LM4702 Audio Power Amplifier Series Stereo High Fidelity 200 Volt ...

LM4702 Audio Power Amplifier Series 

Stereo High Fidelity 200 Volt Driver with Mute 

General Description 

The LM4702 is a high fidelity audio power amplifier driver 

designed for demanding consumer and pro-audio applications. 

Amplifier output power may be scaled by changing the 

supply voltage and number of output devices. The LM4702 

is capable of delivering in excess of 300 watts per channel 

single ended into an 8 ohm load in the presence of 10% high 

line headroom and 20% supply regulation. 

The LM4702 includes thermal shut down circuitry that activates 

when the die temperature exceeds 150˚C. The 

LM4702’s mute function, when activated, mutes the input 

drive signal and forces the amplifier output to a quiescent 

state. 

The LM4702 is available in 3 grades that span a wide range 

of applications and performance levels. The LM4702C is 

targeted at high volume applications. The LM4702B includes 

a higher voltage rating along with the tighter specifications. 

The LM4702A* (in development) is the premium part with the 

highest voltage rating, fully specified with limits over voltage 

and temperature, and is offered in a military 883 compliant 

TO-3 package. 

* Tentative Max Operating voltage for the LM4702A (in development) 

Typical Application and Connection Diagrams 

20158319 

FIGURE 1. Typical Audio Amplifier Application Circuit 

Overture ® is a registered trademark of National Semiconductor Corporation. 

Key Specifications 

j Wide operating voltage range 

LM4702A* (in development) ±20V to ±100V 

LM4702B ±20V to ±100V 

LM4702C ±20V to ±75V 

j Equivalent Noise 3µV 

j PSRR 110dB (typ) 

j THD+N (A and B Grades) 0.0003% 

Features 

n Very high voltage operation 

n Scalable output power 

n Minimum external components 

n External compensation 

n Thermal Shutdown and Mute 

Applications 

n AV receivers 

n Audiophile power amps 

n Pro Audio 

n High voltage industrial applications 

20158302 

Plastic Package — 15 Lead TO-220 

(for LM4702BTA, LM4702CTA) 

20158320 

Metal Can — 15 Lead TO-3 

(for LM4702A, in development) 

September 2006 

© 2006 National Semiconductor Corporation DS201583 www.national.com 

LM4702 Stereo High Fidelity 200 Volt Driver with Mute

LM4702 

Typical Application and Connection Diagrams (Continued) 

FIGURE 1. Typical Audio Amplifier Application Circuit 

www.national.com 2 

20158319

Connection Diagram 

Plastic Package (For B and C) (Note 13) 

Top View 

Order Number LM4702BTA, LM4702CTA 

See NS Package Number TA15A 

3 

20158301 

www.national.com 

LM4702


Absolute Maximum Ratings (Notes 1, 

2) 

If Military/Aerospace specified devices are required, 

please contact the National Semiconductor Sales Office/ 

Distributors for availability and specifications. 

Supply Voltage |V + |+|V- | 

C Part 200V 

A, B Parts 200V 

Differential Input Voltage +/-6V 

Common Mode Input Range 0.4 Vee to 0.4 Vcc 

Power Dissipation (Note 3) 4W 

ESD Susceptibility (Note 4) 1.5kV 

ESD Susceptibility (Note 5) 200V 

Junction Temperature (TJMAX) (Note 9) 

Soldering Information 

150˚C 

T Package (10 seconds) 260˚C 

Storage Temperature -40˚C to +150˚C 

Thermal Resistance 

θJA 30˚C/W 

1˚C/W 

θ JC 

Operating Ratings (Notes 1, 2) 

Temperature Range 

TMIN ≤ TA ≤ TMAX Supply Voltage |V 

−20˚C ≤ TA ≤ +75˚C 

+ |+|V- | 

LM4702A (in development) +/-20V ≤ VTOTAL ≤ +/-100V 

LM4702B +/-20V ≤ VTOTAL ≤ +/-100V 

LM4702C +/-20V ≤ VTOTAL ≤ +/-75V 

Electrical Characteristics (LM4702C) Vcc = +75V, Vee = –75V (Notes 1, 2) 

The following specifications apply for IMUTE = 1.5mA, Figure 1, unless otherwise specified. Limits apply for TA = 25˚C. 

Symbol Parameter Conditions LM4702 Units 

Typical Limit (Limits) 

(Note 6) (Notes 7, 8) 

Total Quiescent Power Supply 

Current 

VCM = 0V, VO = 0V, IO = 0A 25 30 mA (max) 

I CC 

THD+N 

Total Harmonic Distortion + 

Noise 

No load, A V = 30dB 

V OUT = 14V RMS @ 1kHz 

0.005 % 

RS Input Bias Resistor 50 100 kΩ (max) 

Av Closed Loop Voltage Gain 26 dB (min) 

Av open Open Loop Gain Vin = 1mVrms, f = 1KHz, C = 30pF 93 dB 

Vom Output Voltage Swing THD = 0.05%, Freq = 20Hz to 20KHz 51 Vrms (min) 

Vnoise Output Noise 

Rs = 10kΩ, LPF = 30kHz, Av = 30dB 

A-weighted 

I OUT Output Current Current from Source to Sink Pins 5.5 

I mute Current into Mute Pin To put part in “play” mode 1.5 

150 300 µV (max) 

90 µV 

3 

10 

1 

2 

mA(min) 

mA (max) 

mA(min) 

mA (max) 

X TALK Channel Separation (Note 11) f = 1kHz @ Av = 30dB 85 dB 

SR Slew Rate 

VIN = 1.2VP-P, f = 10kHz square Wave, 

Outputs shorted 

15 V/µs 

VOS Input Offset Voltage VCM = 0V, IO = 0mA 10 35 mV (max) 

IB Input Bias Current VCM = 0V, IO = 0mA 500 nA 

PSRR Power Supply Rejection Ratio 

Rs = 1k, f = 100Hz, 

Vripple = 1Vrms, Input Referred 

110 95 dB (min) 

Electrical Characteristics (LM4702C) Vcc = +50V, Vee = –50V (Notes 1, 2) 






Current 

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

22 30 mA (max) 

I CC 

THD+N 


Noise 




0.005 %

Electrical Characteristics (LM4702C) Vcc = +50V, Vee = –50V (Notes 1, 

2) (Continued) 











A-weighted 

I OUT Output Current Outputs Shorted 5.2 


150 300 µV (max) 

90 µV 

3 

10 

1 

2 

mA(min) 

mA (max) 

mA(min) 

mA (max) 

X TALK Channel Separation (Note 11) f = 1kHz at Av = 30dB 85 dB 

SR Slew Rate 



15 V/µs 


IB Input Bias Current VCM = 0V, IO = 0mA 500 nA 


Rs = 1k, f = 100Hz, 


110 95 dB (min) 

Electrical Characteristics (LM4702B) Vcc = +100V, Vee = –100V (Notes 1, 2) 






Current 

VCM = 0V, VO = 0V, IO = 0A 27 35 mA (max) 

I CC 

THD+N 


Noise 



0.0003 0.001 % (max) 







A-weighted 



150 300 

90 

3 

8 

1 

2 

µV (max) 

mA(min) 

mA (max) 

mA(min) 

mA (max) 

X TALK Channel Separation (Note 11) f = 1kHz at Av = 30dB 87 85 dB (min) 

SR Slew Rate 



17 15 V/µs (min) 


IB Input Bias Current VCM = 0V, IO = 0mA 200 nA (max) 


Rs = 1k, f = 100Hz, 


5 

110 100 dB (min) 




Electrical Characteristics (LM4702A) Vcc = +100V, Vee = –100V 

(Pre-release information) (Notes 1, 2) 






Current 

VCM = 0V, VO = 0V, IO = 0A 27 TBD mA (max) 

I CC 

THD+N 


Noise 


V OUT = 20V RMS 

f = 1kHz 0.001 TBD 

f = 10kHz TBD TBD % (max) 

f = 100Hz TBD TBD 

RS Input Bias Resistor 50 TBD kΩ (max) 

Av Closed Loop Voltage Gain TBD dB (min) 


Vom Output Voltage Swing THD = 0.05%, Freq = 20Hz to 20KHz 57 TBD Vrms (min) 



A-weighted 


I mute 

X TALK 

Current into Mute Pin 

Channel Separation (Note 11) 

To put part in “play” mode 

100 

80 

1.5 

TBD 

TBD 

TBD 

TBD 

TBD 

TBD 

Av = 30dB 

f = 1kHz 90 TBD 

f = 10kHz TBD TBD 

f = 100Hz TBD TBD 

µV (max) 

mA(min) 

mA (max) 

mA(min) 

mA (max) 

dB (min) 

SR Slew Rate 



TBD TBD V/µs (min) 

VOS Input Offset Voltage VCM = 0V, IO = 0mA 5 TBD mV (max) 

IB Input Bias Current VCM = 0V, IO = 0mA 150 TBD nA (max) 


IMD Intermodulation Distortion 

Rs = 1k, f = 100Hz, 


at 20kHz / 19kHz 

at 60Hz / 7kHz 

110 TBD dB (min) 

TBD TBD dB 

Note 1: All voltages are measured with respect to the ground pins, 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 condition 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’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 LM4702, TJMAX = 150˚C 

and the typical θJC is 1˚C/W. Refer to the Thermal Considerations section for more information. 

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

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

Note 6: Typical specifications are measured 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 maximum operating junction temperature is 150˚C. 

Note 10: PCB layout will affect cross talk. It is recommended that input and output traces be separated by as much distance as possible. Return ground traces from 

outputs should be independent back to a single ground point and use as wide of traces as possible. 

Note 11: The TA15A is a non-isolated package. The package’s metal back and any heat sink to which it is mounted are connected to the Vee potential when 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 

Vee. 

www.national.com 6

Typical Performance Characteristics for LM4702C 

THD+N vs Output Voltage 

V DD = ±50V, f = 1kHz, outputs shorted 

THD+N vs Frequency 

V DD = ±50V, V OUT = 10Vrms, outputs shorted 

Crosstalk vs Frequency 

V DD = ±50V 


V DD = ±75V, f = 1kHz, outputs shorted 

20158308 20158338 


V DD = ±75V, V OUT = 14Vrms, outputs shorted 

20158310 20158339 

Crosstalk vs Frequency 

V DD = ±75V 

20158335 20158336 

7 




Typical Performance Characteristics for LM4702C (Continued) 

+PSRR vs Frequency 

V DD = ±50V, R S =1kΩ, Ripple on V CC 

+PSRR vs Frequency 

V DD = ±75V, R S =1kΩ, Ripple on V CC 

Open Loop and Phase 

Upper-Phase, Lower-Gain 

−PSRR vs Frequency 

V DD = ±50V, R S =1kΩ, Ripple on V ee 

20158331 20158333 

−PSRR vs Frequency 

V DD = ±75V, R S =1kΩ, Ripple on V ee 

20158332 20158334 

20158337 

www.national.com 8

Typical Performance Characteristics for LM4702B 


V DD = 100V 

PSRR vs Frequency 

V DD = 100V 


V DD = 100V, V OUT = 30V RMS 

20158341 20158340 

X TALK vs Frequency 

B grade Demo Amp @ V DD = 50V 

20158343 20158342 

9 




Test Circuit 

FIGURE 1. 


20158303

Application Information 

MUTE FUNCTION 

The mute function of the LM4702 is controlled by the amount 

of current that flows into the mute pin. If there is less than 

1mA of current flowing into the mute pin, the part will be in 

mute. This can be achieved by shorting the mute pin to 

ground or by floating the mute pin. If there is between 1mA 

and 2mA of current flowing into the mute pin, the part will be 

in “play” mode. This can be done by connecting a power 

supply (Vmute) to the mute pin through a resistor (Rm). The 

current into the mute pin can be determined by the equation 

Imute = (Vmute – 2.9) / Rm. For example, if a 5V power 

supply is connected through a 1.4k resistor to the mute pin, 

then the mute current will be 1.5mA, at the center of the 

specified range. It is also possible to use Vcc as the power 

supply for the mute pin, though Rm will have to be recalculated 

accordingly. It is not recommended to flow more than 

2mA of current into the mute pin because damage to the 

LM4702 may occur. 

It is highly recommended to switch between mute and “play” 

modes rapidly. This is accomplished most easily through 

using a toggle switch that alternatively connects the mute pin 

through a resistor to either ground or the mute pin power 

supply. Slowly increasing the mute current may result in 

undesired voltages on the outputs of the LM4702, which can 

damage an attached speaker. 

THERMAL PROTECTION 

The LM4702 has a sophisticated thermal protection scheme 

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

temperature on the die exceeds 150˚C, the LM4702 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 between 

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 so that 

thermal shutdown is not activated during normal operation. 

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. 

POWER DISSIPATION AND HEAT SINKING 

When in “play” mode, the LM4702 draws a constant amount 

of current, regardless of the input signal amplitude. Consequently, 

the power dissipation is constant for a given supply 

voltage and can be computed with the equation PDMAX = Icc 

* (Vcc – Vee). For a quick calculation of PDMAX, approximate 

the current to be 25mA and multiply it by the total supply 

voltage (the current varies slightly from this value over the 

operating range). 

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 is not activated under 

normal circumstances. 

11 

The thermal resistance from the die to the outside air, θJA (junction to ambient), is a combination of three thermal resistances, 

θJC (junction to case), θCS (case to sink), and θSA (sink to ambient). The thermal resistance, θJC (junction to 

case), of the LM4702T is 0.8˚C/W. Using Thermalloy Thermacote 

thermal compound, the thermal resistance, 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 LM4702 is equal to the following: 

PDMAX =(TJMAX−TAMB) /θJA (1) 

where T JMAX = 150˚C, T AMB is the system ambient temperature 

and θ JA = θ JC + θ CS + θ SA. 

20158355 

Once the maximum package power dissipation has been 

calculated using equation 2, 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 4 

which is derived by solving for θSA in equation 3. 

θSA = [(TJMAX−TAMB)−PDMAX(θJC +θCS)]/PDMAX (2) 

Again it must be noted that the value of θ SA 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. 

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 

response 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 (3) below: 

AV =1+Rf /Ri (V/V) (3) 

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 LM4702 

the gain should be set no lower than 26dB. Gain settings 

below 26dB may experience instability. 

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 (4) shown below: 

fi =1/(2πRiCi) (Hz) (4) 

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

inputs as shown in Figure 5, 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 




Application Information (Continued) 

bias point on the amplifier’s input terminal. The resulting 

-3dB frequency response due to the combination of CIN and 

RIN can be found from Equation (5) shown below: 

fIN =1/(2πRINCIN) (Hz) (5) 

With large values of RIN oscillations may be observed on the 

outputs when the inputs are left floating. Decreasing the 

value of RIN or not letting the inputs float will remove the 

oscillations. If the value of RIN is decreased then the value of 

CIN will need to increase in order to maintain the same -3dB 

frequency response. 

AVOIDING THERMAL RUNAWAY WHEN USING 

BIPOLAR OUTPUT STAGES 

When using a bipolar output stage with the LM4702 (as in 

Figure 1), the designer must beware of thermal runaway. 

Thermal runaway is a result of the temperature dependence 

of Vbe (an inherent property of the transistor). As temperature 

increases, Vbe decreases. In practice, current flowing 

through a bipolar transistor heats up the transistor, which 

lowers the Vbe. This in turn increases the current again, and 

the cycle repeats. If the system is not designed properly, this 

positive feedback mechanism can destroy the bipolar transistors 

used in the output stage. 


One of the recommended methods of preventing thermal 

runaway is to use a heat sink on the bipolar output transistors. 

This will keep the temperature of the transistors lower. 

A second recommended method is to use emitter degeneration 

resistors (see Re1, Re2, Re3, Re4 in Figure 1). As 

current increases, the voltage across the emitter degeneration 

resistor also increases, which decreases the voltage 

across the base and emitter. This mechanism helps to limit 

the current and counteracts thermal runaway. 

A third recommended method is to use a “Vbe multiplier” to 

bias the bipolar output stage (see Figure 1). The Vbe multiplier 

consists of a bipolar transistor (Qmult, see Figure 1) 

and two resistors, one from the base to the collector (Rb2, 

Rb4, see Figure 1) and one from the base to the emitter 

(Rb1, Rb3, see Figure 1). The voltage from the collector to 

the emitter (also the bias voltage of the output stage) is 

Vbias = Vbe(1+Rb2/Rb1), which is why this circuit is called 

the Vbe multiplier. When Vbe multiplier transistor (Qmult, 

see Figure 1) is mounted to the same heat sink as the bipolar 

output transistors, its temperature will track that of the output 

transistors. Its Vbe is dependent upon temperature as well, 

and so it will draw more current as the output transistors heat 

it up. This will limit the base current into the output transistors, 

which counteracts thermal runaway.

LM4702 Demo Board Artwork 

Top Overlay 

Top Layer 

13 

20158330 

20158329 




LM4702 Demo Board Artwork (Continued) 

Bottom Layer 


20158328

Revision History 

Rev Date Description 

1.0 8/31/05 Initial WEB. 

1.1 9/09/05 Taken out Limits on Vom (under the 

+75V and +50V). 

1.2 9/14/05 Changed TM to R ( Overture R) in the 

doc title. 

1.3 03/08/06 Text edits. 

1.4 04/26/04 Edited Limit values on the LM4702B spec 

table. 

1.5 08/09/06 Released the D/S to the WEB with the 

LM4702B data. 

1.6 09/19/06 Removed the “Overture R” from the 

document title, then released the D/S to 

the WEB 

15 



LM4702 Stereo High Fidelity 200 Volt Driver with Mute 

Physical Dimensions inches (millimeters) unless otherwise noted 

Non-Isolated TO-220 15-Lead Package 

Order Number LM4702BTA, LM4702CTA 

NS Package Number TA15A 

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. 

For the most current product information visit us at www.national.com. 

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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National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances 

and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at: 

www.national.com/quality/green. 

Lead free products are RoHS compliant. 

National Semiconductor 

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Support Center 

Email: new.feedback@nsc.com 

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