LM4671.pdf

March 2005

LM4671

Filterless High Efficiency 2.5W Switching Audio

Amplifier

General Description

The LM4671 is a single supply, high efficiency 2.5W switch-

ing audio amplifier. A low noise, filterless PWM architecture

eliminates the output filter, reducing external component

count, board area consumption, system cost, and simplifying

design.

The LM4671 is designed to meet the demands of mobile

phones and other portable communication devices. Operat-

ing on a single 5V supply, it is capable of driving a 4

Key Specifications

j Efficiency at 3.6V, 100mW into 8

Ω

speaker 80% (typ)

j Efficiency at 3.6V, 400mW into 8

Ω

speaker 88% (typ)

j Efficiency at 5V, 1W into 8

Ω

speakerr

86% (typ)

j Quiescent current, 3.6V supply

2.8mA (typ)

j Total shutdown power supply current

0.01µA (typ)

Ω

speaker load at a continuous average output of 2.1W with

less than 1% THD+N. Its flexible power supply requirements

allow operation from 2.4V to 5.5V.

The LM4671 has high efficiency with speaker loads com-

pared to a typical Class AB amplifier. With a 3V supply

driving an 8

j Single supply range

2.4V to 5.5V

speaker, the IC’s efficiency for a 100mW

power level is 80%, reaching 88% at 400mW output power.

The LM4671 features a low-power consumption shutdown

mode. Shutdown may be enabled by driving the Shutdown

pin to a logic low (GND).

The gain of the LM4671 is externally configurable which

allows independent gain control from multiple sources by

summing the signals.

Features

n No output filter required for inductive loads

n Externally configurable gain

n Very fast turn on time: 1ms (typ)

n Minimum external components

n "Click and pop" suppression circuitry

n Micro-power shutdown mode

n Available in space-saving microSMD package

Applications

n Mobile phones

n PDAs

n Portable electronic devices

Typical Application

201073J3

FIGURE 1. Typical Audio Amplifier Application Circuit

Boomer ® is a registered trademark of National Semiconductor Corporation.

DS201073

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Ω

Connection Diagrams

9 Bump micro SMD Package

micro SMD Marking

201073C6

Top View

X — Date Code

T— Die Traceability

G — Boomer Family

E7 — LM4671ITL

20107336

Top View

Order Number LM4671ITL, LM4671ITLX

See NS Package Number TLA09AAA

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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 (Note 1)

Thermal Resistance

θ JA (micro SMD)

220˚C/W

6.0V

Soldering Information

See AN-1112 "microSMD Wafers Level Chip Scale

Package."

Storage Temperature

−65˚C to +150˚C

Voltage at Any Input Pin

V DD + 0.3V

≥

GND - 0.3V

Operating Ratings (Note 1) (Note 2)

Temperature Range

T MIN ≤

Power Dissipation (Note 3)

Internally Limited

ESD Susceptibility, all other pins (Note 4)

2.0kV

T A ≤

T MAX

−40˚C

≤

T A ≤

85˚C

ESD Susceptibility (Note 5)

200V

Supply Voltage

2.4V ≤ V DD ≤ 5.5V

Junction Temperature (T JMAX )

150˚C

Electrical Characteristics (Notes 1, 2)

The following specifications apply for A V = 2V/V (R I = 150k Ω ), R L =15µH+8 Ω + 15µH unless otherwise specified. Limits ap-

ply for T A = 25˚C.

LM4671

Units

(Limits)

Symbol

Parameter

Conditions

Typical

Limit

(Note 6)

(Notes 7, 8)

|V OS |

Differential Output Offset Voltage

V I = 0V, A V = 2V/V,

V DD = 2.4V to 5.0V

mV (max)

PSRR GSM GSM Power Supply Rejection Ratio V DD = 2.4V to 5.0V

dB (min)

CMRR GSM

GSM Common Mode Rejection

Ratio

V DD = 2.4V to 5.0V

V IC =V DD /2 to 0.5V,

V IC =V DD /2 to V DD – 0.8V

dB (min)

|I IH |

Logic High Input Current

V DD = 5.0V, V I = 5.5V

100

µA (max)

|I IL |

Logic Low Input Current

V DD = 5.0V, V I = –0.3V

0.9

µA (max)

V IN = 0V, No Load, V DD = 5.0V

6.4

mA (max)

I DD

Quiescent Power Supply Current

V IN = 0V, No Load, V DD = 3.6V

3.8

6.2

V IN = 0V, No Load, V DD =2.4V

2.0

3.0

mA (max)

I SD

Shutdown Current

V SHUTDOWN =0V

V DD = 2.4V to 5.0V

0.01

µA (max)

V SDIH

Shutdown voltage input high

1.2

1.4

V (min)

V SDIL

Shutdown voltage input low

1.1

0.4

V (max)

R OSD

Output Impedance

V SHUTDOWN = 0.4V

100

Ω

A V

Gain

300k

Ω

/R I

270k

Ω

/R I

V/V (min)

V/V (max)

330k

Ω

/R I

R SD

Resistance from Shutdown Pin to

GND

300

Ω

+ 15µH

THD = 10% (max)

f = 1kHz, 22kHz BW

V DD =5V

V DD = 3.6V

V DD = 2.5V

Ω

P O

Output Power

2.5

1.3

520

R L =15µH+4

Ω

+ 15µH

THD = 1% (max)

f = 1kHz, 22kHz BW

V DD =5V

V DD = 3.6V

V DD = 2.5V

2.21

1.06

420

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R L =15µH+4

Electrical Characteristics (Notes 1, 2)

The following specifications apply for A V = 2V/V (R I = 150k

Ω

), R L =15µH+8

Ω

+ 15µH unless otherwise specified. Limits

apply for T A = 25˚C. (Continued)

LM4671

Units

(Limits)

Symbol

Parameter

Conditions

Typical

Limit

(Note 6)

(Notes 7, 8)

R L =15µH+8 Ω + 15µH

THD = 10% (max)

f = 1kHz, 22kHz BW

V DD =5V

V DD = 3.6V

870

P O

Output Power

V DD = 2.5V

425

R L =15µH+8

Ω

+ 15µH

THD = 1% (max)

f = 1kHz, 22kHz BW

V DD = 5V

1.19

V DD = 3.6V

700

600

V DD = 2.5V

350

V DD = 5V, P O = 0.1W RMS ,

f = 1kHz

0.09

THD+N

Total Harmonic Distortion + Noise

V DD = 3.6V, P O = 0.1W RMS ,

f = 1kHz

0.04

V DD = 3.6V, P O = 0.1W RMS ,

f = 5kHz

0.12

V DD = 3.6V, P O = 0.1W RMS ,

f = 10kHz

0.05

V DD = 3.6V, 5V

V Ripple = 200mV PP Sine,

f Ripple = 217Hz

Inputs to AC GND, C I = 2µF

61.8

V DD = 3.6V, 5V

V Ripple = 200mV PP Sine,

f Ripple = 1kHz

Inputs to AC GND, C I = 2µF

59.8

PSRR

Power Supply Rejection Ratio

V DD = 3.6V, 5V

V Ripple = 200mV PP Sine,

f Ripple = 10kHz

Inputs to AC GND, C I = 2µF

48.65

V DD = 3.6V, 5V

V Ripple = 200mV PP Sine,

f Ripple = 217Hz

f IN = 1kHz, P O = 10mW RMS

65.71

SNR

Signal to Noise Ratio

V DD = 5V, P O =1W RMS

V DD = 3.6V, f = 20Hz – 20kHz

Inputs to AC GND, C I = 2µF

No Weighting

µV RMS

e OUT

Output Noise

V DD = 3.6V, Inputs to AC GND

C I = 2µF, A Weighted

µV RMS

CMRR

Common Mode Rejection Ratio

V DD = 3.6V, V Ripple =1V PP Sine

f Ripple = 217Hz

68.3

T WU

Wake-up Time

V DD = 3.6V

µs

T SD

Shutdown Time

140

µs

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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

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

JA , and the ambient temperature T A . The maximum

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

θ JA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4671, T JMAX = 150˚C.

JA is 220˚C/W for the microSMD package.

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

resistor.

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

Note 6: Typical specifications are specified 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: Shutdown current is measured in a normal room environment. Exposure to direct sunlight will increase I SD by a maximum of 2µA. The Shutdown pin should

be driven as close as possible to GND for minimal shutdown current and to V DD for the best THD performance in PLAY mode. See the Application Information

section under SHUTDOWN FUNCTION for more information.

Note 10: The performance graphs were taken using the Audio Precision AUX-0025 Switching Amplifier measurement Filter in series with the LC filter on the demo

board.

External Components Description

( Figure 1 )

Ω

Components

Functional Description

C S

Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing

section for information concerning proper placement and selection of the supply bypass capacitor.

C I

Input AC coupling capacitor which blocks the DC voltage at the amplifier’s input terminals.

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The typical

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