LM4682SQ - National Semiconductor

LM4682

LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo

Headphone Amplifier and DC Volume Control

Literature Number: SNAS271D

LM4682 OBSOLETE

September 24, 2011

10 Watt Stereo CLASS D Audio Power Amplifier with Stereo

Headphone Amplifier and DC Volume Control

General Description

The LM4682 is a fully integrated single supply, high efficiency

audio power amplifier solution. The LM4682 utilizes a propri-

etary balanced pulse-width modulation technique that lowers

output noise and THD and improves PSRR when compared

to conventional pulse width modulators.

The LM4682 also features a stereo headphone amplifier that

delivers 60mW into a 32Ω headset with less than 0.5% THD.

The LM4682's DC volume control has a +30dB to –48dB

range when speakers are driven and a range of +13dB to –

65dB when headphones are connected. All amplifiers are

protected by thermal shutdown. Additionally, all amplifiers in-

corporate output current limiting function to protect their out-

puts from short circuit.

The LM4682 features a low-power consumption shutdown

mode. And its efficiency reaches 85% for a 10W output power

with an 8Ω load. External heatsink is not required when play-

ing music. The IC features click and pop reduction circuitry

that minimizes audible popping during device turn-on and

turn-off. The LM4682 is available in a 48-lead LLP package,

ideal for portable and desktop computer applications.

Key Specifications

■PO at THD+N = 10%, VDD = 14V 10W (typ)

■THD+N at 1kHz at 6W into 8Ω (Power Amp) 0.2% (typ)

■Efficiency at 7W into 8Ω84% (typ)

■Total quiescent power supply current 52mA (typ)

■Total shutdown power supply current 0.1mA (typ)

■THD+N 1kHz, 20mW, 32Ω (Headphone) 0.02% (typ)

■Single supply range 8.5V to 15V

Features

■Pulse-width modulator.

■DC Volume Control

■Stereo headphone amplifier.

■“Click and pop” suppression circuitry.

■Micropower shutdown mode.

■48 lead LLP package (No heatsink required).

Applications

■Flat Panel Displays

■Televisions

■Multimedia Monitors

Boomer® is a registered trademark of National Semiconductor Corporation.

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LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and

DC Volume Control

Block Diagram

20119622

Block Diagram for LM4682

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LM4682

Connection Diagram

LLP Package

20119618

Top View

Order Number LM4682SQ

See NS Package Number SQA48A

(LLP Package)

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LM4682

Typical Application

20119630

FIGURE 1. Typical Stereo Audio Amplifier with Headphone Selection Circuit

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LM4682

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 15.5V

Input Voltage −0.3V to VDD +0.3V

Power Dissipation (Note 3) Internally Limited

ESD Susceptibility (Note 4) 2000V

ESD Susceptibility (Note 5) 200V

Junction Temperature (Note 6) 150°C

Storage Temperature −65°C ≤ TA ≤ 150°C

Soldering Information

LLP 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.

Operating Ratings (Note 1, Note 2)

Temperature Range

TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ +85°C

Supply Voltage 8.5V ≤ VDD ≤ 15V

Thermal Resistance (LLP Package)

θJA 28°C/W

θJC 20°C/W

Electrical Characteristics (Note 1, Note 2, Note 7)

The following specifications apply for VDD = 12V, VOLVDD = 5V, RL = 8Ω, LC filter values as shown in Figure 1, unless otherwise

specified.

Limits apply for TA = 25°C.

Symbol Parameter Conditions

LM4682

Units

Typica

lMax Min

VDD Operating Supply Voltage Range 12 15 8.5 V

Quiescent Power Supply Current,

Class D Mode VIN = 0VRMS, VHPSEL = 0V 52 70 mA

Quiescent Power Supply Current,

Headphone Mode VIN = 0VRMS, VHPSEL = 12V 30 40 mA

ISD

Quiescent Power Supply Current,

Shutdown Mode SDB = 0V 0.1 mA

RIN Input Resistance in Both Modes 8 kΩ

VOLVDD DC Reference Supply Voltage 5.5 3 V

VIH Minimum Logic High Input Voltage SDB, MUTEB pins 0.7xVOLVDD V

VIL Maximum Logic Low Input Voltage 0.3xVOLVDD V

VHPIH HP Sense High Input Voltage VDD-1 V

VHPIL HP Sense Low Input Voltage VDD/2 V

Power Amplifiers

POROutput Power, Per Channel THD+N ≤ 1%, fIN = 1kHz 6.0 5.5 W

PD1 Power Dissipation PO = 7W/Chan, fIN = 1kHz 2.6 W

EFF1 Efficiency PO = 7W/Chan, fIN = 1kHz 84.4 %

THD+N Harmonic Distortion + Noise PO = 6W/Chan, fIN = 1kHz 0.2 %

VNOISE

Output Noise Voltage, RMS.

A−Weighted

RSOURCE = 50Ω, CIN = 1µF,

BW = 8Hz to 22kHz

A-weighted, input referred

µV

PSRR Power Supply Rejection Ratio

VRIPPLE = 200mVpp, 1kHz,

VIN = 0, input referred

f = 50Hz 94

f = 60Hz 94

f 100Hz 93

f = 120Hz 93

f = 1kHz 84

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LM4682

Symbol Parameter Conditions

LM4682

Units

Typica

lMax Min

Headphone Amplifiers

POPower Out Per Channel THD+N ≤ 1%, RL = 32Ω, fIN = 1kHz 80 60 mW

THD+N Distortion + Noise PO = 20mW, RL = 32Ω, fIN = 1kHz 0.02 %

VNOISE Output Noise Voltage, RMS

RIN = 50Ω, CIN = 1µF, BW = 20Hz

to 20kHz

A-weighted, input referred

µV

PSRR Power Supply Rejection Ratio

(Referred to Input) 200mV, 1kHz, VIN = 0, RL = 32Ω 88 dB

Electrical Characteristics for Volume Control (Note 1, Note 2)

The following specifications apply for VDD = 12V. Limits apply for TA = 25°C.

Symbol Parameter Conditions

LM4682 Units

(Limits )

Typical

(Note 8)

Limit

(Note 7)

CRANGE Gain Range

VOL_CTL voltage = VOLVDD voltage,

No Load

Power Amplifier

Headphone Amplifier

dB (min)

VOL_CTL voltage = 0.069 x VOLVDD

No Load

Power Amplifier

Headphone Amplifier

–48

–65

–46

–63

dB (min)

AMMute Gain

VMUTE voltage = 0V, No Load

Power Amplifier

Headphone Amplifier

–80

–70

–60

dB (max)

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: For operating at case temperatures above 25°C, the device must be derated based on a 150°C maximum junction temperature and a thermal resistance

of θJA = 28°C/W (junction to ambient).

Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Device pin 16 has ESD HBM rating = 1500V.

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

Note 6: The operating junction temperature maximum is 150°C.

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

Note 8: Typicals are measured at 25°C and represent the parametric norm.

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LM4682

Typical Performance Characteristics (Power Amplifier)

THD+N vs Frequency

VDD = 9V, RL = 8Ω, PO = 1W

20119658

THD+N vs Frequency

VDD = 12V, RL = 8Ω, PO = 1W

20119659

THD+N vs Frequency

VDD = 15V, RL = 8Ω, PO = 1W

20119660

THD+N vs Output Power Per Channel

VDD = 9V, fIN = 1kHz, RL = 8Ω

20119661

THD+N vs Output Power Per Channel

VDD = 12V, fIN = 1kHz, RL = 8Ω

20119662

THD+N vs Output Power Per Channel

VDD = 15V, fIN = 1kHz, RL = 8Ω

20119663

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LM4682

THD+N vs Output Power Per Channel

VDD = 12V, fIN = 10kHz, RL = 8Ω

20119664

THD+N vs Output Power Per Channel

VDD = 12V, fIN = 20Hz, RL = 8Ω

20119665

Output Power vs Supply Voltage

fIN = 1kHz, RL = 8Ω

20119667

Amplifiers Gain vs Frequency

VDD = 9V, RL = 8Ω, PO = 1W

20119647

Amplifiers Gain vs Frequency

VDD = 12V, RL = 8Ω, PO = 1W

20119648

Amplifiers Gain vs Frequency

VDD = 15V, RL = 8Ω, PO = 1W

20119649

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LM4682

PSRR vs Frequency

VDD = 9V

20119644

PSRR vs Frequency

VDD = 12V

20119645

PSRR vs Frequency

VDD = 15V

20119646

Class-D Amplifier Dissipation vs Load Dissipation

Per Channel, VDD = 9V, RL = 8Ω

(both channels driven and measured)

20119638

Class-D Amplifier Dissipation vs Load Dissipation

Per Channel, VDD = 12V, RL = 8Ω

(both channels driven and measured)

20119639

Class-D Amplifier Dissipation vs Load Dissipation

Per Channel, VDD = 15V, RL = 8Ω

(both channels driven and measured)

20119640

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LM4682

Efficiency vs Output Power

VDD = 9V, RL = 8Ω

(both channels driven and measured)

20119641

Efficiency vs Output Power

VDD = 12V, RL = 8Ω

(both channels driven and measured)

20119642

Efficiency vs Output Power

VDD = 15V, RL = 8Ω

(both channels driven and measured)

20119643

Output Power vs Load Resistance

VDD = 9V, fIN = 1kHz

(both channels driven and measured)

20119655

Output Power vs Load Resistance

VDD = 12V, fIN = 1kHz

(both channels driven and measured)

20119656

Output Power vs Load Resistance

VDD = 15V, fIN = 1kHz

(both channels driven and measured)

20119657

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LM4682

Power Supply Current vs Power Supply Voltage

20119654

Class-D Amplifier Gain vs

Volume Control Voltage

VDD = 15V

20119628

Typical Performance Characteristics (Headphone Amplifier)

THD+N vs Frequency

VDD = 9V, RL = 32Ω, PO = 20mW

20119651

THD+N vs Frequency

VDD = 12V, RL = 32Ω, PO = 20mW

20119652

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LM4682

THD+N vs Frequency

VDD = 15V, RL = 32Ω, PO = 20mW

20119653

THD+N vs Output Power

VDD = 9V, RL = 32Ω, fIN = 1kHz

20119668

THD+N vs Output Power

VDD = 12V, RL = 32Ω, fIN = 1kHz

20119669

THD+N vs Output Power

VDD = 15V, RL = 32Ω, fIN = 1kHz

20119670

Output Power vs Supply Voltage Per Channel

fIN = 1kHz, RL = 32Ω

20119671

Power Supply Current vs Power Supply Voltage

20119650

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LM4682

Headphone Amplifier Gain vs

Volume Control Voltage

VDD = 15V

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LM4682

General Features

SYSTEM FUNCTIONAL INFORMATION

Modulation Technique

Unlike typical Class D amplifiers that use single-ended com-

parators to generate a pulse-width modulated switching

waveform and RC timing circuits to set the switching frequen-

cy, the LM4682 uses a balanced differential floating modula-

tor. Oscillation is a result of injecting complimentary currents

onto the respective plates of a floating, on-die capacitor. The

value of the floating capacitor and value of the components

in the modulator’s feedback network set the nominal switch-

ing frequency at 450kHz. Modulation results from imbalances

in the injected currents. The amount of current imbalance is

directly proportional to the applied input signal’s magnitude

and frequency.

Using a balanced, floating modulator produces a Class D am-

plifier that is immune to common mode noise sources such

as substrate noise. This noise occurs because of the high

frequency, high current switching in the amplifier’s output

stage. The LM4682 is immune to this type of noise because

the modulator, the components that set its switching frequen-

cy, and even the load all float with respect to ground.

The balanced modulator’s pulse width modulated output

drives the gates of the LM4682’s H-bridge configured output

power MOSFETs. The pulse-train present at the power MOS-

FETs’ output is applied to an LC low pass filter that removes

the 450kHz energy component. The filter’s output signal,

which is applied to the driven load, is an amplified replica of

the audio input signal.

Shutdown Function

The LM4682’s active-low shutdown function allows the user

to place the amplifier in a shutdown mode while the system

power supply remains active. Activating shutdown stops the

output switching waveform and minimizes the quiescent cur-

rent. Applying logic “0” to SDB pin enables the shutdown

function. Applying logic “1” to SDB pin disables the shutdown

function and restores full amplifier operation.

Mute Function

The LM4682’s active-low mute function allows the user to

place the amplifier outputs in muted mode while the

amplifier’s analog input signals remain active. Activating mute

internally removes the analog input signal from the Class D

and headphone amplifier inputs. While muted the amplifier

inputs and outputs retain in their VDD/2 operational bias. Ap-

plying logic “0” to MUTEB pin activates mute. Applying logic

“1” to MUTEB pin deactivates mute. The MUTEB pin is pull-

down internally to put both Class D and headphone amplifier

outputs mute.

Stereo Headphone Amplifier

The LM4682’s stereo headphone amplifier operates continu-

ously, even while the Class D amplifiers are active. When

using headphones to listen to program material, it is usually

desirable to stop driving external speakers. This is easily

achieved by using the active high HPSEL input. As shown in

typical application schematic in Figure 1, with no headphones

connected to the headphone jack, the input voltage applied

to the HPSEL pin is a logic low. In this state, the Class D am-

plifiers are active and able to drive external speakers. When

headphones are plugged into the headphone jack, the switch

inside the jack is opened. This changes the voltage applied

to the HPSEL pin to a logic high, shutting off the LM4682’s

Class D amplifiers. The headphone control of the output con-

figuration is shown in Table 1.

TABLE 1. Headphone Controls

HP Sense Pin, HPSEL Output Stage Configuration

0 Class D Amps Active

1 Class D Amps Inactive

Under Voltage Protection

The under voltage protection disables the output driver sec-

tion of the LM4682 while the supply voltage is below 8V. This

condition may occur as power is first applied or during low line

conditions, changes in load resistance, or when power supply

sag occurs. The under voltage protection ensures that all of

the LM4682’s power MOSFETs are off. This action eliminates

shoot-through current and minimizes output transients during

turn-on and turn-off. The under voltage protection gives the

digital logic time to stabilize into known states, further mini-

mizing turn on output transients.

Power Supply Sequencing

In order to stabilize LM4682 before any operation, a power-

up sequence for the power supplies is recommended. The

Power VDD should be applied first. Without deactivating the

mute and shutdown function of the amplifiers, the VOLVDD is

then applied. Prior to removing the two supply voltages, acti-

vate shutdown and mute.

Turn-On Time

The LM4682 has an internal timer that determines the

amplifier’s turn-on time. After power is first applied or the part

returns from shutdown, the nominal turn-on time is 600ms.

This delay allows all externally applied capacitors to charge

to a final value of VDD/2. Further, during turn-on, the outputs

are muted. This minimizes output transients that may occur

while the part settles into its quiescent operating mode.

Output Stage Current Limit and Fault Detection

Protection

The output stage MOSFETs are protected against output

conditions that could otherwise compromise their operational

status. The first stage of protection is output current limiting.

When conditions that require high currents to drive a load, the

LM4682’s current limit circuitry clamps the output current at a

nominal value of 2.5A. The output waveform is present, but

may be clipped or its amplitude reduced. The same 2.5A

nominal current limit also occurs if the amplifier outputs are

shorted together or either output is shorted to VDD or GND.

The second stage of protection is an onboard fault detection

circuit that continuously monitors the signal on each output

MOSFET’s gate and compares it against the respective drain

voltage. When a condition is detected that violates a

MOSFET’s Safe Operating Area (SOA) and the drive signal

is disconnected from the output MOSFETs’ gates. The fault

detect circuit maintains this protective condition for approxi-

mately 600ms, at which time the drive signal is reconnected.

If the fault condition is no longer present, normal operation

resumes. If the fault condition remains, however, the drive

signal is again disconnected.

Thermal Protection

The LM4682 has thermal shutdown circuitry that monitors the

die temperature. Once the LM4682 die temperature reaches

170°C, the LM4682 disables the output switching waveform

and remains disabled until the die temperature falls below

140°C (typ).

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LM4682

Over-Modulation Protection

The LM4682’s over-modulation protection is a result of the

preamplifier’s inability to produce signal magnitudes that

equal the power supply voltages. Since the preamplifier’s out-

put magnitude will always be less than the supply voltage, the

duty cycle of the amplifier’s switching output will never reach

zero. Peak modulation is limited to a nominal 95%.

DC Volume Control

The LM4682 has an internal stereo volume control whose

setting is a function of the DC voltage applied to the volume

control pin VOLCTL.

The LM4682 volume control consists of 31 steps, which are

individually selected by a variable DC voltage level on the

VOLCTL pin. A linear type 100kΩ potentiometer is used to

adjust the VOLCTL voltage in the LM4682 demonstration

board as shown in application circuit (see Figure 1). The re-

sistance value of potentiometer fall in the range from 10kΩ to

100kΩ is recommended to be used with only small amount of

current dissipation and large enough for the VOLCTL pin to

function properly. The Volume Control Characteristics of

LM4682 can be found in the Typical Performance Character-

istics section. The gain range of Class D amplifiers are from

–48dB to 30dB. The gain range of headphone amplifiers are

from –65dB to 13dB. Each gain step corresponds to specific

input voltage of both Class D amplifiers and headphone am-

plifiers are shown in Table 2.

To minimize the effect of noise on the volume control VOLCTL

pin, which can affect the selected gain level, hysteresis has

been implemented. The amount of hysteresis corresponds to

half of the step width. For highest accuracy, the voltage shown

in the “recommended voltage” column of the table is used to

select a desired gain. The recommended voltage is exactly

halfway between the two closest transitions to the next high-

est or next lowest gain levels.

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LM4682

TABLE 2. Volume Control Table

Step

Voltage Range (% of VOLVDD) Voltage Range (V), VOLVDD = 5V Gain (dB)

Low High Recommended Low High Recommended Class D

Amplifier

Headphone

Amplifier

1 77.50% 100.00% 100.000% 3.875 5.000 5.000 29.97 13.06

2 75.00% 78.50% 76.875% 3.750 3.925 3.844 28.97 12.07

3 72.50% 76.25% 74.375% 3.625 3.813 3.719 27.97 11.07

4 70.00% 73.75% 71.875% 3.500 3.688 3.594 26.96 10.06

5 67.50% 71.25% 69.375% 3.375 3.563 3.469 25.98 9.07

6 65.00% 68.75% 66.875% 3.250 3.438 3.344 24.97 8.07

7 62.50% 66.25% 64.375% 3.125 3.313 3.219 23.95 7.05

8 60.00% 63.75% 61.875% 3.000 3.188 3.094 21.98 5.08

9 57.50% 61.25% 59.375% 2.875 3.063 2.969 19.95 3.05

10 55.00% 58.75% 56.785% 2.750 2.983 2.844 17.96 1.06

11 52.50% 56.25% 54.375% 2.625 2.813 2.719 15.97 –0.93

12 50.00% 53.75% 51.875% 2.500 2.688 2.594 13.99 –2.91

13 47.50% 51.25% 49.375% 2.375 2.563 2.469 11.99 –4.91

14 45.00% 48.75% 46.875% 2.250 2.438 2.344 9.95 –6.96

15 42.50% 46.25% 44.375% 2.125 2.313 2.219 7.96 –8.94

16 40.00% 43.75% 41.875% 2.000 2.188 2.094 5.96 –10.95

17 37.50% 41.25% 39.375% 1.875 2.063 1.969 3.99 –12.91

18 35.00% 38.75% 36.875% 1.750 1.938 1.844 2.03 –14.87

19 32.50% 36.25% 34.375% 1.625 1.813 1.719 –0.02 –16.92

20 30.00% 33.75% 31.875% 1.500 1.688 1.594 –2.11 –19.02

21 27.50% 31.25% 29.375% 1.375 1.563 1.469 –4.16 –21.06

22 25.00% 28.75% 26.875% 1.250 1.438 1.344 –5.97 –22.87

23 22.50% 26.25% 24.375% 1.125 1.313 1.219 –8.77 –25.68

24 20.00% 23.75% 21.875% 1.000 1.188 1.094 –12.06 –28.96

25 17.50% 21.25% 19.375% 0.875 1.063 0.969 –14.84 –31.75

26 15.00% 18.75% 16.875% 0.750 0.938 0.844 –17.36 –34.26

27 12.50% 16.25% 14.375% 0.625 0.813 0.719 –20.89 –37.79

28 10.00% 13.75% 11.875% 0.500 0.688 0.594 –26.92 –43.83

29 7.50% 11.25% 9.375% 0.375 0.563 0.469 –32.95 –49.85

30 5.00% 8.75% 6.875% 0.250 0.438 0.344 –38.97 –55.88

31 0.00% 6.25% 0.000% 0.000 0.313 0.000 –48.03 –64.94

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LM4682

Application Hints

SUPPLY BYPASSING

The major source of noises to be taken care and applying

bypassing technique in using LM4682 are those transients

response coming from its output stage. During the switching

operations of the output stage of LM4682, the switching fre-

quencies vary when the internal modulator react to the input

signals. This creates a band of switching transients giving

back to the power supply terminals of LM4682. A single ca-

pacitor may not bypass those transients well. Two capacitors

which values are closed to each other are used to bypass this

range of frequencies to the ground. 10μF tantalum capacitors

and 4.7μF ceramic capacitors are needed for this kind of de-

coupling of LM4682 switching operation. This results an im-

provement in terms of both stability and audio performance of

LM4682. In addition, these capacitors should be placed as

close as possible to each IC’s supply pin(s) using leads as

short as possible. Apart from the power supply de-coupling

capacitors, the four bootstrapping capacitors (at pins

BST1_A, BST2_A, BST1_B and BST2_B) should also be

placed close to their corresponding pins. This could minimize

the undesirable switching noise coupled to the supply rail.

The LM4682 has two different sets of VDD pins: a set for power

VDD (PVDD_A and P VDD _B) and a set for signal VDD _A and

HP_ VDD. The parallel combination of the low value ceramic

(4.7μF) and high value tantalum (10μF) should be used to

bypass the power VDD pins. A small value (1μF) ceramic or

tantalum can be used to bypass the signal VDD _A and HP_

VDD pin.

OUTPUT STAGE FILTERING

The LM4682 requires a low pass filter connected between the

amplifier’s bridge output and the load. Figure 1 shows the

recommended LC filter. A minimum value of 22µH is recom-

mended. As shown in Figure 1, using the values of the com-

ponents connected between the amplifier BTL outputs and

the load achieves a 2nd-order lowpass filter response which

optimizes the amplifier's performance within the audio band.

THD+N MEASUREMENTS AND OUT OF AUDIO BAND

NOISE

THD+N (Total Harmonic Distortion plus Noise) is a very im-

portant parameter by which all audio amplifiers are measured.

Often it is shown as a graph where either the output power or

frequency is changed over the operating range. A very im-

portant variable in the measurement of THD+N is the band-

width-limiting filter at the input of the test equipment. Class D

amplifiers, by design, switch their output power devices at a

much higher frequency than the accepted audio range (20Hz

- 20kHz). Alternately switching the output voltage between

VDD and GND allows the LM4682 to operate at much higher

efficiency than that achieved by traditional Class AB ampli-

fiers. Switching the outputs at high frequency also increases

the out-of-band noise. Under normal circumstances the out-

put lowpass filter significantly reduces this out-of-band noise.

If the low pass filter is not optimized for a given switching fre-

quency, there can be significant increase in out-of-band

noise. THD+N measurements can be significantly affected by

out-of-band noise, resulting in a higher than expected THD+N

measurement. To achieve a more accurate measurement of

THD, the test equipment’s input bandwidth of the must be

limited. Some common upper filter points are 22kHz, 30kHz,

and 80kHz. The input filter limits the noise component of the

THD+N measurement to a smaller bandwidth resulting in a

more real-world THD+N value.

RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT

Figures 2 through 6 show the recommended four-layer PCB

board layout that is optimized for the 48-pin LLP packaged

LM4682 and associated external components. This circuit is

designed for use with an external 12V supply and 8Ω speak-

ers (or load resistors). Apply 12V and ground to board’s VDD

and GND terminals respectively. And apply 5V to the

VOLVDD (refer to power supply sequencing for details). Con-

nect speakers (or load resistors) between the board’s OUTA

+ and OUTA-, and between the board’s OUTB+ and OUTB-.

Apply the stereo input signals to IN_A and IN_B. When de-

signing the layout of the PCB layout, please pay attention to

the output terminals of LM4682.

17 www.national.com

201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06

LM4682

20119626

FIGURE 2. Top Layer

20119627

FIGURE 3. Top Silkscreen Layer

www.national.com 18

201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06

LM4682

20119623

FIGURE 4. Upper Middle Layer

20119624

FIGURE 5. Lower Middle Layer

19 www.national.com

201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06

LM4682

20119625

FIGURE 6. Bottom Layer

www.national.com 20

201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06

LM4682

Revision History

Rev Date Description

1.0 02/22/06 Initial WEB release of the document.

1.1 02/24/06 Edited art 201196 71 (changed the y-axis unit from mA to mW.

1.2 03/08/06 Did few texts clean-up and re-released D/S to the WEB (per Kevin H.).

1.3 06/29/06 Added 2 columns on ( Gain dB) Table 2 and re-released the D/S to the

WEB (per Alex CK Wong).

1.4 04/09/08 Added volume control curves and input some text edits.

1.5 04/15/08 Changed the titles on curves 20119628 and 29.

1.6 04/21/08 Text edits.

21 www.national.com

201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06

LM4682

Physical Dimensions inches (millimeters) unless otherwise noted

Order Number LM4682SQ

NS Package Number SQA48A

www.national.com 22

201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06

LM4682

Notes

23 www.national.com

201196 Version 5 Revision 2 Print Date/Time: 2011/09/24 10:13:06

LM4682

Notes

LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and

DC Volume Control

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