LM3875.pdf

August 2000

LM3875 Overture ™ Audio Power Amplifier Series

High-Performance 56W Audio Power Amplifier

General Description

The LM3875 is a high-performance audio power amplifier

capable of delivering 56W of continuous average power to

an 8

Ω

n 100W instantaneous peak output power capability

n Signal-to-Noise Ratio > 95dB (min)

n Output protection from a short to ground or to the

supplies via internal current limiting circuitry

n Output over-voltage protection against transients from

inductive loads

n Supply under-voltage protection, not allowing internal

biasing to occur when |V+| + |V−| ≤ 12V, thus eliminating

turn-on and turn-off transients

n 11 lead TO-220 package

n Wide supply voltage range: |V+| + |V−| = 20V to 84V

load with 0.1% THD+N from 20Hz to 20kHz.

The performance of the LM3875, utilizing its Self Peak In-

stantaneous Temperature (˚Ke) ( SPiKe ™ ) protection cir-

cuitry, puts it in a class above discrete and hybrid amplifiers

by providing an inherently, dynamically protected Safe Op-

erating Area (SOA). SPiKe protection means that these

parts are completely safeguarded at the output against ov-

ervoltage, undervoltage, overloads, caused by shorts to the

supplies, thermal runaway, and instantaneous temperature

peaks.

The LM3875 maintains an excellent signal-to-noise ratio of

greater than 95dB(min) with a typical low noise floor of

2.0µV. It exhibits extremely low THD+N values of 0.06% at

the rated output into the rated load over the audio spectrum,

and provides excellent linearity with an IMD (SMPTE) typical

rating of 0.004%.

Applications

n Component or compact stereos

n Self-powered speakers

n Surround-sound amplifiers

n High-end stereo TVs

Typical Application

DS011449-1

*Optional components dependent upon specific design requirements. Refer to the External Components Description section for a component function

description.

FIGURE 1. Typical Audio Amplifier Application Circuit

Overture ™ and SPiKe ™ are trademarks of National Semiconductor Corporation.

www.national.com

Features

n 56W continuous average output power into 8

Ω

Connection Diagram

Plastic Package (Note 8)

DS011449-2

Top View

Order Number LM3875T or LM3875TF

See NS Package Number TA11B for

Staggered Lead Non-Isolated Package

or TF11B for Staggered Lead Isolated Package

Equivalent Schematic (Excluding active protection circuitry)

DS011449-6

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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 − | (No Signal)

Storage Temperature

−40˚C to +150˚C

Thermal Resistance

θ JC

1˚C/W

θ JA

43˚C/W

94V

Operating Ratings (Notes 1, 2)

Supply Voltage |V + |+|V − | (Input Signal)

84V

Common Mode Input Voltage

(V + or V − ) and

|V + |+|V − |

Temperature Range

T MIN ≤

≤

80V

+85˚C

Supply Voltage |V + |+|V − | 20V to 84V

Note: Operation is guaranteed up to 84V, however, distortion may be intro-

duced from the SPiKe Protection Circuitry when operating above 70V if

proper thermal considerations are not taken into account. Refer to the

Thermal Considerations section for more information. (See SPiKe Protection

Response)

T A ≤

T MAX

−20˚C

≤

T A ≤

Differential Input Voltage

60V

Output Current

Internally Limited

Power Dissipation (Note 3)

125W

ESD Susceptibility (Note 4)

2500V

Junction Temperature (Note 5)

150˚C

Soldering Information

T package (10 seconds)

260˚C

Electrical Characteristics (Notes 1, 2)

The following specifications apply for V + = +35V, V − = −35V with R L =8

Ω

unless otherwise specified. Limits apply for T A =

25˚C.

LM3875

Units

(Limits)

Symbol

Parameter

Conditions

Typical

(Note 6)

Limit

(Note 7)

|V + |+|V − | Power Supply Voltage

V (Min)

V (Max)

**P O Output Power (Continuous Average) THD + N = 0.1% (Max)

f = 1 kHz, f = 20 kHz

40 W (Min)

Peak P O Instantaneous Peak Output Power

100

THD + N Total Harmonic Distortion Plus Noise 40W, 20 Hz ≤ f ≤ 20 kHz

A V =26dB

0.06

**SR

Slew Rate (Note 9)

V IN = 1.414 Vrms,f=10kHz

Square-wave, R L =2k

V/µs

(Min)

Ω

*I+

Total Quiescent Power Supply

Current

V CM = 0V, V O = 0V, I o =0mA

(Max)

*V OS

Input Offset Voltage

V CM = 0V, I o =0mA

(Max)

I B

Input Bias Current

V CM = 0V, I o =0mA

0.2

µA

(Max)

I OS

Input Offset Current

V CM = 0V, I o =0mA

0.01

0.2

µA

(Max)

I o

Output Current Limit

|V + |=|V − | = 10V, t on = 10 ms, V O = 0V

A(Min)

*V od

Output Dropout Voltage

|V + −V o − |, V + = 20V, I o = +100 mA

|V o −V − |, V − = −20V, I o = −100 mA

1.6

2.7

V (Max)

*PSRR Power Supply Rejection Ratio

V + = 40V to 20V, V − = −40V,

V cm = 0V, I o =0mA

V + = 40V, V = −40V to −20V,

V cm = 0V, I o =0mA

120

dB (Min)

*CMRR Common Mode Rejection Ratio

V + = 60V to 20V, V − = −20V to −60V,

V cm = 20V to −20V, I o =0mA

120

dB (Min)

*A VOL Open Loop Voltage Gain

|V + |=|V − | = 40V, R L =2k Ω , ∆ V O = 60V 120

dB (Min)

GBWP Gain-Bandwidth Product

|V + |=|V − | = 40V

f O = 100 kHz, V IN = 50 mVrms

MHz

(Min)

**e IN

Input Noise

IHF − A Weighting Filter

R IN = 600

2.0

8.0

µV

(Max)

Ω

(Input Referred)

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Electrical Characteristics (Notes 1, 2) (Continued)

The following specifications apply for V + = +35V, V − = −35V with R L =8 Ω unless otherwise specified. Limits apply for T A =

25˚C.

LM3875

Units

(Limits)

Symbol

Parameter

Conditions

Typical

(Note 6)

Limit

(Note 7)

SNR

Signal-to-Noise Ratio

P O = 1W, A-Weighted,

Measured at 1 kHz, R S =25

98 dB

Ω

P O = 40W, A-Weighted,

Measured at 1 kHz, R S =25 Ω

114 dB

P pk = 100W, A-Weighted,

Measured at 1 kHz, R S =25

Ω

122 dB

IMD

Intermodulation Distortion Test

60 Hz, 7 kHz, 4:1 (SMPTE)

60 Hz, 7 kHz, 1:1 (SMPTE)

0.004

0.006

* DC Electrical Test; refer to Test Circuit # 1.

** AC Electrical Test; refer to Test Circuit #2.

Note 1: 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 device performance.

Note 2: All voltages are measured with respect to supply GND, unless otherwise specified.

Note 3: 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

resistor.

Note 5: The operating junction temperature maximum is 150˚C, however, the instantaneous Safe Operating Area temperature is 250˚C.

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

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

Note 8: The LM3875T package TA11B is a non-isolated package, setting the tab of the device and the heat sink at V − potential when the LM3875 is directly mounted

to the heat sink using only thermal compound. If a mica washer is used in addition to thermal compound,

Ω

CS (case to sink) is increased, but the heat sink will be

isolated from V − .

Note 9: The feedback compensation network limits the bandwidth of the closed-loop response and so the slew rate will be reduced due to the high frequency roll-off.

Without feedback compensation, the slew rate is typically 16V/µs.

Note 10: The output dropout voltage is the supply voltage minus the clipping voltage. Refer to the Clipping Voltage vs. Supply Voltage graph in the Typical

Performance Characteristics section.

Test Circuit #1 (DC Electrical Test Circuit)

DS011449-3

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θ JC = 1.0˚C/W (junction to case). Refer to the Thermal Resistance figure in the Application Information section under Thermal Considerations .

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

Test Circuit #2 (AC Electrical Test Circuit)

DS011449-4

Single Supply Application Circuit

DS011449-5

*Optional components dependent upon specific design requirements. Refer to the External Components Description section for a component function

description.

FIGURE 2. Typical Single Supply Audio Amplifier Application Circuit

External Components Description

( Figure 1 and Figure 2 )

Components

Functional Description

1. R IN

Acts as a volume control by setting the voltage level allowed to the amplifier’s input terminals.

2. R A

Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal.

3. C A

Provides bias filtering.

4. C

Provides AC coupling at the input and output of the amplifier for single supply operation.

5. 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 under-voltage

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

* C C

Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of

the output transistor. The capacitor also suppresses external electromagnetic switching noise created from

fluorescent lamps.

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