MAX9704ETJ+ - Maxim - Datasheet.Live

General Description

The MAX9703/MAX9704 mono/stereo Class D audio

power amplifiers provide Class AB amplifier performance

with Class D efficiency, conserving board space and

eliminating the need for a bulky heatsink. Using a Class

D architecture, these devices deliver up to 15W while

offering up to 78% efficiency. Proprietary and protected

modulation and switching schemes render the traditional

Class D output filter unnecessary.

The MAX9703/MAX9704 offer two modulation schemes:

a fixed-frequency mode (FFM), and a spread-spectrum

mode (SSM) that reduces EMI-radiated emissions due

to the modulation frequency. The device utilizes a fully

differential architecture, a full bridged output, and com-

prehensive click-and-pop suppression.

The MAX9703/MAX9704 feature high 80dB PSRR, low

0.07% THD+N, and SNR in excess of 95dB. Short-cir-

cuit and thermal-overload protection prevent the

devices from being damaged during a fault condition.

The MAX9703 is available in a 32-pin TQFN (5mm x

5mm x 0.8mm) package. The MAX9704 is available in a

32-pin TQFN (7mm x 7mm x 0.8mm) package. Both

devices are specified over the extended -40°C to

+85°C temperature range.

Applications

Features

♦Filterless Class D Amplifier

♦Unique Spread-Spectrum Mode Offers 5dB

Emissions Improvement Over Conventional

Methods

♦Up to 78% Efficient (RL= 8Ω)

♦Up to 88% Efficient (RL= 16Ω)

♦15W Continuous Output Power into 8Ω(MAX9703)

♦2x10W Continuous Output Power into 8Ω(MAX9704)

♦Low 0.07% THD+N

♦High PSRR (80dB at 1kHz)

♦10V to 25V Single-Supply Operation

♦Differential Inputs Minimize Common-Mode Noise

♦Pin-Selectable Gain Reduces Component Count

♦Industry-Leading Click-and-Pop Suppression

♦Low Quiescent Current (24mA)

♦Low-Power Shutdown Mode (0.2µA)

♦Short-Circuit and Thermal-Overload Protection

♦Available in Thermally Efficient, Space-Saving

Packages

32-Pin TQFN (5mm x 5mm x 0.8mm)–MAX9703

32-Pin TQFN (7mm x 7mm x 0.8mm)–MAX9704

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

________________________________________________________________ Maxim Integrated Products 1

19-3160; Rev 7; 3/06

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Ordering Information

PART PIN-PACKAGE AMP PKG CODE

MAX9703ETJ+ 32 TQFN-EP* Mono T3255-3

MAX9704ETJ+ 32 TQFN-EP* Stereo T3277-2

Note: All devices specified for over -40°C to +85°C operating

temperature range.

*EP = Exposed paddle.

+Denotes lead-free package.

LCD TVs

LCD Monitors

Desktop PCs

LCD Projectors

Hands-Free Car

Phone Adaptors

Automotive

Pin Configurations appear at end of data sheet.

MAX9704

0.47μFINL+ OUTL+

OUTL-INL-

0.47μFH-BRIDGE

0.47μFINR+ OUTR+

OUTR-INR-

0.47μFH-BRIDGE

MAX9703

0.47μFIN+ OUT+

OUT-

IN-

0.47μFH-BRIDGE

Block Diagrams

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

(All voltages referenced to PGND.)

VDD to PGND, AGND .............................................................30V

OUTR_, OUTL_, C1N..................................-0.3V to (VDD + 0.3V)

C1P............................................(VDD - 0.3V) to (CHOLD + 0.3V)

CHOLD........................................................(VDD - 0.3V) to +40V

All Other Pins to PGND...........................................-0.3V to +12V

Duration of OUTR_/OUTL_

Short Circuit to PGND, VDD ................................................10s

Continuous Input Current (VDD, PGND) ...............................1.6A

Continuous Input Current......................................................0.8A

Continuous Input Current (all other pins)..........................±20mA

Continuous Power Dissipation (TA= +70°C)

Single-Layer Board:

MAX9703 32-Pin TQFN (derate 21.3mW/°C

above +70°C)..........................................................1702.1mW

MAX9704 32-Pin TQFN (derate 27mW/°C

above +70°C)..........................................................2162.2mW

Multilayer Board:

MAX9703 32-Pin TQFN (derate 34.5mW/°C

above +70°C)..........................................................2758.6mW

MAX9704 32-Pin TQFN (derate 37mW/°C

above +70°C)..........................................................2963.0mW

Junction Temperature......................................................+150°C

Operating Temperature Range ...........................-40°C to +85°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

ELECTRICAL CHARACTERISTICS

(VDD = 15V, AGND = PGND = 0V, SHDN ≥VIH, AV= 16dB, CSS = CIN = 0.47µF, CREG = 0.01µF, C1 = 100nF, C2 = 1µF, FS1 = FS2

= PGND (fS= 660kHz), RLconnected between OUTL+ and OUTL- and OUTR+ and OUTR-, TA= TMIN to TMAX, unless otherwise

noted. Typical values are at TA= +25°C.) (Notes 1, 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

GENERAL

Supply Voltage Range VDD Inferred from PSRR test 10 25 V

MAX9703 14 22

Quiescent Current IDD RL = OPEN MAX9704 24 34 mA

Shutdown Current ISHDN 0.2 1.5 µA

CSS = 470nF 100

Turn-On Time tON CSS = 180nF 50 ms

Amplifier Output Resistance in

Shutdown SHDN = PGND 150 330 kΩ

AV = 13dB 35 58 80

AV = 16dB 30 48 65

AV = 19.1dB 23 39 55

Input Impedance RIN

AV = 29.6dB 10 15 22

kΩ

G1 = L, G2 = L 29.4 29.6 29.8

G1 = L, G2 = H 18.9 19.1 19.3

G1 = H, G2 = L 12.8 13 13.2

Voltage Gain AV

G1 = H, G2 = H 15.9 16 16.3

Gain Matching Between channels (MAX9704) 0.5 %

Output Offset Voltage VOS ±6±30 mV

Common-Mode Rejection Ratio CMRR fIN = 1kHz, input referred 60 dB

VDD = 10V to 25V 54 80

fRIPPLE = 1kHz 80

Power-Supply Rejection Ratio

(Note 3) PSRR 200mVP-P ripple fRIPPLE = 20kHz 66

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDD = 15V, AGND = PGND = 0V, SHDN ≥VIH, AV= 16dB, CSS = CIN = 0.47µF, CREG = 0.01µF, C1 = 100nF, C2 = 1µF, FS1 = FS2

= PGND (fS= 660kHz), RLconnected between OUTL+ and OUTL- and OUTR+ and OUTR-, TA= TMIN to TMAX, unless otherwise

noted. Typical values are at TA= +25°C.) (Notes 1, 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

RL = 4Ω10

RL = 8Ω15

Continuous Output Power

(MAX9703) PCONT

TH D + N = 10%, VDD =

16V, f = 1kH z, TA =

+ 25°C , tCONT = 15min

(Note 4) RL = 16Ω, VDD = 24V 18

RL = 4Ω2x5

RL = 8Ω2x10

Continuous Output Power

(MAX9704) PCONT

TH D + N = 10%, VDD =

16V, f = 1kH z, TA =

+ 25°C , tCONT = 15min

(Note 4) RL = 16Ω, VDD = 24V 2x16

Total Harmonic Distortion Plus

Noise THD+N fIN = 1kHz, either FFM or SSM, RL = 8Ω,

POUT = 4W 0.07 %

FFM 94

BW = 22Hz to

22kHz SSM 88

FFM 97

Signal-to-Noise Ratio SNR RL = 8Ω, POUT =

10W, f = 1kHz

A-weighted SSM 91

Crosstalk Left to right, right to left, 8Ω load, fIN = 10kHz 65 dB

FS1 = L, FS2 = L 560 670 800

FS1 = L, FS2 = H 940

FS1 = H, FS2 = L 470

Oscillator Frequency fOSC

FS1 = H, FS2 = H (spread-spectrum mode) 670

±7%

kHz

POUT = 15W, f = 1kHz, RL = 8Ω78

Efficiency η

POUT = 10W, f = 1kHz, RL = 16Ω88

Regulator Output VREG 6V

DIGITAL INPUTS (SHDN, FS_, G_)

VIH 2.5

Input Thresholds VIL 0.8 V

Input Leakage Current ±1µA

Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.

Note 2: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For RL= 8Ω, L = 68µH.

For RL= 4Ω, L = 33µH.

Note 3: PSRR is specified with the amplifier inputs connected to AGND through CIN.

Note 4: The MAX9704 continuous 8Ωand 16Ωpower measurements account for thermal limitations of the 32-pin TQFN-EP package.

Continuous 4Ωpower measurements account for short-circuit protection of the MAX9703/MAX9704 devices.

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

4 _______________________________________________________________________________________

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. FREQUENCY

MAX9703/04 toc01

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

0.01

10 100k

VDD = 15V

RL = 4Ω

AV = 16dB

POUT = 4W

POUT = 500mW

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. FREQUENCY

MAX9703/04 toc02

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

0.01

10 100k

VDD = 15V

RL = 8Ω

AV = 16dB

POUT = 500mW

POUT = 8W

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. FREQUENCY

MAX9703/04 toc03

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

0.01

10 100k

VDD = 20V

RL = 8Ω

AV = 16dB

POUT = 8W

POUT = 500mW

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. FREQUENCY

MAX9703/04 toc04

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

0.01

10 100k

VDD = 20V

RL = 8Ω

AV = 16dB

POUT = 8W

SSM

FFM

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. OUTPUT POWER

MAX9703/04 toc07

OUTPUT POWER (W)

THD+N (%)

26 8 10 12 14 16 18

0.1

100

0.01

020

VDD = 20V

RL = 8Ω

AV = 16dB

f = 100Hz

f = 1kHz

f = 10kHz

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. OUTPUT POWER

MAX9703/04 toc05

OUTPUT POWER (W)

THD+N (%)

0.1

100

0.01

010978

VDD = 15V

RL = 4Ω

AV = 16dB

f = 10kHz

f = 1kHz

f = 100Hz

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. OUTPUT POWER

MAX9703/04 toc06

OUTPUT POWER (W)

THD+N (%)

12345678910 11 12 13 14

0.1

0.01

015

VDD = 15V

RL = 8Ω

AV = 16dB

f = 100Hz

f = 1kHz

f = 10kHz

TOTAL HARMONIC DISTORTION PLUS

NOISE vs. OUTPUT POWER

MAX9703/04 toc08

OUTPUT POWER (W)

THD+N (%)

12345678910 11 12 1314 15 16 17 18 19

0.1

0.01

020

FFM (335kHz)

SSM

VDD = 20V

RL = 8Ω

AV = 16dB

f = 1kHz

EFFICIENCY vs. OUTPUT POWER

MAX9703/04 toc09

OUTPUT POWER (W)

EFFICIENCY (%)

86423 5 7 9

100

010

VDD = 12V

AV = 16dB

f = 1kHz

RL = 4Ω

RL = 8Ω

Typical Operating Characteristics

(33µH with 4Ω, 68µH with 8Ω, part in SSM mode, 136µH with 16Ω, measurement BW = 22Hz to 22kHz, unless otherwise noted.)

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

_______________________________________________________________________________________ 5

EFFICIENCY vs. OUTPUT POWER

MAX9703/04 toc10

OUTPUT POWER (W)

EFFICIENCY (%)

2610 14 18

100

020

VDD = 15V

AV = 16dB

f = 1kHz

RL = 16Ω

RL = 8Ω

OUTPUT POWER

vs. SUPPLY VOLTAGE

MAX9703/04 toc11

SUPPLY VOLTAGE (V)

OUTPUT POWER (W)

10 1613 19 22 25

RL = 8Ω

RL = 16Ω

AV = 16dB

THD+N = 10%

110100

OUTPUT POWER

vs. LOAD RESISTANCE

MAX9703/04 toc12

LOAD RESISTANCE (Ω)

OUTPUT POWER (W)

THD+N = 1%

THD+N = 10%

VDD = 15V

AV = 16dB

110100

OUTPUT POWER

vs. LOAD RESISTANCE

MAX9703/04 toc13

LOAD RESISTANCE (Ω)

OUTPUT POWER (W)

VDD = 20V

AV = 16dB THD+N = 10%

THD+N = 1%

CROSSTALK vs. FREQUENCY

MAX9703/04 toc16

FREQUENCY (Hz)

CROSSTALK (dB)

10k1k100

-80

-100

-60

-40

-20

-120

10 100k

LEFT TO RIGHT

RIGHT TO LEFT

AV = 16dB

1% THD+N

VDD = 15V

8Ω LOAD

COMMON-MODE REJECTION RATIO

vs. FREQUENCY

MAX9703/04 toc14

FREQUENCY (Hz)

CMRR (dB)

10k1k100

-70

-60

-50

-40

-30

-20

-10

-80

10 100k

VDD = 15V

RL = 8Ω

AV = 16dB

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

MAX9703/04 toc15

FREQUENCY (Hz)

PSRR (dB)

10k1k100

-100

-80

-60

-40

-20

-120

10 100k

AV = 16dB

RL = 8Ω

200mVP-P INPUT

VDD = 15V

OUTPUT FREQUENCY SPECTRUM

MAX9703/04 toc17

FREQUENCY (kHz)

OUTPUT MAGNITUDE (dB)

-120

-100

-80

-60

-40

-20

-140

181612 144 6 8 102020

FFM MODE

AV = 16dB

UNWEIGHTED

fIN = 1kHz

POUT = 5W

RL = 8Ω

OUTPUT FREQUENCY SPECTRUM

MAX9703/04 toc18

FREQUENCY (kHz)

OUTPUT MAGNITUDE (dB)

-120

-100

-80

-60

-40

-20

-140

181612 144 6 8 102020

SSM MODE

AV = 16dB

UNWEIGHTED

fIN = 1kHz

POUT = 5W

RL = 8Ω

Typical Operating Characteristics (continued)

(33µH with 4Ω, 68µH with 8Ω, part in SSM mode, 136µH with 16Ω, measurement BW = 22Hz to 22kHz, unless otherwise noted.)

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

6 _______________________________________________________________________________________

OUTPUT FREQUENCY SPECTRUM

MAX9703/04 toc19

FREQUENCY (kHz)

OUTPUT MAGNITUDE (dB)

-120

-100

-80

-60

-40

-20

-140

181612 144 6 8 102020

SSM MODE

AV = 16dB

A-WEIGHTED

fIN = 1kHz

POUT = 5W

RL = 8Ω

100k 1M 10M 100M

WIDEBAND OUTPUT SPECTRUM

(FFM MODE)

MAX9703/04 toc20

FREQUENCY (Hz)

OUTPUT AMPLITUDE (dBV)

-120

-100

-80

-60

-40

-20

RBW = 10kHz

VDD = 15V

100k 1M 10M 100M

WIDEBAND OUTPUT SPECTRUM

(SSM MODE)

MAX9703/04 toc21

FREQUENCY (Hz)

OUTPUT AMPLITUDE (dBV)

-120

-100

-80

-60

-40

-20

RBW = 10kHz

VDD = 15V

TURN-ON/TURN-OFF RESPONSE

MAX9703/04 toc22

20ms/div

OUTPUT

1V/div

5V/div

SHDN

f = 1kHz

RL = 8Ω

CSS = 180pF

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX9703/04 toc23

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

22191613

10 25

SHUTDOWN CURRENT

vs. SUPPLY VOLTAGE

MAX97703/04 toc24

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT (μA)

18161412

0.10

0.05

0.15

0.20

0.25

0.30

0.35

10 20

Typical Operating Characteristics (continued)

(33µH with 4Ω, 68µH with 8Ω, part in SSM mode, 136µH with 16Ω, measurement BW = 22Hz to 22kHz, unless otherwise noted.)

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

_______________________________________________________________________________________ 7

MAX9703 MAX9704 NAME FUNCTION

1, 2, 23, 24 1, 2, 23, 24 PGND Power Ground

3, 4, 21, 22 3, 4, 21, 22 VDD Power-Supply Input

5 5 C1N Charge-Pump Flying Capacitor Negative Terminal

6 6 C1P Charge-Pump Flying Capacitor Positive Terminal

7 7 CHOLD Charge-Pump Hold Capacitor. Connect a 1µF capacitor from CHOLD to VDD.

8, 17, 20, 25,

26, 31, 32 8 N.C. No Connection. Not internally connected.

9 14 REG 6V Internal Regulator Output. Bypass with a 0.01µF capacitor to AGND.

10 13 AGND Analog Ground

11 — IN- Negative Input

12 — IN+ Positive Input

13 12 SS Soft-Start. Connect a 0.47µF capacitor from SS to PGND to enable soft-start feature.

14 11 SHDN Active-Low Shutdown. Connect SHDN to PGND to disable the device. Connect to a

logic-high for normal operation.

15 17 G1 Gain-Select Input 1

16 18 G2 Gain-Select Input 2

18 19 FS1 Frequency-Select Input 1

19 20 FS2 Frequency-Select Input 2

27, 28 — OUT- Negative Audio Output

29, 30 — OUT+ Positive Audio Output

— 9 INL- Left-Channel Negative Input

— 10 INL+ Left-Channel Positive Input

— 15 INR- Right-Channel Negative Input

— 16 INR+ Right-Channel Positive Input

— 25, 26 OUTR- Right-Channel Negative Audio Output

— 27, 28 OUTR+ Right-Channel Positive Audio Output

— 29, 30 OUTL- Left-Channel Negative Audio Output

— 31, 32 OUTL+ Left-Channel Positive Audio Output

— — EP Exposed Paddle. Connect to GND.

Pin Description

MAX9703/MAX9704

Detailed Description

The MAX9703/MAX9704 filterless, Class D audio power

amplifiers feature several improvements to switch-

mode amplifier technology. The MAX9703 is a mono

amplifier, the MAX9704 is a stereo amplifier. These

devices offer Class AB performance with Class D effi-

ciency, while occupying minimal board space. A

unique filterless modulation scheme and spread-spec-

trum switching mode create a compact, flexible, low-

noise, efficient audio power amplifier. The differential

input architecture reduces common-mode noise pick-

up, and can be used without input-coupling capacitors.

The devices can also be configured as a single-ended

input amplifier.

Comparators monitor the device inputs and compare

the complementary input voltages to the triangle wave-

form. The comparators trip when the input magnitude of

the triangle exceeds their corresponding input voltage.

Operating Modes

Fixed-Frequency Modulation (FFM) Mode

The MAX9703/MAX9704 feature three FFM modes with

different switching frequencies (Table 1). In FFM mode,

the frequency spectrum of the Class D output consists of

the fundamental switching frequency and its associated

harmonics (see the Wideband Output Spectrum (FFM

Mode) graph in the Typical Operating Characteristics).

The MAX9703/ MAX9704 allow the switching frequency to

be changed by ±35%, should the frequency of one or

more of the harmonics fall in a sensitive band. This can be

done at any time and does not affect audio reproduction.

Spread-Spectrum Modulation (SSM) Mode

The MAX9703/MAX9704 feature a unique spread-spec-

trum mode that flattens the wideband spectral compo-

nents, improving EMI emissions that may be radiated

by the speaker and cables. This mode is enabled by

setting FS1 = FS2 = H. In SSM mode, the switching fre-

quency varies randomly by ±7% around the center fre-

quency (670kHz). The modulation scheme remains the

same, but the period of the triangle waveform changes

from cycle to cycle. Instead of a large amount of spec-

tral energy present at multiples of the switching fre-

quency, the energy is now spread over a bandwidth

that increases with frequency. Above a few megahertz,

the wideband spectrum looks like white noise for EMI

purposes (see Figure 1).

Efficiency

Efficiency of a Class D amplifier is attributed to the

region of operation of the output stage transistors. In a

Class D amplifier, the output transistors act as current-

steering switches and consume negligible additional

power. Any power loss associated with the Class D out-

put stage is mostly due to the I2R loss of the MOSFET

on-resistance, and quiescent current overhead.

The theoretical best efficiency of a linear amplifier is

78%; however, that efficiency is only exhibited at peak

output powers. Under normal operating levels (typical

music reproduction levels), efficiency falls below 30%,

whereas the MAX9704 still exhibits >78% efficiency

under the same conditions (Figure 2).

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

8 _______________________________________________________________________________________

Table 1. Operating Modes

FS1 FS2 SWITCHING MODE

(kHz)

L L 670

L H 940

H L 470

H H 670 ±7%

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

_______________________________________________________________________________________ 9

Figure 1. MAX9704 EMI Spectrum, 9in PC Board trace, 3in Twisted-Pair Speaker Cable

MAX9704

VDD

CIN L1*

L2*

1000pF

L3*

L4*

1000pF

*L1–L4 = 0.05Ω DCR, 70Ω AT 100MHz, 3A FAIR RITE FERRITE BEAD (2512067007Y3).

1000pF

CIN

FREQUENCY (MHz)

AMPLITUDE (dBuV/m)

900800100 200 300 500 600400 700

30 1000

CE LIMIT

MAX9704 OUTPUT

SPECTRUM

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

10 ______________________________________________________________________________________

Shutdown

The MAX9703/MAX9704 have a shutdown mode that

reduces power consumption and extends battery life.

Driving SHDN low places the device in low-power

(0.2µA) shutdown mode. Connect SHDN to a logic high

for normal operation.

Click-and-Pop Suppression

The MAX9703/MAX9704 feature comprehensive click-

and-pop suppression that eliminates audible transients

on startup and shutdown. While in shutdown, the H-

bridge is pulled to PGND through 330kΩ. During start-

up, or power-up, the input amplifiers are muted and an

internal loop sets the modulator bias voltages to the cor-

rect levels, preventing clicks and pops when the H-

bridge is subsequently enabled. Following startup, a

soft-start function gradually unmutes the input amplifiers.

The value of the soft-start capacitor has an impact on the

click/pop levels. For optimum performance, CSS should

be at least 0.18µF with a voltage rating of at least 7V.

Mute Function

The MAX9703/MA9704 features a clickless/popless

mute mode. When the device is muted, the outputs

stop switching, muting the speaker. Mute only affects

the output stage and does not shut down the device.

To mute the MAX9703/MAX9704, drive SS to PGND by

using a MOSFET pulldown (Figure 3). Driving SS to

PGND during the power-up/down or shutdown/turn-on

cycle optimizes click-and-pop suppression.

Applications Information

Filterless Operation

Traditional class D amplifiers require an output filter to

recover the audio signal from the amplifier’s PWM out-

put. The filters add cost, increase the solution size of

the amplifier, and can decrease efficiency. The tradi-

tional PWM scheme uses large differential output

swings (2 ✕VDD peak-to-peak) and causes large ripple

currents. Any parasitic resistance in the filter compo-

nents results in a loss of power, lowering the efficiency.

The MAX9703/MAX9704 do not require an output filter.

The devices rely on the inherent inductance of the

speaker coil and the natural filtering of both the speak-

er and the human ear to recover the audio component

of the square-wave output. Eliminating the output filter

results in a smaller, less-costly, more-efficient solution.

Because the frequency of the MAX9703/MAX9704 out-

put is well beyond the bandwidth of most speakers,

voice coil movement due to the square-wave frequency

is very small. Although this movement is small, a speak-

er not designed to handle the additional power can be

damaged. For optimum results, use a speaker with a

series inductance > 30µH. Typical 8Ωspeakers exhibit

series inductances in the range of 30µH to 100µH.

Optimum efficiency is achieved with speaker induc-

tances > 60µH.

Internal Regulator Output (VREG)

The MAX9703/MAX9704 feature an internal, 6V regula-

tor output (VREG). The MAX9703/MAX9704 REG output

pin simplifies system design and reduces system cost

by providing a logic voltage high for the MAX9703/

MAX9704 logic pins (G_, FS_). VREG is not available as a

logic voltage high in shutdown mode. Do not apply VREG

as a 6V potential to surrounding system components.

Bypass REG with a 6.3V, 0.01µF capacitor to AGND.

Figure 2. MAX9704 Efficiency vs. Class AB Efficiency

100

06810 12 14 16 18

24 20

EFFICIENCY vs. OUTPUT POWER

OUTPUT POWER (W)

EFFICIENCY (%)

VDD = 15V

f = 1kHz

RL = 8Ω

MAX9704

CLASS AB

MAX9703/

MAX9704

0.18μF

GPIO

MUTE SIGNAL

Figure 3. MAX9703/MAX9704 Mute Circuit

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

______________________________________________________________________________________ 11

Gain Selection

The MAX9703/MAX9704 feature an internally set, logic-

selectable gain. The G1 and G2 logic inputs set the

gain of the MAX9703/MAX9704 speaker amplifier

(Table 2).

Output Offset

Unlike a Class AB amplifier, the output offset voltage of

Class D amplifiers does not noticeably increase quies-

cent current draw when a load is applied. This is due to

the power conversion of the Class D amplifier. For

example, an 8mV DC offset across an 8Ωload results

in 1mA extra current consumption in a class AB device.

In the Class D case, an 8mV offset into 8Ωequates

to an additional power drain of 8µW. Due to the high

efficiency of the Class D amplifier, this represents an

additional quiescent current draw of: 8µW/(VDD/100 ✕η),

which is in the order of a few microamps.

Input Amplifier

Differential Input

The MAX9703/MAX9704 feature a differential input struc-

ture, making them compatible with many CODECs, and

offering improved noise immunity over a single-ended

input amplifier. In devices such as PCs, noisy digital sig-

nals can be picked up by the amplifier’s input traces.

The signals appear at the amplifiers’ inputs as common-

mode noise. A differential input amplifier amplifies the

difference of the two inputs, any signal common to both

inputs is canceled.

Single-Ended Input

The MAX9703/MAX9704 can be configured as single-

ended input amplifiers by capacitively coupling either

input to AGND and driving the other input (Figure 4).

Component Selection

Input Filter

An input capacitor, CIN, in conjunction with the input

impedance of the MAX9703/MAX9704, forms a high-

pass filter that removes the DC bias from an incoming

signal. The AC-coupling capacitor allows the amplifier

to bias the signal to an optimum DC level. Assuming

zero-source impedance, the -3dB point of the highpass

filter is given by:

Choose CIN so f-3dB is well below the lowest frequency

of interest. Setting f-3dB too high affects the low-fre-

quency response of the amplifier. Use capacitors with

dielectrics that have low-voltage coefficients, such as

tantalum or aluminum electrolytic. Capacitors with high-

voltage coefficients, such as ceramics, may result in

increased distortion at low frequencies.

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 100mΩfor opti-

mum performance. Low-ESR ceramic capacitors mini-

mize the output resistance of the charge pump. For

best performance over the extended temperature

range, select capacitors with an X7R dielectric.

Flying Capacitor (C1)

The value of the flying capacitor (C1) affects the load

regulation and output resistance of the charge pump. A

C1 value that is too small degrades the device’s ability to

provide sufficient current drive. Increasing the value of

C1 improves load regulation and reduces the charge-

pump output resistance to an extent. Above 1µF, the on-

resistance of the switches and the ESR of C1 and C2

dominate.

Hold Capacitor (C2)

The output capacitor value and ESR directly affect the rip-

ple at CHOLD. Increasing C2 reduces output ripple.

Likewise, decreasing the ESR of C2 reduces both ripple

and output resistance. Lower capacitance values can be

used in systems with low maximum output power levels.

Output Filter

The MAX9703/MAX9704 do not require an output filter

and can pass FCC emissions standards with unshield-

ed speaker cables. However, output filtering can be

fRC

-3dB IN IN

=π

MAX9703/

MAX9704

IN+

IN-

0.47μF

SINGLE-ENDED

AUDIO INPUT

Figure 4. Single-Ended Input

Table 2. Gain Selection

G1 G2 GAIN (dB)

0 0 29.6

0 1 19.1

1013

1116

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

12 ______________________________________________________________________________________

used if a design is failing radiated emissions due to

board layout or cable length, or the circuit is near EMI-

sensitive devices. Use a ferrite bead filter when radiat-

ed frequencies above 10MHz are of concern. Use an

LC filter when radiated frequencies below 10MHz are of

concern, or when long leads connect the amplifier to

the speaker. Refer to the MAX9704 Evaluation Kit

schematic for details of this filter.

Sharing Input Sources

In certain systems, a single audio source can be shared

by multiple devices (speaker and headphone ampli-

fiers). When sharing inputs, it is common to mute the

unused device, rather than completely shutting it down,

preventing the unused device inputs from distorting the

input signal. Mute the MAX9703/MAX9704 by driving SS

low through an open-drain output or MOSFET (see the

System Diagram). Driving SS low turns off the Class D

output stage, but does not affect the input bias levels of

the MAX9703/MAX9704. Be aware that during normal

operation, the voltage at SS can be up to 7V, depending

on the MAX9703/MAX9704 supply.

Supply Bypassing/Layout

Proper power-supply bypassing ensures low distortion

operation. For optimum performance, bypass VDD to

PGND with a 0.1µF capacitor as close to each VDD pin

as possible. A low-impedance, high-current power-sup-

ply connection to VDD is assumed. Additional bulk

capacitance should be added as required depending on

the application and power-supply characteristics. AGND

and PGND should be star connected to system ground.

Refer to the MAX9704 Evaluation Kit for layout guidance.

Class D Amplifier

Thermal Considerations

Class D amplifiers provide much better efficiency and

thermal performance than a comparable Class AB ampli-

fier. However, the system’s thermal performance must be

considered with realistic expectations and include con-

sideration of many parameters. This section examines

Class D amplifiers using general examples to illustrate

good design practices.

Continuous Sine Wave vs. Music

When a Class D amplifier is evaluated in the lab, often a

continuous sine wave is used as the signal source. While

this is convenient for measurement purposes, it repre-

sents a worst-case scenario for thermal loading on the

amplifier. It is not uncommon for a Class D amplifier to

enter thermal shutdown if driven near maximum output

power with a continuous sine wave.

Audio content, both music and voice, has a much lower

RMS value relative to its peak output power. Figure 5

shows a sine wave and an audio signal in the time

domain. Both are measured for RMS value by the oscillo-

scope. Although the audio signal has a slightly higher

peak value than the sine wave, its RMS value is almost

half that of the sine wave. Therefore, while an audio sig-

nal may reach similar peaks as a continuous sine wave,

the actual thermal impact on the Class D amplifier is

highly reduced. If the thermal performance of a system is

being evaluated, it is important to use actual audio sig-

nals instead of sine waves for testing. If sine waves must

be used, the thermal performance will be less than the

system’s actual capability.

PC Board Thermal Considerations

The exposed pad is the primary route of keeping heat

away from the IC. With a bottom-side exposed pad, the

PC board and its copper becomes the primary heatsink

for the Class D amplifier. Solder the exposed pad to a

large copper polygon. Add as much copper as possible

from this polygon to any adjacent pin on the Class D

amplifier as well as to any adjacent components, provid-

ed these connections are at the same potential. These

copper paths must be as wide as possible. Each of

these paths contributes to the overall thermal capabilities

of the system.

The copper polygon to which the exposed pad is

attached should have multiple vias to the opposite side

of the PC board, where they connect to another copper

polygon. Make this polygon as large as possible within

the system’s constraints for signal routing.

Figure 5. RMS Comparison of Sine Wave vs. Audio Signal

20ms/div

MAX9703/MAX9704

10W Stereo/15W Mono, Filterless,

Spread-Spectrum, Class D Amplifiers

______________________________________________________________________________________ 13

Additional improvements are possible if all the traces

from the device are made as wide as possible. Although

the IC pins are not the primary thermal path of the pack-

age, they do provide a small amount. The total improve-

ment would not exceed about 10%, but it could make the

difference between acceptable performance and ther-

mal problems.

Auxiliary Heatsinking

If operating in higher ambient temperatures, it is possible

to improve the thermal performance of a PC board with

the addition of an external heatsink. The thermal resis-

tance to this heatsink must be kept as low as possible to

maximize its performance. With a bottom-side exposed

pad, the lowest resistance thermal path is on the bottom

of the PC board. The topside of the IC is not a significant

thermal path for the device, and therefore is not a cost-

effective location for a heatsink.

Thermal Calculations

The die temperature of a Class D amplifier can be esti-

mated with some basic calculations. For example, the

die temperature is calculated for the below conditions:

•TA= +40°C

•POUT = 2x8W = 16W

•RL= 16Ω

•Efficiency (η) = 87%

•θ

JA = 27°C/W

First, the Class D amplifier’s power dissipation must be

calculated.

Then the power dissipation is used to calculate the die

temperature, TC, as follows:

TC= TA+ PDISS x θJA

= 40°C + 2.4W x 27°C/W

= 104.8°C

Decreasing the ambient temperature or reducing θJA will

improve the die temperature of the MAX9704. θJA can

be reduced by increasing the copper size/weight of the

ground plane connected to the exposed paddle of the

MAX9704 TQFN package. Additionally, θJA can be

reduced by attaching a heatsink, adding a fan, or mount-

ing a vertical PC board.

Load Impedance

The on-resistance of the MOSFET output stage in Class

D amplifiers affects both the efficiency and the peak-cur-

rent capability. Reducing the peak current into the load

reduces the I2R losses in the MOSFETs, thereby increas-

ing efficiency. To keep the peak currents lower, choose

the highest impedance speaker which can still deliver

the desired output power within the voltage swing limits

of the Class D amplifier and its supply voltage.

Although most loudspeakers are either 4Ωor 8Ω, there

are other impedances available which can provide a