MAX9773EBP+ - Maxim Integrated Products, Inc.

General Description

The MAX9773 3rd-generation, ultra-low EMI, stereo,

Class D audio power amplifier provides Class AB per-

formance with Class D efficiency. The MAX9773 deliv-

ers 1.8W per channel into a 4Ωload, and offers

efficiencies above 90%. Active emissions limiting (AEL)

circuitry greatly reduces EMI by actively controlling the

output FET gate transitions under all possible transient

conditions. AEL controls high-frequency emissions

resulting from conventional Class D free-wheeling

behavior in the presence of an inductive load. Zero-

dead-time (ZDT) technology maintains state-of-the-art

efficiency and THD+N performance by allowing the out-

put FETs to switch simultaneously without cross con-

duction. A patented spread-spectrum modulation

scheme eliminates the need for output filtering found in

traditional Class D devices. These design concepts

reduce component count and extend battery life.

The MAX9773 offers two modulation schemes: a fixed-

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

mode that reduces EMI-radiated emissions. The

MAX9773 oscillator can be synchronized to an external

clock through the SYNC input, allowing synchroniza-

tion of multiple Maxim Class D amplifiers. The sync

output (SYNC_OUT) can be used for a master-slave

application where more channels are required. The

MAX9773 features a fully differential architecture, a full

bridge-tied load (BTL) output, and comprehensive

click-and-pop suppression. The device features inter-

nally set gains of 12dB, 15.6dB, 20dB, and 26dB

selected through two gain-select inputs, further reduc-

ing external component count.

The MAX9773 features high 80dB PSRR, less than

0.1% THD+N, and SNR in excess of 88dB. Short-circuit

and thermal-overload protection prevent the device

from being damaged during a fault condition. The

MAX9773 is available in 24-pin thin QFN-EP (4mm x

4mm x 0.8mm), and 20-bump UCSP™ (2mm x 2.5mm x

0.6mm) packages. The MAX9773 is specified over the

extended -40°C to +85°C temperature range.

Applications

Cellular/Multimedia Phones

Notebooks

Handheld Gaming Consoles

MP3 Players

Features

♦Filterless Amplifier Passes FCC-Radiation

Emissions Standards with 6in of Cable

♦Unique Spread-Spectrum Mode and Active

Emissions Limiting Achieves Better than 15dB

Margin Under FCC Limit

♦Zero Dead Time (ZDT) H-Bridge Maintains Good

THD+N Performance

♦Single-Supply Operation (2.5V to 5.5V)

♦Stereo Output (4Ω, VDD = 5V, THD+N = 1%,

POUT = 1.8W)

♦No LC Output Filter Required

♦85% Efficiency (RL= 8Ω, PO= 600mW)

♦Less Than 0.1% THD+N

♦High 80dB PSRR

♦Fully Differential Inputs

♦Integrated Click-and-Pop Suppression

♦Low-Power Shutdown Mode (0.1µA)

♦Short-Circuit and Thermal-Overload Protection

♦Pin-for-Pin Compatible with the MAX9701

♦Available in Thermally Efficient, Space-Saving

Packages

24-Pin TQFN-EP (4mm x 4mm x 0.8mm)

20-Bump UCSP (2mm x 2.5mm x 0.6mm)

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

________________________________________________________________ Maxim Integrated Products 1

MAX9773

GAIN2

GAIN1

VDD

GAIN

RIGHT

MODULATOR

AND H-BRIDGE

SYNC OSCILLATOR

LEFT

MODULATOR

AND H-BRIDGE

INR+

INR-

INL+

INL-

SYNC_OUT

Block Diagram

Ordering Information

19-3976; Rev 0; 1/06

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.

PART

TEMP RANGE

PIN-

PACKAGE

PKG

CODE

MAX9773EBP-T -40°C to +85°C 20 UCSP-20

B20-1

MAX9773ETG+ -40°C to +85°C 24 TQFN-EP*

T2444-4

Pin Configurations and Gain Selection appear at end of

data sheet.

UCSP is a trademark of Maxim Integrated Products, Inc.

+Denotes lead-free package.

*EP = Exposed paddle.

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

2_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), RLconnected between

OUT+ and OUT-, RL= ∞, TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)

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.

VDD to GND..............................................................................6V

VDD to PVDD ..........................................................-0.3V to +0.3V

PVDD to PGND .........................................................................6V

GND to PGND .......................................................-0.3V to +0.3V

All Other Pins to GND.................................-0.3V to (VDD + 0.3V)

Continuous Current In/Out of PVDD, PGND, OUT_.........±800mA

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

Duration of OUT_ Short Circuit to

VDD/GND/PVDD/PGND...........................................Continuous

Duration of Short Circuit Between OUT+ and OUT- ......Continuous

Continuous Power Dissipation (TA= +70°C)

20-Bump UCSP (derate 10mW/°C above +70°C) ...........800mW

24-Pin Thin QFN (derate 20.8mW/°C above +70°C) ..1666.7mW

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

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

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

Bump Temperature (soldering) Reflow............................+235°C

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

PARAMETER

SYMBOL

CONDITIONS

MIN TYP MAX

UNITS

GENERAL

Supply Voltage Range VDD Inferred from PSRR test 2.6 5.5 V

Quiescent Current IDD Per channel 5.5 7.5 mA

Shutdown Current ISHDN 0.1 10 µA

Common-Mode Rejection Ratio CMRR fIN = 1kHz 66 dB

Input Bias Voltage VBIAS

1.125 1.25 1.375

Turn-On Time tON 80 ms

Output Offset Voltage VOS TA = +25oC±10

±50

VDD = 2.5V to 5.5V, VIN = 0V, TA = +25oC5980

TMIN < TA < TMAX 56

fRIPPLE = 217Hz 72

Power-Supply Rejection Ratio PSRR

100mVP-P ripple,

VIN = 0V fRIPPLE = 20kHz 50

RL = 8Ω

500

VDD = 3.3V RL = 4Ω

750

RL = 8Ω1300

Output Power (Note 3) POUT THD+N = 1%,

TA = +25oCVDD = 5V

RL = 4Ω1800

RL = 8Ω (POUT = 400mW), f = 1kHz

0.04

Total Harmonic Distortion Plus

Noise (Note 3)

THD+N

RL = 4Ω (POUT = 600mW), f = 1kHz

0.08

FFM 86

BW = 22Hz

to 22kHz SSM 86

FFM

88.5

Signal-to-Noise Ratio SNR VOUT = 1VRMS

A-weighted

SSM

88.5

SYNC = GND, TA = +25oC

950 1100 1250

SYNC = unconnected, TA = +25oC

1200 1400 1600

Oscillator Frequency fOSC

SYNC = VDD, TA = +25oC

1200

±60

kHz

Minimum On-Time tMIN 200 ns

SYNC Frequency Lock Range fSYNC

1000 2000

kHz

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

_______________________________________________________________________________________ 3

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= 4Ω, L = 33µH.

For RL= 8Ω, L = 68µH.

Note 3: When driving speakers below 4Ωwith large signals, exercise care to avoid violating the absolute maximum rating for continuous

output current.

Note 4: Testing performed with 8Ωresistive load in series with 68µH inductive load connected across the BTL output. Mode transi-

tions are controlled by SHDN. KCP level is calculated as: 20 x log[(peak voltage during mode transition, no input signal)].

Units are expressed in dBV.

ELECTRICAL CHARACTERISTICS (continued)

(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), RLconnected between

OUT+ and OUT-, RL= ∞, TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

SYNC_OUT Capacitance Drive

CSYNC_OUT

100 pF

Bridge-tied capacitance 200

Capacitive Drive CLSingle ended 400 pF

Into shutdown

-50

Click-and-Pop Level KCP

Peak reading, A-weighted,

32 samples per second

(Note 4)

Out of

shutdown -50 dBV

Efficiency ηPOUT = 600mW per channel,

fIN = 1kHz, RL = 8Ω85 %

GAIN1 = 0, GAIN2 = 0 10 16

GAIN1 = 1, GAIN2 = 0 30

GAIN1 = 0, GAIN2 = 1 45

Input Resistance RIN

GAIN1 = 1, GAIN2 = 1 60

kΩ

GAIN1 = 0, GAIN2 = 0 26

GAIN1 = 1, GAIN2 = 0 20

GAIN1 = 0, GAIN2 = 1

15.6

Gain AV

GAIN1 = 1, GAIN2 = 1 12

Channel-to-Channel Gain

Tracking 1%

Crosstalk L to R, R to L, f = 10kHz, RL = 8Ω,

POUT = 300mW 80 dB

DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)

Input-Voltage High VINH 2V

Input-Voltage Low VINL 0.8 V

Input Leakage Current

(SHDN, GAIN1, GAIN2) ±1µA

VSYNC = GND, normal operation -15 -7

Input Leakage Current (SYNC) VSYNC = VDD, normal operation 12 25 µA

DIGITAL OUTPUTS (SYNC_OUT)

Output-Voltage High VOH IOH = 3mA, VDD = 3.3V 2.4 V

Output-Voltage Low VOL IOL = 3mA 0.4 V

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

4_______________________________________________________________________________________

Typical Operating Characteristics

(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9773 toc01

FREQUENCY (Hz)

THD+N (%)

10k1k10010 100k

VDD = 5V

RL = 4Ω

OUTPUT POWER = 600mW

OUTPUT POWER = 300mW

OUTPUT POWER = 100mW

0.1

0.01

0.001

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9773 toc02

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

0.01

0.001

10 100k

VDD = 5V

RL = 8Ω

OUTPUT POWER = 250mW

OUTPUT POWER = 100mW

OUTPUT POWER = 500mW

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9773 toc03

FREQUENCY (Hz)

THD+N (%)

10k1k10010 100k

VDD = 3.3V

RL = 4Ω

OUTPUT POWER = 100mW

OUTPUT POWER = 600mW

OUTPUT POWER = 300mW

0.1

0.01

0.001

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9773 toc04

FREQUENCY (Hz)

THD+N (%)

10k1k10010 100k

VDD = 3.3V

RL = 8Ω

OUTPUT POWER = 100mW

OUTPUT POWER = 400mW

OUTPUT POWER = 250mW

0.1

0.01

0.001

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9773 toc05

FREQUENCY (Hz)

THD+N (%)

10k1k10010 100k

VDD = 5V

RL = 8Ω

POUT = 800mW

FFM

SSM

0.1

0.01

0.001

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9773 toc06

OUTPUT POWER (W)

THD+N (%)

2.52.01.51.00.5

0.1

0.01

100

0.001

VDD = 5V

RL = 4Ω

fIN = 20Hz fIN = 20kHz

fIN = 1kHz

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9773 toc07

OUTPUT POWER (W)

THD+N (%)

1.51.20.90.60.3

0.01

0.1

100

0.001

01.8

VDD = 5V

RL = 8Ω

fIN = 1kHz

fIN = 20Hz fIN = 20kHz

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9773 toc08

OUTPUT POWER (W)

THD+N (%)

1.00.80.60.40.2

0.1

0.01

1.0

100

0.001

VDD = 3.3V

RL = 4Ω

fIN = 20Hz

fIN = 1kHz fIN = 20kHz

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9773 toc09

OUTPUT POWER (W)

THD+N (%)

0.60.40.2

0.1

0.01

100

0.001

00.8

VDD = 3.3V

RL = 8Ω

fIN = 1kHz

fIN = 20Hz fIN = 20kHz

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

_______________________________________________________________________________________ 5

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9773 toc10

OUTPUT POWER (W)

THD+N (%)

1.61.20.80.4

0.01

0.1

100

0.001

02.0

VDD = 5V

RL = 8Ω

fIN = 1kHz

FFM

SSM

EFFICIENCY vs. OUTPUT POWER

MAX9773 toc11

OUTPUT POWER (W)

EFFICIENCY (%)

2.52.01.51.00.5

100

0 3.0

RL = 8Ω

RL = 4Ω

VDD = 5V

fIN = 1kHz

OUTPUT POWER PER CHANNEL

EFFICIENCY vs. OUTPUT POWER

MAX9773 toc12

OUTPUT POWER (W)

EFFICIENCY (%)

1.00.80.60.40.2

100

01.2

RL = 8Ω

RL = 4Ω

VDD = 3.3V

fIN = 1kHz

OUTPUT POWER PER CHANNEL

OUTPUT POWER vs. SUPPLY VOLTAGE

MAX9773 toc13

SUPPLY VOLTAGE (V)

OUTPUT POWER (W)

5.04.54.03.53.0

0.5

1.0

1.5

2.0

2.5

3.0

2.5 5.5

RL = 4Ω

fIN = 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. SUPPLY VOLTAGE

MAX9773 toc14

SUPPLY VOLTAGE (V)

OUTPUT POWER (W)

5.04.54.03.53.0

0.5

1.0

1.5

2.0

2.5 5.5

RL = 8Ω

fIN = 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. LOAD RESISTANCE

MAX9773 toc15

LOAD RESISTANCE (Ω)

OUTPUT POWER (W)

0.5

1.0

1.5

2.0

2.5

3.0

1100

VDD = 5V, f = 1kHz,

ZLOAD = 33µH

IN SERIES WITH RL

THD+N = 10%

THD+N = 1%

Typical Operating Characteristics (continued)

(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

6_______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).

CROSSTALK vs. FREQUENCY

MAX9773 toc19

FREQUENCY (Hz)

CROSSTALK (dB)

10k1k100

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-140

10 100k

RIGHT TO LEFT

LEFT TO RIGHT

POUT = 300mW

RL = 8Ω

CROSSTALK vs. INPUT AMPLITUDE

MAX9773 toc20

INPUT AMPLITUDE (dB)

CROSSTALK (dBV)

-14-34-54-74

-90

-100

-110

-80

-70

-60

-50

-40

-30

-20

-10

-120

-94 6

fIN = 1kHz

RL = 8Ω

ONE CHANNEL DRIVEN

OUTPUT FREQUENCY SPECTRUM

MAX9773 toc21

FREQUENCY (kHz)

OUTPUT MAGNITUDE (dBV)

15105

-120

-100

-80

-60

-40

-20

-140

020

FFM MODE

VOUT = -60dBV

f = 1kHz

RL = 8Ω

UNWEIGHTED

OUTPUT FREQUENCY SPECTRUM

MAX9773 toc22

FREQUENCY (kHz)

OUTPUT MAGNITUDE (dBV)

15105

-120

-100

-80

-60

-40

-20

-140

020

SSM MODE

VOUT = -60dB

f = 1kHz

RL = 8Ω

UNWEIGHTED

OUTPUT POWER vs. LOAD RESISTANCE

MAX9773 toc16

LOAD RESISTANCE (Ω)

OUTPUT POWER (W)

0.2

0.4

0.6

0.8

1.0

1.2

1100

VDD = 3.3V, f = 1kHz,

ZLOAD = 33µH

IN SERIES WITH RL

THD+N = 10%

THD+N = 1%

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

MAX9773 toc17

FREQUENCY (Hz)

PSRR (dB)

10k1k100

-90

-80

-70

-60

-50

-40

-30

-20

-10

-100

10 100k

VRIPPLE = 100mVP-P

RL = 8Ω

COMMON-MODE REJECTION RATIO

vs. FREQUENCY

MAX9773 toc18

FREQUENCY (Hz)

CMRR (dB)

10k1k100

100

10 100k

VRIPPLE = 100mVP-P

RL = 8Ω

VDD = 5V

VDD = 3.3V

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

_______________________________________________________________________________________ 7

TURN-ON/TURN-OFF RESPONSE

MAX9773 toc25

20ms/div

SHDN 2V/div

1V/div

MAX9773

DIFFERENTIAL

OUTPUT

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX9773 toc26

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

4.5 5.55.03.0 3.5 4.0

2.5 6.0

SSM

FFM

BOTH CHANNELS DRIVEN

SHUTDOWN CURRENT

vs. SUPPLY VOLTAGE

MAX9773 toc27

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT (µA)

4.5 5.55.03.0 3.5 4.0

0.08

0.06

0.10

0.12

0.14

0.16

2.5 6.0

Typical Operating Characteristics (continued)

(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).

WIDEBAND OUTPUT SPECTRUM

(FFM MODE)

MAX9773 toc23

FREQUENCY (MHz)

OUTPUT AMPLITUDE (dBV)

101

-90

-70

-50

-30

-10

-80

-60

-40

-20

-100

0.1 100

RL = 8Ω,

VDD = 5V

INPUTS

AC-GROUNDED

WIDEBAND OUTPUT SPECTRUM

(SSM MODE (SPEAKER MODE))

MAX9773 toc24

FREQUENCY (MHz)

OUTPUT AMPLITUDE (dBV)

101

-90

-70

-50

-30

-10

-80

-60

-40

-20

-100

0.1 100

RL = 8Ω,

VDD = 5V

INPUTS

AC-GROUNDED

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

8_______________________________________________________________________________________

Pin Description

TQFN UCSP NAME FUNCTION

1A2SHDN Active-Low Shutdown. Connect to VDD for normal operation.

2B3SYNC

Frequency Select and External Clock Input:

SYNC = GND: Fixed-frequency mode with fS = 1100kHz.

SYNC = Unconnected: Fixed-frequency mode with fS = 1400kHz.

SYNC = VDD: Spread-spectrum mode with fS = 1200kHz ±60kHz.

SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency.

3, 8, 11, 16

—N.C. No Connection. Not internally connected.

4A3OUTL+ Left-Channel Amplifier Output Positive Phase

5, 14 A4, D4 PVDD H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1µF capacitor to PGND.

6, 13 B4, C4 PGND Power Ground

7A5OUTL- Left-Channel Amplifier Output Negative Phase

9, 22 B1, B5 GND Analog Ground

10 C5

SYNC_OUT

Clock Signal Output

12 D5 OUTR- Right-Channel Amplifier Output Negative Phase

15 D3 OUTR+ Right-Channel Amplifier Output Positive Phase

17 C3 GAIN1 Gain-Select Input 1

18 D2 GAIN2 Gain-Select Input 2

19 D1 INR- Right-Channel Inverting Input

20 C2 INR+ Right-Channel Noninverting Input

21 C1 VDD Analog Power Supply. Connect to PVDD. Bypass with a 10µF capacitor to GND.

23 B2 INL+ Left-Channel Noninverting Input

24 A1 INL- Left-Channel Inverting Input

EP — EP Exposed Pad. Connect the exposed thermal pad to the GND plane (see the Supply

Bypassing, Layout, and Grounding section).

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

_______________________________________________________________________________________ 9

Functional Diagram

VBIAS

CLASS D

MODULATOR

AND H-BRIDGE

CLASS D

MODULATOR

AND H-BRIDGE

BIAS

GENERATOR

OSCILLATOR

AND

SAWTOOTH

GAIN

CONTROL

OUTL+

VBIAS

MAX9773

GND PGND

OUTR+

OUTL-

OUTR-

SYNC_OUT

PVDD

SYNC

INL+

INL-

INR+

INR-

GAIN1

GAIN2

*BULK CAPACITANCE.

SHDN

RIN

470nF

VDD

0.1µF10µF*

MAX9773

Detailed Description

The MAX9773 ultra-low EMI, filterless, stereo Class D

audio power amplifier incorporates several improve-

ments to switch-mode amplifier topology. The MAX9773

features output-driver AEL circuitry to reduce EMI. Zero

dead time technology maintains state-of-the art efficien-

cy and THD+N performance by allowing the output FETs

to switch simultaneously without cross conduction. The

MAX9773 offers Class AB performance with Class D effi-

ciency, while occupying minimal board space. A unique,

filterless modulation scheme, synchronizable switching

frequency, and spread-spectrum switching mode create

a compact, flexible, low-noise, efficient audio power

amplifier. The differential input architecture reduces

common-mode noise pickup, and can be used without

input-coupling capacitors. The inputs can also be config-

ured to accept a single-ended input signal.

Comparators monitor the MAX9773 inputs and compare

the complementary input voltages to the sawtooth wave-

form. The comparators trip when the input magnitude of

the sawtooth exceeds their corresponding input voltage.

Both comparators reset at a fixed time after the rising

edge of the second comparator trip point, generating a

minimum-width pulse (tON(MIN)) at the output of the sec-

ond comparator (Figure 1). As the input voltage increases

or decreases, the duration of the pulse at one output

increases while the other output pulse duration remains

the same. This causes the net voltage across the speaker

(VOUT+ - VOUT-) to change. The minimum-width pulse

helps the device to achieve high levels of linearity.

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

10 ______________________________________________________________________________________

OUT+

OUT-

VIN-

VIN+

VOUT+ - VOUT-

tON(MIN)

tSW

Figure 1. MAX9773 Outputs with an Input Signal Applied

Operating Modes

Fixed-Frequency (FFM) Mode

The MAX9773 features two fixed-frequency modes.

Connect SYNC to GND to select a 1.1MHz switching fre-

quency. Leave SYNC unconnected to select a 1.4MHz

switching frequency. The frequency spectrum of the

MAX9773 consists of the fundamental switching frequen-

cy and its associated harmonics (see the Wideband FFT

graph in the Typical Operating Characteristics). Program

the switching frequency so the harmonics do not fall

within a sensitive frequency band (Table 1). Audio repro-

duction is not affected by changing the switching fre-

quency.

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

______________________________________________________________________________________ 11

VOUT_+ - VOUT_-

tSW tSW tSW tSW

VIN_-

VIN_+

OUT_+

OUT_-

tON(MIN)

Figure 2. MAX9773 Outputs with an Input Signal Applied (SSM Mode)

Table 1. Operating Modes

SYNC MODE

GND FFM with fOSC = 1100kHz

Unconnected FFM with fOSC = 1400kHz

VDD SSM with fOSC = 1200kHz ±60kHz

Clocked FFM with fOSC = external clock frequency

MAX9773

Spread-Spectrum (SSM) Mode

The MAX9773 features a unique, patented spread-

spectrum mode that flattens the wideband spectral

components, improving EMI emissions that may be

radiated by the speaker and cables. This mode is

enabled by connecting SYNC to VDD (Table 1). In SSM

mode, the switching frequency varies randomly by

±60kHz around the center frequency (1.2MHz). The

modulation scheme remains the same, but the period

of the sawtooth waveform changes from cycle to cycle

(Figure 2). Instead of a large amount of spectral energy

present at multiples of the switching frequency, 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

(Figure 3). A proprietary amplifier topology ensures this

does not corrupt the noise floor in the audio bandwidth.

Synchronous Switching Mode

SYNC

The SYNC input allows the MAX9773 to be synchronized

to a user-defined clock, or another Maxim Class D ampli-

fier, creating a fully synchronous system, minimizing

clock intermodulation, and allocating spectral compo-

nents of the switching harmonics to insensitive frequency

bands. Applying a TTL clock signal between 1000kHz

and 2000kHz to SYNC synchronizes the MAX9773. The

period of the SYNC clock can be randomized, allowing

the MAX9773 to be synchronized to another Maxim Class

D amplifier operating in SSM mode.

SYNC_OUT

SYNC_OUT allows several MAX9773s as well as other

Class D amplifiers (such as the MAX9700) to be cas-

caded. The synchronized output minimizes interfer-

ence due to clock intermodulation caused by the

switching spread between single devices. Using

SYNC_OUT, the modulation scheme remains the same

and audio reproduction is not affected by changing the

switching frequency.

Filterless Modulation/Common-Mode Idle

The MAX9773 uses Maxim’s unique, patented modulation

scheme that eliminates the LC filter required by traditional

Class D amplifiers, improving efficiency, reducing com-

ponent count, conserving board space and system cost.

Conventional Class D amplifiers output a 50% duty cycle,

180°out-of-phase square wave when no signal is pre-

sent. With no filter, the square wave appears across the

load as a DC voltage, resulting in finite load current,

which increases power consumption especially when

idling. When no signal is present at the input of the

MAX9773, the amplifiers output an in-phase square wave

as shown in Figure 4. Because the MAX9773 drives the

speaker differentially, the two outputs cancel each other,

resulting in no net idle mode voltage across the speaker,

minimizing power consumption.

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

12 ______________________________________________________________________________________

FREQUENCY (MHz)

AMPLITUDE (dBµV/m)

280260240200 22080 100 120 140 160 18060

30 300

Figure 3. EMI Spectrum of MAX9773 with 6in of Twisted-Pair Speaker Cable with TDK Ferrite Beads MPZ1608S300A

Efficiency

Efficiency of a Class D amplifier is due to the switching

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 output

stage is mostly due to the I*R 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 MAX9773 still exhibits >80% efficiencies

under the same conditions (Figure 5).

Shutdown

The MAX9773 has a shutdown mode that reduces power

consumption and extends battery life. Driving SHDN low

places the MAX9773 in a low-power (0.1µA) shutdown

mode. Connect SHDN to VDD for normal operation.

Click-and-Pop Suppression

The MAX9773 features comprehensive click-and-pop

suppression that eliminates audible transients on startup

and shutdown. While in shutdown, the H-bridge is in a

high-impedance state. During startup, or power-up, the

input amplifiers are muted and an internal loop sets the

modulator bias voltages to the correct levels, preventing

clicks and pops when the H-bridge is subsequently

enabled. For 80ms following startup, a soft-start function

gradually unmutes the input amplifiers.

Applications Information

Filterless Operation

Traditional Class D amplifiers require an output filter to

recover the audio signal from the amplifier’s PWM output.

The filters add cost, increase the solution size of the

amplifier, and can decrease efficiency. The traditional

PWM scheme uses large differential output swings (2 x

VDD(P-P)) and causes large ripple currents. Any parasitic

resistance in the filter components results in a loss of

power, lowering the efficiency.

The MAX9773 does not require an output filter. The

device relies on the inherent inductance of the speaker

coil and the natural filtering of both the speaker 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 MAX9773 output 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 speaker not

designed to handle the additional power can be dam-

aged. For optimum results, use a speaker with a series

inductance >10µH. Typical 8Ωspeakers, for portable

audio applications, exhibit series inductances in the

range of 20µH to 100µH.

Output Offset

Unlike a Class AB amplifier, the output offset voltage of a

Class D amplifier does not noticeably increase quiescent

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 x η), which is on the

order of a few µA.

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

______________________________________________________________________________________ 13

VIN_ = 0V

OUT_-

OUT_+

VOUT_+ - VOUT_- = 0V

Figure 4. MAX9773 Outputs with No Input Signal

EFFICIENCY vs. OUTPUT POWER

MAX9773 fig05

OUTPUT POWER (W)

EFFICIENCY (%)

0.60.50.3 0.40.20.1

100

00.7

MAX9773

CLASS AB VDD = 3.3V

f = 1kHz

RL - 8Ω

Figure 5. MAX9773 Efficiency vs. Class AB Efficiency

MAX9773

Selectable Gain

The MAX9773 features four selectable gain settings,

minimizing external component count. Gains of 12dB,

15.6dB, 20dB, and 26dB are set through gain-select

inputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can be

hardwired or digitally controlled. Table 2 shows the

suggested gain settings to attain a maximum output

power from a given peak input voltage and given load

at VDD = 3.3V and THD+N = 10%.

Custom Gain Settings

The MAX9773 can be set up with any gain setting by

adding three external resistors per amplifier. Figure 6

shows the required circuit for setting up custom gain.

Table 3 displays a list of the components to use for sev-

eral gain settings.

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

14 ______________________________________________________________________________________

GAIN1

GAIN2

GAIN

(dB)

INPUT

(VRMS)

(Ω)

POUT

(mW)

00+26

0.097699

4950

10+20

0.194936

4950

+15.6 0.323513

4950

1112

0.489657

4950

00+26

0.114288

8650

10+20

0.228035

8650

+15.6 0.378444

8650

1112

0.572798

8650

Table 2. Gain Settings (VDD = 3.3V,

THD+N = 10%)

GAIN_ SETTINGS

GAIN1 GAIN2 GAIN (dB) R1 (Ω) R2 (Ω)C

IN (µF)

GAIN TOLERANCE (dB)

0026—— 1 —

0025 750 20k 1 +0.12/-0.07

0024 1k 10k 1.5 +0.14/-0.08

0023 1k 6k 2.2 +0.13/-0.08

0022 1.5k 6k 2.2 +0.16/-0.1

0021 2k 6k 2 +0.19/-0.12

1020—— 1 —

1019 1.2k 30k 1 +0.1/-0.06

1018 2k 20k 1 +0.15/-0.09

1017 2k 10k 1.2 +0.12/-0.07

1016 2.5k 10k 1.2 +0.15/-0.09

0115 1k 40k 0.86 +0.06/-0.03

0114 2.8k 40k 0.68 +0.15/-0.09

0113 2.8k 20k 0.86 +0.14/-0.08

1112—— 1 —

1111 1.8k 40k 0.86 +0.08/-0.05

1110 4k 40k 0.68 +0.15/-0.09

11 95k30k 0.68 +0.17/-0.1

11 85k20k 0.68 +0.15/-0.09

11 75.5k 16k 0.68 +0.15/-0.09

11 67k16k 0.68 +0.17/-0.1

11 58k14k 0.68 +0.17/-0.1

11 48k12k 0.68 +0.16/-0.1

11 310k 12k 0.68 +0.17/-0.1

11 211k 10k 0.68 +0.16/-0.1

11 112k 10k 0.58 +0.16/-0.1

11 014k 10k 0.47 +0.17/-0.1

Table 3. Custom Gain Components

The internal input resistance, RIN, changes with each

gain setting. The R1 resistors attenuate the gain and

resistors R2 compensate for RIN’s tolerance, which can

be as high as 25%. CIN must be adjusted to compen-

sate for the total change in input impedance or the low-

frequency roll-off point shifts.

Input Amplifier

Differential Input

The MAX9773 features a differential input structure,

making it compatible with many CODECs and offers

improved noise immunity over a single-ended input

amplifier. In devices such as cellular phones, high-fre-

quency signals from the RF transmitter can be picked

up by the amplifier’s input traces. The signals appear at

the amplifier’s inputs as common-mode noise. A differ-

ential input amplifier amplifies the difference of the two

inputs, any signal common to both inputs is canceled.

Single-Ended Input

The MAX9773 can be configured as a single-ended

input amplifier by capacitively coupling either input to

GND, and driving the other input (Figure 7).

Component Selection

Input Filter

An input capacitor, CIN, in conjunction with the

MAX9773 input impedance (RIN) forms a highpass filter

that removes the DC bias from an incoming signal. The

AC-coupling capacitor allows the amplifier to automati-

cally 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. Use capacitors whose dielectrics 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.

Other considerations when designing the input filter

include the constraints of the overall system and the

actual frequency band of interest. Although high-fidelity

audio calls for a flat-gain response between 20Hz and

20kHz, portable voice-reproduction devices such as

cellular phones and two-way radios need only concen-

trate on the frequency range of the spoken human voice

(typically 300Hz to 3.5kHz). In addition, speakers used

in portable devices typically have a poor response

below 300Hz. Taking these two factors into considera-

tion, the input filter may not need to be designed for a

20Hz to 20kHz response, saving both board space and

cost due to the use of smaller capacitors.

fRC

dB IN IN

−=

2π

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

______________________________________________________________________________________ 15

MAX9773

0.1µF10µF

2.5V TO 5.5V

0.47µF

SINGLE-ENDED

LEFT AUDIO INPUT

SINGLE-ENDED

RIGHT AUDIO INPUT

OUTL+

OUTL-

OUTR+

OUTR-

GAIN1

GND

PGND

SYNC

INL+

INR+

INL-

INR-

GAIN2

SHDN

VDD

PVDD

FFM MODE WITH fOSC = 1100kHz, GAIN = 15.6dB.

Figure 7. Single-Ended Input

MAX9773

INL+

INL-

CIN

CIN R1

RIN

INR+

INR-

CIN

CIN R1

RIN

Figure 6. Custom Gain Setting

MAX9773

Output Filter

The MAX9773 does not require an output filter. The

device passes FCC emissions standards with 6in of

unshielded speaker cables. However, output filtering

can be used if a design is failing radiated emissions due

to board layout or cable length, or if the circuit is near

EMI-sensitive devices. Use a ferrite bead filter when

radiated frequencies above 10MHz are of concern. Use

an LC filter or a common-mode choke when radiated

emissions below 10MHz are of concern, or when long

leads (>6in) connect the amplifier to the speaker.

2.1 Channel Configuration

The typical 2.1 channel application circuit (Figure 8)

shows the MAX9773 configured as a mid/high-frequency

amplifier and the MAX9705 configured as a mono bass

amplifier. Input capacitors (CIN) set the highpass cutoff

frequency according to the following equation:

where RIN is the typical input resistance of the

MAX9773. The 10µF capacitors on the output of the

MAX9773 ensure a two-pole highpass filter.

fRC

IN IN

=××

2π

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

16 ______________________________________________________________________________________

MAX9773

MAX9705

MAX4238

INR+

INL+

INL-

INR-

SYNC

OUTL+

OUTL-

OUTR+

OUTR-

8Ω

SYNC_OUT

10µF

CIN

2200pF

1µF

NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V.

FFM MODE WITH fOSC = 1100kHz.

OUT+

OUT-

SYNC

IN+

IN-

1.25V

10kΩ

1nF

20kΩ

39kΩ

0.01µF

VDD

CIN

2200pF

CIN

2200pF

CIN

2200pF

4Ω

Figure 8. 2.1 Channel Application Circuit

Low frequencies are summed through a two-pole low-

pass filter and sent to the MAX9705 mono speaker

amplifier. The passband gain of the lowpass filter is

unity for in-phase stereo signals:

where R1 = R2 and R3 = R1//R2. The cutoff frequency

of the lowpass filter is set by the following equation:

Supply Bypassing, Layout, and Grounding

Proper layout and grounding are essential for optimum

performance. Use large traces for the power-supply

inputs and amplifier outputs to minimize losses due to

parasitic trace resistance. Large traces also aid in moving

heat away from the package. Proper grounding improves

audio performance, minimizes crosstalk between chan-

nels, and prevents any switching noise from coupling into

the audio signal. Connect PGND and GND together at a

single point on the PC board. Route all traces that carry

switching transients away from GND and the traces/com-

ponents in the audio signal path.

Bypass VDD with a 0.1µF capacitor to GND and PVDD

with a 10µF capacitor to PGND. Place the bypass

capacitors as close to the MAX9773 as possible. Use

large, low-resistance output traces. Current drawn from

the outputs increases as load impedance decreases.

High-output trace resistance decreases the power deliv-

ered to the load. Large output, supply, and GND traces

allow more heat to move from the MAX9773 to the air,

decreasing the thermal impedance of the circuit.

The MAX9773 thin QFN-EP package features an

exposed thermal pad on its underside. This pad lowers

the package’s thermal impedance by providing a direct

heat conduction path from the die to the PC board.

Connect the exposed thermal pad to the GND plane.

UCSP Applications Information

For the latest application details on UCSP construction,

dimensions, tape carrier information, printed circuit board

techniques, bump-pad layout, and recommended reflow

temperature profile, as well as the latest information on

reliability testing results, refer to Application Note:

UCSP—A Wafer-Level Chip-Scale Package available on

Maxim’s website at www.maxim-ic.com/ucsp.

fCC R R

LP =× ×××

12 34π

VLP

=−×23

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

______________________________________________________________________________________ 17

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

18 ______________________________________________________________________________________

MAX9773

GAIN1

GAIN2

SYNC SYNC_OUT

INR+

INR-

GND

SHDN PGND

OUTR+

OUTR-

0.47µF

1µF

OUTL+

OUTL-

PVDD

INL+

INL-

0.47µF

1µF

VDD

1.8V TO 3.6V 4.2V BATTERY

MAX9850

INL OUTR

AGND

DGND

10kΩ

DVDD

10kΩ

PVSS SVSS

OUTL

REF

RECEIVER

INR

0.47µF

GPIO

HPL

HPR

AVDD

PVDD

DVDD

HPS

C1P

2.2µF

C1N

PGND

MCLK

SDIN

APPLICATIONS

PROCESSOR

1µF1µF

BCLK

LRCLK

SDA

SCL

System Diagram

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

______________________________________________________________________________________ 19

Chip Information

PROCESS: BiCMOS

GND INL+ SYNC PGND GND

VDD INR+ GAIN1 PGND SYNC

_OUT

INR- GAIN2 OUTR+ PVDD OUTR-

INL- SHDN OUTL+ PVDD OUTL-A

12345

MAX9773

UCSP

TOP VIEW

(BUMPS ON BOTTOM)

MAX9773

18 17 16 15 14

TQFN

TOP VIEW

1 2 3 4 5 6

24 +

INL+

VDD

INR+

INR-

INL-

GND

N.C.

SYNC_OUT

N.C.

OUTR-

OUTL-

GND

SHDN

SYNC

N.C.

OUTL+

PVDD

PGND

GAIN2

GAIN1

N.C.

OUTR+

PVDD

PGND

Pin Configurations

Gain Selection

GAIN SELECTION GAIN (dB)

GAIN1 = 0, GAIN2 = 0 26

GAIN1 = 1, GAIN2 = 0 20

GAIN1 = 0, GAIN2 = 1 15.6

GAIN1 = 1, GAIN2 = 1 12

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

20 ______________________________________________________________________________________

24L QFN THIN.EPS

PACKAGE OUTLINE,

21-0139

12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm

PACKAGE OUTLINE,

21-0139 2

12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

MAX9773 Package Code: T2444-4

MAX9773

1.8W, Filterless, Ultra-Low EMI,

Stereo Class D Audio Power Amplifier

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21

Heaney

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

5x4 UCSP.EPS

21-0095

PACKAGE OUTLINE, 5x4 UCSP

MAX9773 Package Code: B20-1