1.3W, Filterless, Stereo Class D Audio Power Amplifier · The MAX9701 stereo Class D audio power...

General DescriptionThe MAX9701 stereo Class D audio power amplifier pro-vides Class AB amplifier audio performance with thebenefits of Class D efficiency, eliminating the need for aheatsink while extending battery life. The MAX9701delivers up to 1.3W per channel into an 8Ω load whileoffering 87% efficiency. Maxim’s next-generation, low-EMI modulation scheme allows the amplifier to operatewithout an external LC filter while still meeting FCC EMIemission levels.

The MAX9701 offers two modulation schemes: a fixed-fre-quency (FFM) mode, and a spread-spectrum (SSM)mode that reduces EMI-radiated emissions. TheMAX9701 oscillator can be synchronized to an externalclock through the SYNC input, allowing synchronization ofmultiple Maxim Class D amplifiers. The sync output(SYNC_OUT) can be used for a master-slave applicationwhere more channels are required. The MAX9701 fea-tures a fully differential architecture, a full bridge-tied load(BTL) output, and comprehensive click-and-pop suppres-sion. The device features internally set gains of 0dB, 6dB,12dB, and 18dB selected through two gain-select inputs,further reducing external component count.

The MAX9701 features high 80dB PSRR, less than 0.1%THD+N, and SNR in excess of 88dB. Short-circuit andthermal-overload protection prevent the device frombeing damaged during a fault condition. The MAX9701 isavailable in 24-pin thin QFN-EP (4mm x 4mm x 0.8mm),and 20-bump UCSP™ (2mm x 2.5mm x 0.6mm) pack-ages. The MAX9701 is specified over the extended -40°C to +85°C temperature range.

ApplicationsCellular Phones

Notebooks

Handheld Gaming Consoles

Docking Stations

MP3 Players

Features♦ Patented Spread-Spectrum Modulation Lowers

Radiated Emissions

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

♦ 1.3W Stereo Output (8Ω, VDD = 5V, THD+N = 1%)

♦ No LC Output Filter Required

♦ 87% Efficiency (RL = 8Ω, POUT = 1000mW)

♦ Less Than 0.1% THD+N

♦ High 80dB PSRR

♦ Fully Differential Inputs

♦ Integrated Click-and-Pop Suppression

♦ Typical Low Quiescent Current (9mA)

♦ Typical Low-Power Shutdown Mode (0.1µA)

♦ Short-Circuit and Thermal-Overload Protection

♦ Available in Thermally Efficient, Space-SavingPackages

24-Pin Thin QFN-EP (4mm x 4mm x 0.8mm)20-Bump UCSP (2mm x 2.5mm x 0.6mm)

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1.3W, Filterless, Stereo Class D Audio Power Amplifier

________________________________________________________________ Maxim Integrated Products 1

MAX9701

GAIN2GAIN1

VDD

GAIN

RIGHTMODULATOR

AND H-BRIDGE

SYNC OSCILLATOR

LEFTMODULATOR

AND H-BRIDGE

INR+

INR-

INL+

INL-

SYNC_OUT

Block Diagram

Ordering Information

19-3457; Rev 2; 2/07

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 RANGEPIN-PACKAGE

PKGCODE

MAX9701EBP-T -40°C to +85°C 20 UCSP-20 B20-1

MAX9701ETG+ -40°C to +85°C 24 TQFN-EP* T2444-4

Pin Configurations appear at end of data sheet.

UCSP is a trademark of Maxim Integrated Products, Inc.

+Denotes lead-free package.*EP = Exposed paddle.

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2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected betweenOUT+ 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 functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.

VDD to GND..............................................................................6VVDD to PVDD ..........................................................-0.3V to +0.3VPVDD to PGND .........................................................................6VGND to PGND .......................................................-0.3V to +0.3VAll Other Pins to GND.................................-0.3V to (VDD + 0.3V)Continuous Current In/Out of PVDD, PGND, OUT_.........±800mAContinuous Input Current (all other pins)..........................±20mADuration of OUT_ Short Circuit to GND or PVDD........ContinuousDuration of Short Circuit Between OUT+ and OUT- ......Continuous

Continuous Power Dissipation (TA = +70°C)20-Bump UCSP (derate 10mW/°C above +70°C) ...........800mW24-Pin Thin QFN (derate 20.8mW/°C above +70°C) ..1666.7mW

Junction Temperature ......................................................+150°COperating Temperature Range ...........................-40°C to +85°CStorage Temperature Range .............................-65°C to +150°CBump Temperature (soldering) Reflow............................+235°CLead Temperature (soldering, 10s) .................................+300°C

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

GENERAL

Supply Voltage Range VDD Inferred from PSRR test 2.5 5.5 V

VDD = 3.3V, per channel 4.5 8Quiescent Current IDD

VDD = 5V, per channel 6.3 10mA

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 V

Turn-On Time tON 40 ms

TA = +25oC ±10 ±30Output Offset Voltage VOS

TMIN < TA < TMAX ±55mV

VDD = 2.5V to 5.5V, VIN = 0V 60 80

fRIPPLE = 217Hz 72Power-Supply Rejection Ratio PSRR 100mVP-P ripple,VIN = 0V fRIPPLE = 20kHz 50

dB

RL = 8Ω 460VDD = 3.3V

RL = 4Ω 750

RL = 8Ω 1300Output Power (Note 3) POUT

THD+N = 1%,TA = +25oC

VDD = 5VRL = 4Ω 2200

mW

RL = 8Ω (POUT = 300mW), f = 1kHz 0.08Total Harmonic Distortion PlusNoise (Note 3)

THD+NRL = 4Ω (POUT = 400mW), f = 1kHz 0.15

%

FFM 86BW = 22Hzto 22kHz SSM 86

FFM 88.5Signal-to-Noise Ratio SNR VOUT = 1VRMS

A-weightedSSM 88.5

dB

SYNC = GND 950 1100 1250SYNC = unconnected 1200 1400 1600

Oscillator Frequency fOSCSYNC = VDD

1200±60

kHz

Minimum On-Time tMIN 200 ns

SYNC Frequency Lock Range fSYNC 1000 1600 kHz

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_______________________________________________________________________________________ 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 4Ω with large signals, exercise care to avoid violating the absolute maximum rating for continuous

output current.Note 4: Testing performed with 8Ω resistive 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 under normal operation at rated powerlevel) / (peak voltage during mode transition, no input signal)]. Units are expressed in dB.

ELECTRICAL CHARACTERISTICS (continued)(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected betweenOUT+ 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 200Capacitive Drive CL

Single ended 400pF

Into shutdown 66.16Click-and-Pop Level KCP

Peak reading, TH D + N = 1%A-weighted, 32 samplesper second (Note 4) Out of

shutdown66.26

dB

VDD = 3.3V, POUT = 500mW per channel,fIN = 1kHz, RL = 8Ω

87

Efficiency ηVDD = 5V, POUT = 1000mW per channel,fIN = 1kHz, RL = 8Ω

87.4

%

GAIN1 = 0, GAIN2 = 0 10.5 15 19.5

GAIN1 = 1, GAIN2 = 0 25

GAIN1 = 0, GAIN2 = 1 37.4Input Resistance RIN

GAIN1 = 1, GAIN2 = 1 50

kΩ

GAIN1 = 0, GAIN2 = 0 18

GAIN1 = 1, GAIN2 = 0 12

GAIN1 = 0, GAIN2 = 1 6Gain AV

GAIN1 = 1, GAIN2 = 1 0

dB

Channel-to-Channel GainTracking

1 %

CrosstalkL to R, R to L, f = 10kHz, RL = 8Ω,POUT = 300mW

70 dB

DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)

Input-Voltage High VINH 2 V

Input-Voltage Low VINL 0.8 V

Input Leakage Current(SHDN, GAIN1, GAIN2)

±1 µA

VIN = GND, normal operation -15 -7Input Leakage Current (SYNC)

VIN = VDD, normal operation 12 25µA

DIGITAL OUTPUTS (SYNC_OUT)

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

Output-Voltage Low VOL IOL = 3mA 0.08 V

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4 _______________________________________________________________________________________

Typical Operating Characteristics(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).

TOTAL HARMONIC DISTORTIONPLUS NOISE vs. FREQUENCY

MAX

9701

toc0

1

FREQUENCY (Hz)

THD+

N (%

)

10k1k100

0.1

1

10

0.0110 100k

VDD = 5VRL = 4Ω

OUTPUT POWER = 300mWOUTPUT POWER = 100mW

OUTPUT POWER = 600mW


MAX

9701

toc0

2

FREQUENCY (Hz)

THD+

N (%

)

10k1k100

0.1

1

10

0.0110 100k

VDD = 5VRL = 8Ω




MAX

9701

toc0

3

FREQUENCY (Hz)

THD+

N (%

)

10k1k100

0.1

1

10

0.0110 100k

VDD = 3.3VRL = 4Ω




MAX

9701

toc0

4

FREQUENCY (Hz)

THD+

N (%

)

10k1k100

0.1

1

10

0.0110 100k

VDD = 3.3VRL = 8Ω





MAX

9701

toc0

5

FREQUENCY (Hz)

THD+

N (%

)

10k1k100

0.1

1

10

0.0110 100k

VDD = 5VRL = 8ΩPOUT = 800mW

FFM

SSM

TOTAL HARMONIC DISTORTIONPLUS NOISE vs. OUTPUT POWER

MAX

9701

toc0

6

OUTPUT POWER (W)

THD+

N (%

)

2.52.01.51.00.5

0.1

1

10

100

0.010 3.0

VDD = 5VRL = 4Ω

fIN = 10kHz

fIN = 20kHz

fIN = 1kHz


MAX

9701

toc0

7

OUTPUT POWER (W)

THD+

N (%

)

1.51.00.5

0.01

0.1

1

10

100

0.0010 2.0

VDD = 5VRL = 8Ω

fIN = 10kHz

fIN = 20kHz fIN = 1kHz


MAX

9701

toc0

8

OUTPUT POWER (W)

THD+

N (%

)

1.00.80.60.40.2

0.1

1

10

100

0.010 1.2

VDD = 3.3VRL = 4Ω

fIN = 10kHz

fIN = 20kHz

fIN = 1kHz


MAX

9701

toc0

9

OUTPUT POWER (mW)

THD+

N (%

)

600500400300200100

0.1

1

10

100

0.010 700

VDD = 3.3VRL = 8Ω

fIN = 10kHz

fIN = 20kHz

fIN = 1kHz

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MAX

9701

toc1

0

OUTPUT POWER (W)

THD+

N (%

)

1.61.20.80.4

0.01

0.1

1

10

100

0.0010 2.0

VDD = 5VRL = 8ΩfIN = 1kHz

SSM

FFM

EFFICIENCY vs. OUTPUT POWER

MAX

9701

toc1

1

OUTPUT POWER (W)

EFFI

CIEN

CY (%

)

2.01.51.00.5

10

20

30

40

50

60

70

80

90

100

00 2.5

RL = 8Ω

RL = 4Ω

VDD = 5VfIN = 1kHz


MAX

9701

toc1

2

OUTPUT POWER (W)

EFFI

CIEN

CY (%

)

1.00.80.60.40.2

10

20

30

40

50

60

70

80

90

100

00 1.2

RL = 8Ω

RL = 4Ω

VDD = 3.3VfIN = 1kHz

OUTPUT POWER vs. SUPPLY VOLTAGE

MAX

9701

toc1

3

SUPPLY VOLTAGE (V)

OUTP

UT P

OWER

(W)

5.04.54.03.53.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

02.5 5.5

RL = 4ΩAV = 12dBfIN = 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. SUPPLY VOLTAGEM

AX97

01 to

c14

SUPPLY VOLTAGE (V)

OUTP

UT P

OWER

(W)

5.04.54.03.53.0

0.4

0.8

1.2

1.6

2.0

02.5 5.5

RL = 8ΩAV = 12dBfIN = 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. LOAD RESISTANCE

MAX

9701

toc1

5

LOAD RESISTANCE (Ω)

OUTP

UT P

OWER

(W)

80604020

0.5

1.0

1.5

2.0

2.5

3.0

00 100

VDD = 5VfIN = 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. LOAD RESISTANCE

MAX

9701

toc1

6

LOAD RESISTANCE (Ω)

OUTP

UT P

OWER

(W)

80604020

0.4

0.8

1.2

1.6

2.0

00 100

fIN = 1kHz

THD+N = 10%

THD+N = 1%

POWER-SUPPLY REJECTION RATIOvs. FREQUENCY

MAX

9701

toc1

7

FREQUENCY (Hz)

PSRR

(dB)

10k1k100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-10010 100k

VRIPPLE = 100mVP-PRL = 8Ω

COMMON-MODE REJECTION RATIOvs. FREQUENCY

MAX

9701

toc1

8

FREQUENCY (Hz)

CMRR

(dB)

10k1k100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-10010 100k

VCM = 100mVP-PRL = 8Ω

VDD = 5V

VDD = 3.3V

Typical Operating Characteristics (continued)(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).

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6 _______________________________________________________________________________________


CROSSTALK vs. FREQUENCY

MAX

9701

toc1

9

FREQUENCY (Hz)

CROS

STAL

K (d

B)

10k1k100

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-13010 100k

RIGHT TO LEFT

LEFT TO RIGHT

POUT = 300mWRL = 8Ω

CROSSTALK vs. INPUT AMPLITUDE

MAX

9701

toc2

0

INPUT AMPLITUDE (dB)CR

OSST

ALK

(dB)

-14-34-54-74

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-130-94 6

RL = 8ΩfIN = 1kHz

RIGHT TO LEFT

LEFT TO RIGHT

OUTPUT FREQUENCY SPECTRUM

MAX

9701

toc2

1

FREQUENCY (Hz)

OUTP

UT M

AGNI

TUDE

(dBV

)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-1400 20k

FFM MODEVOUT = -60dBVf = 1kHzRL = 8ΩUNWEIGHTED


MAX

9701

toc2

2

FREQUENCY (Hz)

OUTP

UT M

AGNI

TUDE

(dBV

)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-1400 20k

FFM MODEVOUT = -60dBVf = 1kHzRL = 8ΩA-WEIGHTED


MAX

9701

toc2

3

FREQUENCY (Hz)

OUTP

UT M

AGNI

TUDE

(dBV

)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-1400 20k

SSM MODEVOUT = -60dBVf = 1kHzRL = 8ΩUNWEIGHTED


MAX

9701

toc2

4

FREQUENCY (Hz)

OUTP

UT M

AGNI

TUDE

(dBV

)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-1400 20k

SSM MODEVOUT = -60dBVf = 1kHzRL = 8ΩA-WEIGHTED

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_______________________________________________________________________________________ 7

WIDEBAND OUTPUT SPECTRUM(FFM MODE)

MAX

9701

toc2

5

FREQUENCY (Hz)

OUTP

UT M

AGNI

TUDE

(dB)

100k10k

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-1001k 1M

RBW = 10kHzINPUT AC GROUNDED

WIDEBAND OUTPUT SPECTRUM(SSM MODE)

MAX

9701

toc2

6

FREQUENCY (Hz)OU

TPUT

MAG

NITU

DE (d

B)100k10k

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-1001k 1M

RBW = 10kHzINPUT AC GROUNDED

TURN-ON/TURN-OFF RESPONSE

MAX

9701

toc2

7

MAX9701OUTPUT

SHDN

0V

250mV/div

2V/div

10ms/div

SUPPLY CURRENTvs. SUPPLY VOLTAGE

MAX

9701

toc2

8

SUPPLY VOLTAGE (V)

SUPP

LY C

URRE

NT (m

A)

5.04.54.03.53.0

8

11

14

17

20

52.5 5.5

SSM

FFM

BOTH CHANNELS

SHUTDOWN CURRENTvs. SUPPLY VOLTAGE

MAX

9701

toc2

9

SUPPLY VOLTAGE (V)

SHUT

DOW

N CU

RREN

T (µ

A)

5.04.54.03.53.0

1

2

3

4

5

02.5 5.5

BOTH CHANNELS


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8 _______________________________________________________________________________________

Pin Description

PIN

TQFN UCSPNAME FUNCTION

1 A2 SHDN Active-Low Shutdown. Connect to VDD for normal operation.

2 B3 SYNC

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.

4 A3 OUTL+ 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

7 A5 OUTL- 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 — EPExposed Pad. Connect the exposed thermal pad to the GND plane (see the SupplyBypassing, Layout, and Grounding section).

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Functional Diagram

VBIAS

VBIAS

CLASS DMODULATOR

AND H-BRIDGE

CLASS DMODULATOR

AND H-BRIDGE

BIASGENERATOR

OSCILLATORAND

SAWTOOTH

GAINCONTROL

OUTL+

VBIAS

MAX9701

GND PGND

OUTR+

OUTL-

OUTR-

SYNC_OUT

PVDD

SYNC

INL+

INL-

INR+

INR-

GAIN1

GAIN2

SHDN

RIN

RIN

RIN

RIN

470nF

470nF

470nF

470nF

VDD

VDD

10µF 0.1µF

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Detailed DescriptionThe MAX9701 filterless, stereo Class D audio poweramplifier features several improvements to switch-modeamplifier technology. The MAX9701 offers Class AB per-formance with Class D efficiency, while occupying mini-mal board space. A unique, filterless modulationscheme, synchronizable switching frequency, andspread-spectrum switching mode create a compact,flexible, low-noise, efficient audio power amplifier. Thedifferential input architecture reduces common-modenoise pickup, and can be used without input-couplingcapacitors. The inputs can also be configured to accepta single-ended input signal.

Comparators monitor the MAX9701 inputs and comparethe complementary input voltages to the sawtooth wave-form. The comparators trip when the input magnitude ofthe sawtooth exceeds their corresponding input voltage.Both comparators reset at a fixed time after the risingedge of the second comparator trip point, generating aminimum-width pulse (tON(MIN)) at the output of the sec-ond comparator (Figure 1). As the input voltage increasesor decreases, the duration of the pulse at one outputincreases while the other output pulse duration remainsthe same. This causes the net voltage across the speaker(VOUT+ - VOUT-) to change. The minimum-width pulsehelps the device to achieve high levels of linearity.


10 ______________________________________________________________________________________

OUT+

OUT-

VIN-

VIN+

VOUT+ - VOUT-

tON(MIN)

tSW

Figure 1. MAX9701 Outputs with an Input Signal Applied

Operating ModesFixed-Frequency (FFM) Mode

The MAX9701 features two fixed-frequency modes.Connect SYNC to GND to select a 1.1MHz switching fre-quency. Leave SYNC unconnected to select a 1.4MHzswitching frequency. The frequency spectrum of theMAX9701 consists of the fundamental switching frequen-cy and its associated harmonics (see the WidebandOutput Spectrum (FFM Mode) graph in the TypicalOperating Characteristics). Program the switching fre-quency so the harmonics do not fall within a sensitive fre-quency band (Table 1). Audio reproduction is notaffected by changing the switching frequency.

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______________________________________________________________________________________ 11

VOUT_+ - VOUT_-

tSW tSW tSW tSW

VIN_-

VIN_+

OUT_+

OUT_-

tON(MIN)

Figure 2. MAX9701 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

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Spread-Spectrum (SSM) ModeThe MAX9701 features a unique, patented spread-spectrum mode that flattens the wideband spectralcomponents, improving EMI emissions that may beradiated by the speaker and cables. This mode isenabled by setting SYNC = VDD (Table 1). In SSMmode, the switching frequency varies randomly by±60kHz around the center frequency (1.2MHz). Themodulation scheme remains the same, but the periodof the sawtooth waveform changes from cycle to cycle(Figure 2). Instead of a large amount of spectral energypresent at multiples of the switching frequency, theenergy is now spread over a bandwidth that increaseswith frequency. Above a few megahertz, the widebandspectrum looks like white noise for EMI purposes(Figure 3). A proprietary amplifier topology ensures thisdoes not corrupt the noise floor in the audio bandwidth.

Synchronous Switching ModeSYNC

The SYNC input allows the MAX9701 to be synchronizedto a user-defined clock, or another Maxim Class D ampli-fier, creating a fully synchronous system, minimizingclock intermodulation, and allocating spectral compo-nents of the switching harmonics to insensitive frequencybands. Applying a TTL clock signal between 1000kHzand 1600kHz to SYNC synchronizes the MAX9701. Theperiod of the SYNC clock can be randomized, allowingthe MAX9701 to be synchronized to another Maxim ClassD amplifier operating in SSM mode.

SYNC_OUTSYNC_OUT allows several MAX9701s as well as otherClass D amplifiers (such as the MAX9700) to be cas-caded. The synchronized output minimizes interfer-ence due to clock intermodulation caused by theswitching spread between single devices. UsingSYNC_OUT, the modulation scheme remains the sameand audio reproduction is not affected by changing theswitching frequency.

Filterless Modulation/Common-Mode IdleThe MAX9701 uses Maxim’s unique, patented modulationscheme that eliminates the LC filter required by traditionalclass D amplifiers, improving efficiency, reducing compo-nent 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 theload as a DC voltage, resulting in finite load current,which increases power consumption especially whenidling. When no signal is present at the input of theMAX9701, the amplifiers will output an in-phase squarewave as shown in Figure 4. Because the MAX9701 drivesthe speaker differentially, the two outputs cancel eachother, resulting in no net idle mode voltage across thespeaker, minimizing power consumption.

EfficiencyEfficiency of a Class D amplifier is due to the switchingoperation of the output stage transistors. In a Class Damplifier, the output transistors act as current-steeringswitches and consume negligible additional power.Any power loss associated with the Class D outputstage is mostly due to the I2R loss of the MOSFET on-resistance, and quiescent-current overhead.


12 ______________________________________________________________________________________

VIN_ = 0V

OUT_-

OUT_+

VOUT_+ - VOUT_- = 0V

Figure 4. MAX9701 Outputs with No Input Signal

FREQUENCY (MHz)

AMPL

ITUD

E (d

BµV/

m)

280260240200 22080 100 120 140 160 18060

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

0.0

30 300

Figure 3. MAX9701 with 76mm of Speaker Cable with TDKCommon-Mode Choke: TDK ACM4532-801-20-X

The theoretical best efficiency of a linear amplifier is78%, however that efficiency is only exhibited at peakoutput powers. Under normal operating levels (typicalmusic reproduction levels), efficiency falls below 30%,whereas the MAX9701 still exhibits >80% efficienciesunder the same conditions (Figure 5).

ShutdownThe MAX9701 has a shutdown mode that reduces powerconsumption and extends battery life. Driving SHDN lowplaces the MAX9701 in a low-power (0.1µA) shutdownmode. Connect SHDN to VDD for normal operation.

Click-and-Pop SuppressionThe MAX9701 features comprehensive click-and-popsuppression that eliminates audible transients on startupand shutdown. While in shutdown, the H-bridge is in ahigh-impedance state. During startup, or power-up, theinput amplifiers are muted and an internal loop sets themodulator bias voltages to the correct levels, preventingclicks and pops when the H-bridge is subsequentlyenabled. For 40ms following startup, a soft-start functiongradually unmutes the input amplifiers.

Applications InformationFilterless Operation

Traditional Class D amplifiers require an output filter torecover the audio signal from the amplifier’s PWM out-put. The filters add cost, increase the solution size ofthe amplifier, and can decrease efficiency. The tradi-tional PWM scheme uses large differential outputswings (2 x VDD(P-P)) and causes large ripple currents.Any parasitic resistance in the filter components resultsin a loss of power, lowering the efficiency.

The MAX9701 does not require an output filter. Thedevice relies on the inherent inductance of the speakercoil and the natural filtering of both the speaker and thehuman ear to recover the audio component of thesquare-wave output. Eliminating the output filter resultsin a smaller, less costly, more efficient solution.

Because the frequency of the MAX9701 output is wellbeyond the bandwidth of most speakers, voice coilmovement due to the square-wave frequency is verysmall. Although this movement is small, a speaker notdesigned to handle the additional power can be dam-aged. For optimum results, use a speaker with a seriesinductance >10µH. Typical 8Ω speakers, for portableaudio applications, exhibit series inductances in therange of 20µH to 100µH.

Output OffsetUnlike a Class AB amplifier, the output offset voltage of aClass D amplifier does not noticeably increase quiescentcurrent draw when a load is applied. This is due to thepower conversion of the Class D amplifier. For example,an 8mV DC offset across an 8Ω load results in 1mA extracurrent consumption in a Class AB device. In the Class Dcase, an 8mV offset into 8Ω equates to an additionalpower drain of 8µW. Due to the high efficiency of theClass D amplifier, this represents an additional quiescentcurrent draw of: 8µW/(VDD / 100 x η), which is on theorder of a few µA.

Selectable GainThe MAX9701 features four selectable gain settings,minimizing external component count. Gains of 0dB,3dB, 12dB, and 18dB are set through gain-selectinputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can behard-wired or digitally controlled. Table 2 shows thesuggested gain settings to attain a maximum outputpower from a given peak input voltage and given loadat VDD = 3.3V and THD+N = 10%.

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0

30

20

10

50

40

90

80

70

60

100

0 0.1 0.2 0.40.3 0.5


OUTPUT POWER (W)

EFFI

CIEN

CY (%

)

MAX9701

CLASS AB VDD = 3.3Vf = 1kHzRL - 8Ω

Figure 5. MAX9701 Efficiency vs. Class AB Efficiency

GAIN1 GAIN2GAIN(dB)

INPUT(VRMS)

RL(Ω)

POUT(mW)

0 0 +18 0.305 4 1100

1 0 +12 0.615 4 1100

0 1 +6 1.213 4 1100

1 1 0 2.105 4 1100

0 0 +18 0.345 8 725

1 0 +12 0.686 8 725

0 1 +6 1.360 8 725

1 1 0 2.705 8 725

Table 2. Gain Settings

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Input AmplifierDifferential Input

The MAX9701 features a differential input structure,making it compatible with many CODECs and offersimproved noise immunity over a single-ended inputamplifier. In devices such as cellular phones, high-fre-quency signals from the RF transmitter can be pickedup by the amplifier’s input traces. The signals appear atthe amplifier’s inputs as common-mode noise. A differ-ential input amplifier amplifies the difference of the twoinputs, any signal common to both inputs is canceled.

Single-Ended InputThe MAX9701 can be configured as a single-endedinput amplifier by capacitively coupling either input toGND, and driving the other input (Figure 6).

DC-Coupled InputsThe input amplifier can accept DC-coupled inputs thatare biased within the amplifier’s common-mode range(see the Typical Operating Characteristics). DC cou-pling eliminates the input-coupling capacitors, reduc-ing component count to potentially two externalcomponents (Figure 7). However, the highpass filteringeffect of the capacitors is lost, allowing low-frequencysignals to feed through to the load.

Component SelectionInput Filter

An input capacitor, CIN, in conjunction with theMAX9701 input impedance (RIN) forms a highpass filterthat removes the DC bias from an incoming signal. TheAC-coupling capacitor allows the amplifier to automati-cally bias the signal to an optimum DC level. Assumingzero-source impedance, the -3dB point of the highpassfilter is given by:

Choose CIN so f-3dB is well below the lowest frequency ofinterest. Use capacitors whose dielectrics have low-volt-age coefficients, such as tantalum or aluminum electrolyt-ic. Capacitors with high-voltage coefficients, such asceramics, may result in increased distortion at low fre-quencies.

Other considerations when designing the input filterinclude the constraints of the overall system and theactual frequency band of interest. Although high-fidelityaudio calls for a flat-gain response between 20Hz and20kHz, portable voice-reproduction devices such ascellular 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

fR CdB

IN IN− =3

12π


14 ______________________________________________________________________________________

MAX9701

0.1µF10µF

2.5V TO 5.5V

0.47µF

0.47µF

0.47µF

0.47µFSINGLE-ENDED

LEFT AUDIO INPUT

SINGLE-ENDEDRIGHT AUDIO INPUT

OUTL+

OUTL-

OUTR+

OUTR-

GAIN1

GND

PGND

SYNC

INL+

INR+

INL-

INR-

GAIN2

SHDN

VDD

PVDD

FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB.

Figure 6. Single-Ended Input

MAX9701

0.1µF10µF

2.5V TO 5.5V

OUTL+

OUTL-

OUTR+

OUTR-

GAIN1

GND

PGND

SYNC

INL+

INR+

INL-

INR-

GAIN2

SHDN

VDD

PVDD

FFM MODE WITH fOSC = 1100kHz, GAIN = 6dBCODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE.

CODEC

Figure 7. DC-Coupled Inputs

in portable devices typically have a poor responsebelow 300Hz. Taking these two factors into considera-tion, the input filter may not need to be designed for a20Hz to 20kHz response, saving both board space andcost due to the use of smaller capacitors.

Output FilterThe MAX9701 does not require an output filter. Thedevice passes FCC emissions standards with 76mm ofunshielded speaker cables. However, output filteringcan be used if a design is failing radiated emissions dueto board layout or cable length, or if the circuit is nearEMI-sensitive devices. Use a ferrite bead filter whenradiated frequencies above 10MHz are of concern. Usean LC filter or a common-mode choke when radiatedemissions below 10MHz are of concern, or when longleads (>76mm) connect the amplifier to the speaker.

2.1 Channel ConfigurationThe typical 2.1 channel application circuit (Figure 8)shows the MAX9701 configured as a mid-/high-frequencyamplifier and the MAX9700 configured as a mono bassamplifier. Input capacitors (CIN) set the highpass cutofffrequency according to the following equation:

where RIN is the typical input resistance of theMAX9701. The 10µF capacitors on the output of theMAX9701 ensure a two-pole highpass filter.

fR CIN IN

=× ×

12π

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______________________________________________________________________________________ 15

MAX9701

MAX9700

MAX4238

INR+

INL+

INL-

INR-

SYNC

5V

OUTL+

OUTL-

OUTR+

OUTR-

8Ω

8Ω

SYNC_OUT

10µF

10µFCIN

2200pF

1µF

1µF

5V

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

R310kΩ

C21nF

R120kΩ

R220kΩ

R439kΩ

C20.01µF

VDD

CIN2200pF

CIN2200pF

CIN2200pF

4Ω

Figure 8. 2.1 Channel Application Circuit

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where R1 = R2 and R3 = R1//R2. The cutoff frequencyof the lowpass filter is set by the following equation:

Supply Bypassing, Layout, and GroundingProper layout and grounding are essential for optimumperformance. Use large traces for the power-supplyinputs and amplifier outputs to minimize losses due toparasitic trace resistance. Large traces also aid in movingheat away from the package. Proper grounding improvesaudio performance, minimizes crosstalk between chan-nels, and prevents any switching noise from coupling intothe audio signal. Connect PGND and GND together at asingle point on the PC board. Route all traces that carryswitching transients away from GND and the traces/com-ponents in the audio signal path.

Bypass VDD with 10µF to GND and PVDD with 0.1µF toPGND. Place the bypass capacitors as close to theMAX9701 as possible. Use large, low-resistance outputtraces. Current drawn from the outputs increases as loadimpedance decreases. High-output trace resistancedecreases the power delivered to the load. Large output,supply, and GND traces allow more heat to move fromthe MAX9701 to the air, decreasing the thermal imped-ance of the circuit.

The MAX9701 thin QFN-EP package features anexposed thermal pad on its underside. This pad lowersthe package’s thermal impedance by providing adirect heat conduction path from the die to the printedcircuit board. Connect the exposed thermal pad to theGND plane.

UCSP Applications InformationFor the latest application details on UCSP construction,dimensions, tape carrier information, printed circuit boardtechniques, bump-pad layout, and recommended reflowtemperature profile as well as the latest information onreliability testing results, refer to Application Note:UCSP—A Wafer-Level Chip-Scale Package available onMaxim’s website at www.maxim-ic.com/ucsp.

fC C R R

= ×× × ×

12

11 2 3 4π

− ×2 3

1

RR


16 ______________________________________________________________________________________

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______________________________________________________________________________________ 17

MAX4060

MAX9701

MAX9722B

CODEC

AUX_IN

BIAS

IN+

IN-

VCC

OUTL-

OUTL+

OUTR+

OUTR-

INL

INR

C1P CINSVSS

PVSS

OUTR

OUTL

VDD

0.1µF

0.1µF

0.1µF

2.2kΩ

2.2kΩ

VDD

µCONTROLLER

INL+

SYNC

OUT

1µF

1µF

1µF

1µF

1µF

SHDN

SHDN

GND

470nF

470nF

470nF

470nF

GAIN1

GAIN2

INL-

INR-

INR+

0.1µF10µF

VDD

VDD PVDD

GND PGND

0.1µF

System Diagram

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18 ______________________________________________________________________________________

Chip InformationTRANSISTOR COUNT: 5688

PROCESS: BiCMOS

GND INL+ SYNC PGND GND

VDD INR+ GAIN1 PGND SYNC_OUT

INR- GAIN2 OUTR+ PVDD OUTR-

INL- SHDN OUTL+ PVDD OUTL-A

B

C

D

1 2 3 4 5

MAX9701

UCSP

TOP VIEW(BUMPS ON BOTTOM)

MAX9701

18 17 16 15 14

19

TQFN

TOP VIEW

13

1 2 3 4 5 6

24

23

22

21

20

12

7

8

9

10

11

INL+

VDD

INR+

INR-

INL-

GND

N.C.

SYNC_OUT

N.C.

OUTR-

OUTL-

GND

SHDN

SYNC N.C.

OUTL

+

PVDD

PGND

GAIN

2

GAIN

1

N.C.

OUTR

+

PVDD

PGND

Pin Configurations

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______________________________________________________________________________________ 19

24L

QFN

TH

IN.E

PS

PACKAGE OUTLINE,

21-0139 21

F

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

PACKAGE OUTLINE,

21-0139 22

F

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.)

MAX9701 Package Code: T2444-4

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Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses areimplied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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

UC

SP

.EP

SMAX9701 Package Code: B20-1

Revision HistoryPages changed at Rev 2: 1, 5, 20

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