coupling capacitor blocks DC voltage at the amplifier’s terminals. Combined with Ri, it creates a
high pass filter with R
for an explanation of how to determine the value of C

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

i

.

i

Combined with Ri, this is the feedback resistor that sets the closed-loop gain: Av= 2(RF/Ri).
This is the power supply bypass capacitor that filters the voltage applied to the power supply pin. Refer to

the Application Information section for proper placement and selection of C

5. C

This is the bypass pin capacitor that filters the voltage at the BYPASS pin. Refer to the section, Proper

B

Selection of External Components for information concerning proper placement and selection of C

6. C

This is an optional capacitor that is not needed in the majority of applications. If the capacitor is not used,

B2

pin 3 should be connected directly to pin2. Refer to the section Proper Selection of External Components
for more information concerning C

.

B2

Typical Performance Characteristics

.

s

.

B

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Typical Performance Characteristics (Continued)

LM4818

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Typical Performance Characteristics (Continued)

LM4818

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Output Power vs Supply Voltage
R

=8Ω

L

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Output Power vs Supply Voltage
R

=16Ω

L

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Typical Performance Characteristics (Continued)

LM4818

Output Power vs Supply Voltage
R

=32Ω

L

Power Dissipation vs
Output Power
V

=5V

DD

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Output Power vs Load Resistance

Power Dissipation vs
Output Power
V

=3V

DD

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Power Derating Curves

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Frequency Response vs
Input Capacitor Size

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Typical Performance Characteristics (Continued)

LM4818

Supply Current vs
Supply Voltage

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Application Information

BRIDGE CONFIGURATION EXPLANATION

As shown in
amplifiers. External resistors, R
gain of the first amplifier (and the amplifier overall), whereas
two internal 20kΩ resistors set the second amplifier’s gain at

-1. The LM4818 is typically used to drive a speaker con­nected between the two amplifier outputs.

Figure 1

to Amp2, which results in both amplifiers producing signals
identical in magnitude but 180˚ out of phase. Taking advan­tage of this phase difference, a load is placed between V
and V02and driven differentially (commonly referred to as
’bridge mode’). This results in a differential gain of

Bridge mode is different from single-ended amplifiers that
drive loads connected between a single amplifier’s output
and ground. For a given supply voltage, bridge mode has a
distinct advantage over the single-ended configuration: its
differential output doubles the voltage swing across the load.
This results in four times the output power when compared
to a single-ended amplifier under the same conditions. This
increase in attainable output assumes that the amplifier is
not current limited or the output signal is not clipped. To
ensure minimum output signal clipping when choosing an
amplifier’s closed-loop gain, refer to the Audio Power Am-
plifier Design Example section.

Another advantage of the differential bridge output is no net
DC voltage across the load. This results from biasing V
and V02at half-supply. This eliminates the coupling capacitor
that single supply, single-ended amplifiers require. Eliminat­ing an output coupling capacitor in a single-ended configu­ration forces a single supply amplifier’s half-supply bias volt­age across the load. The current flow created by the half­supply bias voltage increases internal IC power dissipation
and may permanently damage loads such as speakers.

POWER DISSIPATION

Power dissipation is a major concern when designing a
successful bridged or single-ended amplifier. Equation (2)
states the maximum power dissipation point for a single­ended amplifier operating at a given supply voltage and
driving a specified load.

However, a direct consequence of the increased power de­livered to the load by a bridged amplifier is an increase in the
internal power dissipation point for a bridge amplifier oper­ating at the same given conditions. Equation (3) states the
maximum power dissipation point for a bridged amplifier
operating at a given supply voltage and driving a specified
load.

The LM4818 has two operational amplifiers in one package
and the maximum internal power dissipation is four times
that of a single-ended amplifier. However, even with this
substantial increase in power dissipation, the LM4818 does
not require heatsinking. From Equation (3), assuming a 5V
power supply and an 8Ω load, the maximum power dissipa­tion point is 633mW. The maximum power dissipation point
obtained from Equation (3) must not exceed the power dis­sipation predicted by Equation (4):

Figure 1

, the LM4818 consist of two operational

and RFset the closed-loop

i

shows that the output of Amp1 servers as the input

A

= 2 *(Rf/Ri) (1)

VD

P

=(VDD)2/(2π2RL) (W) Single-ended (2)

DMAX

P

= 4(VDD)2/(2π2RL) (W) Bridge Mode (3)

DMAX

P

DMAX

=(T

JMAX-TA

)/θJA(W) (4)

LM4818

For the M08A package, θ

= 170˚C/W and T

JA

for the LM4818. For a given ambient temperature, T
tion (4) can be used to find the maximum internal power
dissipation supported by the IC packaging. If the result of
Equation (3) is greater than the result of Equation (4), then
decrease the supply voltage, increase the load impedance,
or reduce the ambient temperature. For a typical application
using the M08A packaged LM4818 with a 5V power supply
and an 8Ω load, the maximum ambient temperature that
does not violate the maximum junction temperature is ap­proximately 42˚C. It is assumed that a device is a surface
mount part operating around the maximum power dissipation
point. The assumption that the device is operating around

01

the maximum power dissipation point is incorrect for an 8Ω
load. The maximum power dissipation point occurs when the
output power is equal to the maximum power dissipation or
50% efficiency. The LM4818 is not capable of the output
power level (633mW) required to operate at the maximum
power dissipation point for an 8Ω load. To find the maximum
power dissipation, the graph Power Dissipation vs. Output
Power must be used. From the graph, the maximum power
dissipation for an 8Ω load and a 5V supply is approximately
575mW. Substituting this value back into equation (4) for
P

and using θJA= 170˚C/W for the M08A package, the

DMAX

maximum ambient temperature is 52˚C. Refer to the Typical
Performance Characteristics curves for power dissipation
information for lower output powers and maximum power
dissipation for each package at a given ambient tempera­ture.

POWER SUPPLY BYPASSING

01

As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. The capacitors connected to the bypass and power
supply pins should be placed as close to the LM4818 as
possible. The capacitor connected between the bypass pin
and ground improves the internal bias voltage’s stability,
producing improved PSRR. The improvements to PSRR
increase as the bypass pin capacitor value increases. Typi­cal applications employ a 5V regulator with 10µF and 0.1µF
filter capacitors that aid in supply stability. Their presence,
however, does not eliminate the need for bypassing the
supply nodes of the LM4818. The selection of bypass ca­pacitor values, especially C

, depends on desired PSRR

B

requirements, click and pop performance as explained in the
section, Proper Selection of External Components, as
well as system cost and size constraints.

SHUTDOWN FUNCTION

The voltage applied to the LM4818’s SHUTDOWN pin con­trols the shutdown function. Activate micro-power shutdown
by applying V

to the SHUTDOWN pin. When active, the

DD

LM4818’s micro-power shutdown feature turns off the ampli­fier’s bias circuitry, reducing the supply current. The logic
threshold is typically 1/2V

. The low 0.7µA typical shut-

DD

down current is achieved by applying a voltage that is as
near as V
that is less than V

as possible to the SHUTDOWN pin. A voltage

DD

may increase the shutdown current.

DD

Avoid intermittent or unexpected micro-power shutdown by
ensuring that the SHUTDOWN pin is not left floating but
connected to either V

DD

or GND.

There are a few ways to activate micro-power shutdown.
These included using a single-pole, single-throw switch, a
microcontroller, or a microprocessor. When using a switch,
connect an external 10kΩ to 100kΩ pull-up resistor between
the SHUTDOWN pin and V

. Connect the switch between

DD

the SHUTDOWN pin and ground. Select normal amplifier

JMAX

= 150˚C

, Equa-

A

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Application Information (Continued)

operation by closing the switch. Opening the switch con-

LM4818

nects the shutdown pin to V
activating micro-power shutdown. The switch and resistor
guarantee that the SHUTDOWN pin will not float. This pre­vents unwanted state changes. In a system with a micropro­cessor or a microcontroller, use a digital output to apply the
control voltage to the SHUTDOWN pin. Driving the SHUT­DOWN pin with active circuitry eliminates the pull-up resistor

PROPER SELECTION OF EXTERNAL COMPONENTS

Optimizing the LM4818’s performance requires properly se­lecting external components. Though the LM4818 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val­ues.

The LM4818 is unity gain stable, giving the 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 ra­tio. 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 of 1V
Audio Power Amplifier Design section for more informa­tion on selecting the proper gain.

Another important consideration is the amplifier’s close-loop
bandwidth. To a large extent, the bandwidth is dictated by
the choice of external components shown in
input coupling capacitor, C
that limits low frequency response. This value should be
chosen based on needed frequency response for a few
distinct reasons discussed below

Input Capacitor Value Selection

Amplifying the lowest audio frequencies requires a high
value input coupling capacitor (C
capacitor can be expensive and may compromise space
efficiency in portable designs. In many cases the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with limited frequency response reap little
improvement by using a large input capacitor.

Besides affecting system cost and size, C
the LM4818’s click and pop performance. When the supply
voltage is first applied, a transient (pop) is created as the
charge on the input capacitor changes from zero to a quies­cent state. The magnitude of the pop is directly proportional
to the input capacitor’s value. Higher value capacitors need
more time to reach a quiescent DC voltage (usually 1/2 V
when charged with a fixed current. The amplifier’s output
charges the input capacitor through the feedback resistor,
R

. Thus, selecting an input capacitor value that is no higher

F

than necessary to meet the desired -3dB frequency can
minimize pops.

As shown in
capacitor, C

Figure 1

produce a -3dB high pass filter cutoff frequency

i

, the input resistor (Ri) and the input

that is found using Equation (5).

f

= 1/(2 πRiCi) (Hz) (5)

-3dB

As an example when using a speaker with a low frequency
limit of 150Hz, C

, using Equation (5) is 0.063µF. The 0.39µF

i

through the pull-up resistor,

DD

(2.83V

RMS

, forms a first order high pass filter

i

). Please refer to the

P-P

in

i

Figure 1

). A high value

has an effect on

i

Figure 1

. The

DD

shown in

C

i

Figure 1

allows the LM4818 to drive a high
efficiency, full range speaker whose response extends down
to 20Hz.

Besides optimizing the input capacitor value, the bypass
capacitor value, C

requires careful consideration. The by-

B

pass capacitor’s value is the most critical to minimizing
turn-on pops because it determines how fast the LM4818
turns on. The slower the LM4818’s outputs ramp to their
quiescent DC voltage (nominally 1/2V

), the smaller the

DD

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

less than 1.0µF, the

B

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

equal to or greater than 1.0µF is

B

recommended in all but the most cost sensitive designs.

Bypass Capacitor Value Selection

Besides minimizing the input capacitor size, careful consid­eration should be paid to the value of C
connected to the BYPASS pin. Since C

, the capacitor

B

determines how

B

fast the LM4818 settles to quiescent operation, its value is
critical when minimizing turn-on pops. The slower the
LM4818’s outputs ramp to their quiescent DC voltage (nomi­nally 1/2V

), the smaller the turn-on pop. Choosing C

DD

B

equal to 1.0µF along with a small value of Ci(in the range of

0.1µF to 0.39µF) produces a click-less and pop-less shut­down function. As discussed above, choosing C

no larger

i

than necessary for the desired bandwidth helps minimize
clicks and pops. If using the optional capacitor, C
capacitance see at the BYPASSpin is C

B+CB2

, the total

B2

. When using
the values shown in Figure 1, Typical Audio Amplifier
Application Circuit, for C

and CB2the change in the

B

capacitance seen by the BYPASS pin is not significant rela­tive to capacitor value tolerances.

Optimizing Click and Pop Reduction Performance

The LM4818 contains circuitry that minimizes turn-on and
shutdown transients or ’clicks and pops’. For this discussion,
turn on refers to either applying the power or supply voltage
or when the shutdown mode is deactivated. While the power
supply is ramping to it’s final value, the LM4818’s internal
amplifiers are configured as unity gain buffers. An internal
current source charges the voltage of the bypass capacitor,
C

, connected to the BYPASS pin in a controlled, linear

B

manner. Ideally, the input and outputs track the voltage
charging on the bypass capacitor. The gain of the internal
amplifiers remains unity until the bypass capacitor is fully
charged to 1/2V

. As soon as the voltage on the bypass

DD

capacitor is stable, the device becomes fully operational.
Although the BYPASS pin current cannot be modified,
changing the size of the bypass capacitor, C

, alters the

B

device’s turn-on time and magnitude of ’clicks and pops’.

)

Increasing the value of C
pops. However, this presents a tradeoff: as the size of C

reduces the magnitude of turn-on

B

B

increases, the turn-on time (Ton) increases. There is a linear
relationship between the size of C
using the optional capacitor, C
at the BYPASSpin is C

and CB2. The total capacitance see

B

and the turn on time. If

B

, the total capacitance see

B2

at the BYPASS pin must be considered for the table below
and when optimizing click and pop performance. Below are
some typical turn-on times for various values of C

C

B

T

ON

:

B

0.01µF 20ms

0.1µF 200ms

0.22µF 440ms

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Application Information (Continued)

C

B

0.47µF 940ms

1.0µF 2S

In order to eliminate ’clicks and pops’, all capacitors must be
discharged before turn-on. Rapidly switching V
allow the capacitors to fully discharge, which may cause
’clicks and pops’.

AUDIO POWER AMPLIFIER DESIGN EXAMPLE

The following are the desired operational

parameters:

Given:

Power Output 100mW
Load Impedance 16Ω
Input Level 1Vrms (max)
Input Impedance 20kΩ
Bandwidth 100Hz–20kHz

The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. To find this
minimum supply voltage, use the Output Power vs. Supply
Voltagegraph in the Typical Performance Characteristics
section. From the graph for a 16Ω load, (graphs are for 8Ω,
16Ω, and 32Ω loads) the supply voltage for 100mW of output
power with 1% THD+N is approximately 3.15 volts.

Additional supply voltage creates the benefit of increased
headroom that allows the LM4818 to reproduce peaks in
excess of 100mW without output signal clipping or audible
distortion. The choice of supply voltage must also not create
a situation that violates maximum dissipation as explained
above in the Power Dissipation section. For example, if a

3.3V supply is chosen for extra headroom then according to
Equation (3) the maximum power dissipation point with a
16Ω load is 138mW. Using Equation (4) the maximum am­bient temperature is 126˚C for the M08A package.

After satisfying the LM4818’s power dissipation require­ments, the minimum differential gain is found using Equation
(6).

T

ON

may not

DD

±

0.25dB

The last step in this design example 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 least 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 is 0.17dB, well with in the

±

0.25dB
desired limit.

The results are:

f

= 100Hz/5 = 20Hz

L

f

= 20 kHz*5 = 100kHz

H

As mentioned in the External Components section, R
C

create a high pass filter that sets the amplifier’s lower

i

i

and

band pass frequency limit. Find the coupling capacitor’s
value using Equation (8).

C

≥ 1/(2πRifc) (F) (8)

i

C

≥ 0.398µF, a standard value of 0.39µF will be used. The

i

product of the desired high frequency cutoff (100kHz in this
example) and the differential gain, A
per pass band response limit. With A

, determines the up-

VD

= 1.27 and fH=

VD

100kHz, the closed-loop gain bandwidth product (GBWP) is
127kHz. This is less than the LM4818’s 900kHz GBWP.With
this margin the amplifier can be used in designs that require
more differential gain while avoiding performance restricting
bandwidth limitations.

LM4818

(6)

Thus a minimum gain of 1.27 V/V allows the LM4818 to
reach full output swing and maintain low noise and THD+N
performance. For this example, let A
er’s overall gain is set using the input (R

= 1.27. The amplifi-

VD

) and feedback (RF)

i

resistors. With the desired input impedance set to 20kΩ, the
feedback resistor is found using Equation (7).

The value of R

R

is 13kΩ.

F

F/Ri=AVD

/2 (V/V) (7)

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Application Information (Continued)

HIGHER GAIN AUDIO AMPLIFIER

LM4818

The LM4818 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 (C

) may be

4

needed as shown in Figure 2 to bandwidth limit the amplifier.
This feedback capacitor creates a low pass filter that elimi­nates possible high frequency oscillations. Care should be

Figure 2

DS200389-75

taken when calculating the -3dB frequency in that an incor­rect combination of R

and C4will cause rolloff before

3

20kHz. A typical combination of feedback resistor and ca­pacitor that will not produce audio band high frequency rolloff
is R

= 20kΩ and C4= 25pF. These components result in a

3

-3dB point of approximately 320 kHz. It is not recommended
that the feedback resistor and capacitor be used to imple­ment a band limiting filter below 100kHz.

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Application Information (Continued)

REFERENCE DESIGN BOARD and PCB LAYOUT GUIDELINES

LM4818

Figure 4

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Application Information (Continued)

LM4818

Composite View

LM4818 SO DEMO BOARD ARTWORK

Silk Screen

Top Layer

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DS200389-79

DS200389-78

Bottom Layer

DS200389-80

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Application Information (Continued)
Mono LM4818 Reference Design Boards

Bill of Material for all Demo Boards

Item Part Number Part Description Qty Ref Designator

1 551011208-001 LM4818 Mono Reference Design Board 1
10 482911183-001 LM4818 Audio AMP 1 U1
20 151911207-001 Tant Cap 1uF 16V 10 1 C1
21 151911207-002 Cer Cap 0.39uF 50V Z5U 20% 1210 1 C2
25 152911207-001 Tant Cap 1uF 16V 10 1 C3
30 472911207-001 Res 20K Ohm 1/10W 5 3 R1, R2, R3
35 210007039-002 Jumper Header Vertical Mount 2X1

0.100

LM4818

2J1

PCB LAYOUT GUIDELINES

This section provides practical guidelines for mixed signal
PCB layout that involves various digital/analog power and
ground traces. Designers should note that these are only
’rule-of-thumb’ recommendations and the actual results will
depend heavily on the final layout.

General Mixed Signal Layout Recommendation

Power and Ground Circuits

For two layer mixed signal design, it is important to isolate
the digital power and ground trace paths from the analog
power and ground trace paths. Star trace routing techniques
(bringing individual traces back to a central point rather than
daisy chaining traces together in a serial manner) can have
a major impact on low level signal performance. Star trace
routing refers to using individual traces to feed power and
ground to each circuit or even device. This technique will
take require a greater amount of design time but will not
increase the final price of the board. The only extra parts
required will be some jumpers.

Single-Point Power / Ground Connections

The analog power traces should be connected to the digital
traces through a single point (link). A ’Pi-filter’can be helpful
in minimizing high frequency noise coupling between the
analog and digital sections. It is further recommended to put
digital and analog power traces over the corresponding digi­tal and analog ground traces to minimize noise coupling.

Placement of Digital and Analog Components

All digital components and high-speed digital signals traces
should be located as far away as possible from analog
components and circuit traces.

Avoiding Typical Design / Layout Problems

Avoid ground loops or running digital and analog traces
parallel to each other (side-by-side) on the same PCB layer.
When traces must cross over each other do it at 90 degrees.
Running digital and analog traces at 90 degrees to each
other from the top to the bottom sideas much as possible will
minimize capacitive noise coupling and cross talk.

www.national.com15

Physical Dimensions inches (millimeters) unless otherwise noted

SO

Order Number LM4818M

NS Package Number M08A

LM4818 350mW 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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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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