Datasheet LM831N Datasheet (NSC)

LM831 Low Voltage Audio Power Amplifier

LM831 Low Voltage Audio Power Amplifier

December 1994

General Description

The LM831 is a dual audio power amplifier optimized for
very low voltage operation. The LM831 has two indepen­dent amplifiers, giving stereo or higher power bridge (BTL)
operation from two- or three-cell power supplies.

The LM831 uses a patented compensation technique to re­duce high-frequency radiation for optimum performance in
AM radio applications. This compensation also results in
lower distortion and less wide-band noise.

The input is direct-coupled to the LM831, eliminating the
usual coupling capacitor. Voltage gain is adjustable with a
single resistor.

Typical Application

Dual Amplifier with Minimum Parts

Features

Y

Low voltage operation, 1.8V to 6.0V

Y

High power, 440 mW, 8X, BTL, 3V

Y

Low AM radiation

Y

Low noise

Y

Low THD

Applications

Y

Portable tape recorders

Y

Portable radios

Y

Headphone stereo

Y

Portable speakers

TL/H/6754– 1

e

A

46 dB,BWe250 Hz to 35 kHz

V

e

P

220 mW/Ch,R

OUT

C

1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.

TL/H/6754

e

4X

L

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.

Supply Voltage, V
Input Voltage, V
Power Dissipation (Note 1), P

S

IN

D

Operating Temperature (Note 1), T

1.3W (M Package)

1.4W (N Package)

b

opr

40§Ctoa85§C

7.5V

g

0.4V

b

Storage Temperature, T
Junction Temperature, T
Lead Temp. (Soldering, 10 sec.), T

stg

j

Thermal Resistance

i

(DIP) 27§C/W

JC

i

(DIP) 75§C/W

JA

i

(SO Package) 20§C/W

JC

i

(SO Package) 95§C/W

JA

65§Ctoa150§C

L

a
a

150§C
260§C

Electrical Characteristics

Unless otherwise specified, T

e

25§C, V

A

Symbol Parameter Conditions Typ Tested Limit Unit (Limit)

V

S

I

Q

V

OS

R

IN

A

V

Operating Voltage 3 1.8 V(Min)

Supply Current V

Output DC Offset V

Input Resistance 25 15 k (Min)

Voltage Gain V

PSRR Supply Rejection V

P

OD

P

ODL

P

OB

P

OBL

Power Out V

Power Out Low, V

S

Power Out V

Power Out Low, V

S

Sep Channel Separation Referenced to V

I

B

E

n0

Input Bias Current 1 2 mA (Max)

Output Noise Wide Band (250E35 kHz) 250 500 mV (Max)

THD Distortion V

Note 1: For operation in ambient temperatures above 25§C, the device must be derated based on a 150§C maximum junction temperature and a thermal resistance

C/W junction to ambient for the M package or 90§C/W junction to ambient for the N package.

of 98

§

e

3V, fe1 kHz, test circuit is dual or BTL amplifier with minimum parts.

S

3 6 V(Max)

e

0, Dual Mode 5 10 mA (Max)

IN

e

0, BTL Mode 6 15 mA (Max)

V

IN

e

0, BTL Mode 10 50 mV (Max)

IN

35 k (Max)

e

2.25 mV

IN

Dual Mode 48 dB (Max)

e3Va

S

e

3V, R

S

10% THD, Dual Mode

e

V

1.8V, R

S

10% THD, Dual Mode

e

3V, R

S

10% THD, BTL Mode

e

V

1.8V, R

S

10% THD, BTL Mode

e

3V, P

S

e

f

1 kHz, Dual

,fe1 kHz, 46 44 dB (Min)

rms

4X,

e

4X,

8X,

e

8X,

e

O

50 mW,

@

fe1 kHz 46 30 dB (Min)

rms

220 150 mW (Min)

45 10 mW (Min)

440 300 mW (Min)

90 20 mW (Min)

200 mV

rms

52 40 dB (Min)

0.25 1 % (Max)

200 mV

e

L

L

e

L

L

e

O

Connection Diagram

Dual-In-Line Package

TL/H/6754– 2

Top View

Order Number LM831M or N

See NS Package Number M16B or N16E

2

Typical Performance Characteristics

Supply Current vs Supply Voltage PSRR vs Supply Voltage

Supply Current vs Temperature PSRR vs Supply Voltage

DC Output vs Supply Voltage Separation vs Supply Voltage

3

TL/H/6754– 4

Typical Performance Characteristics (Continued)

Separation vs Frequency Power Output vs Supply Voltage

Gain vs Frequency Power Output vs Temperature

Gain vs Frequency Bandwidth vs BW Capacitance

4

TL/H/6754– 5

Typical Performance Characteristics (Continued)

e

Dual Mode, R

Distortion vs Power Output (Note 2) Distortion vs Power Output (Note 2)

4X Distortion vs Frequency Dual Mode, R

L

e

8X Distortion vs Frequency

L

Power Dissipation vs Power Output Power Dissipation vs Power Output

5

TL/H/6754– 6

Typical Performance Characteristics (Continued)

e

BTL Mode, R

Distortion vs Power Output (Note 2) Supply Current vs Power Output

8X Distortion vs Frequency Device Dissipation vs Ambient Temperature

L

Power Dissipation vs Power Output

Note 2: 1 kHz curve is measured with 400 Hz– 30 kHz Filter.

TL/H/6754– 7

6

Typical Applications

BTL Amplifier with Minimum Parts

e

A

52 dB, BWe250 Hz to 25 kHz

V

e

P

440 mW, R

OUT

e

8X

L

BTL Amplifier for Hi-Fi Quality

e

A

40 dB, BWe20 Hz to 20 kHz

V

e

P

440 mW, R

OUT

(Dynamic Range Over 80 dB)

e

8X

L

TL/H/6754– 8

TL/H/6754– 9

7

Typical Applications (Continued)

Dual Amplifier for Hi-Fi Quality

e

A

34 dB, BWe50 Hz to 20 kHz

V

e

P

220 mW/Ch, R

OUT

(Dynamic Range Over 80 dB)

e

4X

L

Low-Cost Power Amplifier (No Bootstrap)

e

P

150 mW/Ch, BWe300 Hz to 35 kHz

OUT

*For 3-cell applications, the 120k resistor should be changed to 20K.

BTL Mode is also possible

TL/H/6754– 10

TL/H/6754– 11

8

LM831 Circuit Description Refer to the external component diagram and equivalent schematic.

The power supply is applied to Pin 9 and is filtered by resis­tor R

and capacitor CBYon Pin 16. This filtered voltage at

1

Pin 16 is used to bias all of the LM831 circuits except the
power output stage. Resistor R
that sets the output DC voltage for optimum output power

generates a biasing current

0

for any given supply voltage.

Feedback is provided to the input transistor Q
R

and R7.

6

emitter by

1

External Component Diagram

The capacitor C
mum DC accuracy.

Q

provides voltage gain and the rest of the devices buffer

2

the output load from Q

on Pin 2 provides unity DC gain for maxi-

NF

’s collector.

2

Bootstrapping of Pin 5 by CBSallows maximum output
swing and improved supply rejection.

R

is provided for bridge (BTL) operation.

5

TL/H/6754– 12

9

LM831 Circuit Description (Continued)

TL/H/6754– 13

LM831 Equivalent Schematic

10

External Components (Refer to External Component Diagram)

Component Comments Min Max

C

O

C

c

C

BS

C

S

C

BY

C

NF

C

BTL

C

BW

R

AV

Required to stabilize output stage. 0.33 mF1mF

Output coupling capacitors for Dual Mode. Sets a low-frequency pole in 100 mF 10,000 mF
the frequency response.

1

e

f

L

2qCcR

L

Bootstrap capacitors. Sets a low-frequency pole in the power BW. 22 mF or 470 mF
Recommended value is

1

e

C

BS

10#2q#f

R

#

L

L

(short Pins

4&12to9)

Supply bypass. Larger values improve low-battery performance by 47 mF 10,000 mF
reducing supply ripple.

Filters the supply for improved low-voltage operation. Also sets 47 mF 470 mF
turn-on delay.

Sets a low-frequency response. Also affects turn-on delay. 10 mF 100 mF

NF

1

a

(R

80)

#

AV

e

f

L

2q#C

In BTL Mode, C
frequency response. However, the turn-on ‘‘POP‘‘ will be worsened.

on Pin 15 can be reduced without affecting the

NF

Used only in the Bridge Mode. Connects the output of the first amplifier to 0.1 mF1mF
the inverting input of the other through an internal resistor. Sets a low­frequency pole in one-half the frequency response.

1

e

f

L

2q#C

Improves clipping waveform and sets the high-frequency bandwidth. See table below
Works with an internal 16k resistor. (This equation applies for R
For 46 dB application, see BW–CBWcurve.)

e

f

H

2q#C

BTL

1

BW

#

#

16k

16k

i

0.

AV

Used to reduce the gain and improve the distortion and signal to noise. If See table below
this is desired, C

must also be used.

BW

C

Typical A

V

R

AV

Min Max

BW

46 dB Short Open 4700 pF

40 dB 82 100 pF 4700 pF

34 dB 240 270 pF 4700 pF

28 dB 560 500 pF 4700 pF

11

Printed Circuit Layout for LM831N (Foil Side View) Refer to External Component Diagram

Note: Power ground pattern should be as wide as possible. Supply bypass capacitor should be as close to the IC as possible. Output compensation capacitors

should also be close to the IC.

TL/H/6754– 14

12

Physical Dimensions inches (millimeters)

Molded SO Package (M)

Order Number LM831M

NS Package Number M16B

13

Physical Dimensions inches (millimeters) (Continued)

Molded Dual-In-Line Package (N)

Order Number LM831N

NS Package Number N16E

LM831 Low Voltage Audio Power Amplifier

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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:

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systems which, (a) are intended for surgical implant support device or system whose failure to perform can
into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life
failure to perform, when properly used in accordance support device or system, or to affect its safety or
with instructions for use provided in the labeling, can effectiveness.
be reasonably expected to result in a significant injury
to the user.

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