LM4701T_技术文档

March 1998

Ovture

™

LM4701 Overture Audio Power Amplifier Series

30W Audio Power Amplifier with

Mute and Standby Modes

General Description

The LM4701 is an audio power amplifier capable of deliver-

ing typically 30W of continuous average output power into an

8Ω load with less than 0.1% (THD + N).

Key Specifications

n THD+N at 1 kHz at continuous average output power of

25W into 8Ω: 0.1% (max)

n THD+N from 20 Hz to 20 kHz at 30W of continuous

average output power into 8Ω:

n Standby current:

0.08% (typ)

2.1 mA (typ)

The LM4701 has an independent smooth transition fade-in/

out mute and a power conserving standby mode which can

be controlled by external logic.

Features

n SPiKe Protection

The performance of the LM4701, utilizing its Self Peak In-

™

stantaneous Temperature (˚Ke) (SPiKe ) Protection Cir-

cuitry, places it in a class above discrete and hybrid amplifi-

ers by providing an inherently, dynamically protected Safe

Operating Area (SOA). SPiKe Protection means that these

parts are completely safeguarded at the output against over-

voltage, undervoltage, overloads, including thermal runaway

and instantaneous temperature peaks.

n Minimal amount of external components necessary

n Quiet fade-in/out mute function

n Power conserving standby-mode

n Non-Isolated 9-lead TO-220 package

Applications

n TVs

n Component stereo

n Compact stereo

Typical Application

Connection Diagram

Plastic Package

DS100835-2

Top View

Order Number LM4701T

See NS Package Number TA9A

For Staggered Lead Non-Isolated Package

Only a 9-Pin Package

DS100835-1

*

Optional components dependent upon specific design requirements. Refer

to the External Components Description section for a component functional

description.

FIGURE 1. Typical Audio Amplifier Application Circuit

™

SPiKe Protection and Overture are trademarks of National Semiconductor Corporation.

DS100835

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Absolute Maximum Ratings (Notes 5, 4)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Junction Temperature (Note 8)

Thermal Resistance

θ_JC

150˚C

1.8˚C/W

43˚C/W

θ_JA

Soldering Information

TF Package (10 sec.)

Storage Temperature

Supply Voltage |V_CC| + |V_EE

(No Signal)

|

260˚C

66V

−40˚C ≤ T_A

≤

Supply Voltage |V_CC| + |V_EE

(with Input and Load)

|

+150˚C

64V

(V_CCor V_EE) and

|V_CC| + |V_EE| ≤ 60V

60V

Common Mode Input Voltage

Operating Ratings (Notes 4, 5)

Temperature Range

Differential Input Voltage

Output Current

T_MIN≤ T_A≤ T_MAX

−20˚C ≤ T_A≤ +85˚C

Internally Limited

62.5W

Supply Voltage |V_CC| + |V_EE| (Note 1)

20V to 64V

Power Dissipation (Note 6)

ESD Susceptibility (Note 7)

2000V

Electrical Characteristics

=

(Notes 4, 5) The following specifications are for V_CC+28V, V_EE−28V with R_L8Ω, unless otherwise specified. Limits ap-

=

ply for T_A25˚C.

Symbol

Parameter

Conditions

LM4701

Typical Limit

(Note 9) (Note 10)

Units

(Limits)

|V_CC| + |V_EE

|

Power Supply Voltage

(Note 11)

GND − V_EE≥ 9V

18

20

64

V (min)

V (max)

= =

THD + N 0.1% (max), f 1 kHz

P_O

Output Power

=

(Note 3)

(Continuous Average)

R_L8Ω, |V_CC

|

|V_EE

|

28V

30

22

25

15

W/ch

(min)

=

R_L4Ω, |V_CC

|

|V_EE

|

20V (Note 13)

W/ch

(min)

=

THD + N

Total Harmonic Distortion

Plus Noise

30W/ch, R_L8Ω,

0.08

%

=

20 Hz ≤ f ≤ 20 kHz, A_V26 dB

=

SR (Note 3)

I_TOTAL

Slew Rate

V_IN1.414 Vrms, t_rise2 ns

18

12

40

V/µs (min)

=

Total Quiescent Power

Supply Current

V_CM0V, V_O0V, I_O0 mA

(Note 2)

Standby: Off

25

mA (max)

mA

Standby: On

2.1

Standby Pin

V_IL

V_IH

Standby Low Input Voltage

Standby High Input Voltage

Not in Standby Mode

In Standby Mode

0.8

2.5

V (max)

V (min)

2.0

Mute Pin

V_IL

Mute Low Input Voltage

Mute High Input Voltage

Mute Attenuation

Output Not Muted

Output Muted

0.8

2.5

80

V (max)

V (min)

V_IH

2.0

115

2.0

=

A_M

V_PIN82.5V

dB (min)

mV (max)

µA (max)

A_PK(min)

=

V_OS(Note 2)

Input Offset Voltage

Input Bias Current

V_CM0V, I_O0 mA

15

=

I_B

V_CM0V, I_O0 mA

0.2

0.5

0.2

2.9

=

I_OS

I_O

Input Offset Current

Output Current Limit

V_CM0V, I_O0 mA

0.002

3.5

=

= =

10V, t_ON10 ms,

|V_CC

|

|V_EE

V_O0V

|V_CC− V_O|, V_CC20V, I_O+100 mA

|

=

V_OD

Output Dropout Voltage

(Note 12)

1.8

2.5

115

2.3

3.2

85

V (max)

dB (min)

= =

|V_O− V_EE|, V_EE−20V, I_O−100 mA

(Note 2)

PSRR

(Note 2)

= =

V_CC30V to 10V, V_EE−30V,

Power Supply Rejection Ratio

=

V_CM0V, I_O0 mA

=

V_CC30V, V_EE−30V to −10V

110

85

dB (min)

=

V_CM0V, I_O0 mA

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2

Electrical Characteristics (Continued)

=

(Notes 4, 5) The following specifications are for V_CC+28V, V_EE−28V with R_L8Ω, unless otherwise specified. Limits ap-

=

ply for T_A25˚C.

Symbol

Parameter

Conditions

LM4701

Typical Limit

(Note 9) (Note 10)

Units

(Limits)

=

CMRR (Note

2)

Common Mode Rejection Ratio

V_CC35V to 10V, V_EE−10V to −35V,

110

80

dB (min)

=

V_CM10V to −10V, I_O0 mA

=

A_VOL(Note 2) Open Loop Voltage Gain

R_L2 kΩ, ∆V_O30V

110

7.5

2.0

90

5

dB (min)

MHz (min)

µV (max)

=

GBWP

e_IN

Gain-Bandwidth Product

Input Noise

f_O100 kHz, V_IN50 mVrms

IHF — A Weighting Filter

8

=

R_IN600Ω (Input Referred)

(Note 3)

SNR

=

Signal-to-Noise Ratio

P_O1W, A-Weighted,

98

dB

=

Measured at 1 kHz, R_S25Ω

=

P_O25W, A-Weighted

108

=

Measured at 1 kHz, R_S25Ω

Note 1: Operation is guaranteed up to 64V, however, distortion may be introduced from SPiKe Protection Circuitry if proper thermal considerations are not taken into

account. Refer to the Application Information section for a complete explanation.

Note 2: DC Electrical Test; Refer to Test Circuit #1.

Note 3: AC Electrical Test; Refer to Test Circuit #2.

Note 4: All voltages are measured with respect to the GND (pin 7), unless otherwise specified.

Note 5: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-

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

antee 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 6: 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

=

θ

1.8 ˚C/W (junction to case). Refer to the section, Determining the Correct Heat Sink, in the Application Information section.

JC

Note 7: Human body model, 100 pF discharged through a 1.5 kΩ resistor.

Note 8: The operating junction temperature maximum is 150˚C, however, the instantaneous Safe Operating Area temperature is 250˚C.

Note 9: Typicals are measured at 25˚C and represent the parametric norm.

Note 10: Limits are guarantees that all parts are tested in production to meet the stated values.

Note 11:

V

must have at least −9V at its pin with reference to ground in order for the under-voltage protection circuitry to be disabled. In addition, the voltage dif-

EE

ferential between V

and V must be greater than 14V.

EE

CC

Note 12: The output dropout voltage, V , is the supply voltage minus the clipping voltage. Refer to the Clipping Voltage vs. Supply Voltage graph in the Typical Per-

OD

formance Characteristics section.

±

Note 13: For a 4Ω load, and with 20V supplies, the LM4701 can deliver typically 22 Watts of continuous average power per channel with less than 0.1% (THD+N).

±

With supplies above 20V, the LM4701 cannot deliver more than 22 watts into 4Ω due to current limiting of the output transistors. Thus, increasing the power supply

±

above 20V will only increase the internal power dissipation, not the possible output power. Increased power dissipation will require a larger heat sink as explained

in the Application Information section.

3

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#

Test Circuit 1 (Note 2) (DC Electrical Test Circuit)

DS100835-3

#

Test Circuit 2 (Note 3) (AC Electrical Test Circuit)

DS100835-4

Bridged Amplifier Application Circuit

DS100835-5

FIGURE 2. Bridged Amplifier Application Circuit

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Single Supply Application Circuit

DS100835-6

FIGURE 3. Single Supply Amplifier Application Circuit

Auxillary Amplifier Application Circuit

DS100835-7

FIGURE 4. Auxillary Amplifier Application Circuit

5

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Equivalent Schematic (Excluding Active Protection Circuitry)

DS100835-8

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External Components Description

Components

Functonal Description

1

2

R_B

Prevents 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.

R_I

Inverting input resistance to provide AC gain in conjunction with R_F. Also creates a highpass filter with C_I

=

at f_C1/(2πR_IC_I).

3

4

5

R_F

Feedback resistance to provide AC gain in conjunction with R_I.

Feedback capacitor which ensures unity gain at DC.

C_I(Note 14)

C_S

Provides power supply filtering and bypassing. Refer to the Supply Bypassing application section for

proper placement and selection of bypass capacitors.

6

7

R_V

(Note 14)

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

R_IN

Sets the amplifier’s input terminals DC bias point when C_INis present in the circuit. Also works with C_IN

=

(Note 14)

to create a highpass filter at f_C1/(2πR_INC_IN). Refer to Figure 4.

8

C_IN

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

(Note 14)

9

R_SN

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

=

(Note 14)

The pole is set at f_C1/(2πR_SNC_SN). Refer to Figure 4.

10

C_SN

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

(Note 14)

11

12

L (Note 14)

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.

R (Note 14)

13

14

15

R_A

C_A

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

Provides bias filtering for single supply operation.

R_INP

Limits the voltage difference between the amplifier’s inputs for single supply operation. Refer to the

(Note 14)

Clicks and Pops application section for a more detailed explanation of the function of R_INP

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 R_BI

.

16

17

R_BI

.

R_E

Establishes a fixed DC current for the transistor Q1 in single supply operation. This resistor stabilizes the

half-supply point along with C_A.

Note 14: Optional components dependent upon specific design requirements.

7

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Typical Performance Characteristics

THD + N vs Frequency

THD + N vs Output Power

THD + N vs Frequency

THD + N vs Output Power

DS100835-10

DS100835-13

DS100835-16

DS100835-11

DS100835-12

THD + N vs Output Power

DS100835-14

DS100835-15

THD + N vs Output Power

DS100835-17

DS100835-18

Clipping Voltage vs

Supply Voltage

Clipping Voltage vs

Supply Voltage

Clipping Voltage vs

Supply Voltage

DS100835-19

DS100835-20

DS100835-21

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Typical Performance Characteristics (Continued)

Power Dissipation vs

Output Power

Power Dissipation vs

Ouput Power

Power Dissipation vs

Output Power

DS100835-22

DS100835-23

DS100835-24

Output Power vs

Load Resistance

Output Power vs

Supply Voltage

Output Mute vs

Mute Pin Voltage

DS100835-25

DS100835-26

DS100835-27

Pulse Response

Large Signal Response

Output Mute vs

Mute Pin Voltage

DS100835-28

DS100835-29

DS100835-30

9

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Typical Performance Characteristics (Continued)

Power Supply

Rejection Ratio

Common-Mode

Rejection Ratio

Open Loop

Frequency Response

DS100835-31

DS100835-32

DS100835-33

Safe Area

Spike Protection Response

Supply Current vs

Supply Voltage

DS100835-35

DS100835-34

DS100835-36

Pulse Thermal

Resistance

Pulse Thermal

Resistance

Supply Current vs

Output Voltage

DS100835-37

DS100835-39

DS100835-38

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Typical Performance Characteristics (Continued)

Pulse Power Limit

Supply Current vs

Case Temperature

DS100835-40

DS100835-41

DS100835-42

Standby Current (I_CC) vs

Standby Pin Voltage

Supply Current (I_EE) vs

Standby Pin Voltage

Input Bias Current vs

Case Temperature

DS100835-44

DS100835-43

DS100835-45

turn-off, the output of the LM4701 is brought to ground be-

fore the power supplies such that no transients occur at

power-down.

Application Information

MUTE MODE

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

going into the amplifiers will be muted. If the mute pin is left

floating or connected to a logic-low level, the amplifier will be

in a non-muted state. Refer to the Typical Performance

Characteristics section for curves concerning Mute Attenu-

ation vs Mute Pin Voltage.

OVER-VOLTAGE PROTECTION

The LM4701 contains over-voltage protection circuitry that

limits the output current to approximately 3.5 Apk while also

providing voltage clamping, though not through internal

clamping diodes. The clamping effect is quite the same,

however, the output transistors are designed to work alter-

nately by sinking large current spikes.

STANDBY MODE

The standby mode of the LM4701 allows the user to drasti-

cally reduce power consumption when the amplifier is idle.

By placing a logic-high voltage on the standby pin, the ampli-

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

drawn from the V_CCsupply is typically less than 10 µA total

for both amplifiers. The current drawn from the V_EEsupply is

typically 2.1 mA. Clearly, there is a significant reduction in

idle power consumption when using the standby mode. Re-

fer to the Typical Performance Characteristics section for

curves showing Supply Current vs Standby Pin Voltage for

both supplies.

SPiKe PROTECTION

The

LM4701

is

protected

from

instantaneous

peak-temperature stressing of the power transistor array.

The Safe Operating Area graph in the Typical Performance

Characteristics section shows the area of device operation

where SPiKe Protection Circuitry is not enabled. The wave-

form to the right of the SOA graph exemplifies how the dy-

namic protection will cause waveform distortion when en-

abled.

THERMAL PROTECTION

The LM4701 has a sophisticated thermal protection scheme

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

temperature on the die reaches 165˚C, the LM4701 shuts

down. It starts operating again when the die temperature

drops to about 155˚C, but if the temperature again begins to

rise, shutdown will occur again at 165˚C. Therefore, the de-

vice is allowed to heat up to a relatively high temperature if

UNDER-VOLTAGE PROTECTION

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

cuitry allows the power supplies and their corresponding ca-

pacitors to come up close to their full values before turning

on the LM4701 such that no DC output spikes occur. Upon

11

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SUPPLY BYPASSING

Application Information (Continued)

The LM4701 has excellent power supply rejection and does

not require a regulated supply. However, to improve system

performance as well as eliminate possible oscillations, the

LM4701 should have its supply leads bypassed with

low-inductance capacitors having short leads that are lo-

cated close to the package terminals. Inadequate power

supply bypassing will manifest itself by a low frequency oscil-

lation known as “motorboating” or by high frequency insta-

bilities. These instabilities can be eliminated through multiple

bypassing utilizing a large tantalum or electrolytic capacitor

(10 µF or larger) which is used to absorb low frequency

variations and a small ceramic capacitor (0.1 µF) to prevent

any high frequency feedback through the power supply lines.

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 165˚C and

155˚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 opera-

tion. Using the best heat sink possible within the cost and

space constraints of the system will improve the long-term

reliability of any power semiconductor device, as discussed

in the Determining the Correct Heat Sink Section.

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

distortion at high frequencies requiring that the supplies be

bypassed at the package terminals with an electrolytic ca-

pacitor of 470 µF or more.

DETERMINING MAXIMUM POWER DISSIPATION

Power dissipation within the integrated circuit package is a

very important parameter requiring a thorough understand-

ing if optimum power output is to be obtained. An incorrect

maximum power dissipation calculation may result in inad-

equate heat sinking causing thermal shutdown and thus lim-

iting the output power.

BRIDGED AMPLIFIER APPLICATION

One common power amplifier configuration is shown in Fig-

ure 2 and is referred to as “bridged mode” operation. Bridged

mode operation is different from the classical single-ended

amplifier configuration where one side of the output load is

connected to ground.

Equation (1) exemplifies the theoretical maximum power dis-

sipation point of each amplifier where V_CCis the total supply

voltage.

P_DMAXV_CC²/2π²R_L

(1)

=

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.

Thus by knowing the total supply voltage and rated output

load, the maximum power dissipation point can be calcu-

lated. Refer to the graphs of Power Dissipation vs 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 equation (1).

DETERMINING THE CORRECT HEAT SINK

A direct consequence of the increased power delivered to

the load by a bridge amplifier is an increase in internal power

dissipation. For each operational amplifier in a bridge con-

figuration, the internal power dissipation will increase by a

factor of two over the single ended dissipation. Since there

are two amplifiers used in a bridge configuration, the maxi-

mum system power dissipation point will increase by a factor

of four over the figure obtained by equation (1).

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,

θ_JC, θ_CSand θ_SA. The thermal resistance, θ_JC(junction to

case), of the LM4701 is 2˚C/W. Using Thermalloy Therma-

cote thermal compound, the thermal resistance, θ_CS(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 LM4701 is equal to the following:

This value of P_DMAXcan be used to calculate the correct size

heat sink for a bridged amplifier application, assuming that

both IC’s are mounted on the same heatsink. Since the inter-

nal dissipation for a given power supply and load is in-

creased by using bridged-mode, the heatsink’s θ_SAwill 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 appli-

cation.

=

P_DMAX(T_JMAX− T_AMB)/θ_JA

(2)

=

where T_JMAX150˚C, T_AMBis the system ambient tempera-

=

ture and θ_JAθ_JC+ θ_CS+ θ_SA

.

Once the maximum package power dissipation has been

calculated using equation (1), the maximum thermal resis-

tance, θ_SA, (in ˚C/W) for a heat sink can be calculated. This

calculation is made using equation (3) which is derived by

solving for θ_SAin equation (2).

SINGLE-SUPPLY AMPLIFIER APPLICATION

The typical application of the LM4701 is a split supply ampli-

fier. But as shown in Figure 3, the LM4701 can also be used

in a single power supply configuration. This involves using

some external components to create

a half-supply bias

=

θ_SA[(T_JMAX−T_AMB)−P_DMAX(θ_JC+θ_CS)]/P_DMAX(3)

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 LM4701

functions.

Again it must be noted that the value of θ_SAis 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.

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12

based upon a specific application loading and thus, the sys-

tem designer may need to adjust these values for optimum

performance.

Application Information (Continued)

The LM4701 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 LM4701, a “level shifter”, like the one shown

in Figure 5, must be employed. A level shifter is not needed

As shown in Figure 3, the resistors labeled R_BIhelp bias up

the LM4701 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 R_BI, namely 10 kΩ and 200 kΩ. These re-

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

less turn-on. Adjusting these resistors values slightly may re-

duce pops resulting from power supplies that ramp

extremely quick or exhibit overshoot during system turn-on.

in

a split-supply configuration since ground is also

half-supply.

AUDIO POWER AMPLlFIER DESIGN

Design a 25W/8Ω Audio Amplifier

Given:

Power Output

Load Impedance

Input Level

25 Wrms

8Ω

1 Vrms(max)

47 kΩ

Input Impedance

Bandwidth

±

20 Hz to 20 kHz 0.25 dB

A designer must first determine the power supply require-

ments in terms of both voltage and current needed to obtain

the specified output power. V_OPEAKcan be determined from

equation (4) and I_OPEAKfrom equation (5).

DS100835-9

FIGURE 5. Level Shift Circuit

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

is “off” and thus resistor R_Cpulls 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. R_SHIFT, along with C_SHIFT, cre-

ates an RC time constant that reduces transients when the

mute or standby functions are enabled or disabled. Addition-

ally, R_SHIFTlimits the current supplied by the internal logic

gates of the LM4701 which insures device reliability. Refer to

the Mute Mode and Standby Mode sections in the Applica-

tion Information section for a more detailed description of

these functions.

(4)

(5)

To determine the maximum supply voltage, the following

conditions must be considered. Add the dropout voltage to

the peak output swing V_OPEAK, to get the supply rail at a cur-

rent of I_OPEAK. The regulation of the supply determines the

unloaded voltage which is usually about 15% higher. The

supply voltage will also rise 10% during high line conditions.

Therefore the maximum supply voltage is obtained from the

following equation:

±

Max Supplies ≈ (V_OPEAK+ V_OD) (1 + Regulation) (1.1)

CLICKS AND POPS

For 25W of output power into an 8Ω load, the required V_O

-

In the typical application of the LM4701 as a split-supply au-

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

performance when utilizing the mute and standby functions.

In addition, the device employs Under-Voltage Protection,

which eliminates unwanted power-up and power-down tran-

sients. The basis for these functions are a stable and con-

±

^PEAKis 20V. A minimum supply rail of 25V results from add-

ing V_OPEAKand V_OD. With regulation, the maximum supplies

are 31.7V and the required I_OPEAKis 2.5A from equation

±

(5). At this point it is a good idea to check the Power Output

vs Supply Voltage to ensure that the required output power is

obtainable from the device while maintaining low THD+N. In

addition, the designer should verify that with the required

power supply voltage and load impedance, that the required

heatsink value θ_SAis feasible given system cost and size

constraints. Once the heatsink issues have been addressed,

the required gain can be determined from equation (6).

stant half-supply potential. In

ground is the stable half-supply potential. But in

single-supply application, the half-supply needs to charge up

just like the supply rail, V_CC

a split-supply application,

a

.

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 dif-

ferential input topology of the LM4701.

(6)

From equation (6), the minimum A_Vis A_V≥ 14.14.

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 LM4701. In Figure 3, the resistor R_INP

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

voltage difference possible between the two nodes. This

should significantly reduce any type of turn-on pop, due to an

uneven charging of the amplifier inputs. This charging is

=

By selecting a gain of 21, and with a feedback resistor, R_F

20 kΩ, the value of R_Ifollows from equation (7).

=

R_IR_F(A_V− 1)

(7)

=

Thus with R_J1 kΩ a non-inverting gain of 21 will result.

Since the desired input impedance was 47 kΩ, a value of 47

kΩ was selected for R_IN. 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

13

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The high frequency pole is determined by the product of the

desired high frequency pole, f_H, and the gain, A_V. With a A_V

Application Information (Continued)

=

point is 0.17 dB down from passband response which is bet-

21 and f_H100 kHz, the resulting GBWP of 2.1 MHz is

±

ter than the required 0.25 dB specified. This fact results in

less than the minimum GBWP of 5 MHz for the LM4701. This

will ensure that the high frequency response of the amplifier

will be no worse than 0.17 dB down at 20 kHz which is well

within the bandwidth requirements of the design.

a low and high frequency pole of 4 Hz and 100 kHz respec-

tively. As stated in the External Components section, R_Iin

conjunction with C_Icreate a high-pass filter.

=

*

C_I≥ 1/(2π 1 kΩ 4 Hz) 39.8 µF; use 39 µF.

www.national.com

14

Physical Dimensions inches (millimeters) unless otherwise noted

Ovture

For Staggered Lead Non-Isolated Package

Only a 9-Pin Package

Order Number LM4701T

NS Package Number TA9A

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.

National Semiconductor

Corporation

Americas

Tel: 1-800-272-9959

Fax: 1-800-737-7018

Email: support@nsc.com

National Semiconductor

Europe

National Semiconductor

Asia Pacific Customer

Response Group

Tel: 65-2544466

Fax: 65-2504466

National Semiconductor

Japan Ltd.

Tel: 81-3-5639-7560

Fax: 81-3-5639-7507

Fax: +49 (0) 1 80-530 85 86

Email: europe.support@nsc.com

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Email: sea.support@nsc.com

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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.


型号：	LM4701T
厂家：	National Semiconductor
描述：	LM4701 Overture⑩ Audio Power Amplifier Series 30W Audio Power Amplifier with Mute and Standby Modes LM4701 Overture⑩音频功率放大器系列30W音频功率放大器静音和待机模式放大器功率放大器
文件：	总15页 (文件大小：544K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LM4701T [NSC]

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