National Semiconductor LM4904 Technical data

LM4904
1 Watt Audio Power Amplifier

LM4904 1 Watt Audio Power Amplifier

May 2004

General Description

The LM4904 is an audio power amplifier primarily designed
for demanding applications in mobile phones and other por­table communication device applications. It is capable of
delivering 1 watt of continuous average power to an 8Ω BTL
load with less than 1% distortion (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. The LM4904 does not require output
coupling capacitors or bootstrap capacitors, and therefore is
ideally suited for mobile phone and other low voltage appli­cations where minimal power consumption is a primary re­quirement.

The LM4904 features a low-power consumption shutdown
mode, which is achieved by driving the shutdown pin with
logic high. Additionally, the LM4904 features an internal ther­mal shutdown protection mechanism.

The LM4904 contains advanced pop & click circuitry which
eliminates noise which would otherwise occur during turn-on
and turn-off transitions.

The LM4904 is unity-gain stable and can be configured by
external gain-setting resistors.

DC

Key Specifications

j

Improved PSRR at 217Hz & 1KHz 62dB

j

Power Output at 5.0V, 1% THD, 8Ω 1.07W (typ)

j

Power Output at 3.0V, 1% THD, 4Ω 525mW (typ)

j

Power Output at 3.0V, 1% THD, 8Ω 390mW (typ)

j

Shutdown Current 0.1µA (typ)

Features

n Available in space-saving micro SMD package
n Ultra low current shutdown mode
n BTL output can drive capacitive loads
n Improved pop & click circuitry eliminates noise during

turn-on and turn-off transitions

n 2.0 - 5.5V operation
n No output coupling capacitors, snubber networks or

bootstrap capacitors required

n Unity-gain stable
n External gain configuration capability

Applications

n Mobile Phones
n PDAs
n Portable electronic devices

Typical Application

FIGURE 1. Typical Audio Amplifier Application Circuit

Boomer®is a registered trademark of National Semiconductor Corporation.

200437B6

© 2004 National Semiconductor Corporation DS200437 www.national.com

Connection Diagrams

LM4904

8 Bump micro SMD

Top View

200437B4

Order Number LM4904ITL, LM4904ITLX

See NS Package Number TLA08AAA

8 Bump micro SMD Marking

Top View

200437C5

X - Date Code

T - Dice Traceability

G - Boomer Family

A6 - LM4904ITL

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LM4904

Absolute Maximum Ratings (Note 2)

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

Supply Voltage (Note 11) 6.0V

Thermal Resistance

θ

(micro SMD) (Note 12) 210˚C/W

JA

Soldering Information

See AN-1112 "microSMD Wafers Level Chip Scale
Package."

Storage Temperature −65˚C to +150˚C

Input Voltage −0.3V to V

DD

+0.3V

Operating Ratings

Power Dissipation (Notes 3, 13) Internally Limited

ESD Susceptibility (Note 4) 2000V

ESD Susceptibility (Note 5) 200V

Junction Temperature 150˚C

Temperature Range

T

≤ TA≤ T

MIN

MAX

Supply Voltage 2.0V ≤ V

Electrical Characteristics VDD=5V (Notes 1, 2)

The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for T

LM4904

Symbol Parameter Conditions

= 0V, Io= 0A, No Load 3 7 mA (max)

V

I

DD

I

SD

V

SDIH

V

SDIL

V

OS

R

OUT

P

o

T

WU

Quiescent Power Supply Current

Shutdown Current VSD=VDD(Note 8) 0.1 2.0 µA (max)

Shutdown Voltage Input High 1.5 V (min)

Shutdown Voltage Input Low 1.3 V (max)

Output Offset Voltage 7 50 mV (max)

Resistor Output to GND (Note 10) 8.5

Output Power THD = 1% (max);f=1kHz 1.07 0.9 W

Wake-up time 100 mS (max)

THD+N Total Harmonic Distortion+Noise P

PSRR Power Supply Rejection Ratio

IN

V

= 0V, Io= 0A, 8Ω Load 4 10 mA (max)

IN

= 0.5 Wrms; f = 1kHz 0.2 %

o

V

= 200mV sine p-p

ripple

Input terminated with 10Ω

Typical Limit

(Note 6) (Notes 7, 9)

60 (f =
217Hz)
64 (f = 1kHz)

9.7 kΩ (max)

7.0 kΩ (min)

55 dB (min)

−40˚C ≤ TA≤ 85˚C

≤ 5.5V

DD

= 25˚C.

A

Units

(Limits)

Electrical Characteristics VDD=3V (Notes 1, 2)

The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for T

LM4904

Symbol Parameter Conditions

= 0V, Io= 0A, No Load 2 7 mA (max)

V

I

DD

I

SD

V

SDIH

V

SDIL

V

OS

R

OUT

P

o

T

WU

Quiescent Power Supply Current

Shutdown Current VSD=VDD(Note 8) 0.1 2.0 µA (max)

Shutdown Voltage Input High 1.1 V (min)

Shutdown Voltage Input Low 0.9 V (max)

Output Offset Voltage 7 50 mV (max)

Resistor Output to GND (Note 10) 8.5

Output Power (8Ω) THD = 1% (max);f=1kHz 390 mW

(4Ω) THD = 1% (max);f=1kHz 525

Wake-up time 75 mS (max)

THD+N Total Harmonic Distortion+Noise P

PSRR Power Supply Rejection Ratio

IN

V

= 0V, Io= 0A, 8Ω Load 3 9 mA (max)

IN

= 0.25 Wrms; f = 1kHz 0.1 %

o

V

= 200mV sine p-p

ripple

Input terminated with 10Ω

Typical Limit

(Note 6) (Notes 7, 9)

62 (f =
217Hz)
68 (f = 1kHz)

9.7 kΩ (max)

7.0 kΩ (min)

55 dB (min)

= 25˚C.

A

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Units

(Limits)

Electrical Characteristics VDD= 2.6V (Notes 1, 2)

The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for T

LM4904

LM4904

Symbol Parameter Conditions

= 0V, Io= 0A, No Load 2.0 mA (max)

V

I

DD

I

SD

V

SDIH

V

SDIL

V

OS

R

OUT

P

o

Quiescent Power Supply Current

Shutdown Current VSD=VDD(Note 8) 0.1 µA (max)

Shutdown Voltage Input High 1.0 V (min)

Shutdown Voltage Input Low 0.9 V (max)

Output Offset Voltage 5 50 mV (max)

Resistor Output to GND (Note 10) 8.5

Output Power ( 8Ω ) THD = 1% (max);f=1kHz 275

IN

V

= 0V, Io= 0A, 8Ω Load 3.0 mA (max)

IN

(4Ω ) THD = 1% (max);f=1kHz 340

T

WU

THD+N Total Harmonic Distortion+Noise P

PSRR Power Supply Rejection Ratio

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 andAC 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
curves for additional information.

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

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

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

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

Note 8: For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase I

Note 9: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Note 10: R

Note 11: If the product is in Shutdown mode and V

If the source impedance limits the current to a max of 10mA, then the device will be protected. If the device is enabled when V

6.5V, no damage will occur, although operation life will be reduced. Operation above 6.5V with no current limit will result in permanent damage.

Note 12: All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. The LM4904ITL demo board (views featured
in the Application Information section) has two inner layers, one for V
and aid in spreading heat due to power dissipation within the IC.

Note 13: Maximum power dissipation in the device (P
Equation 1 shown in the Application Information section. It may also be obtained from the power dissipation graphs.

Wake-up time 70 mS (max)

= 0.15 Wrms; f = 1kHz 0.1 %

o

V

= 200mV sine p-p

ripple

Input terminated with 10Ω

=(T

DMAX

is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the two 20kΩ resistors.

ROUT

)/θJAor the number given inAbsolute Maximum Ratings, whichever is lower. For the LM4904, see power derating

JMAX–TA

exceeds 6V (to a max of 8V VDD), then most of the excess current will flow through the ESD protection circuits.

DD

and one for GND. The planes each measure 600mils x 600mils (15.24mm x 15.24mm)

DD

) occurs at an output power level significantly below full output power. P

DMAX

Typical Limit

(Note 6) (Notes 7, 9)

9.7 kΩ (max)

7.0 kΩ (min)

51 (f =
217Hz)
51 (f = 1kHz)

, θJA, and the ambient temperature TA. The maximum

JMAX

by a maximum of 2µA.

SD

is greater than 5.5V and less than

DD

can be calculated using

DMAX

= 25˚C.

A

Units

(Limits)

mW

dB (min)

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External Components Description

(Figure 1)

Components Functional Description

1. R

2. C

3. R

4. C

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

i

high pass filter with C

Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a

i

highpass filter with R
for an explanation of how to determine the value of C

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

f

Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing

S

at fC= 1/(2π RiCi).

i

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

i

.

i

section for information concerning proper placement and selection of the supply bypass capacitor.

5. C

Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External

B

Components, for information concerning proper placement and selection of C

Typical Performance Characteristics

LM4904

.

B

THD+N vs Frequency

= 5V, 8Ω RL, and PWR = 500mW

at V

DD

THD+N vs Frequency

= 2.6V, 8Ω RL, and PWR = 150mW

at V

DD

THD+N vs Frequency

at VDD= 3V, 8Ω RL, and PWR = 250mW

20043730 20043731

THD+N vs Frequency

at VDD= 2.6V, 4Ω RL, and PWR = 150mW

20043732 20043733

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Typical Performance Characteristics (Continued)

LM4904

THD+N vs Power Out

at V

= 5V, 8Ω RL, 1kHz

DD

THD+N vs Power Out

= 2.6V, 8Ω RL, 1kHz

at V

DD

THD+N vs Power Out

at VDD= 3V, 8Ω RL, 1kHz

20043734 20043783

THD+N vs Power Out

at VDD= 2.6V, 4Ω RL, 1kHz

20043784 20043785

Power Supply Rejection Ratio (PSRR) vs Frequency

= 5V, 8Ω R

at V

DD

L

20043786

Input terminated with 10Ω

Power Supply Rejection Ratio (PSRR) vs Frequency

= 5V, 8Ω R

at V

DD

L

20043787

Input Floating

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Typical Performance Characteristics (Continued)

LM4904

Power Supply Rejection Ratio (PSRR) vs Frequency

at V

= 3V, 8Ω R

DD

L

20043788

Input terminated with 10Ω

Power Supply Rejection Ratio (PSRR) vs Frequency

= 2.6V, 8Ω R

at V

DD

L

Power Supply Rejection Ratio (PSRR) vs Frequency

= 3V, 8Ω R

at V

DD

L

20043789

Input Floating

Power Supply Rejection Ratio (PSRR) vs Frequency

= 2.6V, 8Ω R

at V

DD

L

Input terminated with 10Ω

20043790

Input Floating

20043791

Open Loop Frequency Response, 5V Open Loop Frequency Response, 3V

20043792 20043793

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Typical Performance Characteristics (Continued)

LM4904

Open Loop Frequency Response, 2.6V Noise Floor, 5V, 8Ω

80kHz Bandwidth, Input to GND

20043794

20043795

Power Derating Curves Power Dissipation vs

Output Power, 5V, 8Ω

20043769

200437C8

20043797

200437C9

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Typical Performance Characteristics (Continued)

LM4904

Shutdown Hysteresis Voltage,

5V

Shutdown Hysteresis Voltage,

2.6V

Shutdown Hysteresis Voltage,

3V

200437A0 200437A2

Output Power vs

Supply Voltage, 8Ω

Output Power vs

Supply Voltage, 16Ω

200437A4 200437A6

Output Power vs

Supply Voltage, 32Ω

200437A7

200437A8

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Typical Performance Characteristics (Continued)

LM4904

Frequency Response vs

Input Capacitor Size

20043754

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Application Information

BRIDGE CONFIGURATION EXPLANATION

As shown in Figure 1, the LM4904 has two internal opera­tional amplifiers. 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 20kΩ
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 by 180˚. Consequently, the differential gain for the
IC is

= 2 *(Rf/Ri)

A

VD

By driving the load differentially through outputs Vo1 and
Vo2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is
different from the classical single-ended amplifier configura­tion where one side of the 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. 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, please refer to the Audio Power Amplifier
Design section.

A bridge configuration, such as the one used in LM4904,
also creates a second advantage over single-ended amplifi­ers. Since the differential outputs, Vo1 and Vo2, are biased
at half-supply, no net DC voltage 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, the half-supply
bias across the load would result in both increased internal
IC power dissipation and also possible loudspeaker damage.

to Riwhile

f

especially effective when connected to V

, GND, and the

DD

output pins. Refer to the application information on the
LM4904 reference design board for an example of good heat
sinking. If T

still exceeds 150˚C, then additional

JMAX

changes must be made. These changes can include re­duced supply voltage, higher load impedance, or reduced
ambient temperature. Internal power dissipation is a function
of output power. Refer to the Typical Performance Charac-
teristics curves for power dissipation information for differ­ent output powers and output loading.

POWER SUPPLY BYPASSING

As with any 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. Typical appli­cations employ a 5V regulator with 10 µF tantalum or elec­trolytic capacitor and a ceramic bypass capacitor which aid
in supply stability. This does not eliminate the need for
bypassing the supply nodes of the LM4904. The selection of
a bypass capacitor, especially C

, is dependent upon PSRR

B

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

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the
LM4904 contains shutdown circuitry that is used to turn off
the amplifier’s bias circuitry. This shutdown feature turns the
amplifier off when logic high is placed on the shutdown pin.
By switching the shutdown pin to V

, the LM4904 supply

DD

current draw will be minimized in idle mode. Idle current is
measured with the shutdown pin connected to V

DD

. The
trigger point for shutdown is shown as a typical value in the
Shutdown Hysteresis Voltage graphs in the Typical Perfor-
mance Characteristics section. It is best to switch between
ground and supply for maximum performance. While the
device may be disabled with shutdown voltages in between
ground and supply, the idle current may be greater than the
typical value of 0.1µA. In either case, the shutdown pin
should be tied to a definite voltage to avoid unwanted state
changes.

LM4904

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. Since the LM4904 has two opera­tional amplifiers in one package, the maximum internal
power dissipation is 4 times that of a single-ended amplifier.
The maximum power dissipation for a given application can
be derived from the power dissipation graphs or from Equa­tion 1.

= 4*(VDD)2/(2π2RL) (1)

P

DMAX

It is critical that the maximum junction temperature T
150˚C is not exceeded. T
power derating curves by using P

can be determined from the

JMAX

and the PC board foil

DMAX

JMAX

area. By adding copper foil, the thermal resistance of the
application can be reduced from the free air value of θ
resulting in higher P

values without thermal shutdown

DMAX

JA

protection circuitry being activated. Additional copper foil can
be added to any of the leads connected to the LM4904. It is

In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry, which pro­vides a quick, smooth transition to shutdown. Another solu­tion is to use a single-throw switch in conjunction with an
external pull-up resistor. This scheme guarantees that the
shutdown pin will not float, thus preventing unwanted state
changes.

PROPER SELECTION OF EXTERNAL COMPONENTS

Proper selection of external components in applications us­ing integrated power amplifiers is critical to optimize device
and system performance. While the LM4904 is tolerant of
external component combinations, consideration to compo­nent values must be used to maximize overall system qual­ity.

of

The LM4904 is unity-gain stable which gives the designer
maximum system flexibility. The LM4904 should be used in
low gain configurations to minimize THD+N values, and
maximize the signal to noise ratio. Low gain configurations

,

require large input signals to obtain a given output power.
Input signals equal to or greater than 1 Vrms are available

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Application Information (Continued)

from sources such as audio codecs. Please refer to the

LM4904

section, Audio Power Amplifier Design, for a more com­plete explanation of proper gain selection.

Besides gain, one of the major considerations is the closed­loop bandwidth of the amplifier. To a large extent, the band­width is dictated by the choice of external components
shown in Figure 1. The input coupling capacitor, C
first order high pass filter which limits low frequency re­sponse. This value should be chosen based on needed
frequency response for a few distinct reasons.

Selection Of Input Capacitor Size

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

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

A larger input coupling capacitor requires more charge to

C

i.

reach its quiescent DC voltage (nominally 1/2 V
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 capacitor size, careful consid­eration should be paid to the bypass capacitor value. Bypass
capacitor, C
turn-on pops since it determines how fast the LM4904 turns
on. The slower the LM4904’s outputs ramp to their quiescent
DC voltage (nominally 1/2 V
Choosing C
(in the range of 0.1 µF to 0.39 µF), should produce a virtually
clickless and popless shutdown function. While the device
will function properly, (no oscillations or motorboating), with

equal to 0.1 µF, the device will be much more susceptible

C

B

to turn-on clicks and pops. Thus, a value of C

1.0 µF is recommended in all but the most cost sensitive
designs.

AUDIO POWER AMPLIFIER DESIGN

, is the most critical component to minimize

B

), the smaller the turn-on pop.

equal to 1.0 µF along with a small value of C

B

DD

, forms a

i

). This

DD

equal to

B

Bandwidth 100 Hz– 20 kHz

A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Per-
formance Characteristics section, the supply rail can be
easily found.

5V is a standard voltage in most applications, it is chosen for
the supply rail. Extra supply voltage creates headroom that
allows the LM4904 to reproduce peaks in excess of 1W
without producing audible distortion. 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 2.

R

f/Ri=AVD

/2

From Equation 2, the minimum AVDis 2.83; use AVD=3.
Since the desired input impedance was 20 kΩ, and with a

impedance of 2, a ratio of 1.5:1 of Rfto Riresults in an

A

VD

allocation of R

=20kΩ and Rf=30kΩ. The final design step

i

is to address the bandwidth requirements which must be
stated as a pair of −3 dB frequency points. Five times away
from a −3 dB point is 0.17 dB down from passband response

±

which is better than the required

i

fL= 100 Hz/5 = 20 Hz

=20kHz*5=100kHz

f

H

0.25 dB specified.

As stated in the External Components section, R
junction with C

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

C

i

create a highpass filter.

i

±

0.25 dB

in con-

i

(2)

A 1W/8Ω Audio Amplifier

Given:

Power Output 1 Wrms

Load Impedance 8Ω

Input Level 1 Vrms

Input Impedance 20 kΩ

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

= 3 and fH= 100 kHz, the resulting GBWP =

VD

, and the differential gain, AVD.

H

300kHz which is much smaller than the LM4904 GBWP of

2.5MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4904 can still be used without running into bandwidth
limitations.

Application Information (Continued)

LM4904

FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER

The LM4904 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 (C4) may be
needed as shown in Figure 2 to bandwidth limit the amplifier.
This feedback capacitor creates a low pass filter that elimi-

200437B7

nates possible high frequency oscillations. Care should be
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

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

is R

3

-3dB point of approximately 320 kHz.

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Application Information (Continued)

LM4904

FIGURE 3. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4904

200437B8

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Application Information (Continued)

LM4904

FIGURE 4. REFERENCE DESIGN BOARD SCHEMATIC

200437C7

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Application Information (Continued)

LM4904 micro SMD BOARD ARTWORK

LM4904

Composite View Silk Screen

200437C0

Top Layer Inner VDDLayer

200437C2

Inner GND Layer Bottom Layer

200437C1

200437C3

200437C4

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200437C6

Application Information (Continued)

Mono LM4904 Reference Design Boards

Bill of Material

Part Description Quantity Reference Designator

LM4904 Audio AMP 1 U1

Tantalum Capcitor, 1µF 2 C1, C3

Ceramic Capacitor, 0.39µF 1 C2

Resistor, 20kΩ, 1/10W 2 R2, R3

Resistor, 100kΩ, 1/10W 1 R1

Jumper Header Vertical Mount 2X1 0.100“ spacing 1 J1

LM4904

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 2 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
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 signal 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 side as much as possible will
minimize capacitive noise coupling and cross talk.

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Physical Dimensions inches (millimeters) unless otherwise noted

LM4904 1 Watt Audio Power Amplifier

8-Bump micro SMD

Order Number LM4904ITL, LM4904ITLX

NS Package Number TLA08AAA

= 1.514±0.03, X2= 1.514±0.03, X3= .600±0.075

X

1

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