Maxim MAX9770EUI+ (73-865-84)

Maxim MAX9770EUI+ (73-865-84)

19-3134; Rev 2; 4/08

EVALUATION KIT

AVAILABLE

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

General Description

The MAX9770 combines a mono, filterless, Class D speaker amplifier and stereo DirectDrive

® headphone amplifier in a single device. The MAX9770 operates from a single 2.5V to 5.5V supply and includes features that reduce external component count, system cost, board space, and offer improved audio reproduction.

The speaker amplifier makes use of Maxim’s patented

Class D architecture, providing Class AB performance with Class D efficiency, conserving board space, and extending battery life. The speaker amplifier delivers

1.2W into an 8

Ω load while offering efficiencies above

85%. A spread-spectrum modulation scheme reduces radiated emissions caused by the modulation frequency.

Furthermore, the MAX9770 oscillator can be synchronized to an external clock through the SYNC input, avoiding possible problem frequencies inside a system.

The speaker amplifier features THD+N as low as

0.025%, high 70dB PSRR, and SNR in excess of 90dB.

The headphone amplifiers feature Maxim’s patented

DirectDrive architecture that produces a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors. The headphone amplifiers deliver up to 80mW into a 16

Ω load, feature low

0.015% THD+N, high 85dB PSRR, and

±8kV ESD-protected outputs. A headphone sense input detects the presence of a headphone, and automatically configures the amplifiers for either speaker or headphone mode.

The MAX9770 includes internally set, logic-selectable gain, and a comprehensive input multiplexer/mixer, allowing multiple audio sources to be selected and for true mono reproduction of a stereo source in speaker mode.

Industry-leading click-and-pop suppression eliminates audible transients during power and shutdown cycles. A low-power shutdown mode decreases supply current consumption to 0.1µA, further extending battery life.

The MAX9770 is offered in space-saving, thermally efficient 28-pin TQFN (5mm x 5mm x 0.8mm) and 28-pin

TSSOP packages. The MAX9770 features thermal-overload and output short-circuit protection, and is specified over the extended -40°C to +85°C temperature range.

Applications

Cellular Phones

Compact Notebooks

PDAs

IN1L

IN2L

MONO

Features

1.2W Filterless Class D Amplifiers Pass FCC

Class B Radiated EMI Standards with 100mm of Cable

Patented Spread-Spectrum Mode Offers 5dB EMI

Improvement over Conventional Methods

80mW DirectDrive Headphone Amplifier

Eliminates Bulky DC-Blocking Capacitors

High 85dB PSRR at 217Hz

85% Efficiency

Low 0.015% THD+N

Industry-Leading Click-and-Pop Suppression

Integrated 3-Way Input Mixer/Multiplexer

(MAX9770)

Logic-Adjustable Gain

Short-Circuit and Thermal Protection

Available in Space-Saving, Thermally Efficient

Packages

Ordering Information

PART PIN-PACKAGE SELECTABLE INPUTS

MAX9770ETI+ 28 TQFN-EP*

2 stereo, 1 mono

MAX9770EUI 28 TSSOP

2 stereo, 1 mono

Note: All devices specified over the -40°C to +85°C operating temperature range.

* EP = Exposed pad.

+

Denotes a lead-free package.

Pin Configuration appears at end of data sheet.

IN1R

IN2R

Simplified Block Diagram

V

DD

DirectDrive

STEREO

HEADPHONE

GAIN SEL

INPUT SEL

MUTE

SHDN

HPS

CLASS

D

SPKR

(MONO)

MAX9770

†U.S. Patent #7,061,327

________________________________________________________________ Maxim Integrated Products 1

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

ABSOLUTE MAXIMUM RATINGS

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

V

DD to PV

DD to CPV

DD

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

V

DD to GND ...........................................................................+6V

PV

DD to PGND .......................................................................+6V

CPV

DD to CPGND..................................................................+6V

CPV

SS to CPGND....................................................................-6V

SV

SS to GND ...........................................................................-6V

C1N..........................................(PV

SS

- 0.3V) to (CPGND + 0.3V)

HPOUT_ to GND ....................................................................

±3V

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

DD

+ 0.3V)

Continuous Current Into/Out of:

PV

DD

, PGND, OUT_ ......................................................600mA

PV

SS

..............................................................................260mA

Duration of HPOUT_ Short Circuit to V

DD

, PV

DD

,

GND, PGND ...........................................................Continuous

Duration of Short Circuit Between

HPOUTL and HPOUTR ..........................................Continuous

Duration of OUT_ Short Circuit to V

DD

, PV

DD

, GND, PGND ..10s

Duration of Short Circuit Between OUT+ and OUT-...............10s

Continuous Power Dissipation (T

A

= +70°C)

28-Pin TQFN (derate 20.8mW/°C above +70°C) .......1667mW

28-Pin TSSOP (derate 12.8mW°C above +70°C) ......1026mW

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

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

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

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

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.

ELECTRICAL CHARACTERISTICS

(V

DD

= PV

DD

= CPV

DD

= 3.3V, GND = PGND = CPGND = 0V, SHDN = 3.3V, C1 = C2 = 1µF, C

BIAS

= 0.047µF, SYNC = GND, R

L

=

∞, speaker load connected between OUT+ and OUT-, headphone load connected between HPOUT_ and GND, T

A

= T

MIN to T

MAX

, unless otherwise noted. Typical values are at T

A

= +25°C.) (Notes 1, 2)

MIN TYP MAX UNITS PARAMETER

GENERAL

Supply Voltage Range

SYMBOL CONDITIONS

Quiescent Supply Current

Shutdown Supply Current

Shutdown to Full Operation

V

I

DD

DD

Inferred from PSRR test

Headphone mode

No load

Speaker mode

SHDN = HPS = GND

I

SHDN t

ON

Input Impedance R

IN

(Note 3)

MONO

INL_, INR_

Bias Voltage V

BIAS

Feedthrough

From any unselected input to any output, f = 10kHz

SPEAKER AMPLIFIER (GAIN1 = GAIN2 = V

DD

, HPS = GND)

Output Offset Voltage V

OS

2.5

7

14

1.1

5.5

5.2

0.1

50

10

20

1.25

70

±15

5.5

10

7.5

10

1.4

±70

V mA

µA ms k

Ω

V dB mV

Power-Supply Rejection Ratio

Output Power

PSRR

P

OUT

V

DD

= 2.5V to 5.5V,

T

A

= +25°C

(Note 4)

V

RIPPLE

= 200mV

P-P

, f = 217Hz

V

RIPPLE

= 200mV

P-P

, f = 1kHz f = 1kHz,

V

RIPPLE

= 200mV

P-P

, f = 20kHz

R

L

= 8

Ω

THD+N = 1%,

V

DD

= 3.3V

R

L

= 4

Ω

GAIN1 = 1,

GAIN2 = 0

V

DD

= 5V R

L

= 8

Ω

50 70

70

68

50

550

900

1200 dB mW

2 _______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

ELECTRICAL CHARACTERISTICS (continued)

(V

DD

= PV

DD

= CPV

DD

= 3.3V, GND = PGND = CPGND = 0V, SHDN = 3.3V, C1 = C2 = 1µF, C

BIAS

= 0.047µF, SYNC = GND, R

L

=

∞, speaker load connected between OUT+ and OUT-, headphone load connected between HPOUT_ and GND, T

A

= T

MIN to T

MAX

, unless otherwise noted. Typical values are at T

A

= +25°C.) (Notes 1, 2)

MIN MAX UNITS

Total Harmonic Distortion Plus

Noise

PARAMETER

Signal-to-Noise Ratio

Output Switching Frequency

SYMBOL

THD+N

SNR

CONDITIONS

R

L

= 8

Ω, P

OUT

= 300mW, f = 1kHz

R

L

= 4

Ω, P

OUT

= 300mW, f = 1kHz

R

L

= 8

Ω, P

OUT

= 500mW, f = 1kHz

R

L

= 8

Ω, V

OUT

= 2V

RMS

, A-weighted

SYNC = GND

SYNC = unconnected f

S

SYNC = V

DD

SYNC Frequency Lock Range

Efficiency

Gain (MAX9770) A

η

V

P

O

= 1000mW, f = 1kHz

GAIN1 = 0, GAIN2 = 0

GAIN1 = 0, GAIN2 = 1

GAIN1 = 1, GAIN2 = 0

GAIN1 = 1, GAIN2 = 1

Gain Accuracy

Speaker Path Off-Isolation

Click-and-Pop Level K

CP

HPS = V

DD

, headphone amplifier active, f = 1kHz

Peak voltage,

A-weighted, 32 samples per second

(Notes 4, 5)

Into shutdown

Out of shutdown

Into mute

Out of mute

HEADPHONE AMPLIFIER (GAIN1 = 1, GAIN2 = 0, HPS = V

DD

)

Output Offset Voltage V

OS

Power-Supply Rejection Ratio

Output Power

Total Harmonic Distortion Plus

Noise

PSRR

P

OUT

THD+N

V

DD

= 2.5V to 5.5V, T

A

= +25°C

V

RIPPLE

= 200mV

P-P

, f = 217Hz

(Note 4)

V

RIPPLE

= 200mV

P-P

, f = 1kHz

T

A

= +25°C, f = 1kHz,

V

RIPPLE

= 200mV

P-P

, f = 20kHz

R

L

= 32

Ω

V

DD

= 3.3V

R

L

= 16

Ω

THD+N = 1%

R

L

= 32

Ω

(Note 3)

V

DD

= 5V

R

L

= 16

Ω

R

L

= 32

Ω, P

OUT

= 50mW, f = 1kHz

R

L

= 16

Ω, P

OUT

= 35mW, f = 1kHz

980

1280

800

65

40

102

-76

-55

-83

-69

56

55

40

60

80

±5

76

75

82

0.015

0.03

TYP

0.025

0.03

0.1

85.9

1100

1450

1220

±120kHz

85

6

3

9

0

1220

1620

2000

±5

±10

% dB kHz kHz

% dB

% dB dB mV dB mW

%

_______________________________________________________________________________________ 3

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

ELECTRICAL CHARACTERISTICS (continued)

(V

DD

= PV

DD

= CPV

DD

= 3.3V, GND = PGND = CPGND = 0V, SHDN = 3.3V, C1 = C2 = 1µF, C

BIAS

= 0.047µF, SYNC = GND, R

L

=

∞, speaker load connected between OUT+ and OUT-, headphone load connected between HPOUT_ and GND, T

A

= T

MIN to T

MAX

, unless otherwise noted. Typical values are at T

A

= +25°C.) (Notes 1, 2)

PARAMETER

Signal-to-Noise Ratio

SYMBOL

SNR

CONDITIONS

R

L

= 32

Ω, V

OUT

= 300mV

RMS

,

BW = 22Hz to 22kHz

MIN TYP

101

MAX UNITS

dB

Crosstalk

Between channels, f = 1kHz,

V

IN

= 200mV

P-P

Headphone Off-Isolation

HPS = GND, speaker amplifier active, f = 1kHz

Click-and-Pop Level K

CP

Peak voltage, Aweighted, 32 samples per second

(Notes 4, 5)

Into shutdown

Out of shutdown

Into mute

Out of mute

Capacitive-Load Drive C

L

Gain A

V

GAIN1 = 0, GAIN2 = 0

GAIN1 = 0, GAIN2 = 1

GAIN1 = 1, GAIN2 = 0

GAIN1 = 1, GAIN2 = 1

Gain Accuracy

ESD Protection HPOUTR, HPOUTL, IEC Air Discharge

DIGITAL INPUTS (SHDN, SYNC, HPS, GAIN_, SEL_)

Input Voltage High

Input Voltage Low

V

IH

V

IL

Input Leakage Current (Note 6)

SYNC input

All other logic inputs

HPS Input Current HPS = GND

2

80

96

-58

-53

-92

-73

1000

7

4

-2

1

±8

±2.5

0.8

±25

±1

-10 dB dB dBV pF dB

% kV

V

V

µA

µA

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

Note 2: Speaker amplifier testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For

R

L

= 4

Ω, L = 47µH. For R

L

= 8

Ω, L = 68µH.

Note 3: Guaranteed by design, not production tested.

Note 4: Inputs AC-coupled to GND.

Note 5: Speaker mode testing performed with an 8

Ω resistive load in series with a 68µH inductive load connected across BTL output.

Headphone mode testing performed with a 32

Ω resistive load connected to GND. Mode transitions are controlled by SHDN. K

CP level is calculated as: 20 x log [(peak voltage during mode transition, no input signal)/(peak voltage under normal operation at rated power level)]. Units are expressed in dB. Measured with V

DD

= 5V.

Note 6: SYNC has a 200k

Ω resistor to V

REF

= 1.25V.

4 _______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Typical Operating Characteristics

(V

DD

= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise noted.)

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (SPEAKER MODE)

V

R

DD

= +5V

L

= 4

Ω

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (SPEAKER MODE)

R

L

= 4

Ω

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (SPEAKER MODE)

R

L

= 8

Ω

1 1 1

P

OUT

= 25mW

P

OUT

= 100mW

P

OUT

= 40mW

0.1

0.1

0.1

0.01

P

OUT

= 1000mW

0.01

P

OUT

= 500mW

0.001

10 100 1k

FREQUENCY (Hz)

10k 100k

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (SPEAKER MODE)

V

DD

= 5V

P

R

OUT

L

= 1W

= 8

Ω

1

0.001

10 100 1k

FREQUENCY (Hz)

10k 100k

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (SPEAKER MODE)

V

DD

= 5V

R

L

= 8

Ω

10

1

0.1

SSM MODE f = 1kHz

0.1

f = 20Hz

0.01

FFM MODE

0.001

10 100 1k

FREQUENCY (Hz)

10k 100k

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (SPEAKER MODE)

R

L

= 8

Ω

10

0.01

f = 10kHz

0.001

0 400 800 1200

OUTPUT POWER (mW)

1600

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (SPEAKER MODE)

10

V

DD

= 5V f = 1kHz

R

L

= 8

Ω

1

0.1

f = 20Hz f = 1kHz

1

0.1

SSM MODE

0.01

0.001

0 f = 10kHz

200 400 600

OUTPUT POWER (mW)

800

0.01

0.001

0

FFM MODE

400 800 1200

OUTPUT POWER (mW)

1600

0.01

P

OUT

= 400mW

0.001

10 100 1k

FREQUENCY (Hz)

10k 100k

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (SPEAKER MODE)

R

L

= 4

Ω

10

1

0.1

f = 20Hz f = 1kHz

0.01

f = 10kHz

0.75

0.50

0.25

0.001

0 200

400

600

OUTPUT POWER (mW)

800 1000

1.75

1.50

1.25

1.00

OUTPUT POWER vs. LOAD RESISTANCE (SPEAKER MODE)

V

DD

= 5V f = 1kHz

THD+N = 10%

THD+N = 1%

0

1 10

LOAD RESISTANCE (

Ω)

100

_______________________________________________________________________________________ 5

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Typical Operating Characteristics (continued)

(V

DD

= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise noted.)

OUTPUT POWER vs. LOAD RESISTANCE (SPEAKER MODE)

EFFICIENCY vs. OUTPUT POWER

1.0

0.8

0.6

0.4

0.2

0

1 f = 1kHz

THD+N = 1%

THD+N = 10%

10

LOAD RESISTANCE (

Ω)

100

2.0

OUTPUT POWER vs. SUPPLY VOLTAGE (SPEAKER MODE)

f = 1kHz

R

L

= 8

Ω

THD+N = 10%

1.5

1.0

0.5

0

2.5

3.0

THD+N = 1%

3.5

4.0

4.5

SUPPLY VOLTAGE (V)

5.0

5.5

100

90

80

70

60

50

40

30

20

10

0

0

V

DD

= 5V f = 1kHz

R

L

= 8

Ω

0.2

0.4

0.6

0.8

1.0

1.2

1.4

OUTPUT POWER (W)

100

90

80

70

60

50

40

30

20

10

0

0

EFFICIENCY vs. OUTPUT POWER

R

L

= 8

Ω

R

L

= 4

Ω f = 1kHz

0.2

0.4

0.6

OUTPUT POWER (W)

0.8

1.0

POWER-SUPPLY REJECTION RATIO vs. FREQUENCY (SPEAKER MODE)

0

-50

-60

-70

-10

-20

-30

-40

-80

10

V

RIPPLE

R

L

= 8

Ω

= 200mV

P-P

100 1k

FREQUENCY (Hz)

10k 100k

0

-20

-40

-60

-80

-100

-120

-140

0

OUTPUT SPECTRUM

(SPEAKER MODE)

R

L

= 8

Ω f = 1kHz

FFM MODE

V

IN

= -60dBV

5 10

FREQUENCY (kHz)

15

20

0

-20

-40

-60

-80

-100

-120

-140

0

OUTPUT SPECTRUM

(SPEAKER MODE)

R

L

= 8

Ω f = 1kHz

SSM MODE

V

IN

= -60dBV

5 10

FREQUENCY (kHz)

15

20

-60

-80

-100

-120

-140

0

-20

-40

-160

0

OUTPUT SPECTRUM

(SPEAKER MODE)

R

L

= 8

Ω f = 1kHz

SSM MODE

A-WEIGHTED

V

IN

= -60dBV

5 10

FREQUENCY (kHz)

15

20

40

30

20

10

0

-10

-20

-30

-40

-50

-60

1M

WIDEBAND OUTPUT SPECTRUM

(SPEAKER MODE)

FFM MODE

RBW = 10kHz

10M

FREQUENCY (Hz)

100M

6 _______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Typical Operating Characteristics (continued)

(V

DD

= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise noted.)

40

30

20

10

0

-10

-20

-30

-40

-50

-60

1M

WIDEBAND OUTPUT SPECTRUM

(SPEAKER MODE)

SSM MODE

RBW = 10kHz

10M

FREQUENCY (Hz)

100M

R

L

= 8

Ω f = 1kHz

STARTUP WAVEFORM

(SPEAKER MODE)

MAX9770 toc20

4ms/div

SHDN

2V/div

OUT+ - OUT-

500mV/div

IN1_

MIXER OUTPUT (SPEAKER MODE)

MAX9770 toc21

10kHz

1V/div

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (HEADPHONE MODE)

V

R

DD

L

= 5V

= 16

Ω

1

IN2_

4kHz

1V/div

P

OUT

= 10mW

0.1

MONO

1kHz

2V/div

0.01

OUT

1V/div P

OUT

= 50mW

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (HEADPHONE MODE)

V

R

DD

L

= 5V

= 32

Ω

1

400

μs/div

0.001

10

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (HEADPHONE MODE)

R

L

= 16

Ω

100 1k

FREQUENCY (Hz)

10k 100k

10

TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (HEADPHONE MODE)

R

L

= 32

Ω

1

1

0.1

P

OUT

= 10mW

0.1

P

OUT

= 10mW

0.1

P

OUT

= 10mW

0.01

0.001

10

0.01

P

OUT

= 35mW

0.01

P

OUT

= 50mW

100 1k

FREQUENCY (Hz)

10k 100k

0.001

10 100 1k

FREQUENCY (Hz)

10k 100k

0.001

10

P

OUT

= 50mW

100 1k

FREQUENCY (Hz)

10k 100k

_______________________________________________________________________________________ 7

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Typical Operating Characteristics (continued)

(V

DD

= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise noted.)

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (HEADPHONE MODE)

V

R

DD

L

= 5V

= 16

Ω

10

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (HEADPHONE MODE)

V

R

DD

L

= 5V

= 32

Ω

10

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (HEADPHONE MODE)

R

L

= 16

Ω

10

1

1

1 f = 10kHz f = 1kHz f = 1kHz f = 10kHz f = 1kHz f = 10kHz

0.1

0.1

0.1

0.01

f = 20Hz

0.001

0 20 40 60

OUTPUT POWER (mW)

80 100

100

TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (HEADPHONE MODE)

R

L

= 32

Ω

10

1

0.1

0.01

0.001

0 f = 1kHz f = 10kHz f = 20Hz

20 40

OUTPUT POWER (mW)

60 80

50

40

30

20

10

0

2.5

100

OUTPUT POWER vs. SUPPLY VOLTAGE (HEADPHONE MODE)

90

R

L

= 16

Ω f = 1kHz

80

70

THD+N = 10%

60

3.0

THD+N = 1%

3.5

4.0

4.5

SUPPLY VOLTAGE (V)

5.0

5.5

0.01

0.001

0 f = 20Hz

20 40

OUTPUT POWER (mW)

60 80

40

30

20

10

70

60

50

0

100

90

80

OUTPUT POWER vs. LOAD RESISTANCE (HEADPHONE MODE)

THD+N = 10%

THD+N = 1%

V

DD

= 5V f = 1kHz

10 100

LOAD RESISTANCE (

Ω)

1000

80

OUTPUT POWER vs. SUPPLY VOLTAGE (HEADPHONE MODE)

70

R

L

= 32

Ω f = 1kHz

THD+N = 10%

60

50

40

30

20

10

0

2.5

3.0

THD+N = 1%

3.5

4.0

4.5

SUPPLY VOLTAGE (V)

5.0

5.5

0.01

60

50

40

30

20

10

0

10

0.001

0 f = 20Hz

10 20 30 40

OUTPUT POWER (mW)

50 60

80

OUTPUT POWER vs. LOAD RESISTANCE (HEADPHONE MODE)

f = 1kHz

70

THD+N = 10%

THD+N = 1%

100

LOAD RESISTANCE (

Ω)

1000

300

POWER DISSIPATION vs. OUTPUT POWER (HEADPHONE MODE)

250

200

150

100

50

0

0

R

L

= 16

Ω

R

L

= 32

Ω

30 60 f = 1kHz

P

OUT

= P

OUTL

+ P

OUTR

90

OUTPUT POWER (mW)

120 150

8 _______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

40

30

20

10

Typical Operating Characteristics (continued)

(V

DD

= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise noted.)

POWER-SUPPLY REJECTION RATIO vs. FREQUENCY (HEADPHONE MODE)

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

10

V

DD

= 3.3V

V

RIPPLE

R

L

= 200mV

= 32

Ω

P-P

100 1k

MAX9770

C

BIAS

FREQUENCY (Hz)

= 0.047

μF

10k 100k

60

OUTPUT POWER vs. CHARGE-PUMP CAPACITANCE

AND LOAD RESISTANCE

C1 = C2 = 1

μF

50

0

20

C1 = C2 = 0.47

μF

30 40

LOAD RESISTANCE (

Ω) f = 1kHz

THD+N = 1%

50

-80

-100

-120

-140

0

0

-20

-40

-60

CROSSTALK vs. FREQUENCY

(HEADPHONE MODE)

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

10

R

L

= 32

Ω f = 1kHz

V

IN

= 200mV

P-P

LEFT TO RIGHT

RIGHT TO LEFT

100 1k

FREQUENCY (Hz)

10k 100k

OUTPUT SPECTRUM

(HEADPHONE MODE)

R

L

= 32

Ω f = 1kHz

V

IN

= -60dBV

5 10

FREQUENCY (kHz)

15 20

FEEDTHROUGH vs. FREQUENCY

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

10

SEL1 = 0

SEL2 = 1

IN1_ = GND

IN2_ = DRIVEN

V

IN

= 2V

P-P

HEADPHONE MODE

SPEAKER MODE

100 1k

FREQUENCY (Hz)

10k 100k

R

L

= 32

Ω

EXITING SHUTDOWN

(HEADPHONE MODE)

MAX9770 toc40

2

μs/div

SHDN

2V/div

OUT_

10mV/div

ENTERING SHUTDOWN

(HEADPHONE MODE)

MAX9770 toc41

R

L

= 32

Ω

10

SUPPLY CURRENT vs. SUPPLY VOLTAGE

0.5

SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE

SHDN

2V/div

8

SPEAKER MODE

0.4

6 0.3

HEADPHONE MODE

4 0.2

OUT_

10mV/div

2

0.1

2

μs/div

0

2.5

3.5

4.5

SUPPLY VOLTAGE (V)

5.5

0

2.5

3.5

4.5

SUPPLY VOLTAGE (V)

5.5

_______________________________________________________________________________________ 9

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

13

14

15

16

17

22

23

24

25

18

19

20

21

26

27

28

TQFN-EP

1

PIN

TSSOP

4

2

3

4

5

6

7

9

10

11

7

8

5

6

12

13

14

8

9

10

11

12 15

16

17

18

19

20

25

26

27

28

21

22

23

24

1

2

3

NAME

BIAS

V

DD

HPOUTR

HPOUTL

SV

SS

HPS

CPV

DD

CPV

SS

C1N

C1P

CPGND

SEL1

SEL2

SELM

SHDN

SYNC

PGND

OUT+

OUT-

PV

DD

GAIN2

GAIN1

MONO

IN2L

IN1L

GND

IN2R

IN1R

EP

Pin Description

FUNCTION

Common-Mode Bias Voltage. Bypass with a 0.047µF capacitor to GND.

Power Supply

Right-Channel Headphone Output

Left-Channel Headphone Output

Headphone Amplifier Negative Power Supply

Headphone Sense Input

Positive Charge-Pump Power Supply

Charge-Pump Output. Connect to SV

SS

.

Charge-Pump Flying Capacitor Negative Terminal

Charge-Pump Flying Capacitor Positive Terminal

Charge-Pump Ground

Select Stereo Channel 1 Inputs. Digital input. Drive SEL1 high to select inputs IN1L and

IN1R.

Select Stereo Channel 2 Inputs. Digital input. Drive SEL2 high to select inputs IN2L and

IN2R.

Select Mono Channel Input. Digital input. Drive SELM high to select the MONO input.

Shutdown. Drive SHDN low to disable the device. Connect SHDN to V

DD

for normal operation.

Frequency Select and External Clock Input:

SYNC = GND: fixed-frequency PWM mode with f

S

= 1100kHz.

SYNC = Unconnected: fixed-frequency PWM mode with f

S

= 1450kHz.

SYNC = V

DD

: spread-spectrum PWM mode with f

S

= 1220kHz

±120kHz.

SYNC = Clocked: fixed-frequency PWM mode with f

S

= external clock frequency.

Speaker Amplifier Power Ground

Speaker Amplifier Positive Output

Speaker Amplifier Negative Output

Speaker Amplifier Power Supply

Gain Control Input 2

Gain Control Input 1

Mono Channel Input

Stereo Channel 2, Left Input

Stereo Channel 1, Left Input

Ground

Stereo Channel 2, Right Input

Stereo Channel 1, Right Input

Exposed Paddle. Can be left unconnected or connected to GND. Connect to ground plane for improved thermal performance.

10 ______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Detailed Description

The MAX9770 combines a mono 1.2W Class D speaker amplifiers and stereo 80mW DirectDrive headphone amplifiers with integrated headphone sensing and comprehensive click-and-pop suppression. A mixer/multiplexer allows for selection and mixing between two stereo input sources and a single mono source. The MAX9770 features PSRR as high as 85dB,

THD as low as 0.015%, industry-leading click-and-pop suppression, and a low-power shutdown mode.

Class D Speaker Amplifier

The MAX9770 Class D amplifier features true filterless, low-EMI, switch-mode architecture that provides Class

AB-like performance with Class D efficiency.

Comparators monitor the MAX9770 input and compare the input voltage to a sawtooth waveform. The comparators trip when the input magnitude of the sawtooth exceeds the corresponding input voltage. The comparator resets at a fixed time after the rising edge of the

Table 1. Operating Modes

SYNC INPUT

GND

Unconnected

V

DD

Clocked

MODE

FFPWM with f

S

= 1100kHz

FFPWM with f

S

= 1450kHz

SSPWM with f

S

= 1220kHz

±120kHz

FFPWM with f

S

= external clock frequency second comparator trip point, generating a minimumwidth 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 (the first comparator trip point) while the other output pulse duration remains at t

ON(MIN)

. This causes the net voltage across the speaker (V

OUT+

-

V

OUT-

) to change.

t

SW

V

IN-

V

IN+

OUT-

OUT+ t

ON(MIN)

V

OUT+

- V

OUT-

Figure 1. MAX9770 Outputs with an Input Signal Applied

______________________________________________________________________________________ 11

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Operating Modes

The switching frequency of the charge pump is 1/2 the switching frequency of the Class D amplifier, regardless of the operating mode. When SYNC is driven externally, the charge pump switches at 1/2 f

SYNC

. When

SYNC = V

DD

, the charge pump switches with a spreadspectrum pattern.

Fixed-Frequency Modulation (FFM) Mode

The MAX9770 features two FFM modes. The FFM modes are selected by setting SYNC = GND for a

1.1MHz switching frequency, and SYNC = unconnected for a 1.45MHz switching frequency. In FFM mode, the frequency spectrum of the Class D output consists of the fundamental switching frequency and its associated harmonics (see the Wideband Output Spectrum

(Speaker Mode) graph in the Typical Operating

Characteristics). The MAX9770 allows the switching frequency to be changed by +32% should the frequency of one or more harmonics fall in a sensitive band. This can be done during operation and does not affect audio reproduction.

Spread-Spectrum Modulation (SSM) Mode

The MAX9770 features a unique, patented spreadspectrum mode that flattens the wideband spectral components, improving EMI emissions radiated by the speaker and cables by 5dB. Proprietary techniques ensure that the cycle-to-cycle variation of the switching period does not degrade audio reproduction or efficiency (see the Typical Operating Characteristics).

Select SSM mode by setting SYNC = V

DD

. In SSM mode, the switching frequency varies randomly by

±120kHz around the center frequency (1.22MHz). 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 MHz, the wideband spectrum looks like white noise for EMI purposes (Figure 3).

External Clock Mode

The SYNC input allows the MAX9770 to be synchronized to a system clock (allowing a fully synchronous system), or allocating the spectral components of the switching harmonics to insensitive frequency bands.

Applying an external clock of 800kHz to 2MHz to SYNC synchronizes the switching frequency of both the Class

D and charge pump. The period of the SYNC clock can be randomized, enabling the MAX9770 to be synchronized to another spread-spectrum Class D amplifier operating in SSM mode.

Filterless Modulation/Common-Mode Idle

The MAX9770 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 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, increasing power consumption. When no signal is present at the device input, the outputs switch as shown in Figure 4. Because the

MAX9770 drives the speaker differentially, the two outputs cancel each other, resulting in no net idle mode voltage across the speaker, minimizing power consumption.

Efficiency

The efficiency of a Class D amplifier is attributed to the region of operation of the output stage transistors. In a

Class D amplifier, the output transistors act as currentsteering 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 MAX9770 still exhibits > 80% efficiencies under the same conditions (Figure 5).

DirectDrive

Traditional single-supply headphone drivers have their outputs biased about a nominal DC voltage (typically half the supply) for maximum dynamic range. Large coupling capacitors are needed to block this DC bias from the headphone. Without these capacitors, a significant amount of DC current flows to the headphone, resulting in unnecessary power dissipation and possible damage to both headphone and headphone driver.

12 ______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

t

SW t

SW t

SW t

SW

V

IN-

V

IN+

OUT-

OUT+ t

ON(MIN)

V

OUT+

- V

OUT-

Figure 2. MAX9770 Output with an Input Signal Applied (SSM Mode)

50.0

45.0

40.0

35.0

30.0

25.0

20.0

15.0

10.0

30.0

60.0

80.0

100.0 120.0 140.0 160.0 180.0

200.0

220.0

240.0 260.0

280.0 300.0

FREQUENCY (MHz)

Figure 3. MAX9770 EMI with 75mm of Speaker Cable

FCC LIMIT

MAX9770

______________________________________________________________________________________ 13

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

VIN = 0V

OUT-

OUT+

VOUT+ - VOUT- = 0V

Figure 4. MAX9770 Output with No Signal Applied

Maxim’s patented DirectDrive architecture uses a charge pump to create an internal negative supply voltage. This allows the headphone outputs of the MAX9770 to be biased about GND, almost doubling dynamic range while operating from a single supply. With no DC component, there is no need for the large DC-blocking capacitors. Instead of two large (220µF, typ) tantalum capacitors, the MAX9770 charge pump requires two small ceramic capacitors, which conserves board space, reduces cost, and improves the frequency response of the headphone driver. See the Output Power vs. Charge-Pump Capacitance and Load Resistance graph in the Typical Operating Characteristics for details of the possible capacitor sizes. There is a low DC voltage on the driver outputs due to amplifier offset.

However, the offset of the MAX9770 is typically 5mV, which, when combined with a 32

Ω load, results in less than 160µA of DC current flow to the headphones.

In addition to the cost and size disadvantages of the DCblocking capacitors required by conventional headphone amplifiers, these capacitors limit the amplifier’s low-frequency response and can distort the audio signal.

Previous attempts at eliminating the output-coupling capacitors involved biasing the headphone return

(sleeve) to the DC bias voltage of the headphone amplifiers. This method raises some issues:

1) When combining a microphone and headphone on a single connector, the microphone bias scheme typically requires a 0V reference.

100

90

80

70

60

50

40

30

20

10

0

0

EFFICIENCY vs. OUTPUT POWER

MAX9770

0.1

CLASS AB

0.2

0.3

0.4

OUTPUT POWER (W)

V

DD

= 3.3V

f = 1kHz

R

L

- 8

Ω

0.5

0.6

Figure 5. MAX9770 Efficiency vs. Class AB Efficiency

SHDN

MAX9770

800k

Ω

SHUTDOWN

CONTROL

HPS

HPOUTL

HPOUTR

10k

Ω

10k

Ω

V

DD

Figure 6. HPS Configuration

2) The sleeve is typically grounded to the chassis.

Using the midrail biasing approach, the sleeve must be isolated from system ground, complicating product design.

3) During an ESD strike, the driver’s ESD structures are the only path to system ground. Thus, the driver must be able to withstand the full ESD strike.

4) When using the headphone jack as a line out to other equipment, the bias voltage on the sleeve may conflict with the ground potential from other equipment, resulting in possible damage to the drivers.

14 ______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Table 2. MAX9770 Multiplexer/Mixer Settings

SEL1 SEL2 SELM

0

1

0

0

0

1

1

1

0

0

1

0

1

0

1

1

0

0

0

1

0

1

1

1

HPOUTL

HEADPHONE MODE

HPOUTR

MUTE

IN1L

IN2L

MONO

(IN1L + IN2L) / 2

(IN1L + MONO) /2

(IN2L + MONO) / 2

( IN 1L + IN 2L + M ON O) / 3

MUTE

IN1R

IN2R

MONO

(IN1R + IN2R) / 2

(IN1R + MONO) / 2

(IN2R + MONO) / 2

( IN 1R + IN 2R + M ON O) / 3

SPEAKER MODE

MUTE

(IN1L + IN1R) / 2

(IN2L + IN2R) / 2

MONO

(IN1L + IN1R + IN2L + IN2R) / 4

(IN1L + IN1R + MONO x 2) / 4

(IN2L + IN2R + MONO x 2) / 4

( IN1L + IN 1R + IN 2L + IN 2R + M ON O x 2) / 6

Charge Pump

The MAX9770 features a low-noise charge pump. The switching frequency of the charge pump is 1/2 the switching frequency of the Class D amplifier, regardless of the operating mode. When SYNC is driven externally, the charge pump switches at 1/2 f

SYNC

. When SYNC =

V

DD

, the charge pump switches with a spread-spectrum pattern. The nominal switching frequency is well beyond the audio range, and thus does not interfere with the audio signals, resulting in an SNR of 101dB. The switch drivers feature a controlled switching speed that minimizes noise generated by turn-on and turn-off transients. By limiting the switching speed of the charge pump, the di/dt noise caused by the parasitic bond wire and trace inductance is minimized. Although not typically required, additional high-frequency noise attenuation can be achieved by increasing the size of C2 (see the

Block Diagram). The charge pump is active in both speaker and headphone modes.

Input Multiplexer/Mixer

The MAX9770 features an input multiplexer/mixer that allows multiple audio sources to be selected/mixed.

Driving a SEL_ input high selects the input channel (see

Table 2), and the audio signal is output to the active amplifier. When a stereo path is selected in speaker mode, the left and right inputs are attenuated by 6dB and mixed together, resulting in a true mono reproduction of a stereo signal. When more than one signal path is selected, the sources are attenuated before mixing to preserve overall amplitude. For example, selecting two sources in headphone mode results in 6dB attenuation of the inputs, while selecting three sources in headphone mode results in 9.5dB attenuation of the inputs. Table 2 shows how the input signals are attenuated and mixed for each possible input selection combination.

Headphone Sense Input (HPS)

The headphone sense input (HPS) monitors the headphone jack, and automatically configures the device based upon the voltage applied at HPS. A voltage of less than 0.8V sets the device to speaker mode. A voltage of greater than 2V disables the bridge amplifiers and enables the headphone amplifiers.

For automatic headphone detection, connect HPS to the control pin of a 3-wire headphone jack as shown in

Figure 6. With no headphone present, the output impedance of the headphone amplifier pulls HPS to less than

0.8V. When a headphone plug is inserted into the jack, the control pin is disconnected from the tip contact and

HPS is pulled to V

DD through the internal 800k

Ω pullup.

When driving HPS from an external logic source, ground

HPS when the MAX9770 is shut down. Place a 10k

Ω resistor in series with HPS and the headphone jack to ensure ±8kV ESD protection.

BIAS

The MAX9770 features internally generated, power-supply independent, common-mode bias voltages referenced to GND. BIAS provides both click-and-pop suppression and sets the DC bias level for the amplifiers.

Choose the value of the bypass capacitor as described in the BIAS Capacitor section. No external load should be applied to BIAS. Any load lowers the BIAS voltage, affecting the overall performance of the device.

Gain Selection

The MAX9770 features logic-selectable, internally set gains. GAIN1 and GAIN2 set the gain of the MAX9770 speaker and headphone amplifiers as shown in Table 3.

The MAX9770 can be configured to automatically switch between two gain settings depending on whether the device is in speaker or headphone mode.

By driving one or both gain inputs with HPS, the gain of

______________________________________________________________________________________ 15

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Table 3. Gain Selection

GAIN1 GAIN2

MAX9770

SPEAKER GAIN

(dB)

1

1

0

0

0

1

0

1

9

0

6

3

HEADPHONE

GAIN

(dB)

-2

1

7

4

Table 4. Gain Settings with HPS

Connection

HPS

HPS

0

1

HPS

0

0

1

1

0

1

HPS

HPS

HPS

0

1

0

1

MAX9770 SPEAKER

MODE GAIN

(HPS = 0)

(dB)

3

9

6

6

0

6

9

6

3

HEADPHONE MODE

GAIN

(HPS = 1)

(dB)

4

-2

1

7

1

4

1

-2

1 the device changes when a headphone is inserted or removed. For example, the block diagram shows HPS connected to GAIN2, while GAIN1 is connected to V

DD

.

In this configuration, the gain in speaker mode is 9dB, while the gain in headphone mode is 1dB. The gain settings with the HPS connection are shown in Table 4.

Shutdown

The MAX9770 features a 0.1µA, low-power shutdown mode that reduces quiescent current consumption and extends battery life. Drive SHDN low to disable the drive amplifiers, bias circuitry, and charge pump. Bias is driven to GND and the headphone amplifier output impedance is 10k

Ω in shutdown. Connect SHDN to

V

DD for normal operation.

Click-and-Pop Suppression

Speaker Amplifier

The MAX9770 speaker amplifier 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 Hbridge is subsequently enabled. A soft-start function unmutes the input amplifiers 30ms after startup.

Headphone Amplifier

In conventional single-supply headphone drivers, the output-coupling capacitor is a major contributor of audible clicks and pops. Upon startup, the driver charges the coupling capacitor to its bias voltage, typically half the supply. Likewise, during shutdown, the capacitor is discharged to GND. This results in a DC shift across the capacitor, which in turn, appears as an audible transient at the speaker. Since the MAX9770 headphone amplifier does not require output-coupling capacitors, this does not arise.

Additionally, the MAX9770 features extensive click-andpop suppression that eliminates any audible transient sources internal to the device. The Exiting Shutdown

(Headphone Mode) and Entering Shutdown (Headphone

Mode) graphs in the Typical Operating Characteristics shows that there are minimal spectral components in the audible range at the output upon startup or shutdown.

In most applications, the output of the preamplifier driving the MAX9770 has a DC bias of typically half the supply. During startup, the input-coupling capacitor is charged to the preamplifier’s DC bias voltage through the R

F of the MAX9770, resulting in a DC shift across the capacitor and an audible click-and-pop. An internal delay of 50ms eliminates the click-and-pop caused by the input filter.

Applications Information

Filterless Operation

Traditional Class D amplifiers require an output filter to recover the audio signal from the amplifier’s 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 peak-to-peak) at idle and causes large ripple currents.

Any parasitic resistance in the filter components results in a loss of power, lowering efficiency.

The MAX9770 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, and more efficient solution.

Because the frequency of the MAX9770 output is well beyond the bandwidth of most speakers, voice coil movement due to the square-wave frequency is minimal.

16 ______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Although this movement is small, a speaker not designed to handle the additional power may be damaged. For optimum results, use a speaker with a series inductance

>10µH. Typical small 8

Ω speakers exhibit series inductances in the range of 20µH to 100µH.

Output Offset

Unlike Class AB amplifiers, 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, a

15mV DC offset across an 8

Ω load results in 1.9mA extra current consumption in a Class AB device. In the Class D case, a 15mV offset into 8

Ω equates to an additional power drain of 28µW. Due to the high efficiency of the

Class D amplifier, this represents an additional quiescent current draw of 28µW/(V

DD

/ 100 x

η), which is on the order of a few microamps.

Power Supplies

The MAX9770 has different supplies for each portion of the device, allowing for the optimum combination of headroom and power dissipation and noise immunity.

The speaker amplifier is powered from PV

DD

. PV

DD ranges from 2.5V to 5.5V. The headphone amplifiers are powered from V

DD and SV

SS

. V

DD is the positive supply of the headphone amplifiers and ranges from

2.5V to 5.5V. SV

SS is the negative supply of the headphone amplifiers. Connect SV

SS to CPV

SS

. The charge pump is powered by CPV

DD

. CPV

DD ranges from 2.5V

to 5.5V and should be the same potential as V

DD

. The charge pump inverts the voltage at CPV

DD

, and the resulting voltage appears at CPV

SS

. The remainder of the device is powered by V

DD

.

Component Selection

Input Filter

The input capacitor (C

IN

), in conjunction with the amplifier input resistance (R

IN

), forms a highpass filter that removes the DC bias from an incoming signal (see the

Block Diagram). The AC-coupling capacitor allows the amplifier to bias the signal to an optimum DC level.

Assuming zero-source impedance, the -3dB point of the highpass filter is given by: f

3 dB

=

1

2

π

R C

R

IN is the amplifier’s internal input resistance value given in the Electrical Characteristics. Be aware that the MONO input has a lower input impedance than the other inputs. Choose C

IN such that f

-3dB is below the lowest frequency of interest. Setting f

-3dB too high affects the amplifier’s low-frequency response. Setting f

-3dB too low can affect the click-and-pop performance.

Use capacitors with low-voltage coefficient dielectrics, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as ceramics, may result in increased distortion at low frequencies.

Output Filter

The MAX9770 speaker amplifier does not require an output filter for normal operation and audio reproduction. The device passes FCC Class B radiated emissions standards with 100mm 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 common-mode choke connected in series with the speaker outputs if board space is limited and emissions are a concern. Use of an LC filter is necessary if excessive speaker cable is used.

BIAS Capacitor

BIAS is the output of the internally generated DC bias voltage. The BIAS bypass capacitor, C

BIAS improves

PSRR and THD+N by reducing power supply and other noise sources at the common-mode bias node, and also generates the clickless/popless, startup/shutdown

DC bias waveforms for the speaker amplifiers. Bypass

BIAS with a 0.047µF capacitor to GND.

______________________________________________________________________________________ 17

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Table 5. Suggested Capacitor Manufacturers

SUPPLIER

Taiyo Yuden

TDK

PHONE

800-348-2496

807-803-6100

FAX

847-925-0899

847-390-4405

WEBSITE

www.t-yuden.com

www.component.tdk.com

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 100m

Ω for optimum performance. Low-ESR ceramic capacitors minimize the output resistance of the charge pump. Most surface-mount ceramic capacitors satisfy the ESR requirement. For best performance over the extended temperature range, select capacitors with an X7R dielectric. Table 5 lists suggested manufacturers.

Flying Capacitor (C1)

The value of the flying capacitor (C1) affects the load regulation and output resistance of the charge pump. A

C1 value that is too small degrades the device’s ability to provide sufficient current drive, which leads to a loss of output voltage. Increasing the value of C1 may improve load regulation and reduces the charge-pump output resistance to an extent. Above 1µF, the on-resistance of the switches and the ESR of C1 and C2 dominate.

Output Capacitor (C2)

The output capacitor value and ESR directly affect the ripple at CPV

SS

. Increasing the value of C2 reduces output ripple. Likewise, decreasing the ESR of C2 reduces both ripple and output resistance. Lower capacitance values can be used in systems with low maximum output power levels. See the Output Power vs. Charge-Pump Capacitance and Load Resistance graph in the Typical Operating Characteristics.

CPV

DD

Bypass Capacitor

The CPV

DD bypass capacitor (C3) lowers the output impedance of the power supply and reduces the impact of the MAX9770’s charge-pump switching transients.

Bypass CPV

DD with C3, the same value as C1, and place it physically close to the CPV

DD and PGND (refer to the MAX9770 EV kit for a suggested layout).

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, as well as route the head away from the device. Good grounding improves audio performance, minimizes crosstalk between channels, and prevents any switching noise from coupling into the audio signal. Connect CPGND, PGND, and GND together at a single point on the PC board. Route

CPGND and all traces that carry switching transients away from GND, PGND, and the traces and components in the audio signal path.

Connect all components associated with the charge pump (C2 and C3) to the CPGND plane. Connect SV

SS and CPV

SS together at the device. Place the chargepump capacitors (C1, C2, and C3) as close to the device as possible. Bypass V

DD and PV

DD with a 1µF capacitor to GND. Place the bypass capacitors as close to the device as possible.

Use large, low-resistance output traces. As load impedance decreases, the current drawn from the device outputs increase. At higher current, the resistance of the output traces decrease the power delivered to the load.

Large output, supply, and GND traces also improve the power dissipation of the device.

The MAX9770 thin QFN package features an exposed thermal pad on its underside. This pad lowers the package’s thermal resistance by providing a direct heat conduction path. Due to the high efficiency of the MAX9770’s

Class D amplifier, additional heatsinking is not required. If additional heatsinking is required, connect the exposed paddle to GND. See the MAX9770 EV kit data sheet for suggested component values and layout guidelines.

18 ______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Block Diagram

2.5V TO 5.5V

1

μF

LEFT-CHANNEL

AUDIO INPUT 1

RIGHT-CHANNEL

AUDIO INPUT 1

MONO

AUDIO INPUT

LEFT-CHANNEL

AUDIO INPUT 2

RIGHT-CHANNEL

AUDIO INPUT 2

V

DD

1

μF

V

DD

C

IN

0.47

μF

SYNC

IN1L

16

(19)

25

(28)

C

IN

0.47

μF

IN1R

28

(3)

C

IN

1

μF

MONO

23

(26)

C

IN

0.47

μF

IN2L

24

(27)

C

IN

0.47

V

V

μF

HPS

DD

DD

GND

IN2R

GAIN2

GAIN1

SELM

SEL1

27

(2)

21

(24)

22

(25)

14

(17)

12

(15)

13

(16)

GND

SEL2

V

DD

SHDN

15

(18)

CPV

DD

C1P

7

(10)

10

(13)

C1

1

μF

9

(12)

C1N

CPGND

11

(14)

OSCILLATOR

MIXER/

MUX/GAIN

CONTROL

MUX AND

GAIN CONTROL

HEADPHONE

DETECTION

SHUTDOWN

CONTROL

CHARGE

PUMP

8

(11)

CPV

SS

5

(8)

SV

SS

C2

1

μF

OSC/2

2

(5)

CLASS D

MODULATOR

MAX9770

26

(1)

V

DD

GND

H-BRIDGE

V

DD

20

(23)

PV

DD

18

(21)

19

(22)

OUT+

OUT-

17

(20) PGND

1

(4) BIAS

6

(9)

HPS

4

(7)

HPOUTL

3

(6)

HPOUTR

( ) FOR TSSOP PIN.

2.5V TO 5.5V

0.1

μF

C

BIAS

0.047

μF

______________________________________________________________________________________ 19

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

System Diagram

AUDIO DAC

FM RADIO

MODULE

BASEBAND

PROCESSOR

2.5V TO 5.5V

1

μF

0.47

μF

0.47

μF

0.47

μF

0.47

μF

1

μF

V

DD

V

DD

MONO

SHDN

SEL1

SEL2

SELM

GAIN1

GAIN2

IN1R

IN1L

IN2R

V

DD

PV

DD

HPV

DD

OUT+

OUT-

MAX9770

HPOUTL

HPS

HPOUTR

IN2L

CPV

SS

SV

SS

CPGND

C1P

C1N

CPV

DD

BIAS

GND PGND

1

μF

1

μF

0.047

μF

1

μF

1

μF

2.5V TO 5.5V

20 ______________________________________________________________________________________

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

Pin Configurations

TOP VIEW

GND 1

IN2R 2

IN1R 3

BIAS 4

V

DD

5

HPOUTR 6

HPOUTL 7

SV

SS

8

HPS 9

CPV

DD

10

CPV

SS

11

C1N 12

C1P 13

CPGND 14

MAX9770

TSSOP

28 IN1L

27 IN2L

26 MONO

25 GAIN1

24 GAIN2

23 PV

DD

22 OUT-

21 OUT+

20 PGND

19 SYNC

18 SHDN

17 SELM

16 SEL2

15 SEL1

GAIN1 22

MONO 23

IN2L 24

IN1L

25

GND

26

IN2R 27

IN1R 28

21

20 19 18 17 16 15

MAX9770

1 2

3

4 5 6 7

14 SELM

13 SEL2

12 SEL1

11 CPGND

10 C1P

9 C1N

8

CPV

SS

TQFN

TRANSISTOR COUNT: 7020

PROCESS: BiCMOS

Chip Information

Package Information

For the latest package outline information, go to

www.maxim-ic.com/packages

.

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

28 TQFN-EP

28 TSSOP

T2855N-1

U28-1

21-0140

21-0066

______________________________________________________________________________________ 21

1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers

REVISION

NUMBER

2

REVISION

DATE

4/08

DESCRIPTION

Removing MAX9772 from data sheet

Revision History

PAGES

CHANGED

1–21

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.

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

© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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