MAX9726AETP+T ,DirectDrive, Headphone Amplifier with BassMax, I²C, Volume and Gain ControlApplicationsBassMaxBMLSCL2I C SDAINTERFACEFBLINLOUTLΣVOLUMECONTROLOUTRΣINRFBRMAX9726BMRBassMaxSMBus ..
MAX9726BETP+T ,DirectDrive, Headphone Amplifier with BassMax, I²C, Volume and Gain Controlfeatures Maxim’s♦ Short-Circuit and Thermal-Overload Protectionindustry-leading click-and-pop suppr ..
MAX9728AETC+T ,60mW, DirectDrive, Stereo Headphone Amplifier with ShutdownFeaturesThe MAX9728A/MAX9728B stereo headphone ampli- ♦ No Bulky DC-Blocking Capacitors Requiredfie ..
MAX9728AEUD , 60mW, DirectDrive, Stereo Headphone Amplifiers with Shutdown
MAX9728AEUD+ ,60mW, DirectDrive, Stereo Headphone Amplifier with ShutdownELECTRICAL CHARACTERISTICS(V = 5V, PGND = SGND, SHDN = 5V, C1 = C2 = 1µF, R = ∞, resistive load ref ..
MAX9729ETI+ ,Stereo Headphone Amplifier with BassMax, Volume Control, and Input MuxBlock Diagram1.8V TO 3.6VBML BassMaxSCL2I C INTERFACESDA MAX9729INL1INL2OUTLMIXERΣINL3MUX VOLUMEINR ..
MB89475 ,F2MC-8L/Low Power/Low Voltage Microcontrollersapplications forconsumer product.2* : F MC stands for FUJITSU Flexible Microcontroller.n
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MAX9726AETP+-MAX9726AETP+T-MAX9726BETP+T
DirectDrive, Headphone Amplifier with BassMax, I²C, Volume and Gain Control
General DescriptionThe MAX9726 stereo, DirectDrive™, headphone amplifier
with BassMax and volume control is ideal for portable
audio applications where space is at a premium and per-
formance is essential. The MAX9726 operates from a sin-
gle 2.7V to 5.5V power supply and includes features that
reduce external component count, system cost, board
space, and offer improved audio reproduction. High
85dB PSRR makes the MAX9726 ideal for direct connec-
tion to a battery-powered supply and eliminates the need
for a dedicated LDO. The MAX9726 features Maxim’s
industry-leading click-and-pop suppression circuitry,
which reduces/eliminates audible transients during
power-up and power-down.
The headphone amplifier uses Maxim’s DirectDrive archi-
tecture that produces a ground-referenced output from a
single supply, eliminating the need for large DC-blocking
capacitors. The headphone amplifiers deliver 105mW into
a 32Ωload and feature low 0.02% THD+N.
The BassMax feature boosts the bass response of the
amplifier, improving audio reproduction when using inex-
pensive headphones. The integrated volume control fea-
tures 64 discrete volume levels, eliminating the need for
an external potentiometer. External resistors set the
MAX9726’s overall gain allowing for custom gain settings.
BassMax and the volume control are enabled through the2C/SMBus™-compatible interface. Shutdown can be con-
trolled through the hardware or software interface.
The MAX9726 consumes only 5.5mA of supply current,
provides short-circuit and thermal-overload protection,
and is specified over the -40°C to +85°C extended tem-
perature range. The MAX9726 is available in a tiny
(2mm x 2.5mm x 0.62mm) 20-bump chip-scale pack-
age (UCSP™) and a 20-pin TQFN package (4mm x
4mm x 0.75mm).
Applications
Features105mW DirectDrive Headphone Amplifier
Eliminates Bulky DC-Blocking Capacitors2.7V to 5.5V Single-Supply OperationIntegrated 64-Level Volume ControlHigh 85dB PSRR at 1kHzSoftware-Enabled Bass Boost (BassMax)Industry-Leading Click-and-Pop Suppression±7.5kV HBM ESD-Protected Headphone OutputsShort-Circuit and Thermal-Overload ProtectionLow-Power Shutdown Mode (8µA)Low 0.02% THD+NI2C/SMBus-Compatible InterfaceAvailable in Space-Saving, Thermally Efficient
Packages
20-Bump UCSP (2mm x 2.5mm x 0.62mm)
20-Pin TQFN (4mm x 4mm x 0.75mm)
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
Ordering InformationI2C
INTERFACE
VOLUME
CONTROL
BassMax
BassMax
2.7V TO 5.5V SUPPLY
SCLBML
OUTL
BMR
OUTR
SDA
INL
INR
FBR
FBL
MAX9726
Simplified Block Diagram19-0627; Rev 1; 3/08
Note:All devices specified over the -40°C to +85°C operating
range.
+Denotes lead-free package.
*EP = Exposed pad.
T = Tape and reel.
PARTPIN-PACKAGESLAVE ADDRESSMAX9726AEBP+T20 UCSP-201001100
MAX9726AETP+20 TQFN-EP*1001100
MAX9726BEBP+T20 UCSP-201001101
MAX9726BETP+20 TQFN-EP*1001101
SMBus is a trademark of Intel Corp.
UCSP is a trademark of Maxim Integrated Products, Inc.
EVALUATION KIT
AVAILABLE
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS (5V Supply)(VDD= SHDN= 5V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF = 10kΩ, maximum vol-
ume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA= TMINto TMAX, 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 PGND............................................................-0.3V to +6V
PVSSto SVSS.........................................................-0.3V to +0.3V
SGND to PGND.....................................................-0.3V to +0.3V
C1P to PGND..............................................-0.3V to (VDD+ 0.3V)
C1N to PGND............................................(PVSS- 0.3V) to +0.3V
PVSS, SVSSto PGND................................................+0.3V to -6V
IN_ to SGND...................................(SVSS - 0.3V) to (VDD + 0.3V)
FB_ to SGND..................................(SVSS - 0.3V) to (VDD + 0.3V)
SDA, SCL to PGND....................................-0.3V to (VDD+ 0.3V)
SHDNto PGND..........................................-0.3V to (VDD + 0.3V)
OUT_ to SGND............................................................-3V to +3V
BM_ to SGND..............................................................-3V to +3V
Duration of OUT_ Short Circuit to PGND....................Continuous
Continuous Current Into/Out of:
VDD, C1P, PGND, C1N, PVSS, SVSS, or OUT_...........±850mA
Any Other Pin................................................................±20mA
Continuous Power Dissipation (TA= +70°C, multilayer board)
20-Bump UCSP (derate 10mW/°C above +70°C).......800mW
20-Pin TQFN (derate 25.6mW/°C above +70°C).......2051mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
OUTL and OUTR ESD Protection (Human Body Model)....±7.5kV
Bump Temperature (soldering) Reflow............................+230°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GENERALSupply Voltage RangeVDD2.75.5V
Quiescent Supply CurrentIDDNo load5.510mA
Shutdown Supply CurrentIDD_SHDNSHDN = 0V815µA
Turn-On TimetON440µs
Turn-Off TimetOFF1µs
Thermal-Shutdown ThresholdTTHRES+150°C
Thermal-Shutdown HysteresisTHYST12°C
HEADPHONE AMPLIFIEROutput Offset VoltageVOSHP
Measured between OUT_ and SGND, gain
= 0dB, RIN = RF = 10kΩ, TA = +25°C
(Note 2)
±0.610mV
Input Offset Voltage of Input
AmplifierVOSReferenced to SGND, measured between
FBR, FBL, and SGND3mV
Input Bias CurrentIB±20±100nA
BMR, BML Input Bias CurrentIBIAS_BB±20±100nA
DC, VDD = 2.7V to 5.5V8097
f = 1kHz, 100mVP-P ripple85Power-Supply Rejection Ratio
(Note 2)PSRR
f = 20kHz, 100mVP-P ripple74
RL = 16Ω124Output PowerPOUTTHD+N = 1%,
fIN = 1kHzRL = 32Ω104mW
RL = 16Ω, POUT = 15mW, fIN = 1kHz0.04Total Harmonic Distortion Plus
NoiseTHD+NRL = 32Ω, POUT = 30mW, fIN = 1kHz0.02%
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
ELECTRICAL CHARACTERISTICS (5V Supply) (continued)(VDD= SHDN= 5V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF = 10kΩ, maximum vol-
ume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA= TMINto TMAX, unless
otherwise noted. Typical values are at TA= +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSBW = 22Hz to 22kHz102
Signal-to-Noise RatioSNR
RL = 32Ω,
VOUT =
1.77VRMSA-weighted105
Slew RateSR1V/µs
Capacitive DriveNo sustained oscillations200pF
Output Resistance in ShutdownROUT_SHDNVSHDN = 0V, measured from OUT_ to
SGND50kΩ
Into
shutdown59
Click-and-Pop LevelKCP
Peak voltage, A-weighted,
32 samples per second
(Notes 2, 4)Out of
shutdown61
dBV
Charge-Pump Switching
FrequencyfCP515610705kHz
Crosstalk
L to R, or R to L, f = 10kHz,
VOUT = 1VP-P, RL = 32Ω, both channels
loadeddB
VOLUME CONTROL0 to 64dB±0.1
68dB to 96dB±0.5Attenuator Step Accuracy
100dB to 120dB±2
DIGITAL INPUTS (SHDN, SDA, SCL)Input High VoltageVIH0.7 x
VDDV
Input Low VoltageVIL0.3 x
VDDV
Input Leakage Current±1µA
DIGITAL OUTPUTS (SDA)Output Low VoltageVOLIOL = 3mA0.06V
Output High CurrentIOHVSDA = VDD1µA
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSRL = 16Ω80Output PowerPOUTTHD+N = 1%,
fIN = 1kHzRL = 32Ω70mW
RL = 16Ω, POUT = 15mW, fIN = 1kHz0.05Total Harmonic Distortion Plus
NoiseTHD+NRL = 32Ω, POUT = 30mW, fIN = 1kHz0.03%
ELECTRICAL CHARACTERISTICS (3.3V Supply)(VDD= SHDN= 3.3V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF = 10kΩ, maximum
volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA= TMINto TMAX,
unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSf = 1kHz, 100mVP-P ripple85Power-Supply Rejection Ratio
(Note 2)PSRRf = 20kHz, 100mVP-P ripple73dB
BW = 22Hz to 22kHz101Signal-to-Noise RatioSNRRL = 32Ω,
VOUT = 1.5VRMSA-weighted104dB
Into shutdown62
Click-and-Pop LevelKCP
Peak voltage,
A-weighted, 32
samples per
second
(Notes 2, 4)Out of shutdown67
dBV
ELECTRICAL CHARACTERISTICS (3.3V Supply) (continued)(VDD= SHDN= 3.3V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF = 10kΩ, maximum
volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA= TMINto TMAX,
unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSSerial Clock FrequencyfSCL0400kHz
Bus Free Time Between a STOP and a
START ConditiontBUF1.3µs
Hold Time Repeated for a START
ConditiontHD:STA0.6µs
Low Period of the SCL ClocktLOW1.3µs
High Period of the SCL ClocktHIGH0.6µs
Setup Time for a Repeated START
ConditiontSU:STA0.6µs
Data Hold TimetHD:DAT00.9µs
Data Setup TimetSU:DAT100ns
Rise Time of Both SDA and SCL Signalstr300ns
Fall Time of Both SDA and SCL Signalstf300ns
Setup Time for STOP ConditiontSU:STO0.6µs
Pulse Width of Suppressed SpiketSP50ns
Capacitive Load for Each Bus LineCL_BUS400pF
TIMING CHARACTERISTICS(VDD= SHDN= 5V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN= 10kΩ, RF= 10kΩ, maximum vol-
ume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA= TMINto TMAX, unless
otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 3)
Note 1:All specifications are 100% tested at TA= +25°C. Temperature limits are guaranteed by design.
Note 2:Inputs AC-coupled to SGND.
Note 3:Guaranteed by design.
Note 4:Headphone testing performed with a 32Ωresistive load connected to PGND. Mode transitions are controlled by SHDN. KCP
level is calculated as 20log[(peak voltage during mode transition, no input signal)/1VRMS]. Units are expressed in dBV.
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWEROUTPUT POWER (mW)
THD+N (%)
MAX9726 toc0120406080100120140160
fIN = 10kHz
fIN = 1kHz
VDD = 3.3V
RL = 16Ω
fIN = 20Hz
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWEROUTPUT POWER (mW)
THD+N (%)
MAX9726 toc0220406080100120140160
fIN = 10kHz
fIN = 1kHz
VDD = 3.3V
RL = 32Ω
fIN = 20Hz
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWEROUTPUT POWER (mW)
THD+N (%)
MAX9726 toc0320406080100120140160180200
VDD = 5V
RL = 16ΩfIN = 1kHz
fIN = 10kHz fIN = 20Hz
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWEROUTPUT POWER (mW)
THD+N (%)
MAX9726 toc0420406080100120140160
VDD = 5V
RL = 32ΩfIN = 1kHz
fIN = 10kHz
fIN = 20Hz
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCYFREQUENCY (Hz)
THD+N (%)
MAX9726 toc051001k10k100k
VDD = 3.3V
RL = 16Ω
OUTPUT POWER = 60mW
OUTPUT POWER = 20mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCYTHD+N (%)
MAX9726 toc061001k10k100k
VDD = 3.3V
RL = 32Ω
OUTPUT POWER = 60mW
OUTPUT POWER = 20mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCYTHD+N (%)
MAX9726 toc071001k10k100k
VDD = 5V
RL = 16Ω
OUTPUT POWER = 80mW
OUTPUT POWER = 40mW
Typical Operating Characteristics(VDD= SHDN= 5V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF= 10kΩ, maximum vol-
ume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both
channels loaded. TA= +25°C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit)
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Controlypical Operating Characteristics (continued)(VDD= SHDN= 5V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF= 10kΩ, maximum vol-
ume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both
channels loaded. TA= +25°C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCYFREQUENCY (Hz)
THD+N (%)
MAX9726 toc081001k10k100k
VCC = 5V
RL = 32Ω
OUTPUT POWER = 80mW
OUTPUT POWER = 40mW
POWER DISSIPATION
vs. OUTPUT POWERMAX9726 toc09
TOTAL OUTPUT POWER (mW)
POWER DISSIPATION (mW)
VDD = 3.3V
fIN = 1kHz
POUT = POUTR + POUTL
RL = 32Ω
RL = 16Ω
POWER DISSIPATION
vs. OUTPUT POWERMAX9726 toc10
TOTAL OUTPUT POWER (mW)
POWER DISSIPATION (mW)
VDD = 5V
fIN = 1kHz
POUT = POUTR + POUTL
RL = 16Ω
RL = 32Ω
OUTPUT POWER
vs. LOAD RESISTANCEMAX9726 toc11
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
VDD = 3.3V, fIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER
vs. LOAD RESISTANCEMAX9726 toc12
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
VDD = 5V, fIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER
vs. SUPPLY VOLTAGEMAX9726 toc13
OUTPUT POWER (mW)
RL = 16Ω
fIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER
vs. SUPPLY VOLTAGEMAX9726 toc14
OUTPUT POWER (mW)
THD+N = 10%
THD+N = 1%
RL = 32Ω
fIN = 1kHz
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCYMAX9726 toc15
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-110100k
VDD = 5V + 100mVP-P
RIN = RF = 10kΩ
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCYMAX9726 toc16
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-110100k
VDD = 3.3V + 100mVP-P
RIN = RF = 10kΩ
CROSSTALK vs. FREQUENCYFREQUENCY (Hz)
CROSSTALK (dB)
MAX9726 toc17
-601001k10k100k
VIN = 1VP-P
RL = 32Ω
G = 0dB
RIGHT TO LEFT
LEFT TO RIGHT
ypical Operating Characteristics (continued)(VDD= SHDN= 5V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF= 10kΩ, maximum vol-
ume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both
channels loaded. TA= +25°C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit)
CROSSTALK vs. FREQUENCYFREQUENCY (Hz)
CROSSTALK (dB)
MAX9726 toc18
-401001k10k100k
VIN = 1VP-P
RL = 32Ω
G = -10dB
LEFT TO RIGHT
RIGHT TO LEFT
BassMax FREQUENCY RESPONSEMAX9726 toc19
FREQUENCY (Hz)
GAIN (dB)
10k1k10010100k
R2 = 36kΩ
C3 = 0.068μF
R2 = 22kΩ
C3 = 0.1μF
R2 = 10kΩ
C3 = 0.22μF
R1 = 47kΩ
RL = 32Ω
BassMax DISABLED
OUTPUT FFTMAX9726 toc20
FREQUENCY (kHz)
AMPLITUDE (dBV)105
VIN = 100mVRMS
ATTEN = 60dB
VOUT = -60dBV
RL = 320Ω
fIN = 1kHz
VDD = 5V
OUTPUT POWER vs. CHARGE-PUMP
CAPACITANCE AND LOAD RESISTANCEMAX9726 toc21
OUTPUT POWER (mW)403035202515
VDD = 5V
fIN = 1kHz
THD+N = 1%
C1 = C2 = 2.2μF
C1 = C2 = 1μF
C1 = C2 = 0.68μF
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
OUTPUT POWER vs. CHARGE-PUMP
CAPACITANCE AND LOAD RESISTANCEMAX9726 toc22
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)40353025201550
VDD = 3.3V
fIN = 1kHz
THD+N = 1%
C1 = C2 = 2.2μF
C1 = C2 = 1μF
C1 = C2 = 0.68μF
POWER-UP/POWER-DOWNMAX9726 toc23
20ms/div
VDD
2V/div
VOUT_
10mV/div
RL = 32Ω
EXITING SHUTDOWNMAX9726 toc24
100μs/div
VSHDN
5V/div
VIN_
200mV/div
VOUT_
2V/div
ENTERING SHUTDOWNMAX9726 toc25
20μs/div
VSHDN
5V/div
VIN_
200mV/div
VOUT_
2V/div
SUPPLY CURRENT
vs. SUPPLY VOLTAGEMAX9726 toc26
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)534
NO LOAD
INPUTS AC GROUNDED
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGEMAX9726 toc27
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT (43
NO LOAD
INPUTS AC GROUNDED
ypical Operating Characteristics (continued)(VDD= SHDN= 5V, PGND = SGND = 0V, C1 = C2 = 1µF, CPREG= CNREG= 1µF, BM_ = 0V, RIN = 10kΩ, RF= 10kΩ, maximum vol-
ume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both
channels loaded. TA= +25°C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit)
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
Pin Description
PINBUMP
TQFNUCSPNAMEFUNCTION1A1VDDPower-Supply Input. Bypass VDD to PGND with a 1µF capacitor.A2C1PCharge-Pump Flying Capacitor Positive Terminal. Connect a 1µF capacitor between C1P
and C1N.A3PGNDPower Ground. Connect to SGND.A4C1NCharge-Pump Flying Capacitor Negative Terminal. Connect a 1µF capacitor between C1P
and C1N.
5A5PVSSCharge-Pump Output. Connect to SVSS and bypass with a 1µF capacitor to PGND.B3SDASerial Data Input. Connect a pullup resistor greater than 500Ω from SDA to VDD.C3SCLSerial Clock Input. Connect a pullup resistor greater than 500Ω from SCL to VDD.
8C2SHDNActive-Low Shutdown Input. Drive SHDN low to disable the MAX9726. Connect SHDN to
VDD while bit 7 is high for normal operation (see the Command Register section).B4FBLLeft-Channel Feedback Output. Connect a feedback resistor between FBL and INL. See
the Gain-Setting Components section.B5INLLeft-Channel Input. Connect an input resistor to INL. See the Gain-Setting Components
section.C5INRRight-Channel Input. Connect an input resistor to INR. See the Gain-Setting Components
section.C4FBRRight-Channel Feedback Output. Connect a feedback resistor between FBR and INR. See
the Gain-Setting Components section.D5SGNDSignal Ground. Connect to PGND.D2NREGNegative Supply Regulator Voltage. Bypass NREG to PGND with a 1µF capacitor.D4BMR
Right BassMax Input. Connect an external passive network between OUTR and BMR to
apply bass boost to the right-channel output. See the Gain-Setting Components section.
Connect BMR to SGND if BassMax is not used.D1SVSSHeadphone Amplifier Negative Power-Supply Input. Connect to PVSS and bypass with a
1µF capacitor to PGND.C1OUTRRight Headphone OutputB1OUTLLeft Headphone OutputD3BML
Left BassMax Input. Connect an external passive network between OUTL and BML to
apply bass boost to the right-channel output. See the Gain-Setting Components section.
Connect BML to SGND if BassMax is not used.B2PREGPositive Supply Regulator Voltage. Bypass PREG to PGND with a 1µF capacitor.—EPExposed Pad. Connect EP to SVSS or leave unconnected.
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain Control
Detailed DescriptionThe MAX9726 stereo headphone amplifier features
Maxim’s DirectDrive architecture, eliminating the large
output-coupling capacitors required by conventional
single-supply headphone amplifiers. The MAX9726 con-
sists of two 105mW Class AB headphone amplifiers, two
adjustable gain preamplifiers, hardware/software shut-
down control, inverting charge pump, integrated 64-
level volume control, BassMax feature, comprehensive
click-and-pop suppression circuitry, and an I2C-
/SMBus-compatible interface (see the Functional
Diagram/Typical Operating Circuit). A negative power
supply (PVSS) is created internally by inverting the posi-
tive supply (VDD). Powering the amplifiers from VDDand
PVSSincreases the dynamic range of the amplifiers to
almost twice that of other single-supply amplifiers,
increasing the total available output power. High PSRR
topologies eliminate the need for an external voltage
regulator.
An I2C-/SMBus-compatible interface allows serial com-
munication between the MAX9726 and a microcon-
troller. The internal command register controls the
shutdown status of the MAX9726, enables the BassMax
circuitry, and sets the volume level (see the Volume
Controlsection). The MAX9726’s BassMax circuitry
improves audio reproduction by boosting the bass
response of the amplifier, compensating for any low-
frequency attenuation introduced by the headphone.
External components set the MAX9726’s overall gain
allowing for custom gain settings (see the Gain-Setting
Componentssection). Amplifier volume is digitally pro-
grammable to any one of 64 levels.
DirectDriveTraditional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage, typi-
cally 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 head-
phone, resulting in unnecessary power dissipation and
possible damage to both the headphone and head-
phone amplifier. In addition to the cost and size disad-
vantages, the DC-blocking capacitors required by
conventional headphone amplifiers limit low-frequency
response and can distort the audio signal.
Maxim’s DirectDrive architecture uses a charge pump
to create an internal negative supply voltage. This
allows the MAX9726 headphone amplifier outputs to be
biased about ground, almost doubling the dynamic
range while operating from a single supply (see Figure
1). With no DC component, there is no need for the
large DC-blocking capacitors. Instead of two large (up
to 220µF) tantalum capacitors, the MAX9726 charge
pump requires only two small 1µF ceramic capacitors,
conserving board space, reducing cost, and improving
the frequency response of the headphone amplifier.
See the Output Power vs. Charge-Pump Capacitance
and Load Resistance graphs in the Typical Operating
Characteristicsfor details of the possible capacitor
sizes.
VDD*
*VDD IS INTERNALLY LIMITED TO ±2.5V DUE TO ABSOLUTE MAXIMUM RATINGS
AND TO LIMIT POWER DISSIPATION.
-VDD*
GND
VOUT
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
VDD/2
VDD
VDD
GND
VOUT
2VDD*
Figure 1. Traditional Amplifier Output vs. MAX9726 DirectDrive
Output
Charge PumpThe MAX9726 features a low-noise charge pump. The
610kHz switching frequency is well beyond the audio
range, and does not interfere with the audio signals.
This enables the MAX9726 to achieve an SNR of
102dB. The switch drivers feature a controlled switch-
ing speed that minimizes noise generated by turn-on
and turn-off transients. Limiting the switching speed of
the charge pump also minimizes di/dt noise caused by
the parasitic bond wire and trace inductance.
Click-and-Pop SuppressionIn conventional single-supply headphone amplifiers,
the output coupling capacitor is a major contributor of
audible clicks and pops. The amplifier charges the
coupling capacitor to its output bias voltage at startup.
During shutdown, the capacitor is discharged. This
charging and discharging results in a DC shift across
the capacitor, which appears as an audible transient at
the headphone speaker. Since the MAX9726 head-
phone amplifier does not require output-coupling
capacitors, no audible transients occur.
Additionally, the MAX9726 features extensive click-and-
pop suppression that eliminates any audible transient
sources internal to the device. The Power-Up/Power-
Down graph in the Typical Operating Characteristics
shows that there are minimal transients at the output
upon startup or shutdown.
In most applications, the preamplifier driving the
MAX9726 has a DC bias of typically half the supply.
The input-coupling capacitor is charged to the pream-
plifier’s bias voltage through the MAX9726’s input resis-
tor (RIN) during startup. The resulting voltage shift
across the capacitor creates an audible click-and-pop.
Delay the rise of SHDNby at least four time constants
(4 x RINx CIN) relative to the start of the preamplifier to
avoid clicks/pops caused by the input filter.
ShutdownThe MAX9726 features a 8µA, low-power shutdown
mode that reduces quiescent current consumption and
extends battery life. Shutdown is controlled by a hard-
ware and software interface. Driving the SHDNinput low
disables the drive amplifiers, bias circuitry, charge
pump, and sets the headphone amplifier output resis-
tance to 50kΩ. Similarly, the MAX9726 enters shutdown
when bit seven (B7) in the control register is set to 0 (see
the Command Registersection). SHDNand B7 must be
high to enable the MAX9726. The I2C/SMBus interface is
active and the contents of the command register are not
affected when in shutdown. This allows the master to
write to the MAX9726 while in shutdown.
BassMax (Bass Boost)Typical headphones do not have a flat-frequency
response. The small physical size of the diaphragm
does not allow the headphone speaker to efficiently
reproduce low frequencies. This physical limitation
results in attenuated bass response. The MAX9726
includes a bass-boost feature that compensates for the
headphone’s poor bass response by increasing the
amplifier gain at low frequencies.
The DirectDrive output of the MAX9726 has more head-
room than typical single-supply headphone amplifiers.
This additional headroom allows boosting the bass fre-
quencies without the output signal clipping.
Program the BassMax gain and cutoff frequency with
external components connected between OUT_ and
BM_ (see the Gain-Setting Componentssection and the
Functional Diagram/Typical Operating Circuit). Use the
I2C-compatible interface to program the command reg-
ister to enable/disable the BassMax circuit.
BM_ is connected to the noninverting input of the out-
put amplifier when BassMax is enabled. BM_ is pulled
to SGND when BassMax is disabled. The typical appli-
cation of the BassMax circuit involves feeding a low-
pass version of the output signal back to the amplifier.
This is realized using positive feedback from OUT_ to
BM_. Figure 2 shows the connections needed to imple-
ment BassMax.
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain ControlR2
TO HEADPHONE
SPEAKER
OUT_
BM_
FROM
ATTENUATOR
STAGE
MAX9726
BassMax
ENABLE
Figure 2. BassMax External Connections
MAX9726
Volume ControlThe MAX9726 includes a 64-level volume control that
adjusts the gain of the output amplifiers according to
the code contained in the command register. Volume is
programmed through the command register bits [5:0].
Table 5 shows all possible attenuation settings of the
MAX9726 with respect to the overall gain set by the
external gain-setting resistors (RINand RF). Mute atten-
uation is typically better than 120dB when driving a
32Ωload. To perform smooth-sounding volume
changes, step through all intermediate volume settings
at a rate of approximately 2ms per step when a volume
change occurs.
Serial InterfaceThe MAX9726 features an I2C-/SMBus-compatible,
2-wire serial interface consisting of a serial data line
(SDA) and a serial clock line (SCL). SDA and SCL facili-
tate communication between the MAX9726 and the
master at clock rates up to 400kHz. Figure 3 shows the
2-wire interface timing diagram. The MAX9726 is a
receive-only slave device relying on the master to gen-
erate the SCL signal. The MAX9726 cannot write to the
SDA bus except to acknowledge the receipt of data
from the master. The master, typically a microcontroller,
generates SCL and initiates data transfer on the bus.
A master device communicates to the MAX9726 by
transmitting the slave address with the read/write(R/W)
bit 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 trans-
mitted over the bus is 8 bits long and is always followed
by an acknowledge clock pulse.
The MAX9726 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 MAX9726 SCL
line operates as an input only. A pullup resistor, greater
than 500Ω, is required on SCL if there are multiple mas-
ters on the bus, or if the master in a single-master sys-
tem has an open-drain SCL output. Series resistors in
line with SDA and SCL are optional. Series resistors
protect the digital inputs of the MAX9726 from high-
voltage spikes on the bus lines, and minimize crosstalk
and undershoot of the bus signals.
DirectDrive, Headphone Amplifier with
BassMax, I2C, Volume and Gain ControlSCL
SDA
START
CONDITION
STOP
CONDITION
REPEATED
START
CONDITION
START
CONDITION
tHD, STA
tSU, STA
tHD, STAtSP
tBUF
tSU, STOtLOW
tSU, DAT
tHD, DAT
tHIGHtF
Figure 3. 2-Wire Serial-Interface Timing Diagram
