LM4674TLX - National Semiconductor

LM4674

LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier

Literature Number: SNAS344D

July 2, 2008

LM4674

Filterless 2.5W Stereo Class D Audio Power Amplifier

General Description

The LM4674 is a single supply, high efficiency, 2.5W/channel,

filterless switching audio amplifier. A low noise PWM archi-

tecture eliminates the output filter, reducing external compo-

nent count, board area consumption, system cost, and

simplifying design.

The LM4674 is designed to meet the demands of mobile

phones and other portable communication devices. Operat-

ing from a single 5V supply, the device is capable of delivering

2.5W/channel of continuous output power to a 4Ω load with

less than 10% THD+N. Flexible power supply requirements

allow operation from 2.4V to 5.5V.

The LM4674 features high efficiency compared to conven-

tional Class AB amplifiers. When driving an 8Ω speaker from

a 3.6V supply, the device features 85% efficiency at PO =

500mW. Four gain options are pin selectable through the G0

and G1 pins.

Output short circuit protection prevents the device from being

damaged during fault conditions. Superior click and pop sup-

pression eliminates audible transients on power-up/down and

during shutdown. Independent left/right shutdown control

maximizes power savings in mixed mono/stereo applications.

Key Specifications

■ Efficiency at 3.6V, 100mW into 8Ω80% (typ)

■ Efficiency at 3.6V, 500mW into 8Ω85% (typ)

■ Efficiency at 5V, 1W into 8Ω85% (typ)

■ Quiescent Power Supply Current

at 3.6V supply 4mA

■ Power Output at VDD = 5V,

RL = 4Ω, THD ≤ 10% 2.5W (typ)

■ Power Output at VDD = 5V,

RL = 8Ω, THD ≤ 10% 1.5W (typ)

■ Shutdown current 0.03μA (typ)

Features

■Output Short Circuit Protection

■Stereo Class D operation

■No output filter required

■Logic selectable gain

■Independent shutdown control

■Minimum external components

■Click and Pop suppression

■Micro-power shutdown

■Available in space-saving 2mm x 2mm x 0.6mm micro

SMD, and 4mm x 4mm x 0.8mm LLP packages

Applications

■Mobile phones

■PDAs

■Laptops

Boomer® is a registered trademark of National Semiconductor Corporation.

LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier

Typical Application

20167463

Ci = 1 μF

CS1 = 1 μF

CS2 = 0.1 μF

FIGURE 1. Typical Audio Amplifier Application Circuit

External Components Description

(Figure 1)

Components Functional Description

1. CSSupply 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.

2. CiInput AC coupling capacitor which blocks the DC voltage at the amplifier's input terminals.

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LM4674

Connection Diagrams

TL Package (2mm x 2mm x 0.6mm)

20167461

Top View

Order Number LM4674TL

See NS Package Number TL1611A

LM4674TL Markings

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Top View

XY = 2 Digit date code

TT = Lot traceability

G = Boomer Family

G2 = LM4674TL

LLP Package (4mm x 4mm x 0.8mm)

20167466

Top View

Order Number LM4674SQ

See NS Package Number SQA16A

LM4674SQ Markings

20167465

Top View

U = Wafer Fab Code

Z = Assembly Plant

XY = 2 Digit date code

TT = Lot traceability

L4674SQ = LM4674SQ

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LM4674

BUMP PIN NAME FUNCTION

A1 4 INL+ Non-inverting left channel input

A2 6 PVDD Power VDD

A3 7 OUTLA Left channel output A

A4 8 OUTLB Left channel output B

B1 3 INL- Inverting left channel input

B2 5 G1 Gain setting input 1

B3 10 SDR Right channel shutdown input

B4 9 SDL Left channel shutdown input

C1 2 INR- Inverting right channel input

C2 16 G0 Gain setting input 0

C3 12 GND Ground

C4 11 PGND Power Ground

D1 1 INR+ Non-inverting right channel input

D2 15 VDD Power Supply

D3 14 OUTRA Right channel output A

D4 13 OUTRB Right channel output B

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LM4674

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) 6.0V

Storage Temperature −65°C to +150°C

Input Voltage –0.3V to VDD +0.3V

Power Dissipation (Note 3) Internally Limited

ESD Susceptibility, all other pins (Note 4) 2000V

ESD Susceptibility (Note 5) 200V

Junction Temperature (TJMAX)150°C

Thermal Resistance

θJA (μSMD) 45.7°C/W

θJA (LLP) 38.9°C/W

Operating Ratings (Notes 1, 2)

Temperature Range

TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ 85°C

Supply Voltage 2.4V ≤ VDD ≤ 5.5V

Electrical Characteristics VDD = 3.6V (Notes 1, 2)

The following specifications apply for AV = 6dB, RL = 15µH + 8Ω + 15µH, f = 1kHz unless otherwise specified. Limits apply for TA

= 25°C.

Symbol Parameter Conditions

LM4674 Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

VOS Differential Output Offset Voltage VIN = 0, VDD = 2.4V to 5.0V 5 mV

IDD Quiescent Power Supply Current

VIN = 0, RL = ∞,

Both channels active, VDD = 3.6V 4 6 mA

VIN = 0, RL = ∞,

Both channels active, VDD = 5V 5 7.5 mA

ISD Shutdown Current VSDR = VSDL = GND 0.03 1 μA

VSDIH Shutdown Voltage Input High 1.4 V (min)

VSDIL Shutdown Voltage Input Low 0.4 V (max)

TWU Wake Up Time VSDR/SDL = 0.4V 0.5 ms

AVGain

G0, G1 = GND

RL = ∞6 6 ± 0.5 dB

G0 = VDD, G1 = GND

RL = ∞12 12 ± 0.5 dB

G0 = GND, G1 = VDD

RL = ∞18 18 ± 0.5 dB

G0, G1 = VDD

RL = ∞24 24 ± 0.5 dB

RIN Input Resistance

AV = 6dB 28 kΩ

AV = 12dB 18.75 kΩ

AV = 18dB 11.25 kΩ

AV = 24dB 6.25 kΩ

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LM4674

Symbol Parameter Conditions

LM4674 Units

(Limits)

Typical Limit

(Note 6) (Notes 7, 8)

POOutput Power

RL = 15μH + 4Ω + 15μH, THD ≤ 10%

f = 1kHz, 22kHz BW

VDD = 5V 2.5 W

VDD = 3.6V 1.2 W

VDD = 2.5V 0.530 W

RL = 15μH + 8Ω + 15μH, THD ≤ 10%

f = 1kHz, 22kHz BW

VDD = 5V 1.5 W

VDD = 3.6V 0.78 0.6 W

VDD = 2.5V 0.350 W

RL = 15μH + 4Ω + 15μH, THD ≤ 1%

f = 1kHz, 22kHz BW

VDD = 5V 1.9 W

VDD = 3.6V 1 W

VDD = 2.5V 0.430 W

RL = 15μH + 8Ω + 15μH, THD = 1%

f = 1kHz, 22kHz BW

VDD = 5V 1.25 W

VDD = 3.6V 0.63 W

VDD = 2.5V 0.285 W

THD+N Total Harmonic Distortion PO = 500mW, f = 1kHz, RL = 8Ω0.07 %

PO = 300mW, f = 1kHz, RL = 8Ω0.05 %

PSRR Power Supply Rejection Ratio

VRIPPLE = 200mVP-P Sine,

fRIPPLE = 217Hz, Inputs AC GND,

Ci = 1μF, input referred

VRIPPLE = 1VP-P Sine,

fRIPPLE = 1kHz, Inputs AC GND,

Ci = 1μF, input referred

CMRR Common Mode Rejection Ratio VRIPPLE = 1VP-P

fRIPPLE = 217Hz 67 dB

ηEfficiency PO = 1W, f = 1kHz,

RL = 8Ω, VDD = 5V 85 %

Xtalk Crosstalk PO = 500mW, f = 1kHz 84 dB

SNR Signal to Noise Ratio VDD = 5V, PO = 1W 96 dB

εOS Output Noise Input referred, A-Weighted Filter 20 μV

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 TJMAX, θJA, and the ambient temperature, TA. The maximum

allowable power dissipation is PDMAX = (TJMAX – TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4674 see power

derating currents for more information.

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

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

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: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

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LM4674

Block Diagrams

20167426

FIGURE 2. Differential Input Configuration

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LM4674

20167464

FIGURE 3. Single-Ended Input Configuration

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LM4674

Typical Performance Characteristics

THD+N vs Output Power

f = 1kHz, AV = 24dB, RL = 8Ω

20167439

THD+N vs Output Power

f = 1kHz, AV = 6dB, RL = 8Ω

20167440

THD+N vs Output Power

f= 1kHz, AV = 24dB, RL = 4Ω

20167441

THD+N vs Output Power

f = 1kHz, AV = 6dB, RL = 4Ω

20167442

THD+N vs Frequency

VDD = 2.5V, POUT = 100mW/ch, RL = 8Ω

20167443

THD+N vs Frequency

VDD = 3.6V, POUT = 250mW/ch, RL = 8Ω

20167444

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LM4674

THD+N vs Frequency

VDD = 5V, POUT = 375mW/ch, RL = 8Ω

20167445

THD+N vs Frequency

VDD = 2.5V, POUT = 100mW/ch, RL = 4Ω

20167446

THD+N vs Frequency

VDD = 3.6V, POUT = 250mW/ch, RL = 4Ω

20167447

THD+N vs Frequency

VDD = 5V, POUT = 375mW/ch, RL = 4Ω

20167448

Efficiency vs Output Power/channel

RL = 4Ω, f = 1kHz

20167449

Efficiency vs Output Power/channel

RL = 8Ω, f = 1kHz

20167450

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LM4674

Power Dissipation vs Output Power

RL = 4Ω, f = 1kHz

20167451

Power Dissipation vs Output Power

RL = 8Ω, f = 1kHz

20167452

Output Power/channel vs Supply Voltage

RL = 4Ω, f = 1kHz

20167453

Output Power/channel vs Supply Voltage

RL = 8Ω, f = 1kHz

20167454

PSRR vs Frequency

VDD = 3.6V, VRIPPLE= 200mVP-P, RL = 8Ω

20167455

Crosstalk vs Frequency

VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8Ω

20167422

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LM4674

CMRR vs Frequency

VDD = 3.6V, VCM = 1VP-P, RL = 8Ω

20167457

Supply Current vs Supply Voltage

RL = ∞

20167458

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LM4674

Application Information

GENERAL AMPLIFIER FUNCTION

The LM4674 stereo Class D audio power amplifier features a

filterless modulation scheme that reduces external compo-

nent count, conserving board space and reducing system

cost. The outputs of the device transition from VDD to GND

with a 300kHz switching frequency. With no signal applied,

the outputs for each channel switch with a 50% duty cycle, in

phase, causing the two outputs to cancel. This cancellation

results in no net voltage across the speaker, thus there is no

current to the load in the idle state.

With the input signal applied, the duty cycle (pulse width) of

the LM4674 outputs changes. For increasing output voltage,

the duty cycle of the A output increases, while the duty cycle

of the B output decreases for each channel. For decreasing

output voltages, the converse occurs. The difference between

the two pulse widths yields the differential output voltage.

DIFFERENTIAL AMPLIFIER EXPLANATION

As logic supplies continue to shrink, system designers are in-

creasingly turning to differential analog signal handling to

preserve signal to noise ratios with restricted voltage signs.

The LM4674 features two fully differential amplifiers. A differ-

ential amplifier amplifies the difference between the two input

signals. Traditional audio power amplifiers have typically of-

fered only single-ended inputs resulting in a 6dB reduction of

SNR relative to differential inputs. The LM4674 also offers the

possibility of DC input coupling which eliminates the input

coupling capacitors. A major benefit of the fully differential

amplifier is the improved common mode rejection ratio (CM-

RR) over single ended input amplifiers. The increased CMRR

of the differential amplifier reduces sensitivity to ground offset

related noise injection, especially important in noisy systems.

POWER DISSIPATION AND EFFICIENCY

The major benefit of a Class D amplifier is increased efficiency

versus a class AB amplifier. The efficiency of the LM4674 is

attributed to the region of operation of the transistors in the

output stage. The Class D output stage acts as current steer-

ing switches, consuming negligible amounts of power com-

pared to their Class AB counterparts. Most of the power loss

associated with the output stage is due to the IR loss of the

MOSFET on-resistance (RDS(ON)), along with switching losses

due to gate charge.

SHUTDOWN FUNCTION

The LM4674 features independent left and right channel shut-

down controls, allowing each channel to be disabled inde-

pendently. SDR controls the right channel, while SDL controls

the left channel. Driving either low disables the corresponding

channel.

It is best to switch between ground and VDD for minimum cur-

rent consumption while in shutdown. The LM4674 may be

disabled with shutdown voltages in between GND and VDD,

the idle current will be greater than the typical 0.03µA value.

For logic levels between GND and VDD bypass SD_ with a

0.1μF capacitor.

The LM4674 shutdown inputs have internal pulldown resis-

tors. The purpose of these resistors is to eliminate any un-

wanted state changes when SD_ is floating. To minimize

shutdown current, SD_ should be driven to GND or left float-

ing. If SD_ is not driven to GND or floating, an increase in

shutdown supply current will be noticed.

SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION

The LM4674 is compatible with single-ended sources. When

configured for single-ended inputs, input capacitors must be

used to block any DC component at the input of the device.

Figure 3 shows the typical single-ended applications circuit.

AUDIO AMPLIFIER POWER SUPPLY BYPASSING/

FILTERING

Proper power supply bypassing is critical for low noise per-

formance and high PSRR. Place the supply bypass capacitor

as close to the device as possible. Typical applications em-

ploy a voltage regulator with 10µF and 0.1µF bypass capac-

itors that increase supply stability. These capacitors do not

eliminate the need for bypassing of the LM4674 supply pins.

A 1µF capacitor is recommended.

AUDIO AMPLIFIER INPUT CAPACITOR SELECTION

Input capacitors may be required for some applications, or

when the audio source is single-ended. Input capacitors block

the DC component of the audio signal, eliminating any conflict

between the DC component of the audio source and the bias

voltage of the LM4674. The input capacitors create a high-

pass filter with the input resistance Ri. The -3dB point of the

high pass filter is found using Equation 1 below.

f = 1 / 2πRiCi(1)

The values for Ri can be found in the EC table for each gain

setting.

The input capacitors can also be used to remove low fre-

quency content from the audio signal. Small speakers cannot

reproduce, and may even be damaged by low frequencies.

High pass filtering the audio signal helps protect the speakers.

When the LM4674 is using a single-ended source, power

supply noise on the ground is seen as an input signal. Setting

the high-pass filter point above the power supply noise fre-

quencies, 217 Hz in a GSM phone, for example, filters out the

noise such that it is not amplified and heard on the output.

Capacitors with a tolerance of 10% or better are recommend-

ed for impedance matching and improved CMRR and PSRR.

AUDIO AMPLIFIER GAIN SETTING

The LM4674 features four internally configured gain settings.

The device gain is selected through the two logic inputs, G0

and G1. The gain settings are as shown in the following table.

LOGIC INPUT GAIN

G1 G0 V/V dB

0 0 2 6

0 1 4 12

1 0 8 18

1 1 16 24

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LM4674

PCB LAYOUT GUIDELINES

As output power increases, interconnect resistance (PCB

traces and wires) between the amplifier, load and power sup-

ply create a voltage drop. The voltage loss due to the traces

between the LM4674 and the load results in lower output

power and decreased efficiency. Higher trace resistance be-

tween the supply and the LM4674 has the same effect as a

poorly regulated supply, increasing ripple on the supply line,

and reducing peak output power. The effects of residual trace

resistance increases as output current increases due to high-

er output power, decreased load impedance or both. To main-

tain the highest output voltage swing and corresponding peak

output power, the PCB traces that connect the output pins to

the load and the supply pins to the power supply should be

as wide as possible to minimize trace resistance.

The use of power and ground planes will give the best THD

+N performance. In addition to reducing trace resistance, the

use of power planes creates parasitic capacitors that help to

filter the power supply line.

The inductive nature of the transducer load can also result in

overshoot on one or both edges, clamped by the parasitic

diodes to GND and VDD in each case. From an EMI stand-

point, this is an aggressive waveform that can radiate or

conduct to other components in the system and cause inter-

ference. In is essential to keep the power and output traces

short and well shielded if possible. Use of ground planes

beads and micros-strip layout techniques are all useful in pre-

venting unwanted interference.

As the distance from the LM4674 and the speaker increases,

the amount of EMI radiation increases due to the output wires

or traces acting as antennas become more efficient with

length. Ferrite chip inductors places close to the LM4674 out-

puts may be needed to reduce EMI radiation.

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LM4674

LM4674TL Demo Board Schematic

20167474

LM4674TL Demo Board Schematic

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LM4674

LM4674TL Demonstration Board Layout

20167476

Layer 1

20167477

Layer 2

20167478

Layer 3

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LM4674

20167479

Layer 4

20167480

Top Silkscreen

20167475

Bottom Silkscreen

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LM4674

LM4674SQ Demo Board Schematic

20167481

LM4674SQ Demo Board Schematic

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LM4674

LM4674SQ Demonstration Board Layout

20167485

Layer 1

20167483

Layer 2

20167484

Layer 3

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LM4674

20167486

Top Silkscreen

20167487

Bottom Layer

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LM4674

Revision Table

Rev Date Description

1.0 12/16/06 Initial release.

1.1 05/17/06 Added the LLP package.

1.2 05/31/06 Added the LLP markings.

1.3 09/05/06 Added “No Load” in the Conditions on Av (3.6V table).

1.4 09/21/06 Edited graphics (26, 38, 60) and input some text edits.

1.5 09/27/06 Edited Figure 1 (page 2), TL and LLP pkg/marking drawings (page 3).

Input text edits.

1.6 07/13/07 Added the TL and SQ demo boards and schematics diagrams.

1.7 10/30/07 Updated the SQ schematic diagram and replaced the demo boards.

1.8 07/02/08 Text edits (under SHUTDOWN FUNCTION).

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LM4674

Physical Dimensions inches (millimeters) unless otherwise noted

16 Bump micro SMD

Order Number LM4674TL

NS Package Number TLA1611A

X1 = 2mm X2 = 2mm X3 = 0.6mm

LLP Package

Order Number LM4674SQ

NS Package Number SQA16A

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LM4674

Notes

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LM4674

Notes

LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier

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Products Applications

Audio www.ti.com/audio Communications and Telecom www.ti.com/communications

Amplifiers amplifier.ti.com Computers and Peripherals www.ti.com/computers

Data Converters dataconverter.ti.com Consumer Electronics www.ti.com/consumer-apps

DLP®Products www.dlp.com Energy and Lighting www.ti.com/energy

DSP dsp.ti.com Industrial www.ti.com/industrial

Clocks and Timers www.ti.com/clocks Medical www.ti.com/medical

Interface interface.ti.com Security www.ti.com/security

Logic logic.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense

Power Mgmt power.ti.com Transportation and Automotive www.ti.com/automotive

Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video

RFID www.ti-rfid.com

OMAP Mobile Processors www.ti.com/omap

Wireless Connectivity www.ti.com/wirelessconnectivity

TI E2E Community Home Page e2e.ti.com

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265