MAXIM MAX9775, MAX9776 Technical data

General Description

The MAX9775/MAX9776 combine a high-efficiency Class D, stereo/mono audio power amplifier with a mono DirectDrive

receiver amplifier and a stereo

DirectDrive headphone amplifier.

Maxim’s 3rd-generation, ultra-low-EMI, Class D audio power amplifiers provide Class AB performance with Class D efficiency. The MAX9775/MAX9776 deliver

1.5W per channel into a 4Ω load from a 5V supply and offer efficiencies up to 79%. Active emissions limiting circuitry and spread-spectrum modulation greatly reduce EMI, eliminating the need for output filtering found in traditional Class D devices.

The MAX9775/MAX9776 utilize a fully differential architecture, a full-bridged output, and comprehensive clickand-pop suppression. A 3D stereo enhancement function allows the MAX9775 to widen the stereo sound field immersing the listener in a cleaner, richer sound experience than typically found in portable applications. The devices utilize a flexible, user-defined mixer architecture that includes an input mixer, volume control, and output mixer. All control is done through I2C.

The mono receiver amplifier and stereo headphone amplifier use Maxim’s DirectDrive architecture that produces a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors, saving cost, space, and component height.

The MAX9775 is available in a 36-bump WLP (3mm x 3mm) package. The MAX9776 is available in a 32-pin TQFN (5mm x 5mm) or a 36-bump WLP (3mm x 3mm) package. Both devices are specified over the extended

-40°C to +85°C temperature range.

Applications

Cell Phones Portable Multimedia Players Handheld Gaming Consoles

Features

♦ Unique Spread-Spectrum Modulation and Active

Emissions Limiting Significantly Reduces EMI

♦ 3D Stereo Enhancement (MAX9775 Only) ♦ Up to 3 Stereo Inputs ♦ 1.5W Stereo Speaker Output (4Ω, V

= 5V)

♦ 50mW Mono Receiver/Stereo Headphone Outputs

(32Ω, V

= 3.3V)

♦ High PSRR (68dB at 217Hz) ♦ 79% Efficiency (V

= 3.3V, RL= 8Ω, P

OUT

470mW)

♦ I

C Control—Input Configuration, Volume Control,

Output Mode

♦ Click-and-Pop Suppression ♦ Low Total Harmonic Distortion (0.03% at 1kHz) ♦ Current-Limit and Thermal Protection ♦ Available in Space-Saving, 36-Bump WLP (3mm x

3mm) and 32-Pin TQFN (5mm x 5mm) Packages

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

________________________________________________________________

Maxim Integrated Products

Ordering Information

MAX9775

MIXER/

MUX

GAIN

CONTROL

SOUND

CONTROL

I2C

INTERFACE

SINGLE SUPPLY 2.7V TO 5.5V

MAX9776

MIXER/

MUX

GAIN

CONTROL

I2C

INTERFACE

SINGLE SUPPLY 2.7V TO 5.5V

Simplified Block Diagrams

19-0746; Rev 4; 8/08

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.

Pin Configurations appear at end of data sheet.

PART PIN-PACKAGE

CLASS D

AMPLIFIER

MAX9775EBX+T 36 WLP* Stereo

MAX9776ETJ+ 32 TQFN-EP** Mono

MAX9776EBX+T 36 WLP* Mono

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

Denotes a lead-free/RoHS-compliant package.

Four center bumps depopulated.

EP = Exposed pad.

DirectDrive is a registered trademark of Maxim Integrated Products, Inc.

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= PVDD= CPVDD= 3.3V, V

GND

= V

PGND

= V

CPGND

= 0V, SHDN = VDD, I2C settings (INA gain = +20dB, INB gain = INC gain =

0dB, volume setting = 0dB, mono path gain = 0dB, SHDN = 1, SSM = 1). Speaker load resistors (R

LSP

) are terminated between

OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise noted. C1 = C2 = C3 = 1µF. T

= T

MIN

MAX

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

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

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

CPV

to CPGND ....................................................................6V

CPV

to CPGND .....................................................-6V to +0.3V

to CPGND..........................................................-6V to +0.3V

C1N .......................................(CPV

- 0.3V) to (CPGND + 0.3V)

C1P.......................................(CPGND - 0.3V) to (CPV

+ 0.3V)

HPL, HPR to GND...................(CPV

- 0.3V) to (CPVDD+ 0.3V)

GND to PGND and CPGND................................................±0.3V

to PVDDand CPVDD....................................................±0.3V

SDA, SCL to GND.....................................................-0.3V to +6V

All other pins to GND..................................-0.3V to (V

+ 0.3V)

Continuous Current In/Out of PV

, PGND, CPVDD, CPGND,

OUT__, HPR, and HPL..................................................±800mA

Continuous Input Current CPV

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

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

Duration of Short Circuit Between

OUT_+ and OUT_- ..................................................Continuous

Duration of HP_, OUT_ Short Circuit to

GND or PV

..........................................................Continuous

Continuous Power Dissipation (T

= +70°C) 36-Bump (3mm x 3mm) UCSP Multilayer Board

(derate 17.0mW/°C above +70°C)...........................1360.5mW

32-Pin (5mm x 5mm) TQFN Single-Layer Board

(derate 21.3mW/°C above +70°C)...........................1702.1mW

32-Pin TQFN Multilayer Board (derate 34.5mW/°C

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

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

GENERAL

Supply Voltage Range

Quiescent Current (Mono) I

Quiescent Current (Stereo) I

Mute Current I

Shutdown Current I

Turn-On Time t

Input Resistance R

Common-Mode Rejection Ratio CMRR TA = +25°C, fIN = 1kHz (Note 2) 45 50 60 dB

Input DC Bias Voltage V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

, P

PVDD

MUTE

SHDN

BIAS

VDD

Inferred from PSRR test 2.7 5.5 V

Output mode 1, 6, 11 (Rx mode) 6.3 10

Output mode 4, 9, 14 (HP mode) 8 12.6

Output mode 2, 7, 12 (SP mode) 9.5 15

Output mode 3, 8, 13 (SP and HP mode) 12.9 18

Output mode 1, 6, 11 (Rx mode) 7

Output mode 4, 9, 14 (HP mode) 9

Output mode 2, 7, 12 (SP mode) 16.5

Output mode 3, 8, 13 (SP and HP mode) 20

Current in mute (low power) 4.7 10 mA Hard shutdown SHDN = GND 0.1 10

Soft shutdown

Time from shutdown or power-on to full operation

B and C pair inputs, TA = +25°C, VOL = max

A pair inputs, TA = +25°C, +20dB 3.5 5.5 8.0 kΩ

IN_ inputs 1.12 1.25 1.38 V

See the I section

C Interface

17.5 28 41.0 kΩ

8.5 15

30 ms

µA

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDD= PVDD= CPVDD= 3.3V, V

GND

= V

PGND

= V

CPGND

= 0V, SHDN = VDD, I2C settings (INA gain = +20dB, INB gain = INC gain =

0dB, volume setting = 0dB, mono path gain = 0dB, SHDN = 1, SSM = 1). Speaker load resistors (R

LSP

) are terminated between

OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise noted. C1 = C2 = C3 = 1µF. T

= T

MIN

MAX

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

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

SPEAKER AMPLIFIERS

Output Offset Voltage V

Click-and-Pop Level K

Power-Supply Rejection Ratio (Note 3)

Current Limit 1.6 A

Total Harmonic Distortion Plus Noise (Note 4)

Signal-to-Noise Ratio SNR

Output Frequency f

Efficiency η

Gain A

Channel-to-Channel Gain Tracking (Note 5)

3D Sound Resistors (Note 5) R

Crosstalk (Notes 4, 5)

PSRR T

OUT

THD+N f = 1kHz

OSC

TA = +25°C ±5.5 ±23.5

≤ TA ≤ T

MIN

P eak vol tag e,

= + 25°C ,

A- w ei g hted , 32 sam p l es p er second ( N otes 2, 3)

MAX

Into shutdown -62

Out of shutdown -60

Into mute -63

Out of mute -62

VDD = 2.7V to 5.5V 48 70

f = 217Hz,

P-P

ripple

= +25°C

100mV

f = 1kHz, 100mV

f = 20kHz,

P-P

ripple

100mV

RL = 4Ω, VDD = 5V 1500

THD+N = 1%,

= +25°C

RL = 8Ω, VDD = 3.3V 450Output Power (Note 4) P

= 8Ω, VDD = 5V 1115

RL = 8Ω, P

= 125mW

OUT

= 4Ω,

= 250mW

OUT

= 1.8V

OUT

= 8Ω, 3D not

active (Note 3)

RMS

BW = 20Hz to 20kHz 81

A-weighted 84

Fixed-frequency modulation 1100

Spread-spectrum modulation 1100 ± 30

= 470mW, f = 1kHz both channels

OUT

driven, L = 68µH in series with 8Ω load

= +25°C ±1 %

Used with 22nF and 2.2nF external

capacitors

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

= 300mV

OUT

RMS

= 8Ω,

579kΩ

±40

0.03

0.04

79 %

12 dB

73 dB

kHz

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VDD= PVDD= CPVDD= 3.3V, V

GND

= V

PGND

= V

CPGND

= 0V, SHDN = VDD, I2C settings (INA gain = +20dB, INB gain = INC gain =

0dB, volume setting = 0dB, mono path gain = 0dB, SHDN = 1, SSM = 1). Speaker load resistors (R

LSP

) are terminated between

OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise noted. C1 = C2 = C3 = 1µF. T

= T

MIN

MAX

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

RECEIVER AMPLIFIER

Output Offset Voltage V

Click-and-Pop Level K

Power-Supply Rejection Ratio (Note 3)

Output Power P

Gain A

Total Harmonic Distortion Plus Noise

Signal-to-Noise Ratio SNR

Slew Rate SR 0.3 V/µs

Capacitive Drive C

HEADPHONE AMPLIFIERS

Output Offset Voltage V

Click-and-Pop Level K

ESD Protection HP_

Power-Supply Rejection Ratio (Note 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

PSRR T

OUT

THD+N

PSRR T

TA = +25°C ±1.8 ±5.5 mV

Peak voltage, TA = +25°C, A-weighted, 32 samples per second (Notes 3, 6)

= +25°C

TA = +25°C, THD+N = 1%

RL = 16Ω (V

= 32Ω (V

= 16Ω, V

800mV

TA = +25°C ±1.8 ±5.5 mV

Peak voltage, TA = +25°C, A-weighted, 32 samples per second (Notes 2, 4)

= +25°C

RMS

OUT

(Note 3)

Into shutdown -62

Into mute -67

Out of shutdown -63

Out of mute -66

VDD = 2.7V to 5.5V 58 80

f = 217Hz, 100mV

f = 1kHz, 100mV

f = 20kHz, 100mV

RL = 16Ω 60

= 800mV

BW = 20Hz to 20kHz 87

A-weighted 89

Into shutdown -61

Into mute -65

Out of shutdown -60

Out of mute -64

Contact ±4

Air ±8

VDD = 2.7V to 5.5V 58 80

f = 217Hz, 100mV

f = 1kHz, 100mV

f = 20kHz, 100mV

ripple

P-P

ripple

P-P

ripple

P-P

= 32Ω 50

, f = 1kHz) 0.03

RMS

, f = 1kHz) 0.024

RMS

ripple

P-P

ripple

P-P

ripple

P-P

3dB

300 pF

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

(VDD= PVDD= CPVDD= 3.3V, V

GND

= V

PGND

= V

CPGND

= 0V, SHDN = VDD, I2C settings (INA gain = +20dB, INB gain = INC gain =

0dB, volume setting = 0dB, mono path gain = 0dB, SHDN = 1, SSM = 1). Speaker load resistors (R

LSP

) are terminated between

OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise noted. C1 = C2 = C3 = 1µF. T

= T

MIN

MAX

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

Output Power P

Current Limit 170 mA

Gain A

Channel-to-Channel Gain Tracking

Total Harmonic Distortion Plus Noise

Signal-to-Noise Ratio SNR

Slew Rate SR 0.3 V/µs

Capacitive Drive C

Crosstalk

VOLUME CONTROL

Volume Control

Mono Gain All outputs

Input Pair A Control

Mute Attenuation (Minimum Volume)

DIGITAL INPUTS (SHDN, SDA, SCL)

Input-Voltage High V

Input-Voltage Low V

Input Hysteresis (SDA, SCL) V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

THD+N

OUT

HYS

TA = +25°C, THD+N = 1%

= +25°C ±1 %

RL = 16Ω (V

= 32Ω (V

= 16Ω,

OUT

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

OUT

IN+6dB = 0 (minimum gain setting)

IN+6dB = 1 (maximum gain setting)

INA+20dB = 0 (minimum gain setting) Set by IN+6dB

INA+20dB = 1 (maximum gain setting) 20

= 1V

OUT

= 800mV

= 160mV

RMS

RL = 16Ω 60

= 32Ω 50

= 800mV

, f = 1kHz) 0.03

RMS

, f = 1kHz) 0.024

RMS

BW = 20Hz to 20kHz

A-weighted 93

= 16Ω,

HP gain (max) 3

SP gain (max) 12

HP gain (min) -72

SP gain (min) -63

HP gain (max) 9

SP gain (max) 18

HP gain (min) -61

SP gain (min) -57

Mono+6dB = 0 0

Mono+6dB = 1 6

1.4 V

+3 dB

300 pF

75 dB

80 dB

200 mV

0.4 V

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

6 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VDD= PVDD= CPVDD= 3.3V, V

GND

= V

PGND

= V

CPGND

= 0V, SHDN = VDD, I2C settings (INA gain = +20dB, INB gain = INC gain =

0dB, volume setting = 0dB, mono path gain = 0dB, SHDN = 1, SSM = 1). Speaker load resistors (R

LSP

) are terminated between

OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise noted. C1 = C2 = C3 = 1µF. T

= T

MIN

MAX

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

Note 1: All devices are 100% production tested at room temperature. All temperature limits are guaranteed by design. Note 2: Measured at headphone outputs. Note 3: Amplifier inputs AC-coupled to GND. Note 4: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For R

= 8Ω, L = 68µH;

for R

= 4Ω, L = 47µH.

Note 5: MAX9775 only. Note 6: Testing performed at room temperature with an 8Ω resistive load in series with a 68µH inductive load connected across BTL

outputs for speaker amplifier. Testing performed with a 32Ω resistive load connected between OUT_ and GND for headphone amplifier. Testing performed with 32Ω resistive load connected between OUTRx and GND for mono receiver amplifier. Mode transitions are controlled by I

Note 7: Guaranteed by design.

SDA, SCL Input Capacitance C

Input Leakage Current I

Pulse Width of Spike Suppressed t

DIGITAL OUTPUTS (SDA Open Drain)

Output Low Voltage SDA V

Output Fall Time SDA t

I2C INTERFACE TIMING (Note 7)

Serial Clock Frequency f

Bus Free Time Between STOP and START Conditions

START Condition Hold t

STOP Condition Setup Time t

Clock Low Period t

Clock High Period t

Data Setup Time t

Data Hold Time t

Maximum Receive SCL/SDA Rise Time

Maximum Receive SCL/SDA Fall Time

Setup Time for STOP Condition t

Capacitive Load for Each Bus Line

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

HD:STA

SU:STA

SU:DAT

HD:DAT

SU:STO

SCL

BUF

LOW

HIGH

= 6mA 0.4 V

SINK

H(MIN)

10pF to 400pF, I

10 pF

0.3 5.0 µA

50 ns

to V

bus capacitance =

L(MAX)

SINK

= 3mA

250 ns

DC 400 kHz

1.3 µs

0.6 µs

1.3 µs

0.6 µs

100 ns

0 900 ns

0.6 µs

300 ns

400 pF

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

_______________________________________________________________________________________

Typical Operating Characteristics

(VDD= PVDD= CPVDD= 3.3V, GND = PGND = CPGND = 0V, SHDN = VDD, I2C default gain settings (INA gain = +20dB, INB gain = INC gain = 0dB, volume setting = 0dB, mono path gain = 0dB, SHDN = 1, SSM = 1). Speaker load resistors (R

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

VDD = 5V

= 4Ω

= 400mW

0.1

THD+N (%)

0.01

0.001

OUT

= 1000mW

OUT

10 100k

FREQUENCY (Hz)

10k1k100

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

VDD = 3.3V

= 8Ω

= 300mW

0.1

THD+N (%)

0.01

OUT

= 150mW

MAX9775/76 toc01

MAX9775/76 toc04

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

VDD = 5V

= 8Ω

= 150mW

OUT

0.1

THD+N (%)

0.01

0.001 10 100k

= 750mW

OUT

FREQUENCY (Hz)

10k1k100

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

VDD = 3.3V

= 8Ω

= 500mW

OUT

0.1

THD+N (%)

0.01

FFM

SSM

MAX9775/76 toc02

THD+N (%)

MAX9775/76 toc05

THD+N (%)

TOTAL HARMONIC DISTORTION PLUS NOISE

VDD = 3.3V

= 4Ω

= 400mW

OUT

0.1

0.01

0.001 10 100k

TOTAL HARMONIC DISTORTION PLUS NOISE

100

VDD = 5V

= 4Ω

0.1

0.01 f = 20Hz

vs. FREQUENCY

= 150mW

OUT

FREQUENCY (Hz)

vs. OUTPUT POWER

10k1k100

f = 1kHz

f = 10kHz

MAX9775/76 toc03

MAX9775/76 toc06

0.001 10 100k

FREQUENCY (Hz)

0.001

10k1k100

10 100k

FREQUENCY (Hz)

10k1k100

0.001 0 2.0

OUTPUT POWER (W)

1.61.20.80.4

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. OUTPUT POWER

MAX9775/76 toc07

OUTPUT POWER (W)

THD+N (%)

1.20.90.60.3

0.01

0.1

100

0.001 0 1.5

VDD = 5V R

= 8Ω

f = 10kHz

f = 20Hz

f = 1kHz

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. OUTPUT POWER

MAX9775/76 toc08

OUTPUT POWER (W)

THD+N (%)

0.60.40.2

0.01

0.1

100

0.001 0 0.8

VDD = 3.3V R

= 4Ω

f = 10kHz

f = 20Hz

f = 1kHz

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. OUTPUT POWER

MAX9775/76 toc09

OUTPUT POWER (W)

THD+N (%)

0.40.2

0.01

0.1

100

0.001 0 0.6

VDD = 3.3V R

= 8Ω

f = 10kHz

f = 20Hz

f = 1kHz

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. OUTPUT POWER

MAX9775/76 toc10

OUTPUT POWER (W)

THD+N (%)

1.20.90.60.3

0.01

0.1

100

0.001 0 1.5

VDD = 5V R

= 8Ω

f = 1kHz

SSM

FFM

EFFICIENCY

vs. OUTPUT POWER

MAX9775/76 toc11

OUTPUT POWER (W)

EFFICIENCY (%)

3.22.41.60.8

100

0 4.0

VDD = 5V f

= 1kHz

OUT

= P

OUTL

+ P

OUTR

RL = 8Ω

RL = 4Ω

EFFICIENCY

vs. OUTPUT POWER

MAX9775/76 toc12

OUTPUT POWER (W)

EFFICIENCY (%)

1.61.20.80.4

100

0 2.0

VDD = 3.3V f

= 1kHz

OUT

= P

OUTL

+ P

OUTR

RL = 8Ω

RL = 4Ω

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

_______________________________________________________________________________________

Typical Operating Characteristics (continued)

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

OUTPUT POWER

vs. SUPPLY VOLTAGE

2200

RL = 4Ω

2000

f = 1kHz

1800

1600

1400

1200

1000

800

OUTPUT POWER (mW)

600

400

200

2.7

THD+N = 10%

THD+N = 1%

SUPPLY VOLTAGE (V)

OUTPUT POWER

vs. LOAD

1000

= 3.3V

f = 1kHz

800

THD+N = 10%

600

400

OUTPUT POWER (W)

200

THD+N = 1%

1 100

LOAD (Ω)

1600

RL = 8Ω f = 1kHz

1400

MAX9775/76 toc13

1200

1000

800

600

OUTPUT POWER (mW)

400

200

5.24.74.23.73.2

MAX9775/76 toc16

2.7

-10

V RL = 8Ω

-20

-30

-40

-50

-60

-70

-80

POWER-SUPPLY REJECTION RATIO (dB)

-90

-100 10 100k

OUTPUT POWER

vs. SUPPLY VOLTAGE

THD+N = 10%

THD+N = 1%

5.24.73.2 3.7 4.2

SUPPLY VOLTAGE (V)

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

= 3.3V

= 100mV

P-P

OUTR

OUTL

10k1k100

FREQUENCY (Hz)

MAX9775/76 toc14

OUTPUT POWER (W)

MAX9775/76 toc17

CROSSTALK (dB)

2.5 V

= 5V

f = 1kHz

2.0

1.5

1.0

THD+N = 1%

0.5

1 100

CROSSTALK vs. FREQUENCY

OUT_ = 1V

-10 RL = 8Ω

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120 10 100 1k 10k 100k

LEFT TO RIGHT

OUTPUT POWER

vs. LOAD

THD+N = 10%

LOAD (Ω)

P-P

RIGHT TO LEFT

FREQUENCY (Hz)

MAX9775/76 toc15

MAX9775/6 toc18

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

10 ______________________________________________________________________________________

Typical Operating Characteristics (continued)

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

CROSSTALK vs. INPUT AMPLITUDE

INPUT AMPLITUDE (V

RMS

)

CROSSTALK (dB)

MAX9775/6 toc19

0 0.1 0.2 0.3 0.4 0.5 0.6

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

fIN = 1kHz R

= 8Ω

GAIN = +12dB

LEFT TO RIGHT

RIGHT TO LEFT

IN-BAND OUTPUT SPECTRUM

MAX9775/76 toc20

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dBV)

15k10k5k

-120

-100

-80

-60

-40

-20

-140 0 20k

SSM MODE R

= 8Ω

= 3.3V

= 1kHz

UNWEIGHTED

IN-BAND OUTPUT SPECTRUM

MAX9775/76 toc21

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dBV)

15k10k5k

-120

-100

-80

-60

-40

-20

-140 0 20k

FFM MODE R

= 8Ω

= 3.3V

= 1kHz

UNWEIGHTED

WIDEBAND OUTPUT SPECTRUM

FIXED-FREQUENCY MODE

FREQUENCY (MHz)

OUTPUT MAGNITUDE (dBV)

MAX9775/6 toc22

-140

-120

-100

-80

-60

-40

-20

0.1 1 10 100 1000

VDD = 5V R

= 8Ω

INPUTS AC GROUNDED

WIDEBAND OUTPUT SPECTRUM

SPREAD-SPECTRUM MODE

FREQUENCY (MHz)

OUTPUT MAGNITUDE (dBV)

MAX9775 toc23

-140

-120

-100

-80

-60

-40

-20

0.1 1 10 100 1000

VDD = 5V R

= 8Ω

INPUTS AC GROUNDED

MAX9775 SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX9775/76 toc24

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

5.24.74.23.73.2

2.7

SP MODE INPUTS AC GROUNDED OUTPUTS UNLOADED

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________

Typical Operating Characteristics (continued)

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

MAX9776 SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX9775/76 toc25

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

5.24.74.23.73.2

2.7

SP MODE INPUTS AC GROUNDED OUTPUTS UNLOADED

SHUTDOWN SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX9775/76 toc26

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (nA)

5.24.74.23.73.2

100

2.7

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

MAX9775/76 toc27

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.01

0.1

0.001 10 100k

= 5V

= 32Ω

OUT

= 20mW

OUT

= 40mW

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

MAX9775/76 toc28

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.01

0.1

0.001 10 100k

= 3.3V

= 16Ω

OUT

= 20mW

OUT

= 40mW

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. FREQUENCY

MAX9775/76 toc29

FREQUENCY (Hz)

THD+N (%)

10k1k100

0.01

0.1

0.001 10 100k

= 3.3V

= 32Ω

OUT

= 10mW

OUT

= 40mW

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. OUTPUT POWER

MAX9775/76 toc30

OUTPUT POWER (mW)

THD+N (%)

604020

0.01

0.1

100

0.001 080

VDD = 5V R

= 32Ω

f = 10kHz

f = 20Hz

f = 1kHz

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

12 ______________________________________________________________________________________

Typical Operating Characteristics (continued)

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. OUTPUT POWER

OUTPUT POWER (mW)

THD+N (%)

MAX9775 toc31

0 30 60 90 120

0.001

0.01

0.1

100

f = 20Hz

f = 1kHz

f = 10kHz

VDD = 3.3V R

= 16Ω

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. OUTPUT POWER

MAX9775/76 toc32

OUTPUT POWER (mW)

THD+N (%)

604020

0.01

0.1

100

0.001 080

VDD = 3.3V R

= 32Ω

f = 10kHz

f = 20Hz

f = 1kHz

TOTAL HARMONIC DISTORTION PLUS NOISE

vs. COMMON-MODE VOLTAGE

COMMON-MODE VOLTAGE (V)

THD+N (%)

MAX9775/6 toc33

0 0.5 1.0 1.5 2.0 2.5

0.001

0.01

0.1

100

VDD = 3.3V f

= 1kHz

OUT

= 30mW GAIN = +3dB R

= 32Ω

POWER DISSIPATION

vs. OUTPUT POWER

MAX9775/76 toc34

TOTAL OUTPUT POWER (mW)

POWER DISSIPATION (mW)

8040

100

150

200

250

300

350

400

450

500

0 120

= 5V f = 1kHz R

= 32Ω

OUT

= P

OUTR

+ P

OUTL

POWER DISSIPATION

vs. OUTPUT POWER

MAX9775/76 toc35

TOTAL OUTPUT POWER (mW)

POWER DISSIPATION (mW)

1208040

100

150

200

250

300

350

400

450

500

0 160

= 3.3V f = 1kHz P

OUT

= P

OUTR

+ P

OUTL

RL = 16Ω

RL = 32Ω

OUTPUT POWER

vs. SUPPLY VOLTAGE

MAX9775/76 toc36

SUPPLY VOLTAGE (V)

OUTPUT POWER (mW)

5.24.74.23.73.2

2.7

THD+N = 10%

THD+N = 1%

RL = 32Ω f = 1kHz

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________

Typical Operating Characteristics (continued)

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

OUTPUT POWER

vs. LOAD

MAX9775/76 toc37

LOAD (Ω)

OUTPUT POWER (mW)

100

120

140

160

180

200

10 1000

THD+N = 10%

THD+N = 1%

= 5V

f = 1kHz

OUTPUT POWER

vs. LOAD

MAX9775/76 toc38

LOAD (Ω)

OUTPUT POWER (mW)

100

120

140

160

180

200

10 1000

THD+N = 10%

THD+N = 1%

= 3.3V

f = 1kHz

OUTPUT POWER vs. LOAD RESISTANCE

AND CHARGE-PUMP CAPACITOR SIZE

LOAD (Ω)

OUTPUT POWER (mW)

MAX9775/6 toc39

100

10 100 1000

C1 = C2 = 2.2μF

VDD = 3.3V f

= 1kHz

THD+N = 1%

C1 = C2 = 1μF

C1 = C2 = 0.68μF

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

FREQUENCY (Hz)

POWER-SUPPLY REJECTION RATIO (dB)

MAX9775/6 toc40

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

10 100 1k 10k 100k

HPL

HPR

VDD = 3.3V V

= 100mV

P-P

RL = 32Ω

OUTPUT FREQUENCY SPECTRUM

MAX9775/76 toc41

FREQUENCY (Hz)

OUTPUT MAGNITUDE (dBV)

15k10k5k

-120

-100

-80

-60

-40

-20

-140 0 20k

= 3.3V

= 1kHz

= 32Ω

CROSSTALK vs. FREQUENCY

FREQUENCY (Hz)

CROSSTALK (dB)

MAX9775/6 toc42

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

10 100 1k 10k 100k

OUT_ = 1V

P-P

RL = 32Ω

LEFT TO RIGHT

RIGHT TO LEFT

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

14 ______________________________________________________________________________________

Typical Operating Characteristics (continued)

LSP

) are terminated

between OUT_+ and OUT_-, headphone load resistors are terminated to GND, unless otherwise stated. C1 = C2 = C3 = 1µF. T

+25°C, unless otherwise noted.)

CROSSTALK vs. INPUT AMPLITUDE

INPUT AMPLITUDE (V

RMS

)

CROSSTALK (dB)

MAX9775 toc43

0 0.4 0.8 1.2

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

fIN = 1kHz R

= 32Ω

GAIN = +3dB

LEFT TO RIGHT

RIGHT TO LEFT

TURN-ON RESPONSE

MAX9775/76 toc44

10ms/div

SCL 2V/div

SPEAKER OUTPUT 50mA/div

HEADPHONE OUTPUT 2V/div

TURN-OFF RESPONSE

MAX9775/76 toc45

10ms/div

SCL 2V/div

SPEAKER OUTPUT 50mA/div

HEADPHONE OUTPUT 2V/div

MUTE-ON RESPONSE

MAX9775/76 toc46

10ms/div

SCL 2V/div

SPEAKER OUTPUT 50mA/div

HEADPHONE OUTPUT 2V/div

MUTE-OFF RESPONSE

MAX9775/76 toc47

10ms/div

SCL 2V/div

SPEAKER OUTPUT 50mA/div

HEADPHONE OUTPUT 2V/div

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 15

Pin Description—MAX9775

PIN NAME FUNCTION

F1 PV

E1 OUTL- Negative Left-Speaker Output

D2 SCL Serial Clock Input. Connect a 1kΩ pullup resistor from SCL to VDD.

D1, F3 PGND Power Ground

C1 OUTL+ Positive Left-Speaker Output

C2 SDA Serial Data Input. Connect a 1kΩ pullup resistor from SDA to VDD.

B1 CL_L 3D External Capacitor 3. Connect a 2.2nF capacitor to GND.

B2 CL_H 3D External Capacitor 4. Connect a 22nF capacitor to GND.

A1 CPV

A2 C1P Charge-Pump Flying Capacitor Positive Terminal

B3 VBIAS Common-Mode Bias

A3 CPGND Charge-Pump GND

A4 C1N Charge-Pump Flying Capacitor Negative Terminal

B4 INC1 Input C1. Left input or positive input (see Table 5a).

A5 CPV

A6 HPL Left Headphone Output

B5 V

B6 HPR Right Headphone Output

C5 INC2 Input C2. Right input or negative input (see Table 5a).

C6 OUTRx Mono Receiver Output

D6 V

D5 INB2 Input B2. Right input or negative input (see Table 5a).

E6 CR_L 3D External Capacitor 1. Connect a 2.2nF capacitor to GND.

E5 INB1 Input B1. Left input or positive input (see Table 5a).

F6 GND Analog Ground

F5 CR_H 3D External Capacitor 2. Connect a 22nF capacitor to GND.

E4 INA2 Input A2. Right input or negative input (see Table 5a).

F4 OUTR+ Positive Right Speaker Output

E3 INA1 Input A1. Left input or positive input (see Table 5a).

F2 OUTR- Negative Right Speaker Output E2 SHDN Active-Low Hardware Shutdown

—EP

Class D Power Supply

Charge-Pump Power Supply

Charge-Pump Output. Connect to VSS.

Headphone Amplifier Negative Power Supply. Connect to CPVSS.

Analog Power Supply

Exposed Pad. The external pad lowers the package’s thermal impedance by providing a direct heat conduction path from the die to the PCB. The exposed pad is internally connected to GND. Connect the exposed thermal pad to the GND plane.

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

16 ______________________________________________________________________________________

Pin Description—MAX9776

TQFN UCSP

1F1PVDDClass D Power Supply

2 E1 OUT- Negative Left-Speaker Output

3 D2 SCL Serial Clock Input. Connect a 1kΩ pullup resistor from SCL to VDD.

4, 29 D1, F3 PGND Power Ground

5 C1 OUT+ Positive Left-Speaker Output

6 C2 SDA Serial Data Input. Connect a 1kΩ pullup resistor from SDA to VDD.

7, 8, 23,

26, 28, 31

9 A1 CPV

10 A2 C1P Charge-Pump Flying Capacitor Positive Terminal

11 B3 VBIAS Common-Mode Bias

12 A3 CPGND Charge-Pump GND

13 A4 C1N Charge-Pump Flying Capacitor Negative Terminal

14 B4 INC1 Input C1. Left input or positive input (see Table 5a).

15 A5 CPV

16 A6 HPL Left Headphone Output

17 B5 V

18 B6 HPR Right Headphone Output

19 C5 INC2 Input C2. Right input or negative input (see Table 5a).

20 C6 OUTRx Mono Receiver Output

21 D6 V

22 D5 INB2 Input B2. Right input or negative input (see Table 5a).

24 E5 INB1 Input B1. Left input or positive input (see Table 5a).

25 F6 GND Analog Ground

27 E4 INA2 Input A2. Right input or negative input (see Table 5a).

30 E3 INA1 Input A1. Left input or positive input (see Table 5a). 32 E2 SHDN Active-Low Hardware Shutdown

EP — EP

B1, B2,

E6, F2,

F4, F5

NAME FUNCTION

I.C.

Internal Connection. Leave unconnected. This pin is internally connected to the signal path. Do not connect together or to any other pin.

Charge-Pump Power Supply

Charge-Pump Output. Connect to VSS.

Headphone Amplifier Negative Power Supply. Connect to CPVSS.

Analog Power Supply

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 17

Typical Application Circuits

10kΩ

C2 1μF

CPVSSV

15 (A5) 17 (B5)

13 (A4)

C1N

12 (A3)

1μF

CPGND

C1P

CPV

INA1

INA2

INB1

INB2

INC1

INC2

VBIAS

CHARGE

10 (A2)

9 (A1)

30 (E3)

27 (E4)

24 (E5)

22 (D5)

14 (B4)

19 (C5)

11 (B3)

PUMP

INPUT A: 0dB,

6dB, OR 20dB

INPUT B: 0dB

OR 6dB

INPUT C: 0dB

OR 6dB

INPUT MIXER

1μF

21 (D6)

RIGHT

VOLUME

LEFT

VOLUME

MONO

VOLUME

1μF

OUTPUT

MIXER

1 (F1)

MAXIM 3D

SOUND

DirectDrive

3dB

12dB

CLASS D

AMPLIFIER

12dB

CLASS D

AMPLIFIER

1μF0.1μF

HPL

16 (A6)

HPR

18 (B6)

OUTRx

20 (C6)

OUTL+

5 (C1)

2 (E1)

OUTL-

28 (F4)

OUTR+

31 (F2)

OUTR-

6 (C2)

SDA

SCL

SHDN

3 (D2)

32 (E2)

GND

I2C CONTROL

4 (D1) 29 (F3)

PGND

23 (E6)25 (F6)

CR_L

2.2nF

MAX9775

3D CIRCUIT

26 (F5)

CR_H 22nF

7 (B1)

CL_L

2.2nF

8 (B2)

CL_H 22nF

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

18 ______________________________________________________________________________________

Typical Application Circuits (continued)

CPVSSV

15 (A5) 17 (B5)

13 (A4)

C1N

12 (A3)

1μF

CPGND

C1P

CPV

INA1

INA2

INB1

INB2

INC1

INC2

VBIAS

CHARGE

10 (A2)

9 (A1)

30 (E3)

27 (E4)

24 (E5)

22 (D5)

14 (B4)

19 (C5)

11 (B3)

PUMP

INPUT A: 0dB, 6dB, OR 20dB

INPUT B: 0dB

OR 6dB

INPUT C: 0dB

OR 6dB

10kΩ

1μF

C2 1μF

INPUT MIXER

RIGHT

VOLUME

LEFT

VOLUME

MONO

VOLUME

21 (D6)

OUTPUT

MIXER

1μF

1 (F1)

1μF0.1μF

DirectDrive

16 (A6)

18 (B6)

20 (C6)

5 (C1)

2 (E1)

HPL

HPR

OUTRx

OUT+

OUT-

3dB

12dB

CLASS D

AMPLIFIER

6 (C2)

SDA

SCL

SHDN

3 (D2)

32 (E2)

I2C CONTROL

25 (F6)

GND

4 (D1) 29 (F3)

PGNDPGND

MAX9776

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 19

Detailed Description

The MAX9775/MAX9776 ultra-low-EMI, filterless, Class D audio power amplifiers feature several improvements to switch-mode amplifier technology. The MAX9775/ MAX9776 feature active emissions limiting circuitry to reduce EMI. Zero dead-time technology maintains stateof-the-art efficiency and THD+N performance by allowing the output FETs to switch simultaneously without crossconduction. A unique filterless modulation scheme and spread-spectrum modulation create compact, flexible, low-noise, efficient audio power amplifiers while occupying minimal board space. The differential input architecture reduces common-mode noise pickup with or without the use of input-coupling capacitors. The MAX9775/MAX9776 can also be configured as singleended input amplifiers without performance degradation.

The MAX9775/MAX9776 feature three fully differential input pairs (INA_, INB_, INC_) that can be configured as stereo single-ended or mono differential inputs. I2C provides control for input configuration, volume level, and mixer configuration. The MAX9775’s 3D enhancement feature widens the stereo sound field to improve stereo imaging when stereo speakers are placed in close proximity.

DirectDrive allows the headphone and mono receiver amplifiers to output ground-referenced signals from a single supply, eliminating the need for large DC-blocking capacitors. Comprehensive click-and-pop suppression minimizes audible transients during the turn-on and turn-off of amplifiers.

Class D Speaker Amplifier

Comparators monitor the audio inputs and compare the complementary input voltages to a sawtooth waveform. The comparators trip when the input magnitude of the sawtooth exceeds their corresponding input voltage. The active emissions limiting circuitry slightly reduces the turn-on rate of the output H-bridge by slew-rate limiting the comparator output pulse. 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)

,100ns typ) 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 devices to achieve high levels of linearity.

Figure 1. Outputs with an Input Signal Applied

IN-

IN+

OUT-

OUT+

- V

OUT+

OUT-

ON(MIN)

MAX9775/MAX9776

Operating Modes

Fixed-Frequency Modulation

The MAX9775/MAX9776 feature a fixed-frequency modulation mode with a 1.1MHz switching frequency, set through the I2C interface (Table 2). In fixed-frequency modulation mode, the frequency spectrum of the Class D output consists of the fundamental switching frequency and its associated harmonics (see the Wideband Output Spectrum Fixed-Frequency Mode graph in the

Typical Operating Characteristics

Spread-Spectrum Modulation

The MAX9775/MAX9776 feature a unique spread-spectrum modulation that flattens the wideband spectral components. 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 spread-spec-

trum modulation mode through the I2C interface (Table

2). In spread-spectrum modulation mode, the switching frequency varies randomly by ±30kHz around the center frequency (1.16MHz). 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 (see Figure 3).

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

20 ______________________________________________________________________________________

OUT+

- V

OUT-

IN-

IN+

OUT+

OUT-

ON(MIN)

Figure 2. Output with an Input Signal Applied (Spread-Spectrum Modulation Mode)

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 21

Figure 3. EMI with 76mm of Speaker Cable

40.0

35.0

EN55022B LIMIT

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)

AMPLITUDE (dBμV/m)

30.0

25.0

20.0

15.0

10.0

5.0

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

22 ______________________________________________________________________________________

Filterless Modulation/Common-Mode Idle

The MAX9775/MAX9776 use Maxim’s unique 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, especially when idling. When no signal is present at the input of the MAX9775/MAX9776, the outputs switch as shown in Figure 4. Because the MAX9775/MAX9776 drive the speaker differentially, the two outputs cancel each other, resulting in no net idle mode voltage across the speaker, minimizing power consumption.

DirectDrive

Traditional single-supply headphone amplifiers have outputs biased at 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 amplifier.

Maxim’s DirectDrive architecture uses a charge pump to create an internal negative supply voltage. This allows the headphone outputs of the MAX9775/MAX9776 to be biased at 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 MAX9775/MAX9776 charge pump requires two small ceramic capacitors, conserving board space, reducing cost, and improving the frequency response of the headphone amplifier. See the Output Power vs. Load Resistance and Charge-Pump Capacitor Size graph in the

Typical Operating Characteristics

for details of the possible capacitor sizes. There is a low DC voltage on the amplifier outputs due to amplifier offset. However, the offset of the MAX9775/MAX9776 is typically 1.4mV, which, when combined with a 32Ω load, results in less than 44nA of DC current flow to the headphones.

In addition to the cost and size disadvantages of the DC-blocking 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) The sleeve is typically grounded to the chassis. Using the midrail biasing approach, the sleeve must be isolated from system ground, complicating product design.

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

3) When using the headphone jack as a lineout to other equipment, the bias voltage on the sleeve may conflict with the ground potential from other equipment, resulting in possible damage to the amplifiers.

VIN = 0V

OUT-

OUT+

- V

OUT-

= 0V

Figure 4. Outputs with No Input Signal

Charge Pump

The MAX9775/MAX9776 feature a low-noise charge pump. The switching frequency of the charge pump is half the switching frequency of the Class D amplifier, regardless of the operating mode. The nominal switching frequency is well beyond the audio range, and thus does not interfere with the audio signals, resulting in an SNR of 93dB. Although not typically required, additional high-frequency noise attenuation can be achieved by increasing the size of C2 (see the

Typical Application

Circuits

). The charge pump is active in both speaker

and headphone modes.

3D Enhancement

The MAX9775 features a 3D stereo enhancement function, allowing the MAX9775 to widen the stereo sound field and immerse the listener in a cleaner, richer sound experience. Note the MAX9776, mono Class D speaker amplifier does not feature 3D stereo enhancement.

As stereo speaker applications become more compact, the quality of stereophonic sound is jeopardized.

With Maxim’s 3D stereo enhancement, it is possible to emulate stereo sound in situations where the speakers must be positioned close together. As shown in Figure 6, wave interference can be used to cancel the left channel in the vicinity of the listener’s right ear and vice versa. This technique can yield an apparent separation between the speakers that is a factor of four or greater than the actual physical separation.

The external capacitors CL_L, CL_H, CR_L, and CR_H set the starting and stopping range of the 3D effect. CL_H and CR_H are for the lower limit (in the MAX9775

Typical Application Circuit

, it is 1kHz), CR_L and CL_L are for the higher limit (10kHz). The internal resistor is typically 7kΩ and the frequencies are calculated as:

where R = 7kΩ and C = CR_H and CL_H.

where R = 7kΩ and C = CR_L and CL_L.

For example, with CR_L = CL_L = 2.2nF and CR_H = CL_H = 22nF, the 3D start frequency is 1kHz and the 3D stop frequency is 10kHz.

Enabling the 3D sound effect results in an apparent 6dB gain because the internal left and right signals are mixed together. This gain can be nulled by volume adjusting the left and right signals. The volume control can be programmed through the I2C-compatible interface to compensate for the extra 6dB increase in gain. For example,

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 23

Figure 5. Traditional Amplifier Output vs. MAX9775/MAX9776 DirectDrive Output

Figure 6. MAX9775 3D Stereo Enhancement

RIGHT

OUT

CONVENTIONAL DRIVER-BIASING SCHEME

OUT

DirectDrive BIASING SCHEME

VDD / 2

GND

-V

LEFT

RIGHT

LISTENER

LEFT

D START

_ =

D STOP

_ =

MAX9775/MAX9776

if the right and left volume controls are set for a maximum gain 0dB (11111 in Table 7, IN+6dB = 0 from Table

10) before the 3D effect is activated, the volume control should be programmed to -6dB (11001 in Table 7) immediately after the 3D effect has been activated.

Signal Path

The audio inputs of the MAX9775/MAX9776—INA, INB, and INC—are preamplified and then mixed by the input mixer to create three internal signals: Left (L), Right (R), and Mono (M). Tables 5a and 5b show how the inputs are mixed to create L, R, and M. These signals are then independently volume adjusted by the L, R, and M volume control and routed to the output mixer. The output mixer mixes the internal L, R, and M signals to create a variety of audio mixes that are output to the headphone speaker and mono receiver amplifiers. Figure 6 shows the signal path that the audio signals take.

Signal amplification takes place in three stages. In the first stage, the inputs (INA, INB, and INC) are preamplified. The amount by which each input is amplified is determined by the bits INA+20dB (B4 in the Input Mode Control Register) and IN+6dB (B3 in the Global Control Register). After preamplification, they are mixed

in the Input Mixer to create the internal signals L, R, and M.

In the second stage of amplification, the internal L, R, and M signals are independently volume adjusted.

Finally, each output amplifier has its own internal gain. The speaker, headphone, and mono receiver amplifiers have fixed gains of 12dB, 3dB, and 3dB, respectively.

Current-Limit and Thermal Protection

The MAX9775/MAX9776 feature current limiting and thermal protection to protect the device from short circuits and overcurrent conditions. The headphone amplifier pulses in the event of an overcurrent condition with a pulse every 100µs as long as the condition is present. Should the current still be high, the above cycle is repeated. The speaker amplifier current-limit protection clamps the output current without shutting down the output. This can result in a distorted output. Current is limited to 1.6A in the speaker amplifiers and 170mA in the headphone and mono receiver amplifiers.

The MAX9775/MAX9776 have thermal protection that disables the device at +150°C until the temperature decreases to +120°C.

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

24 ______________________________________________________________________________________

Figure 7. Signal Path

-75dB TO 0dB

RVOL

PREAMPLIFIER

INPUT

INPUT A:

0dB, 6dB, 20dB

INPUT B AND C:

0dB, 6dB

INPUT

MIXER

MONO

-75dB TO 0dB

LVOL

OUTPUT

MIXER

-75dB TO 0dB0dB TO 6dB

MVOLMONO+6dB

12dB

SPEAKER

3dB

HEADPHONE

3dB

RECEIVER

Click-and-Pop Suppression

In conventional single-supply headphone amplifiers, the output-coupling capacitor is a major contributor of audible clicks and pops. Upon startup, the amplifier 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 MAX9775/MAX9776 headphone amplifier does not require output-coupling capacitors, this problem does not arise.

In most applications, the output of the preamplifier driving the MAX9775/MAX9776 has a DC bias of typically half the supply. During startup, the input-coupling capacitor is charged to the preamplifier’s DC bias voltage, resulting in a DC shift across the capacitor and an audible click/pop. An internal delay of 30ms eliminates the click/pop caused by the input filter.

Shutdown

The MAX9775/MAX9776 feature a 0.1µA hard shutdown mode that reduces power consumption to extend battery life and a soft shutdown where current consumption is typically 8.5µA. Hard shutdown is controlled by connecting the SHDN pin to GND, disabling the amplifiers, bias circuitry, charge pump, and I2C. In shutdown, the headphone amplifier output impedance is 1.4kΩ and the speaker output impedance is 300kΩ. Similarly, the MAX9775/MAX9776 enter soft-shutdown when the SHDN bit = 0 (see Table 2). The I

C interface is active and the contents of the command register are not affected when in soft-shutdown. This allows the master to write to the MAX9775/MAX9776 while in shutdown. The I2C interface is completely disabled in hardware shutdown. When the MAX9775/MAX9776 are re-enabled the default settings are applied (see Table 3).

I2C Interface

The MAX9775/MAX9776 feature an I2C 2-wire serial interface consisting of a serial data line (SDA) and a serial clock line (SCL). SDA and SCL facilitate communication between the MAX9775/MAX9776 and the master at clock rates up to 400kHz. Figure 8 shows the 2-wire interface timing diagram. The MAX9775/ MAX9776 are receive-only slave devices relying on the master to generate the SCL signal. The master, typically a microcontroller, generates SCL and initiates data transfer on the bus. The MAX9775/MAX9776 cannot write to the SDA bus except to acknowledge the receipt of data from the master. The MAX9775/MAX9776 will not acknowledge a read command from the master.

A master device communicates to the MAX9775/ MAX9776 by transmitting the proper address followed by the data word. Each transmit sequence is framed by a START (S) or REPEATED START (Sr) condition and a STOP (P) condition. Each word transmitted over the bus is 8 bits long and is always followed by an acknowledge clock pulse.

The MAX9775/MAX9776 SDA line operates as both an input and an open-drain output. A pullup resistor, greater than 500Ω, is required on the SDA bus. The MAX9775/MAX9776 SCL line operates as an input only. A pullup resistor (greater than 500Ω) is required on SCL if there are multiple masters on the bus or if the master in a single-master system has an open-drain SCL output. Series resistors in line with SDA and SCL are optional. Series resistors protect the digital inputs of the MAX9775/MAX9776 from high-voltage spikes on the bus lines, and minimize crosstalk and undershoot of the bus signals.

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

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Figure 8. 2-Wire Serial-Interface Timing Diagram

SDA

SU, DAT

LOW

SCL

HD, STA

START

CONDITION

HIGH

HD, DAT

SU, STA

REPEATED

START

CONDITION

HD, STA

BUF

SU, STO

STOP

CONDITION

START

CONDITION

MAX9775/MAX9776

Bit Transfer

One data bit is transferred during each SCL cycle. The data on SDA must remain stable during the high period of the SCL pulse. Changes in SDA while SCL is high are control signals (see the

START and STOP

Conditions

section). SDA and SCL idle high when the

C bus is not busy.

START and STOP Conditions

A master device initiates communication by issuing a START condition. A START condition is a high-to-low transition on SDA with SCL high. A STOP condition is a low-to-high transition on SDA while SCL is high (Figure

9). A START (S) condition from the master signals the beginning of a transmission to the MAX9775/MAX9776. The master terminates transmission, and frees the bus, by issuing a STOP (P) condition. The bus remains active if a REPEATED START (Sr) condition is generated instead of a STOP condition.

Early STOP Conditions

The MAX9775/MAX9776 recognize a STOP condition at any point during data transmission except if the STOP condition occurs in the same high pulse as a START condition.

Slave Address

The MAX9775/MAX9776 are available with one preset slave address (see Table 1). The address is defined as

the seven most significant bits (MSBs) followed by the Read/Write bit. The address is the first byte of information sent to the MAX9775/MAX9776 after the START condition. The MAX9775/MAX9776 are slave devices only capable of being written to. The Read/Write bit should be a zero when configuring the MAX9775/ MAX9776.

Acknowledge

The acknowledge bit (ACK) is a clocked 9th bit that the MAX9775/MAX9776 use to handshake receipt of each byte of data (see Figure 10). The MAX9775/MAX9776 pull down SDA during the master-generated 9th clock pulse. Monitoring ACK allows for detection of unsuccessful data transfers. An unsuccessful data transfer occurs if a receiving device is busy or if a system fault has occurred. In the event of an unsuccessful data transfer, the bus master may reattempt communications.

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

26 ______________________________________________________________________________________

Figure 9. START, STOP, and REPEATED START Conditions

Figure 10. Acknowledge

Table 1. MAX9775/MAX9776 Address Map

PART

MAX9775 1 0 0 1 1 0 0 0

MAX9776 1 0 0 1 1 0 1 0

A6 A5 A4 A3 A2 A1 A0 R/W

SLAVE ADDRESS

SSrP

START

SCL

SDA

CONDITION

SCL

SDA

289

NOT ACKNOWLEDGE

ACKNOWLEDGE

CLOCK PULSE FOR

ACKNOWLEDGMENT

Write Data Format

A write to the MAX9775/MAX9776 includes transmission of a START condition, the slave address with the R/W bit set to 0 (Table 1), one byte of data to configure the Command Register, and a STOP condition. Figure 11 illustrates the proper format for one frame.

The MAX9775/MAX9776 only accept write data, but they acknowledge the receipt of the address byte with the R/W bit set high. The MAX9775/MAX9776 do not write to the SDA bus in the event that the R/W bit is set high. Subsequently, the master reads all 1’s from the MAX9775/MAX9776. Always set the R/W bit to zero to avoid this situation.

Programming the MAX9775/MAX9776

The MAX9775/MAX9776 are programmed through 6 control registers. Each register is addressed by the 3 MSBs (B5–B7) followed by 5 configure bits (B0–B4) as shown in Table 2. Correct programming of the MAX9775/MAX9776 requires writing to all 6 control registers. Upon power-on, their default settings are as listed in Table 3.

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 27

Figure 11. Write Data Format Example

Table 2. Control Registers

Table 3. Power-On Reset Conditions

COMMAND BYTE IS STORED ON

RECEIPT OF STOP CONDITION

ACKNOWLEDGE FROM

MAX9775/MAX9776

SLAVE ADDRESS COMMAND BYTE

R/W

B7 B6

ACK

FROM MAX9775/MAX9776

B3 B2

ACKNOWLEDGE

B1 B0

ACK

FUNCTION

Input Mode Control 0 0 0 INA+20dB INMODE (Tables 5a and 5b)

Mono Volume Control 0 0 1 MVOL (Table 7)

Left Volume Control 0 1 0 LVOL (Table 7)

Right Volume Control 0 1 1 RVOL (Table 7)

Output Mode Control 1 0 0 MONO+6dB OUTMODE (Table 9) Global Control Register 1 0 1 SHDN IN+6dB MUTE SSM 3D/MONO

B7 B6 B5 B4 B3 B2 B1 B0

COMMAND DATA

COMMAND DATA DESCRIPTION

Input Mode (000) 10000 Input A gain = +20dB; input A, B, and C singled-ended stereo inputs

Mono Volume (001) 11111 Maximum volume

Left Volume (010) 11111 Maximum volume

Right Volume (011) 11111 Maximum volume Output Mode (100) 01000 0dB of extra mono gain, mode 8: stereo headphone, stereo speaker

Global Control Register (101) 00011 Powered-off, input B/C gain = 0dB, MUTE off, SSM on, 3D/MONO on

MAX9775/MAX9776

The MAX9775/MAX9776 have three flexible inputs that can be configured as single-ended stereo inputs or differential mono inputs. All input signals are summed into three unique signals—Left (L), Right (R), and Mono (M)—which are routed to the output amplifiers. The bit INA+20dB allows the option of boosting low-level signals on INA. INA+20dB can be set as follows:

1 = Input A’s gain +20dB for low-level signals such as FM receivers.

0 = Input A’s gain is either 0dB or +6dB as set by IN+6dB (bit B3 of the Control Register).

Tables 5a and 5b show how the inputs—INA, INB, and INC—are mixed to create the internal signals Left (L), Right (R), and Mono (M).

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

28 ______________________________________________________________________________________

Input Mode Control

Table 4. Input Mode Control Register

Table 5a. Input Mode

Table 5b. Internal Signals L, R, and M

Input Mode Control 0 0 0 INA+20dB INMODE (Tables 5a and 5b )

B3 B2 B1 B0

0 0 0 0 LRLRLR 0001LRLRM+M0010LRM+M-LR 0 0 1 1 L R M+M-M+M0100LRR+R-L+L0101LRL+L-R+R0110M+M-LRLR 0 1 1 1 M+M- L R M+M1 0 0 0 M+M-M+M- L R 1 0 0 1 M+M-M+M-M+M1010M+M-R+R-L+L1011M+M-L+L-R+R-

PROGRAMMING MODE INPUT CONFIGURATION

INMODE

INA1 INA2 INB1 INB2 INC1 INC2

PROGRAMMING MODE INTERNAL SIGNALS LEFT (L), RIGHT (R), AND MONO (M)

INMODE

B3 B2 B1 B0

0 0 0 0 INA1 + INB1 + INC1 INA2 + INB2 + INC2 — 0 0 0 1 INA1 + INB1 INA2 + INB2 INC1 - INC2 0 0 1 0 INA1 + INC1 INA2 + INC2 INB1 - INB2 0 0 1 1 INA1 INA2 (INB1 - INB2) + (INC1 - INC2) 0 1 0 0 INA1 + (INC1 - INC2) INA2 + (INB1 - INB2) — 0 1 0 1 INA1 + (INB1 - INB2) INA2 + (INC1 - INC2) — 0 1 1 0 INB1 + INC1 INB2 + INC2 INA1 - INA2 0 1 1 1 INB1 INB2 (INA1 - INA2) + (INC1 - INC2) 1 0 0 0 INC1 INC2 (INA1 - INA2) + (INB1 - INB2)

1001 — —

1 0 1 0 INC1 - INC2 INB1 - INB2 INA1 - INA2 1 0 1 1 INB1 - INB2 INC1 - INC2 INA1 - INA2

LRM

(INA1 - INA2) + (INB1 - INB2)

+ (INC1 - INC2)

The MAX9775/MAX9776 have separate volume controls for each of the internal signals: Left (L), Right (R), and Mono (M). The final gain of each signal is determined by the way the following bits are set: MVOL, LVOL,

RVOL, INA+20dB, IN+6dB, and MONO+6dB. Table 7 shows how to configure the L, R, and M amplifiers for specific gains.

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 29

Mono/Left/Right Volume Control

Table 6. Mono/Left/Right Volume Control Registers

Table 7. Volume Control Settings

Mono Volume Control 0 0 1 MVOL

Left Volume Control 0 1 0 LVOL

Right Volume Control 0 1 1 RVOL

MVOL/LVOL/RVOL

B4 B3 B2 B1 B0

00000 Mute

00001 -75

00010 -71

00011 -67

00100 -63

00101 -59

00110 -55

00111 -51

01000 -47

01001 -44

01010 -41

01011 -38

01100 -35

01101 -32

01110 -29

01111 -26

GAIN (dB)

B4 B3 B2 B1 B0

10000 -23

10001 -21

10010 -19

10011 -17

10100 -15

10101 -13

10110 -11

10111 -9

11000 -7

11001 -6

11010 -5

11011 -4

11100 -3

11101 -2

11110 -1

11111 0

MVOL/LVOL/RVOL

GAIN (dB)

MAX9775/MAX9776

MONO+6dB in the Output Mode Control register allows an extra 6dB of gain on the internal mono signal:

1 = Additional 6dB of gain is applied to the internal Mono (M) signal path.

0 = No additional gain is applied to the Internal Mono (M) signal path.

The MAX9775 has five output amplifiers: a mono receiver amplifier, a stereo DirectDrive headphone

amplifier, and a stereo Class D amplifier. The MAX9776 has four output amplifiers: a mono receiver amplifier, a stereo DirectDrive headphone amplifier, and a mono Class D amplifier.

Table 9 shows how each of the three internal signals— Left (L), Right (R), and Mono (M)—are mixed and routed to the various outputs.

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

30 ______________________________________________________________________________________

Output Mode Control

Table 8. Output Mode Control Register

Table 9. Output Modes

— = Amplifier off. L = Left signal. R = Right signal. M = Mono signal.

Output Mode Control 1 0 0 MONO+6dB OUTMODE (Table 9)

MODE

00000 — — — — — —

10001 M — — — — —

20010 — — — M M M

30011 — M M M M M

40100 — M M — — —

50101 — — — — — —

601101/2 (L + R) — — — — —

70111 — — — L R L + R

81000 — L R L R L + R

91001 — L R — — —

101010 — — — — — —

111011M + 1/2 (L + R) — — — — —

12 1 1 0 0 — — — L + M R + M L + R + 2M

13 1 1 0 1 — L + M R + M L + M R + M L + R + 2M

14 1 1 1 0 — L + M R + M — — —

15 1 1 1 1 MUTE MUTE MUTE MUTE MUTE MUTE

B3 B2 B1 B0

OUTMODE MAX9775 MAX9776

RECEIVER LEFT HP RIGHT HP

LEFT SPK

RIGHT

SPK

The Global Control Register is used for global configurations, those affecting all inputs and outputs. The bits

in the control register are shown in Table 11.

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 31

Global Control Register

Table 10. Global Control Register

Table 11. Global Control Register Configurations

Applications Information

Class D 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 MAX9775/MAX9776 do 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 switching frequency of the MAX9775/ MAX9776 speaker 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 may 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 20µH to 100µH range.

Input Amplifier

Differential Input

The MAX9775/MAX9776 feature a programmable differential input structure, making it compatible with many CODECs, and offering improved noise immunity over a single-ended input amplifier. In devices such as cell 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 commonmode noise. A differential input amplifier amplifies the difference of the two inputs and any signal common to both is cancelled.

Global Control Register 1 0 1 SHDN IN+6dB MUTE SSM 3D/MONO

BIT NAME FUNCTION

B4 SHDN

B3 IN+6dB

B2 MUTE

B1 SSM

B0 3D/MONO

1 = Normal operation 0 = Low-power shutdown mode. I

1 = All input signals are boosted by 6dB. 0 = All input signals are passed un-amplified. This bit does not affect INA if the INA+20dB bit (B4 of the Input Mode Control Register) is set to 1, in which case INA is boosted by 20dB.

1 = Mute all outputs. 0 = All outputs are active.

1 = Spread-spectrum Class D modulation. 0 = Fixed-frequency Class D modulation.

MAX9775: 1 = 3D Enhancement is on. 0 = 3D Enhancement is off. 1 = Speakers will output L+R in modes 7, 8, 12, and 13 (see Table 9). 0 = Speakers will output L in modes 7, 8, 12, and 13 (see Table 9).

C settings are saved.

Single-Ended Input

The MAX9775/MAX9776 can be configured as a singleended input amplifier by appropriately configuring the Input Control Register (see Tables 5a and 5b).

DC-Coupled Input

The input amplifier can accept DC-coupled inputs that are biased to the amplifier’s bias voltage. DC-coupling eliminates the input-coupling capacitors; reducing component count to potentially six external components (see the

Typical Application Circuits

). However, the highpass filtering effect of the capacitors is lost, allowing low-frequency signals to feed through to the load.

Unused Inputs

Connect any unused input pin directly to VBIAS. This saves input capacitors on unused inputs and provides the highest noise immunity on the input.

Component Selection

Input Filter

An input capacitor (CIN) in conjunction with the input impedance of the MAX9775/MAX9776 form a highpass filter that removes the DC bias from the incoming signal. The AC-coupling capacitor allows the amplifiers 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 that 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 cell phones and two-way radios need only concentrate on the frequency range of the spoken human voice (typi-

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

Class D Output Filter

The MAX9775/MAX9776 do not require a Class D output filter. The devices pass EN55022B emission standards with 152mm 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 the circuit is near EMI-sensitive devices. Use a ferrite bead filter when radiated frequencies above 10MHz are of concern. Use an LC filter when radiated frequencies below 10MHz are of concern, or when long leads (> 152mm) connect the amplifier to the speaker. Figure 12 shows optional speaker amplifier output filters.

External Component Selection

BIAS Capacitor

BIAS

is the output of the internally generated DC bias

voltage. The V

BIAS

bypass capacitor, C

VBIAS

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 V

BIAS

with a 1µF capacitor to GND.

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

32 ______________________________________________________________________________________

Figure 12. Speaker Amplifier Output Filter

2π

IN IN

−

OUT_+

OUT_-

33μH

0.1μF

0.47μF

0.1μF

22Ω

0.033μF

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

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Table 12. Suggested Capacitor Manufacturers

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 100mΩ 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 or better. Table 12 lists suggested manufacturers.

Flying Capacitor (C1)

The value of the flying capacitor (C1) affects the 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 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

. 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. Load Resistance and Charge-Pump Capacitor Size graph in the

Typical Operating Characteristics

CPVDDBypass Capacitor (C3)

The CPVDDbypass capacitor (C3) lowers the output impedance of the power supply and reduces the impact of the MAX9775/MAX9776’s charge-pump switching transients. Bypass CPVDDwith C3 to PGND and place it physically close to the CPVDDand PGND. Use a value for C3 that is equal to C1.

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 PCB. Route all traces that carry switching transients away from GND and the traces/components in the audio signal path.

Connect all of the power-supply inputs (CPV

, VDD, and PVDD) together. Bypass CPVDDwith a 1µF capacitor to CPGND. Bypass VDDwith 1µF capacitor to GND. Bypass PVDDwith a 1µF capacitor in parallel with a

0.1µF capacitor to PGND. Place the bypass capacitors as close to the MAX9775/MAX9776 as possible. Place a bulk capacitor between PVDDand PGND if needed.

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 also allow more heat to move from the MAX9775/MAX9776 to the PCB, decreasing the thermal impedance of the circuit.

TQFN Applications Information

The MAX9776 TQFN-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 PCB. The exposed pad is internally connected to GND. Connect the exposed thermal pad to the PCB GND plane.

WLP Applications Information

For the latest application details on WLP construction, dimensions, tape carrier information, PCB techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information of reliability testing results, refer to Application Note 1891:

Understanding the Basics of the Wafer-Level ChipScale Package (WL-CSP)

available on Maxim’s website

at www.maxim-ic.com/ucsp.

WLP Thermal Consideration

When operating at maximum output power, the WLP thermal dissipation can become a limiting factor. The WLP package does not dissipate as much power as a TQFN and as a result will operate at a higher temperature. At peak output power into a 4Ω load, the MAX9775/MAX9776 can exceed its thermal limit, triggering thermal protection. As a result, do not choose the WLP package when maximum output power into 4Ω is required.

SUPPLIER PHONE FAX WEBSITE

Taiyo Yuden 800-348-2496 847-925-0899 www.t-yuden.com

TDK 807-803-6100 847-390-4405 www.component.tdk.com

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

34 ______________________________________________________________________________________

Chip Information

PROCESS: BiCMOS

Pin Configurations

TOP VIEW

(BUMPS ON BOTTOM)

234

CPV

CL_L V

OUTL+

PGND SCL

OUTL- SHDN INA1 INA2 INB1 CR_L

C1P CPGND

CL_H VBIAS

SDA

OUTR- PGND OUTR+

MAX9775

C1N

INC1

CPV

INC2 OUTRx

INB2 V

CR_H GND

WLP

TOP VIEW

1PV

OUT-

SCL

PGND

OUT+

SDA

I.C.

8I.C.

HPL

HPR

I.C.

INA1

SHDN

32 28

PGND

293031

MAX9776

I.C.

CPV

OUT+

PGND SCL

OUT- SHDN INA1 INA2 INB1 I.C.

C1P CPGND

I.C. VBIAS

I.C. V

SDA

C1N

INC1

MAX9776

I.C. PGND I.C.

WLP

INA2

I.C.

GND

24 INB1

I.C.

*EP

INB2

OUTRx

INC2

HPR

CPV

INC2 OUTRx

INB2 V

HPL

HPR

I.C. GND

C1P

VBIAS

CPV

CPGND

C1N

1611 12

HPL

INC1

CPV

TQFN-EP*

MAX9775/MAX9776

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

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 35

QFN THIN.EPS

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

36 ______________________________________________________________________________________

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

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

______________________________________________________________________________________ 37

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

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

36 WLP W363A3+3

21-0024

32 TQFN-EP T3255-4

21-0140

WLP PKG.EPS

MAX9775/MAX9776

2 x 1.5W, Stereo Class D Audio Subsystem with DirectDrive Headphone Amplifier

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

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

Revision History

REVISION

NUMBER

0 3/07 Initial release —

1 7/07 Initial release of MAX9776 UCSP package and updated Tables 3 and 5b 1, 7, 27, 28

2 9/07

3 1/08 Updated the Typical Application Circuits 17, 18

4 8/08 Changed package code and drawing 1, 33, 34, 37

REVISION

DATE

DESCRIPTION

Initial release of MAX9775 UCSP and removal of MAX9775 TQFN, updated Pin Description and Table 9

PAGES

CHANGED

1, 12, 15, 30, 33, 34

MAXIM MAX9775, MAX9776 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual