LM4861.PDF

August 2000

LM4861

1.1W Audio Power Amplifier with Shutdown Mode

General Description

The LM4861 is a bridge-connected audio power amplifier ca-

pable of delivering 1.1W of continuous average power to an

8 W load with 1% THD+N using a 5V power supply.

Boomer audio power amplifiers were designed specifically to

provide high quality output power with a minimal amount of

external components using surface mount packaging. Since

the LM4861 does not require output coupling capacitors,

bootstrap capacitors, or snubber networks, it is optimally

suited for low-power portable systems.

The LM4861 features an externally controlled, low-power

consumption shutdown mode, as well as an internal thermal

shutdown protection mechanism.

The unity-gain stable LM4861 can be configured by external

gain-setting resistors for differential gains of up to 10 without

the use of external compensation components. Higher gains

may be achieved with suitable compensation.

Key Specifications

j THD+N for 1kHz at 1W continuous

average output power into 8

1.0% (max)

j Output power at 10% THD+N

at 1kHz into 8 W

1.5W (typ)

j Shutdown Current

0.6µA (typ)

Features

n No output coupling capacitors, bootstrap capacitors, or

snubber circuits are necessary

n Small Outline (SO) packaging

n Compatible with PC power supplies

n Thermal shutdown protection circuitry

n Unity-gain stable

n External gain configuration capability

Applications

n Personal computers

n Portable consumer products

n Self-powered speakers

n Toys and games

Typical Application

Connection Diagram

Small Outline Package

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Top View

Order Number LM4861M

See NS Package Number M08A

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FIGURE 1. Typical Audio Amplifier Application Circuit

Boomer ® is a registered trademark of National Semiconductor Corporation.

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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

See AN-450 “Surface Mounting and their Effects on

Product Reliability” for other methods of soldering surface

mount devices.

Operating Ratings

6.0V

Temperature Range

T MIN

Storage Temperature

−65˚C to +150˚C

T A

T MAX

−40˚C

T A

+85˚C

Input Voltage

−0.3V to V DD + 0.3V

Supply Voltage

2.0V

V DD

5.5V

Power Dissipation (Note 3)

Internally limited

Thermal Resistance

q JC (typ) — M08A

ESD Susceptibility (Note 4)

3000V

35˚C/W

ESD Susceptibility (Note 5)

250V

JA (typ) — M08A

140˚C/W

Junction Temperature

150˚C

JC (typ) — N08E

37˚C/W

Soldering Information

Small Outline Package

Vapor Phase (60 sec.)

Infrared (15 sec.)

JA (typ) — N08E

107˚C/W

215˚C

220˚C

Electrical Characteristics (Note 1) (Note 2)

The following specifications apply for V DD = 5V, unless otherwise specified. Limits apply for T A = 25˚C.

LM4861

Units

(Limits)

Symbol

Parameter

Conditions

Typical

Limit

(Note 6)

(Note 7)

V DD

Supply Voltage

2.0

V (min)

5.5

V (max)

I DD

Quiescent Power Supply Current

V IN = 0V, I O = 0A (Note 8)

6.5

10.0

mA (max)

I SD

Shutdown Current

V pin1 =V DD

0.6

10.0

µA (max)

V OS

Output Offset Voltage

V IN = 0V

5.0

50.0

mV (max)

P O

Output Power

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

1.1

1.0

W(min)

THD+N

Total Harmonic Distortion +

Noise

P O = 1Wrms; 20 Hz £ f £ 20 kHz

0.72

PSRR

Power Supply Rejection Ratio

V DD = 4.9V to 5.1V

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 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 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by T JMAX ,

q JA , and the ambient temperature T A . The maximum

resistor.

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

Note 6: Typicals are measured at 25˚C and represent the parametric norm.

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

Note 8: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.

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allowable power dissipation is P DMAX =(T JMAX −T A )/

q JA or the number given in the Absolute Maximum Ratings, whichever is lower. For the LM4861, T JMAX = 150˚C,

and the typical junction-to-ambient thermal resistance, when board mounted, is 140˚C/W.

Note 4: Human body model, 100 pF discharged through a 1.5 k

High Gain Application Circuit

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FIGURE 2. Audio Ampiifier with A VD =20

Single Ended Application Circuit

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*C S and C B size depend on specific application requirements and constraints. Typical vaiues of C S and C B are 0.1 µF.

**Pin 1 should be connected to V DD to disable the amplifier or to GND to enable the amplifier. This pin should not be left floating.

***These components create a “dummy” load for pin 8 for stability purposes.

FIGURE 3. Single-Ended Amplifier with A V =−1

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External Components Description (Figures 1, 2)

Components

Functional Description

1. R i

Inverting input resistance which sets the closed-loop gain in conjunction with R f . This resistor also forms a

high pass filter with C i at f C = 1/(2

R i C i ).

2. C i

Input coupling capacitor which blocks DC voltage at the amplifier’s input terminals. Also creates a highpass

filter with R i at f C = 1/(2

R i C i ).

3. R f

Feedback resistance which sets closed-loop gain in conjunction with R i .

4. C S

Supply bypass capacitor which provides power supply filtering. Refer to the Application Information

section for proper placement and selection of supply bypass capacitor.

5. C B

Bypass pin capacitor which provides half supply filtering. Refer to the Application Information section for

proper placement and selection of bypass capacitor.

6. C f (Note 9)

C f in conjunction with R f creates a low-pass filter which bandwidth limits the amplifier and prevents possible

high frequency oscillation bursts. f C = 1/(2

R f C f )

Note 9: Optional component dependent upon specific design requirements. Refer to the Application Information section for more information.

Typical Performance Characteristics

THD+N vs Frequency

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THD+N vs Output Power

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Typical Performance Characteristics (Continued)

Output Power vs

Load Resistance

Output Power vs

Supply Voltage

Power Dissipation vs

Output Power

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Noise Floor vs Frequency

Supply Current Distribution

vs Temperature

Supply Current vs

Supply Voltage

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Power Derating Curve

Power Supply

Rejection Ratio

Open Loop

Frequency Response

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