LM4731TA/NOPB - NATIONAL SEMICONDUCTOR

LM4731

LM4731 Stereo 25W Audio Power Amplifier with Mute and Standby Modes

Literature Number: SNAS197B

LM4731

OBSOLETE

September 24, 2011

Stereo 25W Audio Power Amplifier with Mute and Standby

Modes

General Description

The LM4731 is a stereo audio amplifier capable of delivering

typically 25W per channel of continuous average output pow-

er into a 4Ω or 8Ω load with less than 10% THD+N from 20Hz

- 20kHz.

Each amplifier has an independent smooth transition fade-in/

out mute and a power conserving standby mode which can

be controlled by external logic.

The LM4731 has short circuit protection and a thermal shut

down feature that is activated when the die temperature ex-

ceeds 150°C. The LM4731 also has a under voltage lock out

feature for click and pop free power off and on.

The LM4731 has a wide operating supply range from +/-10V

- +/-28V allowing for lower cost unregulated power supplies

to be used.

Key Specifications

■ Output Power into 4Ω or 8Ω, 10% THD+N 25W (typ)

■ THD+N at 1kHz with 2 x 1W into 8Ω0.02% (typ)

■ Mute Attenuation 85dB (typ)

■ PSRR with fRIPPLE = 120Hz,

VRIPPLE = 1VRMS 50dB (typ)

■ Slew Rate 18V/µs (typ)

■ Standby Current (+/-22V) 4.8mA (typ)

Features

■Minimal amount of external components necessary

■Quiet fade-in/out mute mode

■Low current Standby-mode

Applications

■Audio amplifier for high-end stereo TVs

■Audio amplifier for component stereo

■Audio amplifier for compact stereo

■Audio amplifier for PC satellite speaker systems

■Audio amplifier for self powered speakers

Connection Diagrams

Plastic Package

20060352

Top View

Non-Isolated Package

Order Number LM4731TA

See NS Package Number TA15A

TO-220 Top Marking (Note 12)

20060375

Top View

U - Wafer Fab Code

Z - Assembly Plant Code

XY - Date Code

TT - Die Traceability

LM4731TA - LM4731TA

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LM4731 Stereo 25W Audio Power Amplifier with Mute and Standby Modes

Typical Application

20060353

FIGURE 1. Typical Audio Amplifier Application Circuit

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LM4731

Absolute Maximum Ratings (Note 1, Note

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage |V+| + |V-|56V

Common Mode Input Voltage V+ or V-

Differential Input Voltage 56V

Output Current Internally Limited

Power Dissipation (Note 3) 50W

ESD Susceptability (Note 4) 2.0kV

ESD Susceptability (Note 6) 250V

Junction Temperature (TJMAX) (Note 9)150°C

Soldering Information

T Package (10 sec.) 260°C

Storage Temperature −40°C to +150°C

Thermal Resistance

θJA (TA) 43°C/W

θJC (TA) 1.5°C/W

Operating Ratings (Note 1, Note 2)

Temperature Range

TMIN ≤ TA ≤ TMAX −20°C ≤ TA ≤ +85°C

Supply Voltage |V+| + |V-|20V ≤ VTOTAL ≤ 56V

Electrical Characteristics (Note 1, Note 2)

The following specifications apply for V+ = +22V, V- = −22V and RL = 8Ω unless otherwise specified. Limits apply for TA = 25°C.

Symbol Parameter Conditions

LM4731

Units

(Limits)

Typical

(Note 6)

Limit

(Note 7)

(Note 8)

|V+| + |V-| Power Supply Voltage (Note 10)GND − V- ≥ 9V 20

V (min)

V (max)

AMMute Attenuation 85 dB

POOutput Power (RMS)

THD+N = 10% (max), f = 1kHz

|V+| = |V-| = 18V, RL = 4Ω

|V+| = |V-| = 22V, RL = 8Ω

W (min)

THD+N = 1% (max), f = 1kHz

|V+| = |V-| =18V, RL = 4Ω

|V+| = |V-| = 22V, RL = 8Ω

W (min)

THD+N Total Harmonic Distortion + Noise

PO = 1W, f = 1kHz

AV = 26dB,

|V+| = |V-| = 18V, RL = 4Ω

|V+| = |V-| = 22V, RL = 8Ω

0.03

0.02

0.5

0.3

% (max)

Xtalk Channel Separation

PO = 10W

f = 1kHz

f = 10kHz

SR Slew Rate (Note 11) VIN = 2.0Vp-p, trise = 2ns 18 V/μs

IDD Total Quiescent Power Supply

Current

VCM = 0V, VO = 0V, IO = 0A

Standby off (Play Mode)

Standby on (Standby Mode)

4.8

110

mA (max)

VOS Input Offset Voltage VCM = 0V, IO = 0 mA 2.0 15 mV (max)

IBInput Bias Current VCM = 0V, IO = 0 mA 0.2 μA

PSRR Power Supply Rejection Ratio VRIPPLE = 1VRMS, fRIPPLE = 120Hz sine wave

Inputs terminated to GND 50 dB

AVOL Open Loop Voltage Gain RL = 2 kΩ, Δ VO = 20V 110 dB

eIN Input Noise IHF — A-Weighting Filter 2.0 8 μV (max)

RIN = 600Ω (Input Referred)

Standby

VIL Standby Low Input Voltage Not in Standby Mode (Play) 0.8 V (max)

VIH Standby High Input Voltage In Standby Mode 2.0 2.5 V (min)

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LM4731

Symbol Parameter Conditions

LM4731

Units

(Limits)

Typical

(Note 6)

Limit

(Note 7)

(Note 8)

Mute

VIL Mute Low Input Voltage Not in Mute Mode (Play) 0.8 V (max)

VIH Mute High Input Voltage In Mute Mode 2.0 2.5 V (min)

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 a device's performance.

Note 3: The maximum power dissipation must be de-rated at elevated temperatures and is dictated by TJMAX, θJC, and the ambient temperature TA. The maximum

allowable power dissipation is PDMAX = (TJMAX -TA) / θJC or the number given in the Absolute Maximum Ratings, whichever is lower. For the LM4731, TJMAX =

150°C and the typical θJC is 1.5°C/W for the TA15A package . Refer to the Thermal Considerations section for more information.

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

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

Note 6: Typical specifications are sepcified at 25°C and represent the parametric norm.

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

Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Note 9: The operating junction temperature maximum is 150°C. However, the instantaneous Safe Operating Area temperature is 250°C.

Note 10: V- must have at least -9V at its pin with reference to GND in order for the under-voltage protection circuitry to be disabled. In addition, the voltage

differential between V+ and V- must be greater than 14V.

Note 11: The feedback compensation network limits the bandwidth of the closed-loop response causing the skew rate to be reduced by the high frequency roll-

off. Without feedback compensation the slew rate is typically larger.

Note 12: The LM4731TA package TA15A is a non-isolated package setting the tab of the device and the heat sink to V-potential when the LM4731TA is directly

mounted to the heat sink using only thermal compound. If a mica washer is used in addition to thermal compound, θCS (case to sink) is increased, but the heat

sink will be electrically isolated from V-.

Bridged Amplifier Application Circuit

20060305

FIGURE 2. Bridged Amplifier Application Circuit

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LM4731

Single Supply Application Circuit

20060306

FIGURE 3. Single Supply Amplifier Application Circuit

Note: *Optional components dependent upon specific design requirements.

Auxiliary Amplifier Application Circuit

20060307

FIGURE 4. Special Audio Amplifier Application Circuit

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LM4731

External Components Description

( See Figures 1 - 4 )

Components Functional Description

1 RBPrevents currents from entering the amplifier's non-inverting input which may be passed through to the load

upon power down of the system due to the low input impedance of the circuitry when the undervoltage circuitry

is off. This phenomenon occurs when the supply voltages are below 1.5V.

2 RiInverting input resistance to provide AC gain in conjunction with Rf.

3 RfFeedback resistance to provide AC gain in conjunction with Ri.

4 Ci

(Note 13)

Feedback capacitor which ensures unity gain at DC. Also creates a highpass filter with Ri at fC = 1/(2πRiCi).

5 CSProvides power supply filtering and bypassing. Refer to the Supply Bypassing application section for proper

placement and selection of bypass capacitors.

6 RV

(Note 13)

Acts as a volume control by setting the input voltage level.

7 RIN

(Note 13)

Sets the amplifier's input terminals DC bias point when CIN is present in the circuit. Also works with CIN to create

a highpass filter at fC = 1/(2πRINCIN). Refer to Figure 4.

8 CIN

(Note 13)

Input capacitor which blocks the input signal's DC offsets from being passed onto the amplifier's inputs.

9 RSN

(Note 13)

Works with CSN to stabilize the output stage by creating a pole that reduces high frequency instabilities.

10 CSN

(Note 13)

Works with RSN to stabilize the output stage by creating a pole that reduces high frequency instabilities. The

pole is set at fC = 1/(2πRSNCSN). Refer to Figure 4.

11 L (Note 13) Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the

Q of the series resonant circuit. Also provides a low impedance at low frequencies to short out R and pass audio

signals to the load. Refer to Figure 4.

12 R (Note 13)

13 RAProvides DC voltage biasing for the transistor Q1 in single supply operation.

14 CAProvides bias filtering for single supply operation.

15 RINP

(Note 13)

Limits the voltage difference between the amplifier's inputs for single supply operation. Refer to the Clicks and

Pops application section for a more detailed explanation of the function of RINP.

16 RBI Provides input bias current for single supply operation. Refer to the Clicks and Pops application section for a

more detailed explanation of the function of RBI.

17 REEstablishes a fixed DC current for the transistor Q1 in single supply operation. This resistor stabilizes the half-

supply point along with CA.

Note 13: Optional components dependent upon specific design requirements.

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LM4731

Typical Performance Characteristics

Supply Current vs

Supply Voltage

20060368

PSRR vs Frequency

±22V, VRIPPLE = 1VRMS,

RL = 8Ω, 80kHz BW

20060365

THD+N vs Frequency

±18V, PO = 1W/Channel,

RL = 4Ω, 80kHz BW

20060369

THD+N vs Frequency

±22V, PO = 1W/Channel,

RL = 8Ω, 80kHz BW

20060370

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LM4731

THD+N vs Output Power

±18V, RL = 4Ω, 80kHz BW

20060371

THD+N vs Output Power

±22V, RL = 8Ω, 80kHz BW

20060372

Output Power vs

Supply Voltage

f = 1kHz, RL = 4Ω, 80kHz BW

20060363

Output Power vs

Supply Voltage

f = 1kHz, RL = 8Ω, 80kHz BW

20060364

Power Dissipation vs

Output Power

1% THD (max), RL = 4Ω, 80kHz BW

20060361

Power Dissipation vs

Output Power

1% THD (max), RL = 8Ω, 80kHz BW

20060362

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LM4731

Crosstalk vs Frequency

±18V, PO = 10W,

RL = 4Ω, 80kHz BW

20060373

Crosstalk vs Frequency

±22V, PO = 10W,

RL = 8Ω, 80kHz BW

20060374

Mute Attenuation vs

Mute Pin Voltage

±22V, PO = 1W,

RL = 8Ω, 80kHz BW

20060360

Standby Attenuation vs

Standby Pin Voltage

±22V, PO = 1W,

RL = 8Ω, 80kHz BW

20060366

Supply Current vs

Standby Pin Voltage

±22V

20060367

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LM4731

Application Information

MUTE MODE

By placing a logic-high voltage on the mute pins, the signal

going into the amplifiers will be muted. If the mute pins are left

floating or connected to a logic-low voltage, the amplifiers will

be in a non-muted state. There are two mute pins, one for

each amplifier, so that one channel can be muted without

muting the other if the application requires such a configura-

tion. Refer to the Typical Performance Characteristics

section for curves concerning Mute Attenuation vs Mute Pin

Voltage.

STANDBY MODE

The standby mode of the LM4731 allows the user to drasti-

cally reduce power consumption when the amplifiers are idle.

By placing a logic-high voltage on the standby pins, the am-

plifiers will go into Standby Mode. In this mode, the current

drawn from the VCC supply is typically less than 10 μA total

for both amplifiers. The current drawn from the VEE supply is

typically 4.8mA. Clearly, there is a significant reduction in idle

power consumption when using the standby mode. There are

two Standby pins, so that one channel can be put in standby

mode without putting the other amplifier in standby if the ap-

plication requires such flexibility. Refer to the Typical Per-

formance Characteristics section for curves showing

Supply Current vs. Standby Pin Voltage for both supplies.

UNDER-VOLTAGE PROTECTION

Upon system power-up, the under-voltage protection circuitry

allows the power supplies and their corresponding capacitors

to come up close to their full values before turning on the

LM4731 such that no DC output spikes occur. Upon turn-off,

the output of the LM4731 is brought to ground before the

power supplies such that no transients occur at power-down.

OVER-VOLTAGE PROTECTION

The LM4731 contains over-voltage protection circuitry that

limits the output current while also providing voltage clamp-

ing, though not through internal clamping diodes. The clamp-

ing effect is quite the same, however, the output transistors

are designed to work alternately by sinking large current

spikes.

THERMAL PROTECTION

The LM4731 has a sophisticated thermal protection scheme

to prevent long-term thermal stress of the device. When the

temperature on the die exceeds150°C, the LM4731 shuts

down. It starts operating again when the die temperature

drops to about 145°C, but if the temperature again begins to

rise, shutdown will occur again above 150°C. Therefore, the

device is allowed to heat up to a relatively high temperature

if the fault condition is temporary, but a sustained fault will

cause the device to cycle in a Schmitt Trigger fashion be-

tween the thermal shutdown temperature limits of 150°C and

145°C. This greatly reduces the stress imposed on the IC by

thermal cycling, which in turn improves its reliability under

sustained fault conditions.

Since the die temperature is directly dependent upon the heat

sink used, the heat sink should be chosen such that thermal

shutdown will not be reached during normal operation. Using

the best heat sink possible within the cost and space con-

straints of the system will improve the long-term reliability of

any power semiconductor device, as discussed in the Deter-

mining the Correct Heat Sink Section.

DETERMlNlNG MAXIMUM POWER DISSIPATION

Power dissipation within the integrated circuit package is a

very important parameter requiring a thorough understanding

if optimum power output is to be obtained. An incorrect max-

imum power dissipation calculation may result in inadequate

heat sinking causing thermal shutdown and thus limiting the

output power.

Equation (1) exemplifies the theoretical maximum power dis-

sipation point of each amplifier where VCC is the total supply

voltage.

PDMAX = VCC2/2π2RL(1)

Thus by knowing the total supply voltage and rated output

load, the maximum power dissipation point can be calculated.

The package dissipation is twice the number which results

from equation (1) since there are two amplifiers in each

LM4731. Refer to the graphs of Power Dissipation versus

Output Power in the Typical Performance Characteristics

section which show the actual full range of power dissipation

not just the maximum theoretical point that results from equa-

tion (1).

DETERMINING THE CORRECT HEAT SINK

The choice of a heat sink for a high-power audio amplifier is

made entirely to keep the die temperature at a level such that

the thermal protection circuitry does not operate under normal

circumstances.

The thermal resistance from the die (junction) to the outside

air (ambient) is a combination of three thermal resistances,

θJC, θCS, and θSA. In addition, the thermal resistance, θJC

(junction to case), of the LM4731TA is 1.5°C/W. Using Ther-

malloy Thermacote thermal compound, the thermal resis-

tance, θCS (case to sink), is about 0.2°C/W. Since convection

heat flow (power dissipation) is analogous to current flow,

thermal resistance is analogous to electrical resistance, and

temperature drops are analogous to voltage drops, the power

dissipation out of the LM4731 is equal to the following:

PDMAX = (TJMAX−TAMB)/θJA (2)

where TJMAX = 150°C, TAMB is the system ambient tempera-

ture and θJA = θJC + θCS + θSA.

Once the maximum package power dissipation has been cal-

culated using equation (1), the maximum thermal resistance,

θSA, (heat sink to ambient) in °C/W for a heat sink can be

calculated. This calculation is made using equation (3) which

is derived by solving for θSA in equation (2).

θSA = [(TJMAX−TAMB)−PDMAX(θJC +θCS)]/PDMAX (3)

Again it must be noted that the value of θSA is dependent upon

the system designer's amplifier requirements. If the ambient

temperature that the audio amplifier is to be working under is

higher than 25°C, then the thermal resistance for the heat

sink, given all other things are equal, will need to be smaller.

SUPPLY BYPASSING

The LM4731 has excellent power supply rejection and does

not require a regulated supply. However, to improve system

performance as well as eliminate possible oscillations, the

LM4731 should have its supply leads bypassed with low-in-

ductance capacitors having short leads that are located close

to the package terminals. Inadequate power supply bypass-

ing will manifest itself by a low frequency oscillation known as

“motorboating” or by high frequency instabilities. These in-

stabilities can be eliminated through multiple bypassing uti-

lizing a large tantalum or electrolytic capacitor (10 μF or

larger) which is used to absorb low frequency variations and

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LM4731

a small ceramic capacitor (0.1 μF) to prevent any high fre-

quency feedback through the power supply lines.

If adequate bypassing is not provided, the current in the sup-

ply leads which is a rectified component of the load current

may be fed back into internal circuitry. This signal causes dis-

tortion at high frequencies requiring that the supplies be by-

passed at the package terminals with an electrolytic capacitor

of 470 μF or more.

BRIDGED AMPLIFIER APPLICATION

The LM4731 has two operational amplifiers internally, allow-

ing for a few different amplifier configurations. One of these

configurations is referred to as “bridged mode” and involves

driving the load differentially through the LM4731's outputs.

This configuration is shown in Figure 2. Bridged mode oper-

ation is different from the classical single-ended amplifier

configuration where one side of its load is connected to

ground.

A bridge amplifier design has a distinct advantage over the

single-ended configuration, as it provides differential drive to

the load, thus doubling output swing for a specified supply

voltage. Consequently, theoretically four times the output

power is possible as compared to a single-ended amplifier

under the same conditions. This increase in attainable output

power assumes that the amplifier is not current limited or

clipped.

A direct consequence of the increased power delivered to the

load by a bridge amplifier is an increase in internal power dis-

sipation. For each operational amplifier in a bridge configu-

ration, the internal power dissipation will increase by a factor

of two over the single ended dissipation. Thus, for an audio

power amplifier such as the LM4731, which has two opera-

tional amplifiers in one package, the package dissipation will

increase by a factor of four. To calculate the LM4731's max-

imum power dissipation point for a bridged load, multiply

equation (1) by a factor of four.

This value of PDMAX can be used to calculate the correct size

heat sink for a bridged amplifier application. Since the internal

dissipation for a given power supply and load is increased by

using bridged-mode, the heatsink's θSA will have to decrease

accordingly as shown by equation (3). Refer to the section,

Determining the Correct Heat Sink, for a more detailed

discussion of proper heat sinking for a given application.

SINGLE-SUPPLY AMPLIFIER APPLICATION

The typical application of the LM4731 is a split supply ampli-

fier. But as shown in Figure 3, the LM4731 can also be used

in a single power supply configuration. This involves using

some external components to create a half-supply bias which

is used as the reference for the inputs and outputs. Thus, the

signal will swing around half-supply much like it swings

around ground in a split-supply application. Along with proper

circuit biasing, a few other considerations must be accounted

for to take advantage of all of the LM4731 functions.

The LM4731 possesses a mute and standby function with in-

ternal logic gates that are half-supply referenced. Thus, to

enable either the Mute or Standby function, the voltage at

these pins must be a minimum of 2.5V above half-supply. In

single-supply systems, devices such as microprocessors and

simple logic circuits used to control the mute and standby

functions, are usually referenced to ground, not half-supply.

Thus, to use these devices to control the logic circuitry of the

LM4731, a “level shifter,” like the one shown in Figure 5, must

be employed. A level shifter is not needed in a split-supply

configuration since ground is also half-supply.

20060354

FIGURE 5. Level Shift Circuit

When the voltage at the Logic Input node is 0V, the 2N3904

is “off” and thus resistor Rc pulls up mute or standby input to

the supply. This enables the mute or standby function. When

the Logic Input is 5V, the 2N3904 is “on” and consequently,

the voltage at the collector is essentially 0V. This will disable

the mute or standby function, and thus the amplifier will be in

its normal mode of operation. Rshift, along with Cshift, creates

an RC time constant that reduces transients when the mute

or standby functions are enabled or disabled. Additionally,

Rshift limits the current supplied by the internal logic gates of

the LM4731 which insures device reliability. Refer to the Mute

Mode and Standby Mode sections in the Application Infor-

mation section for a more detailed description of these

functions.

CLICKS AND POPS

In the typical application of the LM4731 as a split-supply audio

power amplifier, the IC exhibits excellent “click” and “pop”

performance when utilizing the mute and standby modes. In

addition, the device employs Under-Voltage Protection, which

eliminates unwanted power-up and power-down transients.

The basis for these functions are a stable and constant half-

supply potential. In a split-supply application, ground is the

stable half-supply potential. But in a single-supply application,

the half-supply needs to charge up just like the supply rail,

VCC. This makes the task of attaining a clickless and popless

turn-on more challenging. Any uneven charging of the ampli-

fier inputs will result in output clicks and pops due to the

differential input topology of the LM4731.

To achieve a transient free power-up and power-down, the

voltage seen at the input terminals should be ideally the same.

Such a signal will be common-mode in nature, and will be

rejected by the LM4731. In Figure 3, the resistor RINP serves

to keep the inputs at the same potential by limiting the voltage

difference possible between the two nodes. This should sig-

nificantly reduce any type of turn-on pop, due to an uneven

charging of the amplifier inputs. This charging is based on a

specific application loading and thus, the system designer

may need to adjust these values for optimal performance.

As shown in Figure 3, the resistors labeled RBI help bias up

the LM4731 off the half-supply node at the emitter of the

2N3904. But due to the input and output coupling capacitors

in the circuit, along with the negative feedback, there are two

different values of RBI, namely 10 kΩ and 200 kΩ. These re-

sistors bring up the inputs at the same rate resulting in a

popless turn-on. Adjusting these resistors values slightly may

reduce pops resulting from power supplies that ramp ex-

tremely quick or exhibit overshoot during system turn-on.

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LM4731

PROPER SELECTION OF EXTERNAL COMPONENTS

Proper selection of external components is required to meet

the design targets of an application. The choice of external

component values that will affect gain and low frequency re-

sponse are discussed below.

The gain of each amplifier is set by resistors Rf and Ri for the

non-inverting configuration shown in Figure 1. The gain is

found by Equation (4) below:

AV = 1 + Rf / Ri (V/V) (4)

For best noise performance, lower values of resistors are

used. A value of 1kΩ is commonly used for Ri and then setting

the value of Rf for the desired gain. For the LM4731 the gain

should be set no lower than 10V/V and no higher than 50V/

V. Gain settings below 10V/V may experience instability and

using the LM4731 for gains higher than 50V/V will see an in-

crease in noise and THD.

The combination of Ri with Ci (see Figure 1) creates a high

pass filter. The low frequency response is determined by

these two components. The -3dB point can be found from

Equation (5) shown below:

fi = 1 / (2πRiCi) (Hz) (5)

If an input coupling capacitor is used to block DC from the

inputs as shown in Figure 4, there will be another high pass

filter created with the combination of CIN and RIN. When using

a input coupling capacitor RIN is needed to set the DC bias

point on the amplifier's input terminal. The resulting -3dB fre-

quency response due to the combination of CIN and RIN can

be found from Equation (6) shown below:

fIN = 1 / (2πRINCIN) (Hz) (6)

PHYSICAL IC MOUNTING CONSIDERATIONS

Mounting of the TO-220 package to a heat sink must be done

such that there is sufficient pressure from the mounting screw

to insure good contact with the heat sink for efficient heat flow.

Over tightening the mounting screw will cause the TO-220

package to warp reducing contact area with the heat sink.

Less contact with the heat sink will increase the thermal re-

sistance from the TO-220 package case to the heat sink

(θCS) resulting in higher operating die temperatures and pos-

sible unwanted thermal shut down activation. Extreme over

tightening of the mounting screw will cause severe physical

stress resulting in cracked die and catastrophic IC failure. The

recommended maximum mounting screw torque is 40 inch-

lbs or 3.3 foot-lbs (4.5 newton-meter).

Additionally, if the mounting screw is used to force the TO-220

package into correct alignment with the heat sink, package

stress will be increased. This increase in package stress will

result in reduced contact area with the heat sink increasing

die operating temperature and possible catastrophic IC fail-

ure.

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LM4731

20060355

FIGURE 6. Reference PCB Schematic

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LM4731

LM4731 REFERENCE BOARD ARTWORK

Composite View

20060356

Silk Screen

20060357

Top Layer

20060358

Bottom Layer

20060359

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LM4731

BILL OF MATERIALS FOR REFERENCE PCB

Symbol Value Toleranc

eType/Description Comments

RIN1, RIN2 47kΩ5% 1/4 Watt

RB1, RB2 1kΩ1% 1/4 Watt

RF1, RF2 20kΩ1% 1/4 Watt

Ri1, Ri2 1kΩ1% 1/4 Watt

RSN1, RSN2 4.7Ω 5% 1/4 Watt

RG2.7Ω 5% 1/4 Watt

CIN1, CIN2 1µF 10% Metallized Polyester Film

Ci1, Ci2 47µF 20% Electrolytic Radial / 35V

CSN1, CSN2 0.1µF 20% Monolithic Ceramic

CV0.1µF 20% Monolithic Ceramic

CM10µF 20% Electrolytic Radial / 16V

CS1, CS2 0.1µF 20% Monolithic Ceramic

CS3, CS4 10µF 20% Electrolytic Radial / 35V

CS5, CS6 1,000µF 20% Electrolytic Radial / 35V

S1, S2 SPDT (on-on) Switch

J1, J2 Non-switched PC Mount RCA Jack

J4, J7, J8 PCB Banana Jack- BLACK

J3, J5, J6, J9 PCB Banana Jack- RED

U1 15 lead TO-220 Power Socket

LM340, 5V Fixed Regulator, TO-263 package

(TS3B)

15 www.national.com

200603 Version 3 Revision 12 Print Date/Time: 2011/09/24 08:30:19

LM4731

Physical Dimensions inches (millimeters) unless otherwise noted

Non-Isolated TO-220 15-Lead Package

Order Number LM4731TA

NS Package Number TA15A

www.national.com 16

200603 Version 3 Revision 12 Print Date/Time: 2011/09/24 08:30:19

LM4731

Notes

17 www.national.com

200603 Version 3 Revision 12 Print Date/Time: 2011/09/24 08:30:19

LM4731

Notes

LM4731 Stereo 25W Audio Power Amplifier with Mute and Standby Modes

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