LM4891M/NOPB - NATIONAL SEMICONDUCTOR

LM4891

1 Watt Audio Power Amplifier

General Description

The LM4891 is an audio power amplifier primarily designed

for demanding applications in mobile phones and other por-

table communication device applications. It is capable of

delivering 1 watt of continuous average power to an 8ΩBTL

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 LM4891 does not require output

coupling capacitors or bootstrap capacitors, and therefore is

ideally suited for mobile phone and other low voltage appli-

cations where minimal power consumption is a primary re-

quirement.

The LM4891 features a low-power consumption shutdown

mode, which is achieved by driving the shutdown pin with

logic high. Additionally, the LM4891 features an internal ther-

mal shutdown protection mechanism.

The LM4891 contains advanced pop & click circuitry which

eliminates noises which would otherwise occur during

turn-on and turn-off transitions.

The LM4891 is unity-gain stable and can be configured by

external gain-setting resistors.

Key Specifications

jPSRR at 217Hz, V

= 5V, 8ΩLoad 62dB (typ)

jPower Output at 5.0V & 1% THD 1.0W (typ)

jPower Output at 3.3V & 1% THD 400mW (typ)

jShutdown Current 0.1µA (typ)

Features

nAvailable in space-saving packages: micro SMD, MSOP,

SOIC, and LLP

nUltra low current shutdown mode

nBTL output can drive capacitive loads

nImproved pop & click circuitry eliminates noises during

turn-on and turn-off transitions

n2.2 to 5.5V operation

nNo output coupling capacitors, snubber networks or

bootstrap capacitors required

nThermal shutdown protection

nUnity-gain stable

nExternal gain configuration capability

Applications

nMobile Phones

nPDAs

nPortable electronic devices

Typical Application

Boomer®is a registered trademark of National Semiconductor Corporation.

20007401

FIGURE 1. Typical Audio Amplifier Application Circuit

October 2002

LM4891 1 Watt Audio Power Amplifier

Connection Diagrams

8 Bump micro SMD Small Outline (SO) Package

20007423

Top View

Order Number LM4891IBP, LM4891IBPX

See NS Package Number BPA08DDB

20007435

Top View

Order Number LM4891M

See NS Package Number M08A

8 Bump micro SMD Marking SO Marking

20007470

Top View

X - Date Code

T - Die Traceability

G - Boomer Family

G - LM4891IBP

20007472

Top View

XY - Date Code

TT - Die Traceability

Bottom 2 lines - Part Number

Mini Small Outline (MSOP) Package MSOP Marking

20007436

Top View

Order Number LM4891MM

See NS Package Number MUA08A

20007471

Top View

G - Boomer Family

91 - LM4891MM

LLP Package 10 Pin LLP Marking

20007480

Top View

Order Number LM4891LD

See NS Package Number LDA10B

20007479

Top View

Z - Assembly Plant Code (M for Malacca)

XY - 2 Digit Datecode

TT - 2 Letter Code for Traceability

L4891 - LM4891LD

LM4891

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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

Storage Temperature −65˚C to +150˚C

Input Voltage −0.3V to V

+0.3V

Power Dissipation (Note 3) Internally Limited

ESD Susceptibility (Note 4) 2000V

ESD Susceptibility (Note 5) 250V

Junction Temperature 150˚C

Thermal Resistance

(SOP) 35˚C/W

(SOP) 150˚C/W

(micro SMD) 220˚C/W

(MSOP) 56˚C/W

(MSOP) 190˚C/W

(LLP) 220˚C/W

Soldering Information

See AN-1112 "microSMD Wafers Level Chip Scale

Package".

See AN-1187 "Leadlesss

Leadframe Package (LLP)".

Operating Ratings

Temperature Range

MIN

≤T

MAX

−40˚C ≤T

≤85˚C

Supply Voltage 2.2V ≤V

≤5.5V

Electrical Characteristics V

=5V (Notes 1, 2, 8)

The following specifications apply for V

= 5V, A

= 2, and 8Ωload unless otherwise specified. Limits apply for T

= 25˚C.

Symbol Parameter Conditions

LM4891 Units

(Limits)

Typical Limit

(Note 6) (Note 7)

Quiescent Power Supply Current V

= 0V, I

= 0A 4 10 mA (max)

Shutdown Current V

shutdown

0.1 µA (max)

Output Power THD = 2% (max);f=1kHz 1 W

THD+N Total Harmonic Distortion+Noise P

= 0.4 Wrms; f = 1kHz 0.1 %

PSRR Power Supply Rejection Ratio V

ripple

= 200mV sine p-p 62 (f =

217Hz)

66 (f = 1kHz)

Electrical Characteristics V

= 3.3V (Notes 1, 2, 8)

The following specifications apply for V

= 3.3V, A

= 2, and 8Ωload unless otherwise specified. Limits apply for T

= 25˚C.

Symbol Parameter Conditions

LM4891 Units

(Limits)

Typical Limit

(Note 6) (Note 7)

Quiescent Power Supply Current V

= 0V, I

= 0A 3.5 mA (max)

Shutdown Current V

shutdown

0.1 µA (max)

Output Power THD = 1% (max); f = 1kHz 0.4 W

THD+N Total Harmonic Distortion+Noise P

= 0.15Wrms; f = 1kHz 0.1 %

PSRR Power Supply Rejection Ratio V

ripple

= 200mV sine p-p 60 (f =

217Hz)

62 (f = 1kHz)

Electrical Characteristics V

= 2.6V (Notes 1, 2, 8)

The following specifications apply for V

= 2.6V, A

= 2, and 8ΩLoad unless otherwise specified. Limits apply for T

25˚C.

Symbol Parameter Conditions

LM4891 Units

(Limits)

Typical Limit

(Note 6) (Note 7)

Quiescent Power Supply Current V

= 0V, I

= 0A 2.6 mA (max)

Shutdown Current V

shutdown

0.1 µA (max)

LM4891

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Electrical Characteristics V

= 2.6V (Notes 1, 2, 8)

The following specifications apply for V

= 2.6V, A

= 2, and 8ΩLoad unless otherwise specified. Limits apply for T

25˚C. (Continued)

Symbol Parameter Conditions

LM4891 Units

(Limits)

Typical Limit

(Note 6) (Note 7)

Output Power ( 8Ω)

Output Power ( 4Ω)

THD = 1% (max);f=1kHzTHD=

1% (max);f=1kHz

0.25

0.28

THD+N Total Harmonic Distortion+Noise P

= 0.1Wrms; f = 1kHz 0.08 %

PSRR Power Supply Rejection Ratio V

ripple

= 200mV sine p-p 44 (f =

217Hz)

44 (f = 1kHz)

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

Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which

guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit

is given, however, the typical value is a good indication of device performance.

Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX,θJA, and the ambient temperature TA. The maximum

allowable power dissipation is PDMAX =(T

JMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4891, see power derating

curves for additional information.

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

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 ISD by a maximum of 2µA.

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

Note 10: ROUT is measured from each of the output pins to ground. This value represents the parallel combination of the 10k ohm output resistors and the two 20k

ohm resistors.

Note 11: If the product is in shutdown mode and VDD exceeds 6V (to a max of 8V VDD), then most of the excess current will flow through the ESD protection circuits.

If the source impedance limits the current to a max of 10 ma, then the part will be protected. If the part is enabled when VDD is greater than 5.5V and less than 6.5V,

no damage will occur, although operational 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. All bumps must be connected to achieve

specified thermal resistance.

Note 13: Maximum power dissipation (PDMAX) in the device occurs at an output power level significantly below full output power. PDMAX can be calculated using

Equation 1 shown in the Application section. It may also be obtained from the power dissipation graphs.

Note 14: PSRR is a function of system gain. Specifications apply to the circuit in Figure 1 where AV= 2. Higher system gains will reduce PSRR value by the amount

of gain increase. A system gain of 10 represents a gain increase of 14dB. PSRR will be reduced by 14dB and applies to all operating voltages.

External Components Description

(Figure 1)

Components Functional Description

1. R

Inverting input resistance which sets the closed-loop gain in conjunction with R

. This resistor also forms a

high pass filter with C

at f

= 1/(2πR

2. C

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

highpass filter with R

at f

= 1/(2πR

). Refer to the section, Proper Selection of External Components,

for an explanation of how to determine the value of C

3. R

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

4. C

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

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

Components, for information concerning proper placement and selection of C

LM4891

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Typical Performance Characteristics

THD+N vs Frequency

at V

= 5V, 8ΩR

, and PWR = 250mW

THD+N vs Frequency

at V

= 3.3V, 8ΩR

, and PWR = 150mW

20007437 20007438

THD+N vs Frequency

at V

= 2.6V, 8ΩR

, and PWR = 100mW

THD+N vs Frequency

at V

= 2.6V, 4ΩR

, and PWR = 100mW

20007439 20007440

THD+N vs Power Out

= 5V, 8ΩR

, 1kHz

THD+N vs Power Out

= 3.3V, 8ΩR

, 1kHz

20007441 20007442

LM4891

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Typical Performance Characteristics (Continued)

THD+N vs Power Out

= 2.6V, 8ΩR

, 1kHz

THD+N vs Power Out

= 2.6V, 4ΩR

, 1kHz

20007443 20007444

Power Supply Rejection Ratio (PSRR) @V

= 5V Power Supply Rejection Ratio (PSRR) @V

=5V

20007445

Input terminated with 10ΩR

20007473

Input Floating

Power Supply Rejection Ratio (PSRR) @V

= 2.6V Power Supply Rejection Ratio (PSRR) @V

= 3.3V

20007447

Input terminated with 10ΩR

20007446

Input terminated with 10ΩR

LM4891

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Typical Performance Characteristics (Continued)

Power Dissipation vs

Output Power

= 3.3V

Power Dissipation vs

Output Power

= 5V, 1kHz, 8Ω, THD ≤1.0%

20007449 20007484

Output Power vs

Load Resistance

Power Dissipation vs

Output Power

= 2.6V

20007451 20007450

Supply Current vs

Shutdown Voltage

Clipping (Dropout) Voltage vs

Supply Voltage

20007474 20007452

LM4891

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Typical Performance Characteristics (Continued)

Open Loop Frequency Response

= 5V No Load

Open Loop Frequency Response

= 3V No Load

20007475 20007476

Power Derating Curves

DMAX

= 670mW)

Power Derating Curves

for 8 Bump microSMD (P

DMAX

= 670mW)

20007481 20007482

Power Derating - 10 Pin LD Pkg

DMAX

= 670mW, 5V, 8Ω

Frequency Response vs

Input Capacitor Size

20007483 20007454

LM4891

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Typical Performance

Characteristics (Continued)

Noise Floor

20007456

Application Information

BRIDGE CONFIGURATION EXPLANATION

As shown in Figure 1, the LM4891 has two operational

amplifiers internally, allowing for a few different amplifier

configurations. The first amplifier’s gain is externally config-

urable, 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

to R

while

the second amplifier’s gain is fixed by the two internal 20 kΩ

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 *(R

)

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 configura-

tion 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 con-

ditions. 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 ex-

cessive clipping, please refer to the Audio Power Amplifier

Design section.

A bridge configuration, such as the one used in LM4891,

also creates a second advantage over single-ended amplifi-

ers. 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 configura-

tion. 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.

EXPOSED-DAP PACKAGE PCB MOUNTING

CONSIDERATIONS FOR THE LM4891LD

The LM4891LD’s exposed-DAP (die attach paddle) package

(LD) provides a low thermal resistance between the die and

the PCB to which the part is mounted and soldered. The

LM4891LD package should have its DAP soldered to the

grounded copper pad (heatsink) under the LM4891LD (the

NC pins, no connect, and ground pins should also be directly

connected to this copper pad-heatsink area). The area of the

copper pad (heatsink) can be determined from the LD Power

Derating graph. If the multiple layer copper heatsink areas

are used, then these inner layer or backside copper heatsink

areas should be connected to each other with 4 (2 x 2) vias.

The diameter for these vias should be between 0.013 inches

and 0.02 inches with a 0.050inch pitch-spacing. Ensure

efficient thermal conductivity by plating through and solder-

filling the vias. Further detailed information concerning PCB

layout, fabrication, and mounting an LLP package is avail-

able from National Semiconductor’s Package Engineering

Group under application note AN1187.

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 LM4891 has two opera-

tional 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 Equa-

tion 1.

DMAX

= 4*(V

)

/(2π

) (1)

It is critical that the maximum junction temperature (T

JMAX

)

of 150˚C is not exceeded. T

JMAX

can be determined from the

power derating curves by using P

DMAX

and the PC board foil

area. By adding additional copper foil, the thermal resistance

of the application can be reduced from a free air value of

150˚C/W, resulting in higher P

DMAX

. Additional copper foil

can be added to any of the leads connected to the LM4891.

It is especially effective when connected to V

, GND, and

the output pins. Refer to the application information on the

LM4891 reference design board for an example of good heat

sinking. If T

JMAX

still exceeds 150˚C, then additional

changes must be made. These changes can include re-

duced 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 differ-

ent 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 appli-

cations employ a 5V regulator with 10 µF tantalum or elec-

trolytic capacitor and a ceramic bypass capacitor which aid

in supply stability. This does not eliminate the need for

bypassing the supply nodes of the LM4891. The selection of

a bypass capacitor, especially C

, is dependent upon PSRR

requirements, click and pop performance (as explained in

the section, Proper Selection of External Components),

system cost, and size constraints.

LM4891

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Application Information (Continued)

SHUTDOWN FUNCTION

In order to reduce power consumption while not in use, the

LM4891 contains a shutdown pin to externally turn off the

amplifier’s bias circuitry. This shutdown feature turns the

amplifier off when a logic high is placed on the shutdown pin.

By switching the shutdown pin to V

, the LM4891 supply

current draw will be minimized in idle mode. While the device

will be disabled with shutdown pin voltages more than

1.0V

, the idle current may be greater than the typical

value of 0.1µA. (Idle current is measured with the shutdown

pin tied to V

In many applications, a microcontroller or microprocessor

output is used to control the shutdown circuitry to provide a

quick, smooth transition into shutdown. Another solution is to

use a single-pole, single-throw switch in conjunction with an

external pull-up resistor. When the switch is closed, the

shutdown pin is connected to ground which enables the

amplifier. If the switch is open, then the external pull-up

resistor to V

will disable the LM4891. This scheme guar-

antees that the shutdown pin will not float thus preventing

unwanted state changes.

PROPER SELECTION OF EXTERNAL COMPONENTS

Proper selection of external components in applications us-

ing integrated power amplifiers is critical to optimize device

and system performance. While the LM4891 is tolerant of

external component combinations, consideration to compo-

nent values must be used to maximize overall system qual-

ity.

The LM4891 is unity-gain stable which gives the designer

maximum system flexibility. The LM4891 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

from sources such as audio codecs. Please refer to the

section, Audio Power Amplifier Design, for a more com-

plete 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 band-

width is dictated by the choice of external components

shown in Figure 1. The input coupling capacitor, C

, forms a

first order high pass filter which limits low frequency re-

sponse. 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 attenu-

ation. 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 perfor-

mance.

In addition to system cost and size, click and pop perfor-

mance is effected by the size of the input coupling capacitor,

A larger input coupling capacitor requires more charge to

reach its quiescent DC voltage (nominally 1/2 V

). 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 capacitor size, careful consid-

eration should be paid to the bypass capacitor value. Bypass

capacitor, C

, is the most critical component to minimize

turn-on pops since it determines how fast the LM4891 turns

on. The slower the LM4891’s outputs ramp to their quiescent

DC voltage (nominally 1/2 V

), the smaller the turn-on pop.

Choosing C

equal to 1.0 µF along with a small value of 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

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

equal to

1.0 µF is recommended in all but the most cost sensitive

designs.

AUDIO POWER AMPLIFIER DESIGN

A 1W/8ΩAUDIO AMPLIFIER

Given:

Power Output 1 Wrms

Load Impedance 8Ω

Input Level 1 Vrms

Input Impedance 20 kΩ

Bandwidth 100 Hz–20 kHz ±0.25 dB

A designer must first determine the 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. A second way to determine the minimum sup-

ply rail is to calculate the required V

opeak

using Equation 2

and add the output voltage. Using this method, the minimum

supply voltage would be (V

opeak

+(V

TOP +V

BOT)), where

BOT and V

TOP are extrapolated from the Dropout Volt-

age vs Supply Voltage curve in the Typical Performance

Characteristics section.

(2)

5V is a standard voltage, in most applications, chosen for the

supply rail. Extra supply voltage creates headroom that al-

lows the LM4891 to reproduce peaks in excess of 1W with-

out 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 Equa-

tion 3.

(3)

=(R

From Equation 3, the minimum A

is 2.83; use A

=3.

Since the desired input impedance was 20 kΩ, and with a

of 3, a ratio of 1.5:1 of R

to R

results in an allocation of

=20kΩand R

=30kΩ. 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

−3 dB point is 0.17 dB down from passband response which

is better than the required ±0.25 dB specified.

= 100 Hz/5 = 20 Hz

=20kHz*5=100kHz

LM4891

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Application Information (Continued)

As stated in the External Components section, R

in con-

junction with C

create a highpass filter.

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

The high frequency pole is determined by the product of the

desired frequency pole, f

, and the differential gain, A

With a A

= 3 and f

= 100 kHz, the resulting GBWP =

300 kHz which is much smaller than the LM4891 GBWP of

2.5 MHz. This figure displays that if a designer has a need to

design an amplifier with a higher differential gain, the

LM4891 can still be used without running into bandwidth

limitations.

The LM4891 is unity-gain stable and requires no external

components besides gain-setting resistors, an input coupling

capacitor, and proper supply bypassing in the typical appli-

cation. 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-

nates possible high frequency oscillations. Care should be

taken when calculating the -3dB frequency in that an incor-

rect combination of R

and C

will cause rolloff before

20kHz. A typical combination of feedback resistor and ca-

pacitor that will not produce audio band high frequency rolloff

is R

= 20kΩand C

= 25pf. These components result in a

-3dB point of approximately 320 kHz.

20007424

FIGURE 2. Higher Gain Audio Amplifier

LM4891

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Application Information (Continued)

20007429

FIGURE 3. Differential Amplifier Configuration for LM4891

20007425

FIGURE 4. Reference Design Board and Layout - micro SMD

LM4891

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Application Information (Continued)

LM4891 micro SMD BOARD ARTWORK

Silk Screen Top Layer

20007457

20007458

Bottom Layer Inner Layer Ground

20007459 20007460

Inner Layer V

20007461

LM4891

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Application Information (Continued)

20007468

FIGURE 5. Reference Design Board and PCB Layout Guidelines - MSOP & SO Boards

LM4891

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Application Information (Continued)

LM4891 SO DEMO BOARD ARTWORK

Silk Screen

20007462

Top Layer

20007463

Bottom Layer

20007464

LM4891 MSOP DEMO BOARD ARTWORK

Silk Screen

20007465

Top Layer

20007466

Bottom Layer

20007467

LM4891

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Application Information (Continued)

Mono LM4891 Reference Design Boards

Bill of Material for all 3 Demo Boards

Item Part Number Part Description Qty Ref Designator

1 551011208-001 LM4891 Mono Reference Design Board 1

10 482911183-001 LM4891 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 2 J1, J2

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 (bring-

ing 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 may 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 digi-

tal 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 side as much as possible will

minimize capacitive noise coupling and cross talk.

LM4891

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Physical Dimensions inches (millimeters) unless otherwise noted

Note: Unless otherwise specified.

1. Epoxy coating.

2. 63Sn/37Pb eutectic bump.

3. Recommend non-solder mask defined landing pad.

4. Pin 1 is established by lower left corner with respect to text orientation pins are numbered counterclockwise.

5. Reference JEDEC registration MO-211, variation BC.

8-Bump micro SMD

Order Number LM4891IBP, LM4891IBPX

NS Package Number BPA08DDB

X1 = 1.361±0.03 X2 = 1.361±0.03 X3 = 0.850±0.10

LM4891

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

MSOP

Order Number LM4891MM

NS Package Number MUA08A

LM4891

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

Order Number LM4891M

NS Package Number M08A

LM4891

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

LLP

Order Number LM4891LD

NS Package Number LDA10B

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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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LM4891 1 Watt Audio Power Amplifier

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.