MAXIM MAX9701 Technical data

General Description

The MAX9701 stereo Class D audio power amplifier pro­vides Class AB amplifier audio performance with the
benefits of Class D efficiency, eliminating the need for a
heatsink while extending battery life. The MAX9701
delivers up to 1.3W per channel into an 8Ω load while
offering 87% efficiency. Maxim’s next-generation, low­EMI modulation scheme allows the amplifier to operate
without an external LC filter while still meeting FCC EMI
emission levels.

The MAX9701 offers two modulation schemes: a fixed-fre­quency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions. The
MAX9701 oscillator can be synchronized to an external
clock through the SYNC input, allowing synchronization 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 MAX9701 fea­tures a fully differential architecture, a full bridge-tied load
(BTL) output, and comprehensive click-and-pop suppres­sion. 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 and
thermal-overload protection prevent the device from
being damaged during a fault condition. The MAX9701 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 MAX9701 is specified over the extended

-40°C to +85°C temperature range.

Applications

Cellular 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, V

DD

= 5V, THD+N = 1%)

♦ No LC Output Filter Required

♦ 87% Efficiency (R

L

= 8Ω, P

OUT

= 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-Saving

Packages

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

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

________________________________________________________________ Maxim Integrated Products 1

MAX9701

GAIN2

GAIN1

V

DD

GAIN

RIGHT

MODULATOR

AND H-BRIDGE

SYNC

OSCILLATOR

LEFT

MODULATOR

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 RANGE

PIN­PACKAGE

PKG

CODE

MAX9701EBP-T

B20-1

MAX9701ETG+

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.

-40°C to +85°C

-40°C to +85°C

20 UCSP-20

24 TQFN-EP*

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= PVDD= SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RLconnected between

OUT+ and OUT-, R

L

= ∞, TA= T

MIN

to T

MAX

, 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.

VDDto GND..............................................................................6V

V

DD

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

PV

DD

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

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

All Other Pins to GND.................................-0.3V to (V

DD

+ 0.3V)

Continuous Current In/Out of PV

DD

, PGND, OUT_.........±800mA

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

Duration of OUT_ Short Circuit to GND or PV

DD

........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 V

DD

Inferred from PSRR test 2.5 5.5 V

VDD = 3.3V, per channel 4.5 8

Quiescent Current I

DD

VDD = 5V, per channel 6.3 10

mA

Shutdown Current I

SHDN

0.1 10 µA

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

Input Bias Voltage V

BIAS

V

Turn-On Time t

ON

40 ms

TA = +25oC

Output Offset Voltage V

OS

T

MIN

< TA < T

MAX

mV

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

f

RIPPLE

= 217Hz 72Power-Supply Rejection Ratio PSRR

100mV

P-P

ripple,

V

IN

= 0V

f

RIPPLE

= 20kHz 50

dB

Output Power (Note 3) P

OUT

THD+N = 1%,
T

A

= +25oC

V

DD

= 5V

mW

RL = 8Ω (P

OUT

= 300mW), f = 1kHz

Total Harmonic Distortion Plus
Noise (Note 3)

RL = 4Ω (P

OUT

= 400mW), f = 1kHz

%

FFM 86

BW = 22Hz
to 22kHz

SSM 86

FFM

Signal-to-Noise Ratio SNR V

OUT

= 1V

RMS

SSM

dB

SYNC = GND
SYNC = unconnected

Oscillator Frequency f

OSC

SYNC = V

DD

kHz

Minimum On-Time t

MIN

ns

SYNC Frequency Lock Range f

SYNC

kHz

THD+N

VDD = 3.3V

A-weighted

RL = 8Ω 460

= 4Ω 750

R

L

RL = 8Ω 1300

RL = 4Ω 2200

1.125 1.25 1.375

±10 ±30

0.08

0.15

88.5

88.5

950 1100 1250

1200 1400 1600

1000 1600

1200

±60

200

±55

MAX9701

1.3W, Filterless, 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 R

L

= 4Ω, L = 33µH.

For R

L

= 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. K

CP

level is calculated as: 20 x log[(peak voltage under normal operation at rated power

level) / (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), RLconnected between
OUT+ and OUT-, R

L

= ∞, TA= T

MIN

to T

MAX

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

PARAMETER

CONDITIONS

UNITS

SYNC_OUT Capacitance Drive

pF

Bridge-tied capacitance

Capacitive Drive C

L

Single ended

pF

Click-and-Pop Level K

CP

A-weighted, 32 samples
per second (Note 4)

Out of
shutdown

dB

VDD = 3.3V, P

OUT

= 500mW per channel,

f

IN

= 1kHz, RL = 8Ω

87

Efficiency η

V

DD

= 5V, P

OUT

= 1000mW per channel,

f

IN

= 1kHz, RL = 8Ω

%

GAIN1 = 0, GAIN2 = 0

15

GAIN1 = 1, GAIN2 = 0 25

GAIN1 = 0, GAIN2 = 1

Input Resistance R

IN

GAIN1 = 1, GAIN2 = 1 50

kΩ

GAIN1 = 0, GAIN2 = 0 18

GAIN1 = 1, GAIN2 = 0 12

GAIN1 = 0, GAIN2 = 1 6

Gain A

V

GAIN1 = 1, GAIN2 = 1 0

dB

Channel-to-Channel Gain
Tracking

1%

Crosstalk

L to R, R to L, f = 10kHz, R

L

= 8Ω,

P

OUT

= 300mW

70 dB

DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)

Input-Voltage High V

INH

2V

Input-Voltage Low V

INL

0.8 V

Input Leakage Current
(SHDN, GAIN1, GAIN2)

±1µA

VIN = GND, normal operation -15 -7

Input Leakage Current (SYNC)

V

IN

= VDD, normal operation 12 25

µA

DIGITAL OUTPUTS (SYNC_OUT)

Output-Voltage High V

OH

IOH = 3mA, VDD = 3.3V 2.4 V

Output-Voltage Low V

OL

IOL = 3mA

V

SYMBOL

C

SYNC_OUT

Peak reading, TH D + N = 1%

Into shutdown 66.16

MIN TYP MAX

100

200

400

66.26

87.4

10.5

37.4

0.08

19.5

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

4 _______________________________________________________________________________________

Typical Operating Characteristics

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

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9701 toc01

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

1

10

0.01
10 100k

VDD = 5V
R

L

= 4

Ω

OUTPUT POWER = 300mW

OUTPUT POWER = 100mW

OUTPUT POWER = 600mW

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9701 toc02

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

1

10

0.01
10 100k

VDD = 5V
R

L

= 8

Ω

OUTPUT POWER = 250mW

OUTPUT POWER = 100mW

OUTPUT POWER = 500mW

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9701 toc03

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

1

10

0.01
10 100k

VDD = 3.3V
R

L

= 4

Ω

OUTPUT POWER = 300mW

OUTPUT POWER = 100mW

OUTPUT POWER = 600mW

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9701 toc04

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

1

10

0.01
10 100k

VDD = 3.3V
R

L

= 8

Ω

OUTPUT POWER = 100mW

OUTPUT POWER = 400mW

OUTPUT POWER = 250mW

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

MAX9701 toc05

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.1

1

10

0.01
10 100k

VDD = 5V
R

L

= 8

Ω

P

OUT

= 800mW

FFM

SSM

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9701 toc06

OUTPUT POWER (W)

THD+N (%)

2.52.01.51.00.5

0.1

1

10

100

0.01

03.0

VDD = 5V
R

L

= 4Ω

fIN = 10kHz

fIN = 20kHz

fIN = 1kHz

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9701 toc07

OUTPUT POWER (W)

THD+N (%)

1.51.00.5

0.01

0.1

1

10

100

0.001

02.0

VDD = 5V
R

L

= 8Ω

fIN = 10kHz

fIN = 20kHz

fIN = 1kHz

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9701 toc08

OUTPUT POWER (W)

THD+N (%)

1.00.80.60.40.2

0.1

1

10

100

0.01
0 1.2

VDD = 3.3V
R

L

= 4Ω

fIN = 10kHz

fIN = 20kHz

fIN = 1kHz

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9701 toc09

OUTPUT POWER (mW)

THD+N (%)

600500400300200100

0.1

1

10

100

0.01
0700

VDD = 3.3V
R

L

= 8Ω

fIN = 10kHz

fIN = 20kHz

fIN = 1kHz

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

_______________________________________________________________________________________ 5

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. OUTPUT POWER

MAX9701 toc10

OUTPUT POWER (W)

THD+N (%)

1.61.20.80.4

0.01

0.1

1

10

100

0.001

02.0

VDD = 5V
R

L

= 8Ω

f

IN

= 1kHz

SSM

FFM

EFFICIENCY vs. OUTPUT POWER

MAX9701 toc11

OUTPUT POWER (W)

EFFICIENCY (%)

2.01.51.00.5

10

20

30

40

50

60

70

80

90

100

0

02.5

RL = 8Ω

RL = 4Ω

VDD = 5V
f

IN

= 1kHz

EFFICIENCY vs. OUTPUT POWER

MAX9701 toc12

OUTPUT POWER (W)

EFFICIENCY (%)

1.00.80.60.40.2

10

20

30

40

50

60

70

80

90

100

0

01.2

RL = 8Ω

RL = 4Ω

VDD = 3.3V
f

IN

= 1kHz

OUTPUT POWER vs. SUPPLY VOLTAGE

MAX9701 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

3.5

0

2.5 5.5

RL = 4Ω
A

V

= 12dB

f

IN

= 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. SUPPLY VOLTAGE

MAX9701 toc14

SUPPLY VOLTAGE (V)

OUTPUT POWER (W)

5.04.54.03.53.0

0.4

0.8

1.2

1.6

2.0

0

2.5 5.5

RL = 8Ω
A

V

= 12dB

f

IN

= 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. LOAD RESISTANCE

MAX9701 toc15

LOAD RESISTANCE (Ω)

OUTPUT POWER (W)

80604020

0.5

1.0

1.5

2.0

2.5

3.0

0

0100

VDD = 5V

f

IN

= 1kHz

THD+N = 10%

THD+N = 1%

OUTPUT POWER vs. LOAD RESISTANCE

MAX9701 toc16

LOAD RESISTANCE (Ω)

OUTPUT POWER (W)

80604020

0.4

0.8

1.2

1.6

2.0

0

0 100

fIN = 1kHz

THD+N = 10%

THD+N = 1%

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

MAX9701 toc17

FREQUENCY (Hz)

PSRR (dB)

10k1k100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-100
10 100k

V

RIPPLE

= 100mV

P-P

RL = 8Ω

COMMON-MODE REJECTION RATIO

vs. FREQUENCY

MAX9701 toc18

FREQUENCY (Hz)

CMRR (dB)

10k1k100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-100
10 100k

VCM = 100mV

P-P

RL = 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)).

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

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

CROSSTALK vs. FREQUENCY

MAX9701 toc19

FREQUENCY (Hz)

CROSSTALK (dB)

10k1k100

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-130
10 100k

RIGHT TO LEFT

LEFT TO RIGHT

P

OUT

= 300mW

R

L

= 8Ω

CROSSTALK vs. INPUT AMPLITUDE

MAX9701 toc20

INPUT AMPLITUDE (dB)

CROSSTALK (dB)

-14-34-54-74

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-130

-94 6

RL = 8Ω
f

IN

= 1kHz

RIGHT TO LEFT

LEFT TO RIGHT

OUTPUT FREQUENCY SPECTRUM

MAX9701 toc21

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dBV)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-140

0 20k

FFM MODE
V

OUT

= -60dBV
f = 1kHz
R

L

= 8Ω

UNWEIGHTED

OUTPUT FREQUENCY SPECTRUM

MAX9701 toc22

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dBV)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-140
020k

FFM MODE
V

OUT

= -60dBV
f = 1kHz
R

L

= 8Ω

A-WEIGHTED

OUTPUT FREQUENCY SPECTRUM

MAX9701 toc23

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dBV)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-140
0 20k

SSM MODE
V

OUT

= -60dBV
f = 1kHz
R

L

= 8Ω

UNWEIGHTED

OUTPUT FREQUENCY SPECTRUM

MAX9701 toc24

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dBV)

15k10k5k

-120

-100

-80

-60

-40

-20

0

-140
020k

SSM MODE
V

OUT

= -60dBV
f = 1kHz
R

L

= 8Ω

A-WEIGHTED

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

_______________________________________________________________________________________ 7

WIDEBAND OUTPUT SPECTRUM

(FFM MODE)

MAX9701 toc25

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dB)

100k10k

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-100
1k 1M

RBW = 10kHz
INPUT AC GROUNDED

WIDEBAND OUTPUT SPECTRUM

(SSM MODE)

MAX9701 toc26

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dB)

100k10k

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-100
1k 1M

RBW = 10kHz
INPUT AC GROUNDED

TURN-ON/TURN-OFF RESPONSE

MAX9701 toc27

MAX9701

OUTPUT

SHDN

0V

250mV/div

2V/div

10ms/div

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX9701 toc28

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

5.04.54.03.53.0

8

11

14

17

20

5

2.5 5.5

SSM

FFM

BOTH CHANNELS

SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE

MAX9701 toc29

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT (µA)

5.04.54.03.53.0

1

2

3

4

5

0

2.5 5.5

BOTH CHANNELS

Typical Operating Characteristics (continued)

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

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

8 _______________________________________________________________________________________

Pin Description

PIN

TQFN UCSP

NAME FUNCTION

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

2 B3 SYNC

Frequency Select and External Clock Input.
SYNC = GND: Fixed-frequency mode with f

S

= 1100kHz.

SYNC = Unconnected: Fixed-frequency mode with f

S

= 1400kHz.

SYNC = V

DD

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

SYNC = Clocked: Fixed-frequency mode with f

S

= 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 PV

DD

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

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 V

DD

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).

SYNC_OUT

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

_______________________________________________________________________________________ 9

Functional Diagram

V

BIAS

V

BIAS

CLASS D

MODULATOR

AND H-BRIDGE

CLASS D

MODULATOR

AND H-BRIDGE

BIAS

GENERATOR

OSCILLATOR

AND

SAWTOOTH

GAIN

CONTROL

OUTL+

V

BIAS

MAX9701

GND

PGND

OUTR+

OUTL-

OUTR-

SYNC_OUT

PV

DD

SYNC

INL+

INL-

INR+

INR-

GAIN1

GAIN2

SHDN

R

IN

R

IN

R

IN

R

IN

470nF

470nF

470nF

470nF

V

DD

V

DD

10µF 0.1µF

MAX9701

Detailed Description

The MAX9701 filterless, stereo Class D audio power
amplifier features several improvements to switch-mode
amplifier technology. The MAX9701 offers Class AB per­formance with Class D efficiency, 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 configured to accept
a single-ended input signal.

Comparators monitor the MAX9701 inputs and compare
the complementary input voltages to the sawtooth wave­form. 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 (t

ON(MIN)

) at the output of the sec­ond 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
(V

OUT+

- V

OUT-

) to change. The minimum-width pulse

helps the device to achieve high levels of linearity.

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

10 ______________________________________________________________________________________

OUT+

OUT-

V

IN-

V

IN+

V

OUT+

- V

OUT-

t

ON(MIN)

t

SW

Figure 1. MAX9701 Outputs with an Input Signal Applied

Operating Modes

Fixed-Frequency (FFM) Mode

The MAX9701 features two fixed-frequency modes.
Connect SYNC to GND to select a 1.1MHz switching fre­quency. Leave SYNC unconnected to select a 1.4MHz
switching frequency. The frequency spectrum of the
MAX9701 consists of the fundamental switching frequen­cy and its associated harmonics (see the Wideband
Output Spectrum (FFM Mode) graph in the Typical
Operating Characteristics). Program the switching fre­quency so the harmonics do not fall within a sensitive fre­quency band (Table 1). Audio reproduction is not
affected by changing the switching frequency.

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

______________________________________________________________________________________ 11

V

OUT_+

- V

OUT_-

t

SW

t

SW

t

SW

t

SW

V

IN_-

V

IN_+

OUT_+

OUT_-

t

ON(MIN)

Figure 2. MAX9701 Outputs with an Input Signal Applied (SSM Mode)

Table 1. Operating Modes

SYNC MODE

GND FFM with f

OSC

= 1100kHz

Unconnected FFM with f

OSC

= 1400kHz

V

DD

SSM with f

OSC

= 1200kHz ±60kHz

Clocked FFM with f

OSC

= external clock frequency

MAX9701

Spread-Spectrum (SSM) Mode

The MAX9701 features a unique, patented spread­spectrum mode that flattens the wideband spectral
components, improving EMI emissions that may be
radiated by the speaker and cables. This mode is
enabled by setting SYNC = V

DD

(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 MAX9701 to be synchronized
to a user-defined clock, or another Maxim Class D ampli­fier, creating a fully synchronous system, minimizing
clock intermodulation, and allocating spectral compo­nents of the switching harmonics to insensitive frequency
bands. Applying a TTL clock signal between 1000kHz
and 1600kHz to SYNC synchronizes the MAX9701. The
period of the SYNC clock can be randomized, allowing
the MAX9701 to be synchronized to another Maxim Class
D amplifier operating in SSM mode.

SYNC_OUT

SYNC_OUT allows several MAX9701s as well as other
Class D amplifiers (such as the MAX9700) to be cas­caded. The synchronized output minimizes interfer­ence 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 MAX9701 uses Maxim’s unique, patented modulation
scheme that eliminates the LC filter required by traditional
class D amplifiers, improving efficiency, reducing compo­nent 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 pre­sent. 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
MAX9701, the amplifiers will output an in-phase square
wave as shown in Figure 4. Because the MAX9701 drives
the speaker differentially, the two outputs cancel each
other, resulting in no net idle mode voltage across the
speaker, minimizing power consumption.

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 I2R loss of the MOSFET on­resistance, and quiescent-current overhead.

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

12 ______________________________________________________________________________________

V

IN_

= 0V

OUT_-

OUT_+

V

OUT_+

- V

OUT_-

= 0V

Figure 4. MAX9701 Outputs with No Input Signal

FREQUENCY (MHz)

AMPLITUDE (dBµV/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 TDK
Common-Mode Choke: TDK ACM4532-801-20-X

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 MAX9701 still exhibits >80% efficiencies
under the same conditions (Figure 5).

Shutdown

The MAX9701 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9701 in a low-power (0.1µA) shutdown
mode. Connect SHDN to V

DD

for normal operation.

Click-and-Pop Suppression

The MAX9701 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 40ms 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 V

DD(P-P)

) and causes large ripple currents.
Any parasitic resistance in the filter components results
in a loss of power, lowering the efficiency.

The MAX9701 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 MAX9701 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 dam­aged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8Ω speakers, 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 8Ω load results in 1mA extra
current consumption in a Class AB device. In the Class D
case, an 8mV offset into 8Ω equates 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/(V

DD

/ 100 x η), which is on the

order of a few µA.

Selectable Gain

The MAX9701 features four selectable gain settings,
minimizing external component count. Gains of 0dB,
3dB, 12dB, and 18dB are set through gain-select
inputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can be
hard-wired 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%.

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

______________________________________________________________________________________ 13

0

30

20

10

50

40

90

80

70

60

100

0 0.1 0.2 0.40.3 0.5

EFFICIENCY vs. OUTPUT POWER

OUTPUT POWER (W)

EFFICIENCY (%)

MAX9701

CLASS AB

VDD = 3.3V
f = 1kHz
R

L

- 8Ω

Figure 5. MAX9701 Efficiency vs. Class AB Efficiency

GAIN1

GAIN

(dB)

INPUT

R

L

(Ω)

P

OUT

(mW)

0 0 +18

4

1100

1 0 +12

4

1100

01+6

4

1100

110

4

1100

0 0 +18

8

725

1 0 +12

8

725

01+6

8

725

110

8

725

Table 2. Gain Settings

GAIN2

(V

RMS

0.305

0.615

1.213

2.105

0.345

0.686

1.360

2.705

)

MAX9701

Input Amplifier

Differential Input

The MAX9701 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-fre­quency 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 differ­ential input amplifier amplifies the difference of the two
inputs, any signal common to both inputs is canceled.

Single-Ended Input

The MAX9701 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND, and driving the other input (Figure 6).

DC-Coupled Inputs

The input amplifier can accept DC-coupled inputs that
are biased within the amplifier’s common-mode range
(see the Typical Operating Characteristics). DC cou­pling eliminates the input-coupling capacitors, reduc­ing component count to potentially two external
components (Figure 7). However, the highpass filtering
effect of the capacitors is lost, allowing low-frequency
signals to feed through to the load.

Component Selection

Input Filter

An input capacitor, CIN, in conjunction with the
MAX9701 input impedance (RIN) forms a highpass filter
that removes the DC bias from an incoming signal. The
AC-coupling capacitor allows the amplifier to automati­cally bias the signal to an optimum DC level. Assuming
zero-source impedance, the -3dB point of the highpass
filter is given by:

Choose CINso 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 concen­trate on the frequency range of the spoken human voice
(typically 300Hz to 3.5kHz). In addition, speakers used

f

RC

dB

IN IN

−=3

1

2π

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

14 ______________________________________________________________________________________

MAX9701

0.1µF10µF

2.5V TO 5.5V

0.47µF

0.47µF

0.47µF

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

V

DD

PV

DD

FFM MODE WITH f

OSC

= 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

V

DD

PV

DD

FFM MODE WITH f

OSC

= 1100kHz, GAIN = 6dB

CODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE.

CODEC

Figure 7. DC-Coupled Inputs

in portable devices typically have a poor response
below 300Hz. Taking these two factors into considera­tion, 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.

Output Filter

The MAX9701 does not require an output filter. The
device passes FCC emissions standards with 76mm 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 (>76mm) connect the amplifier to the speaker.

2.1 Channel Configuration

The typical 2.1 channel application circuit (Figure 8)
shows the MAX9701 configured as a mid-/high-frequency
amplifier and the MAX9700 configured as a mono bass
amplifier. Input capacitors (C

IN

) set the highpass cutoff

frequency according to the following equation:

where RINis the typical input resistance of the
MAX9701. The 10µF capacitors on the output of the
MAX9701 ensure a two-pole highpass filter.

f

RC

IN IN

=

××

1

2π

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

______________________________________________________________________________________ 15

MAX9701

MAX9700

MAX4238

INR+

INL+

INL-

INR-

SYNC

5V

OUTL+

OUTL-

OUTR+

OUTR-

8Ω

8Ω

SYNC_OUT

10µF

10µF

C

IN

2200pF

1µF

1µF

5V

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

OSC

= 1100kHz.

OUT+

OUT-

SYNC

IN+

IN-

1.25V

R3

10kΩ

C2

1nF

R1

20kΩ

R2

20kΩ

R4

39kΩ

C2

0.01µF

V

DD

C

IN

2200pF

C

IN

2200pF

C

IN

2200pF

4Ω

Figure 8. 2.1 Channel Application Circuit

MAX9701

Low frequencies are summed through a two-pole low­pass filter and sent to the MAX9700 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 chan­nels, 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/com­ponents in the audio signal path.

Bypass VDDwith 10µF to GND and PVDDwith 0.1µF to
PGND. Place the bypass capacitors as close to the
MAX9701 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 delivered to the load. Large output,
supply, and GND traces allow more heat to move from
the MAX9701 to the air, decreasing the thermal imped­ance of the circuit.

The MAX9701 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 printed
circuit 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.

f

CC R R

=×

×××

1

2

1

12 34π

− ×2

3

1

R

R

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

16 ______________________________________________________________________________________

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

______________________________________________________________________________________ 17

MAX4060

MAX9701

MAX9722B

CODEC

AUX_IN

BIAS

IN+

IN-

V

CC

OUTL-

OUTL+

OUTR+

OUTR-

INL

INR

C1P CIN

SV

SS

PV

SS

OUTR

OUTL

V

DD

0.1µF

0.1µF

0.1µF

2.2kΩ

2.2kΩ

V

DD

µCONTROLLER

INL+

SYNC

OUT

1µF

1µF

1µF

1µF

1µF

SHDN

SHDN

GND

470nF

470nF

470nF

470nF

GAIN1

GAIN2

INL-

INR-

INR+

0.1µF10µF

V

DD

V

DD

PV

DD

GND PGND

0.1µF

System Diagram

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

18 ______________________________________________________________________________________

Chip Information

TRANSISTOR COUNT: 5688

PROCESS: BiCMOS

GND INL+ SYNC PGND GND

V

DD

INR+ GAIN1 PGND

SYNC
_OUT

INR- GAIN2 OUTR+ PV

DD

OUTR-

INL- SHDN OUTL+ PV

DD

OUTL-A

B

C

D

12345

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+

V

DD

INR+

INR-

INL-

GND

N.C.

SYNC_OUT

N.C.

OUTR-

OUTL-

GND

SHDN

SYNC

N.C.

OUTL+

PV

DD

PGND

GAIN2

GAIN1

N.C.

OUTR+

PV

DD

PGND

Pin Configurations

MAX9701

1.3W, Filterless, Stereo Class D Audio
Power Amplifier

______________________________________________________________________________________ 19

24L QFN THIN.EPS

PACKAGE OUTLINE,

21-0139

2

1

F

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

PACKAGE OUTLINE,

21-0139

2

2

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

MAX9701

1.3W, Filterless, 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.

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

.)

MAX9701 Package Code: B20-1

Revision History

Pages changed at Rev 2: 1, 5, 20

5x4 UCSP.EPS