Datasheet LM4843MHX Datasheet (NSC)

LM4843

Stereo 2W Audio Power Amplifiers
with DC Volume Control

General Description

The LM4843 is a monolithic integrated circuit that provides
DC volume control, and stereo bridged audio power amplifi­ers capable of producing 2W into 4Ω (Note 1) with less than

1.0% THD or 2.2W into 3Ω (Note 2) with less than 1.0%
THD.

Boomer

®

audio integrated circuits were designed specifically
to provide high quality audio while requiring a minimum
amount of external components. The LM4843 incorporates a
DC volume control with stereo bridged audio power amplifi­ers making it optimally suited for multimedia monitors, por­table radios, desktop, and portable computer applications.

The LM4843 features an externally controlled, low-power
consumption shutdown mode, and both a power amplifier
and headphone mute for maximum system flexibility and
performance.

Note 1: When properly mounted to the circuit board, the LM4843MH will
deliver 2W into 4Ω. See the Application Information section for LM4843MH
usage information.

Note 2: LM4843MH that has been properly mounted to the circuit board and
forced-air cooled will deliver 2.2W into 3Ω.

Key Specifications

n POat 1% THD+N
n into 3Ω 2.2W (typ)
n into 4Ω 2.0W (typ)
n into 8Ω 1.1W (typ)
n Shutdown current 0.7µA (typ)

Features

n Acoustically Enhanced DC Volume Control Taper
n Stereo bridged power amplifiers
n “Click and pop” suppression circuitry
n Thermal shutdown protection circuitry

Applications

n Portable and Desktop Computers
n Multimedia Monitors
n Portable Radios, PDAs, and Portable TVs

Block Diagram

Boomer®is a registered trademark of NationalSemiconductor Corporation.

20038389

FIGURE 1. LM4843 Block Diagram

July 2002

LM4843 Stereo 2W Audio Power Amplifiers with DC Volume Control

© 2002 National Semiconductor Corporation DS200383 www.national.com

Connection Diagram

Standard LM4843MH

20038387

Top View

Order Number LM4843MH

See NS Package Number MXA20

LM4843

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Absolute Maximum Ratings (Note 10)

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

DD

+0.3V

Power Dissipation Internally limited

ESD Susceptibility (Note 12) 2000V

ESD Susceptibility (Note 13) 200V

Junction Temperature 150˚C

Soldering Information

Small Outline Package

Vapor Phase (60 sec.) 215˚C

Infrared (15 sec.) 220˚C

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

θ

JC

(typ) —MXA20A 2˚C/W

θ

JA

(typ) —MXA20A (exposed

DAP) (Note 4)

41˚C/W

θ

JA

(typ) —MXA20A (exposed

DAP) (Note 3)

54˚C/W

θ

JA

(typ) —MXA20A (exposed

DAP) (Note 5)

59˚C/W

θ

JA

(typ) —MXA20A (exposed

DAP) (Note 6)

93˚C/W

Operating Ratings

Temperature Range

T

MIN

≤ TA≤T

MAX

−40˚C ≤TA ≤ 85˚C

Supply Voltage 2.7V≤ V

DD

≤ 5.5V

Electrical Characteristics for Entire IC

(Notes 7, 10) The following specifications apply for VDD= 5V unless otherwise noted. Limits apply for TA= 25˚C.

Symbol Parameter Conditions

LM4843

Units

(Limits)

Typical

(Note 14)

Limit

(Note 15)

V

DD

Supply Voltage 2.7 V (min)

5.5 V (max)

I

DD

Quiescent Power Supply Current VIN= 0V, IO= 0A 15 30 mA (max)

I

SD

Shutdown Current V

shutdown

=V

DD

0.7 2.0 µA (max)

Electrical Characteristics for Volume Attenuators

(Notes 7, 10) The following specifications apply for VDD= 5V. Limits apply for TA= 25˚C.

Symbol Parameter Conditions

LM4843

Units

(Limits)

Typical

(Note 14)

Limit

(Note 15)

C

RANGE

Attenuator Range (Note 16) Attenuation with V

DCVol

= 5V, No Load

±

0.75 dB (max)

Attenuation with V

DCVol

= 0V -75 dB (min)

A

M

Mute Attenuation V

mute

= 5V, Bridged Mode (BM) -78 dB (min)

LM4843

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Electrical Characteristics for Bridged Mode Operation

(Notes 7, 10) The following specifications apply for VDD= 5V, unless otherwise noted. Limits apply for TA= 25˚C.

Symbol Parameter Conditions

LM4843

Units

(Limits)

Typical

(Note 14)

Limit

(Note 15)

V

OS

Output Offset Voltage VIN= 0V, No Load 10

±

50 mV (max)

P

O

Output Power THD+N=1.0%; f=1kHz; RL=3Ω

(Note 8)

2.2 W

THD+N=1.0%; f=1kHz; R

L

=4Ω

(Note 9)

2W

THD = 1% (max);f = 1 kHz;
R

L

=8Ω

1.1 1.0 W (min)

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

L

=8Ω 1.5 W

THD+N Total Harmonic Distortion+Noise P

O

= 1W, 20 Hz<f<20 kHz,

R

L

=8Ω,AVD=2

0.3 %

P

O

= 340 mW, RL=32Ω 1.0 %

PSRR Power Supply Rejection Ratio C

B

= 1.0 µF, f = 120 Hz,

V

RIPPLE

= 200 mVrms; RL=8Ω

74 dB

SNR Signal to Noise Ratio V

DD

= 5V, P

OUT

= 1.1W, RL=8Ω,

A-Wtd Filter

93 dB

X

talk

Channel Separation f=1kHz, CB= 1.0 µF 70 dB

Note 3: The θJAgiven is for an MXA20A package whose exposed-DAP is soldered to an exposed 2in2piece of 1 ounce printed circuit board copper.

Note 4: The θ

JA

given is for an MXA20A package whose exposed-DAP is soldered to a 2in2piece of 1 ounce printed circuit board copper on a bottom side layer

through 21 8mil vias.

Note 5: The θ

JA

given is for an MXA20A package whose exposed-DAP is soldered to an exposed 1in2piece of 1 ounce printed circuit board copper.

Note 6: The θ

JA

given is for an MXA20A package whose exposed-DAP is not soldered to any copper.

Note 7: All voltages are measured with respect to the ground pins, unless otherwise specified. All specifications are tested using the typical application as shown
in Figure 1.

Note 8: When driving 3Ω loads from a 5V supply the LM4843MH must be mounted to the circuit board and forced-air cooled.

Note 9: When driving 4Ω loads from a 5V supply the LM4843MH must be mounted to the circuit board.

Note 10: 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. Marshall Chiu feels there are better ways to obtain ’More
Wattage in the Cottage.’ Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device
performance.

Note 11: The maximum power dissipation must be derated at elevated temperatures and is dictated by T

JMAX

, θJA, and the ambient temperature TA. The maximum

allowable power dissipation is P

DMAX

=(T

JMAX−TA

)/θJA. For the LM4843MH, T

JMAX

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

mounted, is 80˚C/W for the MHC20 package.

Note 12: Human body model, 100 pF discharged through a 1.5 kΩ resistor.

Note 13: Machine Model, 220 pF–240 pF discharged through all pins.

Note 14: Typicals are measured at 25˚C and represent the parametric norm.

Note 15: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are guaranteed by design, test, or

statistical analysis.

Note 16: Refers only to the internal Volume Attenuation steps. Overall gain is determined by R

in

(AandB) and RF(AandB) plus another 6dB of gain in the BTL output

stage.

LM4843

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Typical Application

20038388

FIGURE 2. Typical Application Circuit

LM4843

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Typical Performance Characteristics

LM4843MH

THD+N vs Output Power

LM4843MH

THD+N vs Output Power

20038370

20038372

THD+N vs Output Power THD+N vs Output Power

20038324 20038325

THD+N vs Output Power THD+N vs Output Power(Note 17)

20038329

20038330

LM4843

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Typical Performance Characteristics (Continued)

THD+N vs Output Power

LM4843MH

THD+N vs Frequency

20038331

20038371

LM4843MH

THD+N vs Frequency THD+N vs Frequency

20038373

20038357

THD+N vs Frequency THD+N vs Frequency

20038358 20038317

LM4843

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Typical Performance Characteristics (Continued)

THD+N vs Frequency THD+N vs Frequency

20038318 20038319

Output Power vs
Load Resistance

Output Power vs
Load Resistance

20038362

20038307

Power Supply

Rejection Ratio Dropout Voltage

20038339

20038353

LM4843

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Typical Performance Characteristics (Continued)

Volume Control

Characteristics

Power Dissipation vs

Output Power

20038340

20038351

Crosstalk

Output Power vs

Supply Voltage

20038349

20038354

Supply Current vs

Supply Voltage

LM4843MH

Power Dissipation vs Output Power

20038309

20038365

LM4843

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Typical Performance Characteristics (Continued)

LM4843MH (Note 17)

Power Derating Curve

20038364

Note 17: These curves show the thermal dissipation ability of the LM4843MH at different ambient temperatures given these conditions:

500LFPM + 2in

2

: The part is soldered to a 2in2, 1 oz. copper plane with 500 linear feet per minute of forced-air flow across it.

2in

2

on bottom: The part is soldered to a 2in2, 1oz. copper plane that is on the bottom side of the PC board through 21 8 mil vias.

2in

2

: The part is soldered to a 2in2, 1oz. copper plane.

1in

2

: The part is soldered to a 1in2, 1oz. copper plane.

Not Attached: The part is not soldered down and is not forced-air cooled.

LM4843

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Application Information

EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS

The LM4843’s exposed-DAP (die attach paddle) package
(MH) provides a low thermal resistance between the die and
the PCB to which the part is mounted and soldered. This
allows rapid heat transfer from the die to the surrounding
PCB copper traces, ground plane and, finally, surrounding
air. The result is a low voltage audio power amplifier that
produces 2.1W at ≤ 1% THD with a 4Ω load. This high power
is achieved through careful consideration of necessary ther­mal design. Failing to optimize thermal design may compro­mise the LM4843’s high power performance and activate
unwanted, though necessary, thermal shutdown protection.

The MH package must have its exposed DAPs soldered to a
grounded copper pad on the PCB. The DAP’s PCB copper
pad is connected to a large grounded plane of continuous
unbroken copper. This plane forms a thermal mass heat sink
and radiation area. Place the heat sink area on either outside
plane in the case of a two-sided PCB, or on an inner layer of
a board with more than two layers. Connect the DAP copper
pad to the inner layer or backside copper heat sink area with
32(4x8) (MH) vias. The via diameter should be

0.012in–0.013in with a 1.27mm pitch. Ensure efficient ther­mal conductivity by plating-through and solder-filling the
vias.

Best thermal performance is achieved with the largest prac­tical copper heat sink area. If the heatsink and amplifier
share the same PCB layer, a nominal 2.5in

2

(min) area is
necessary for 5V operation with a 4Ω load. Heatsink areas
not placed on the same PCB layer as the LM4843 MH
package should be 5in

2

(min) for the same supply voltage
and load resistance. The last two area recommendations
apply for 25˚C ambient temperature. Increase the area to
compensate for ambient temperatures above 25˚C. In sys­tems using cooling fans, the LM4843MH can take advantage
of forced air cooling. With an air flow rate of 450 linear-feet
per minute and a 2.5in

2

exposed copper or 5.0in2inner layer
copper plane heatsink, the LM4843MH can continuously
drive a 3Ω load to full power. The junction temperature must
be held below 150˚C to prevent activating the LM4843’s
thermal shutdown protection. The LM4843’s power de-rating
curve in the Typical Performance Characteristics shows
the maximum power dissipation versus temperature. Ex­ample PCB layouts for the exposed-DAP TSSOP package
are shown in the Demonstration Board Layout section.
Further detailed and specific information concerning PCB
layout and fabrication is available in National Semiconduc­tor’s AN1187.

PCB LAYOUT AND SUPPLY REGULATION
CONSIDERATIONS FOR DRIVING 3Ω AND 4Ω LOADS

Power dissipated by a load is a function of the voltage swing
across the load and the load’s impedance. As load imped­ance decreases, load dissipation becomes increasingly de­pendent on the interconnect (PCB trace and wire) resistance
between the amplifier output pins and the load’s connec­tions. Residual trace resistance causes a voltage drop,
which results in power dissipated in the trace and not in the
load as desired. For example, 0.1Ω trace resistance reduces
the output power dissipated by a 4Ω load from 2.1W to 2.0W.
This problem of decreased load dissipation is exacerbated
as load impedance decreases. Therefore, to maintain the

highest load dissipation and widest output voltage swing,
PCB traces that connect the output pins to a load must be as
wide as possible.

Poor power supply regulation adversely affects maximum
output power. A poorly regulated supply’s output voltage
decreases with increasing load current. Reduced supply
voltage causes decreased headroom, output signal clipping,
and reduced output power. Even with tightly regulated sup­plies, trace resistance creates the same effects as poor
supply regulation. Therefore, making the power supply
traces as wide as possible helps maintain full output voltage
swing.

BRIDGE CONFIGURATION EXPLANATION

As shown in Figure 2, the LM4843 output stage consists of
two pairs of operational amplifiers, forming a two-channel
(channel A and channel B) stereo amplifier. (Though the
following discusses channel A, it applies equally to channel
B.)

Figure 2 shows that the first amplifier’s negative (-) output
serves as the second amplifier’s input. This 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 −OUTA and +OUTA and driven dif­ferentially (commonly referred to as “bridge mode”). This
results in a differential gain of

A

VD

=2*(Rf/Ri) (1)

Bridge mode amplifiers are 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 produces four times the output
power when 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 that 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 Amplifier Design section.

Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
channel A’s and channel B’s outputs at half-supply. This
eliminates the coupling capacitor that single supply, single­ended 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. This
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 single-ended or bridged amplifier. Equation (2)
states the maximum power dissipation point for a single­ended amplifier operating at a given supply voltage and
driving a specified output load.

P

DMAX

=(VDD)2/(2π2RL) Single-Ended (2)

However, a direct consequence of the increased power de­livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions.

LM4843

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Application Information (Continued)

The LM4843 has two operational amplifiers per channel. The
maximum internal power dissipation per channel operating in
the bridge mode is four times that of a single-ended ampli­fier. From Equation (3), assuming a 5V power supply and a
4Ω load, the maximum single channel power dissipation is

1.27W or 2.54W for stereo operation.

P

DMAX

=4*(VDD)2/(2π2RL) Bridge Mode (3)

The LM4843’s power dissipation is twice that given by Equa­tion (2) or Equation (3) when operating in the single-ended
mode or bridge mode, respectively. Twice the maximum
power dissipation point given by Equation (3) must not ex­ceed the power dissipation given by Equation (4):

P

DMAX

'=(T

JMAX−TA

)/θ

JA

(4)

The LM4843’s T

JMAX

= 150˚C. In the LQ package soldered

to a DAP pad that expands to a copper area of 5in

2

on a

PCB, the LM4843’s θ

JA

is 20˚C/W. In the MH package

soldered to a DAP pad that expands to a copper area of 2in

2

on a PCB, the LM4843MH’s θJAis 41˚C/W. For the
LM4843MH package, θ

JA

= 80˚C/W. At any given ambient

temperature T

A

, use Equation (4) to find the maximum inter­nal power dissipation supported by the IC packaging. Rear­ranging Equation (4) and substituting P

DMAX

for P

DMAX

' re­sults in Equation (5). This equation gives the maximum
ambient temperature that still allows maximum stereo power
dissipation without violating the LM4843’s maximum junction
temperature.

T

A=TJMAX

– 2*P

DMAXθJA

(5)

For a typical application with a 5V power supply and an 4Ω
load, the maximum ambient temperature that allows maxi­mum stereo power dissipation without exceeding the maxi­mum junction temperature is approximately 99˚C for the LQ
package and 45˚C for the MH package.

T

JMAX=PDMAXθJA+TA

(6)

Equation (6) gives the maximum junction temperature
T

JMAX

. If the result violates the LM4843’s 150˚C T

JMAX

,
reduce the maximum junction temperature by reducing the
power supply voltage or increasing the load resistance. Fur­ther allowance should be made for increased ambient tem­peratures.

The above examples assume that a device is a surface
mount part operating around the maximum power dissipation
point. Since internal power dissipation is a function of output
power, higher ambient temperatures are allowed as output
power or duty cycle decreases.

If the result of Equation (2) is greater than that of Equation
(3), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. If these
measures are insufficient, a heat sink can be added to
reduce θ

JA

. The heat sink can be created using additional
copper area around the package, with connections to the
ground pin(s), supply pin and amplifier output pins. External,
solder attached MH heatsinks such as the Thermalloy
7106D can also improve power dissipation. When adding a

heat sink, the θ

JA

is the sum of θJC, θCS, and θSA.(θJCis the

junction-to-case thermal impedance, θ

CS

is the case-to-sink

thermal impedance, and θ

SA

is the sink-to-ambient thermal
impedance.) Refer to the Typical Performance Character-
istics curves for power dissipation information at lower out­put power levels.

POWER SUPPLY BYPASSING

As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a 5V regulator typically
use a 10 µF in parallel with a 0.1 µF filter capacitor to
stabilize the regulator’s output, reduce noise on the supply
line, and improve the supply’s transient response. However,
their presence does not eliminate the need for a local 1.0 µF
tantalum bypass capacitance connected between the
LM4843’s supply pins and ground. Do not substitute a ce­ramic capacitor for the tantalum. Doing so may cause oscil­lation. Keep the length of leads and traces that connect
capacitors between the LM4843’s power supply pin and
ground as short as possible. Connecting a 1µF capacitor,
C

B

, between the BYPASS pin and ground improves the
internal bias voltage’s stability and the amplifier’s PSRR. The
PSRR improvements increase as the bypass pin capacitor
value increases. Too large a capacitor, however, increases
turn-on time and can compromise the amplifier’s click and
pop performance. The selection of bypass capacitor values,
especially C

B

, depends on desired PSRR requirements,
click and pop performance (as explained in the following
section, Selecting Proper External Components), system
cost, and size constraints.

SELECTING PROPER EXTERNAL COMPONENTS

Optimizing the LM4843’s performance requires properly se­lecting external components. Though the LM4843 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val­ues.

The LM4843 is unity-gain stable, giving a 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 circuits demand input
signals with greater voltage swings to achieve maximum
output power. Fortunately, many signal sources such as
audio CODECs have outputs of 1V

RMS

(2.83V

P-P

). Please
refer to the Audio Power Amplifier Design section for more
information on selecting the proper gain.

Input Capacitor Value Selection

Amplifying the lowest audio frequencies requires a high
value input coupling capacitor (0.33µF in Figure 2), but high
value capacitors can be expensive and may compromise
space efficiency in portable designs. In many cases, how­ever, the speakers used in portable systems, whether inter­nal or external, have little ability to reproduce signals below
150 Hz. Applications using speakers with this limited fre­quency response reap little improvement by using a large
input capacitor.

Besides effecting system cost and size, the input coupling
capacitor has an affect on the LM4843’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 size.

LM4843

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Application Information (Continued)

Higher value capacitors need more time to reach a quiescent
DC voltage (usually V

DD

/2) when charged with a fixed cur­rent. The amplifier’s output charges the input capacitor
through the feedback resistor, R

f

. Thus, pops can be mini­mized by selecting an input capacitor value that is no higher
than necessary to meet the desired −6dB frequency.

As shown in Figure 2, the input resistor (R

IR,RIL

= 20k) ( and

the input capacitor (C

IR,CIL

= 0.33µF) produce a −6dB high

pass filter cutoff frequency that is found using Equation (7).

(7)

As an example when using a speaker with a low frequency
limit of 150Hz, the input coupling capacitor, using Equation
(7), is 0.063µF. The 0.33µF input coupling capacitor shown
in Figure 2 allows the LM4843 to drive a high efficiency, full
range speaker whose response extends below 30Hz.

OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE

The LM4843 contains circuitry that minimizes turn-on and
shutdown transients or “clicks and pops”. For this discus­sion, turn-on refers to either applying the power supply volt­age or when the shutdown mode is deactivated. While the
power supply is ramping to its final value, the LM4843’s
internal amplifiers are configured as unity gain buffers. An
internal current source changes the voltage of the BYPASS
pin in a controlled, linear manner. Ideally, the input and
outputs track the voltage applied to the BYPASS pin. The
gain of the internal amplifiers remains unity until the voltage
on the bypass pin reaches 1/2 V

DD

. As soon as the voltage
on the bypass pin is stable, the device becomes fully opera­tional. Although the BYPASS pin current cannot be modified,
changing the size of C

B

alters the device’s turn-on time and
the magnitude of “clicks and pops”. Increasing the value of
C

B

reduces the magnitude of turn-on pops. However, this

presents a tradeoff: as the size of C

B

increases, the turn-on
time increases. There is a linear relationship between the
size of C

B

and the turn-on time. Here are some typical

turn-on times for various values of C

B

:

C

B

T

ON

0.01µF 2ms

0.1µF 20ms

0.22µF 44ms

0.47µF 94ms

1.0µF 200ms

MICRO-POWER SHUTDOWN

The voltage applied to the SHUTDOWN pin controls the
LM4843’s shutdown function. Activate micro-power shut­down by applying V

DD

to the SHUTDOWN pin. When active,
the LM4843’s micro-power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically V

DD

/2. The low 0.7 µA typical
shutdown current is achieved by applying a voltage that is as
near as V

DD

as possible to the SHUTDOWN pin. A voltage

that is less than V

DD

may increase the shutdown current.

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

DD

. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier opera­tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to V

DD

through the pull-up resistor, 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 need for a pull up resistor.

DC VOLUME CONTROL

The LM4843 has an internal stereo volume control whose
setting is a function of the DC voltage applied to the DC VOL
CONTROL pin.

The LM4843 volume control consists of 31 steps that are
individually selected by a variable DC voltage level on the
volume control pin. The range of the steps, controlled by the
DC voltage, are from 0dB - 78dB. Each attenuation step
corresponds to a specific input voltage range, as shown in
table 2.

To minimize the effect of noise on the volume control pin,
which can affect the selected attenuation level, hysteresis
has been implemented. The amount of hysteresis corre­sponds to half of the step width, as shown in Volume Control
Characterization Graph (DS200133-40).

For highest accuracy, the voltage shown in the ’recom­mended voltage’ column of the table is used to select a
desired attenuation level. This recommended voltage is ex­actly halfway between the two nearest transitions to the next
highest or next lowest attenuation levels.

The attenuation levels are 1dB/step from 0dB to -6dB, 2dB/
step from -6dB to -36dB, 3dB/step from -36dB to -47dB,
4dB/step from -47db to -51dB, 5dB/step from -51dB to

-66dB, and 12dB to the last step at -78dB.

LM4843

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Application Information (Continued)

Volume Control Table ( Table 2 )

Gain
(dB)

Voltage Range (% of Vdd) Voltage Range (Vdd = 5) Voltage Range (Vdd = 3)

Low High Recommended Low High Recommended Low High Recommended

0 77.5% 100.00% 100.000% 3.875 5.000 5.000 2.325 3.000 3.000

-1 75.0% 78.5% 76.875% 3.750 3.938 3.844 2.250 2.363 2.306

-2 72.5% 76.25% 74.375% 3.625 3.813 3.719 2.175 2.288 2.231

-3 70.0% 73.75% 71.875% 3.500 3.688 3.594 2.100 2.213 2.156

-4 67.5% 71.25% 69.375% 3.375 3.563 3.469 2.025 2.138 2.081

-5 65.0% 68.75% 66.875% 3.250 3.438 3.344 1.950 2.063 2.006

-6 62.5% 66.25% 64.375% 3.125 3.313 3.219 1.875 1.988 1.931

-8 60.0% 63.75% 61.875% 3.000 3.188 3.094 1.800 1.913 1.856

-10 57.5% 61.25% 59.375% 2.875 3.063 2.969 1.725 1.838 1.781

-12 55.0% 58.75% 56.875% 2.750 2.938 2.844 1.650 1.763 1.706

-14 52.5% 56.25% 54.375% 2.625 2.813 2.719 1.575 1.688 1.631

-16 50.0% 53.75% 51.875% 2.500 2.688 2.594 1.500 1.613 1.556

-18 47.5% 51.25% 49.375% 2.375 2.563 2.469 1.425 1.538 1.481

-20 45.0% 48.75% 46.875% 2.250 2.438 2.344 1.350 1.463 1.406

-22 42.5% 46.25% 44.375% 2.125 2.313 2.219 1.275 1.388 1.331

-24 40.0% 43.75% 41.875% 2.000 2.188 2.094 1.200 1.313 1.256

-26 37.5% 41.25% 39.375% 1.875 2.063 1.969 1.125 1.238 1.181

-28 35.0% 38.75% 36.875% 1.750 1.938 1.844 1.050 1.163 1.106

-30 32.5% 36.25% 34.375% 1.625 1.813 1.719 0.975 1.088 1.031

-32 30.0% 33.75% 31.875% 1.500 1.688 1.594 0.900 1.013 0.956

-34 27.5% 31.25% 29.375% 1.375 1.563 1.469 0.825 0.937 0.881

-36 25.0% 28.75% 26.875% 1.250 1.438 1.344 0.750 0.862 0.806

-39 22.5% 26.25% 24.375% 1.125 1.313 1.219 0.675 0.787 0.731

-42 20.0% 23.75% 21.875% 1.000 1.188 1.094 0.600 0.712 0.656

-45 17.5% 21.25% 19.375% 0.875 1.063 0.969 0.525 0.637 0.581

-47 15.0% 18.75% 16.875% 0.750 0.937 0.844 0.450 0.562 0.506

-51 12.5% 16.25% 14.375% 0.625 0.812 0.719 0.375 0.487 0.431

-56 10.0% 13.75% 11.875% 0.500 0.687 0.594 0.300 0.412 0.356

-61 7.5% 11.25% 9.375% 0.375 0.562 0.469 0.225 0.337 0.281

-66 5.0% 8.75% 6.875% 0.250 0.437 0.344 0.150 0.262 0.206

-78 0.0% 6.25% 0.000% 0.000 0.312 0.000 0.000 0.187 0.000

LM4843

www.national.com 14

Application Information (Continued)

AUDIO POWER AMPLIFIER DESIGN

Audio Amplifier Design: Driving 1W into an 8Ω Load

The following are the desired operational parameters:

Power Output: 1 W

RMS

Load Impedance: 8Ω

Input Level: 1 V

RMS

Input Impedance: 20 kΩ

Bandwidth: 100 Hz−20 kHz

±

0.25 dB

The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. One way to
find the minimum supply voltage is to use the Output Power
vs Supply Voltage curve in the Typical Performance Char-
acteristics section. Another way, using Equation (10), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To ac­count for the amplifier’s dropout voltage, two additional volt­ages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics curves, must be
added to the result obtained by Equation (10). The result is
Equation (11).

(8)

VDD≥ (V

OUTPEAK

+(V

OD

TOP

+V

OD

BOT

)) (9)

The Output Power vs Supply Voltage graph for an 8Ω load
indicates a minimum supply voltage of 4.6V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
LM4843 to produce peak output power in excess of 1W
without clipping or other audible distortion. The choice of
supply voltage must also not create a situation that violates
of maximum power dissipation as explained above in the
Power Dissipation section.

After satisfying the LM4843’s power dissipation require­ments, the minimum differential gain needed to achieve 1W
dissipation in an 8Ω load is found using Equation (12).

(10)

Thus, a minimum overall gain of 2.83 allows the LM4843’s to
reach full output swing and maintain low noise and THD+N
performance.

The last step in this design example is setting the amplifier’s

−6dB 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 within the

±

0.25dB
desired limit. The results are an

f

L

= 100Hz/5 = 20Hz (11)

and an

f

H

= 20kHz x 5 = 100kHz (12)

As mentioned in the Selecting Proper External Compo-
nents section, R

i

(Right & Left) and Ci(Right & Left) create
a highpass filter that sets the amplifier’s lower bandpass
frequency limit. Find the input coupling capacitor’s value
using Equation (14).

C

i

≥ 1/(2πRifL) (13)

The result is

1/(2π

*

20kΩ*20Hz) = 0.397µF (14)

Use a 0.39µF capacitor, the closest standard value.

The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain A

VD

, determines the

upper passband response limit. With A

VD

= 3 and fH=
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4843’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance,restricting
bandwidth limitations.

Recommended Printed Circuit
Board Layout

Figure (6) through (10) show the recommended four-layer
PC board layout that is optimized for the 24-pin
LQ-packaged LM4843 and associated external components.
This circuit is designed for use with an external 5V supply
and 4Ω speakers.

This circuit board is easy to use. Apply 5V and ground to the
board’s V

DD

and GND pads, respectively. Connect 4Ω
speakers between the board’s −OUTA and +OUTA and
OUTB and +OUTB pads.

LM4843

www.national.com15

Analog Audio LM4843 MSOP Eval Board

Assembly Part Number: 980011373-100

Revision: A

Bill of Material

Item Part Number Part Description Qty Ref Designator Remark

1 551011373-001 LM4843 Eval Board PCB etch 001 1

10 482911373-001 LM4843 MSOP 1

25 152911368-001 Tant Cap 0.1µF 10V 10% Size = A 3216 2 C2, C3

26 152911368-002 Tant Cap 0.33µF 10V 10% Size = A 3216 3 C

in

A, CinB

27 152911368-003 Tant Cap 1µF 16V 10% Size = A 3216 1 C

BYP

28 152911368-004 Tant Cap 10µF 10V 10% Size = C 6032 1 C1

31 472911368-002 Res 20K Ohm 1/8W 1% 1206 4 R

in

A, RinB, RFA,R

FB

40 131911368-001 Stereo Headphone Jack W/ Switch 1 Mouser #

41 131911368-002 Slide Switch 2 SD, Mute Mouser # 10SP003

42 131911368-003 Potentiometer 1 Volume Control Mouser # 317-2090-100K

43 131911368-004 RCA Jack 2 In A, In B Mouser # 16PJ097

44 131911368-005 Banana Jack, Black 3 A

out-,Bout-

, GND Mouser # ME164-6219

45 131911368-006 Banana Jack, Red 3 A

out+,Bou+,VDD

Mouser # ME164-6218

LM4843

www.national.com 16

LM4843MH Demo Boards

20038393

Top Layer SilkScreen

20038394

Top Layer TSSOP

LM4843

www.national.com17

LM4843MH Demo Boards (Continued)

20038392

Bottom Layer (2) LM4843MH

LM4843

www.national.com 18

Physical Dimensions inches (millimeters) unless otherwise noted

Exposed-DAP TSSOP Package

Order Number LM4843MH

NS Package Number MXA20A for Exposed-DAP TSSOP

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
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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Corporation

Americas
Email: [e-mail]

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www.national.com

LM4843 Stereo 2W Audio Power Amplifiers with DC Volume Control

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.