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| 19-0627; Rev 0; 9/06 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control General Description The MAX9726 stereo, DirectDriveTM, headphone amplifier with BassMax and volume control is ideal for portable audio applications where space is at a premium and performance is essential. The MAX9726 operates from a single 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 connection 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 patented DirectDrive architecture that produces a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors. The headphone amplifiers deliver 105mW into a 32 load and feature low 0.02% THD+N. The BassMax feature boosts the bass response of the amplifier, improving audio reproduction when using inexpensive headphones. The integrated volume control features 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 the I2C/SMBusTM-compatible interface. Shutdown can be controlled 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 -40C to +85C extended temperature range. The MAX9726 is available in a tiny (2mm x 2.5mm x 0.62mm) 20-bump chip-scale package (UCSPTM) and a 20-pin TQFN package (4mm x 4mm x 0.75mm). Features 105mW DirectDrive Headphone Amplifier Eliminates Bulky DC-Blocking Capacitors 2.7V to 5.5V Single-Supply Operation Integrated 64-Level Volume Control High 85dB PSRR at 1kHz Software-Enabled Bass Boost (BassMax) Industry-Leading Click-and-Pop Suppression 7.5kV HBM ESD-Protected Headphone Outputs Short-Circuit and Thermal-Overload Protection Low-Power Shutdown Mode (8A) Low 0.02% THD+N I2C/SMBus-Compatible Interface Available 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 Ordering Information PART MAX9726AEBP+T* MAX9726AETP+ MAX9726BEBP+T* MAX9726BETP+ PIN-PACKAGE 20 UCSP-20 20 TQFN-EP** 20 UCSP-20 20 TQFN-EP** SLAVE ADDRESS 1001100 1001100 1001101 1001101 PKG CODE B20-1 T2044-3 B20-1 T2044-3 Note: All devices specified over the -40C to +85C operating range. +Denotes lead-free package. *Future product--contact factory for availability. **EP = Exposed pad. Simplified Block Diagram 2.7V TO 5.5V SUPPLY Applications Cell Phones MP3/PMP Players Flat-Panel TVs U.S. Patent # 7,061,327 INR FBR Automotive Rear-Seat Entertainment (RSE) Portable CD/DVD/MD Players SCL SDA FBL INL BML I2C INTERFACE BassMax VOLUME CONTROL OUTL OUTR MAX9726 BMR BassMax SMBus is a trademark of Intel Corp. UCSP is a trademark of Maxim Integrated Products, Inc. Pin Configurations appear at end of data sheet. 1 ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 ABSOLUTE MAXIMUM RATINGS VDD to PGND............................................................-0.3V to +6V PVSS to 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, SVSS to 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) SHDN to 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 = +70C, multilayer board) 20-Bump UCSP (derate 10mW/C above +70C) .......800mW 20-Pin TQFN (derate 25.6mW/C above +70C) .......2051mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C OUTL and OUTR ESD Protection (Human Body Model)....7.5kV Bump Temperature (soldering) Reflow............................+230C Lead Temperature (soldering, 10s) .................................+300C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (5V Supply) (VDD = SHDN = 5V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER GENERAL Supply Voltage Range Quiescent Supply Current Shutdown Supply Current Turn-On Time Turn-Off Time Thermal-Shutdown Threshold Thermal-Shutdown Hysteresis HEADPHONE AMPLIFIER Output Offset Voltage Input Offset Voltage of Input Amplifier Input Bias Current BMR, BML Input Bias Current Power-Supply Rejection Ratio (Note 2) Output Power Total Harmonic Distortion Plus Noise VOSHP Measured between OUT_ and SGND, gain = 0dB, RIN = RF = 10k, TA = +25C (Note 2) Referenced to SGND, measured between FBR, FBL, and SGND 0.6 10 mV VDD IDD IDD_SHDN tON tOFF TTHRES THYST No load SHDN = 0V SYMBOL CONDITIONS MIN 2.7 TYP MAX 5.5 UNITS V mA A s s C C 5.5 8 440 1 +150 12 10 15 VOS IB IBIAS_BB 3 20 20 100 100 mV nA nA dB DC, VDD = 2.7V to 5.5V PSRR f = 1kHz, 100mVP-P ripple f = 20kHz, 100mVP-P ripple POUT THD+N THD+N = 1%, RL = 16 fIN = 1kHz RL = 32 RL = 16, POUT = 15mW, fIN = 1kHz RL = 32, POUT = 30mW, fIN = 1kHz 80 97 85 74 124 104 0.04 0.02 mW % 2 _______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control ELECTRICAL CHARACTERISTICS (5V Supply) (continued) (VDD = SHDN = 5V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Signal-to-Noise Ratio Slew Rate Capacitive Drive Output Resistance in Shutdown SYMBOL SNR SR No sustained oscillations VSHDN = 0V, measured from OUT_ to ROUT_SHDN SGND Peak voltage, A-weighted, 32 samples per second (Notes 2, 4) Into shutdown Out of shutdown 515 L to R, or R to L, f = 10kHz, VOUT = 1VP-P, RL = 32, both channels loaded RL = 32, VOUT = 1.77VRMS CONDITIONS BW = 22Hz to 22kHz A-weighted MIN TYP 102 dB 105 1 200 50 59 dBV 61 610 705 kHz V/s pF k MAX UNITS MAX9726 Click-and-Pop Level KCP Charge-Pump Switching Frequency Crosstalk VOLUME CONTROL fCP 85 dB 0 to 64dB Attenuator Step Accuracy DIGITAL INPUTS (SHDN, SDA, SCL) Input High Voltage Input Low Voltage Input Leakage Current DIGITAL OUTPUTS (SDA) Output Low Voltage Output High Current VOL IOH IOL = 3mA VSDA = VDD VIH VIL 0.7 x VDD 68dB to 96dB 100dB to 120dB 0.1 0.5 2 dB V 0.3 x VDD 1 0.06 1 V A V A ELECTRICAL CHARACTERISTICS (3.3V Supply) (VDD = SHDN = 3.3V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Output Power Total Harmonic Distortion Plus Noise SYMBOL POUT THD+N THD+N = 1%, fIN = 1kHz CONDITIONS RL = 16 RL = 32 MIN TYP 80 70 0.05 0.03 MAX UNITS mW % RL = 16, POUT = 15mW, fIN = 1kHz RL = 32, POUT = 30mW, fIN = 1kHz _______________________________________________________________________________________ 3 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 ELECTRICAL CHARACTERISTICS (3.3V Supply) (continued) (VDD = SHDN = 3.3V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Power-Supply Rejection Ratio (Note 2) Signal-to-Noise Ratio SYMBOL PSRR SNR CONDITIONS f = 1kHz, 100mVP-P ripple f = 20kHz, 100mVP-P ripple RL = 32, VOUT = 1.5VRMS Peak voltage, A-weighted, 32 samples per second (Notes 2, 4) BW = 22Hz to 22kHz A-weighted Into shutdown MIN TYP 85 73 101 104 62 dBV Out of shutdown 67 MAX UNITS dB dB Click-and-Pop Level KCP TIMING CHARACTERISTICS (VDD = SHDN = 5V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 3) PARAMETER Serial Clock Frequency Bus Free Time Between a STOP and a START Condition Hold Time Repeated for a START Condition Low Period of the SCL Clock High Period of the SCL Clock Setup Time for a Repeated START Condition Data Hold Time Data Setup Time Rise Time of Both SDA and SCL Signals Fall Time of Both SDA and SCL Signals Setup Time for STOP Condition Pulse Width of Suppressed Spike Capacitive Load for Each Bus Line SYMBOL fSCL tBUF tHD:STA tLOW tHIGH tSU:STA tHD:DAT tSU:DAT tr tf tSU:STO tSP CL_BUS 0.6 50 400 CONDITIONS MIN 0 1.3 0.6 1.3 0.6 0.6 0 100 300 300 0.9 TYP MAX 400 UNITS kHz s s s s s s ns ns ns s ns pF Note 1: Note 2: Note 3: Note 4: All specifications are 100% tested at TA = +25C. Temperature limits are guaranteed by design. Inputs AC-coupled to SGND. Guaranteed by design. Headphone testing performed with a 32 resistive 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. 4 _______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Typical Operating Characteristics (VDD = SHDN = 5V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both channels loaded. TA = +25C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit) TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9726 toc01 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9726 toc02 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER VDD = 5V RL = 16 MAX9726 toc03 100 VDD = 3.3V RL = 16 100 VDD = 3.3V RL = 32 fIN = 1kHz THD+N (%) 100 fIN = 1kHz 10 10 10 THD+N (%) THD+N (%) 1 fIN = 20Hz fIN = 1kHz 1 fIN = 20Hz 1 fIN = 20Hz 0.1 fIN = 10kHz 0.1 fIN = 10kHz 0.1 fIN = 10kHz 0.01 0.01 0.01 0.001 0 20 40 60 80 100 120 140 160 OUTPUT POWER (mW) 0.001 0 20 40 60 80 100 120 140 160 OUTPUT POWER (mW) 0.001 0 20 40 60 80 100 120 140 160 180 200 OUTPUT POWER (mW) TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9726 toc04 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 3.3V RL = 16 1 OUTPUT POWER = 60mW THD+N (%) MAX9726 toc05 100 VDD = 5V RL = 32 10 fIN = 1kHz 10 THD+N (%) 1 fIN = 20Hz 0.1 fIN = 10kHz 0.01 0.1 0.01 OUTPUT POWER = 20mW 0.001 0 20 40 60 80 100 120 140 160 OUTPUT POWER (mW) 0.001 10 100 1k 10k FREQUENCY (Hz) 100k TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9726 toc06 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 5V RL = 16 1 THD+N (%) MAX9726 toc07 10 VDD = 3.3V RL = 32 1 THD+N (%) OUTPUT POWER = 20mW 0.1 10 OUTPUT POWER = 80mW 0.1 0.01 OUTPUT POWER = 60mW 0.001 10 100 1k 10k FREQUENCY (Hz) 100k 0.01 OUTPUT POWER = 40mW 0.001 10 100 1k 10k FREQUENCY (Hz) 100k _______________________________________________________________________________________ 5 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Typical Operating Characteristics (continued) (VDD = SHDN = 5V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both channels loaded. TA = +25C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit) TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9726 toc08 POWER DISSIPATION vs. OUTPUT POWER MAX9726 toc09 POWER DISSIPATION vs. OUTPUT POWER 900 POWER DISSIPATION (mW) 800 700 600 500 400 300 200 100 RL = 32 RL = 16 VDD = 5V fIN = 1kHz POUT = POUTR + POUTL MAX9726 toc10 10 VCC = 5V RL = 32 1 THD+N (%) OUTPUT POWER = 40mW 0.1 OUTPUT POWER = 80mW 600 500 POWER DISSIPATION (mW) 400 RL = 16 300 200 100 RL = 32 VDD = 3.3V fIN = 1kHz POUT = POUTR + POUTL 1000 0.01 0.001 10 100 1k 10k FREQUENCY (Hz) 100k 0 0 40 80 120 160 200 TOTAL OUTPUT POWER (mW) 0 0 40 80 120 160 200 240 TOTAL OUTPUT POWER (mW) OUTPUT POWER vs. LOAD RESISTANCE MAX9726 toc11 OUTPUT POWER vs. LOAD RESISTANCE VDD = 5V, fIN = 1kHz 180 OUTPUT POWER (mW) 150 120 90 60 30 0 THD+N = 1% THD+N = 10% MAX9726 toc12 120 VDD = 3.3V, fIN = 1kHz 100 OUTPUT POWER (mW) 80 60 40 THD+N = 1% 20 0 10 100 LOAD RESISTANCE () THD+N = 10% 210 1000 10 100 LOAD RESISTANCE () 1000 OUTPUT POWER vs. SUPPLY VOLTAGE MAX9726 toc13 OUTPUT POWER vs. SUPPLY VOLTAGE THD+N = 10% 140 OUTPUT POWER (mW) 120 100 80 60 40 THD+N = 1% MAX9726 toc14 180 160 140 OUTPUT POWER (mW) 120 100 80 60 40 20 0 2.5 3.0 3.5 4.0 4.5 5.0 RL = 16 fIN = 1kHz THD+N = 1% THD+N = 10% 160 20 0 5.5 2.5 3.0 3.5 4.0 4.5 RL = 32 fIN = 1kHz 5.0 5.5 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) 6 _______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Typical Operating Characteristics (continued) (VDD = SHDN = 5V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both channels loaded. TA = +25C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY MAX9726 toc15 POWER-SUPPLY REJECTION RATIO vs. FREQUENCY MAX9726 toc16 CROSSTALK vs. FREQUENCY VIN = 1VP-P RL = 32 G = 0dB LEFT TO RIGHT MAX9726 toc17 0 -10 -20 -30 PSRR (dB) -50 -60 -70 -80 -90 -100 -110 10 100 1k FREQUENCY (Hz) 10k -40 VDD = 5V + 100mVP-P RIN = RF = 10k 0 -10 -20 -30 PSRR (dB) -40 -50 -60 -70 -80 -90 -100 -110 VDD = 3.3V + 100mVP-P RIN = RF = 10k -60 -70 CROSSTALK (dB) -80 -90 -100 -110 -120 RIGHT TO LEFT 100k 10 100 1k FREQUENCY (Hz) 10k 100k 10 100 1k 10k FREQUENCY (Hz) 100k CROSSTALK vs. FREQUENCY MAX9726 toc18 BassMax FREQUENCY RESPONSE R2 = 36k C3 = 0.068F R2 = 22k C3 = 0.1F R2 = 10k C3 = 0.22F R1 = 47k RL = 32 MAX9726 toc19 -40 -50 CROSSTALK (dB) -60 VIN = 1VP-P RL = 32 G = -10dB RIGHT TO LEFT -70 -80 -90 -100 10 100 1k 10k FREQUENCY (Hz) LEFT TO RIGHT 40 35 30 GAIN (dB) 25 20 15 10 BassMax DISABLED 100k 1 10 100 1k 10k 100k FREQUENCY (Hz) OUTPUT FFT MAX9726 toc20 OUTPUT POWER vs. CHARGE-PUMP CAPACITANCE AND LOAD RESISTANCE 150 140 OUTPUT POWER (mW) 130 120 110 100 90 80 70 60 C1 = C2 = 0.68F C1 = C2 = 1F C1 = C2 = 2.2F VDD = 5V fIN = 1kHz THD+N = 1% MAX9726 toc21 0 -20 AMPLITUDE (dBV) -40 -60 -80 -100 -120 -140 0 5 10 FREQUENCY (kHz) 15 VIN = 100mVRMS ATTEN = 60dB VOUT = -60dBV RL = 320 fIN = 1kHz VDD = 5V 160 20 10 15 20 25 30 35 40 45 50 LOAD RESISTANCE () _______________________________________________________________________________________ 7 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Typical Operating Characteristics (continued) (VDD = SHDN = 5V, PGND = SGND = 0V, C1 = C2 = 1F, CPREG = CNREG = 1F, BM_ = 0V, RIN = 10k, RF = 10k, maximum volume (overall gain = 0dB), BassMax disabled. Load connected between OUT_ and PGND where specified. Outputs in phase, both channels loaded. TA = +25C, unless otherwise noted.) (See the Functional Diagram/Typical Operating Circuit) OUTPUT POWER vs. CHARGE-PUMP CAPACITANCE AND LOAD RESISTANCE C1 = C2 = 2.2F 85 OUTPUT POWER (mW) 80 75 70 65 60 10 15 20 25 30 35 40 45 50 VDD = 3.3V fIN = 1kHz THD+N = 1% C1 = C2 = 1F MAX9726 toc22 POWER-UP/POWER-DOWN MAX9726 toc23 EXITING SHUTDOWN MAX9726 toc24 90 RL = 32 VSHDN 5V/div VDD 2V/div C1 = C2 = 0.68F VOUT_ 10mV/div VIN_ 200mV/div VOUT_ 2V/div 20ms/div 100s/div LOAD RESISTANCE () ENTERING SHUTDOWN MAX9726 toc25 SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX9726 toc26 SHUTDOWN CURRENT vs. SUPPLY VOLTAGE NO LOAD INPUTS AC GROUNDED MAX9726 toc27 5.6 5.5 SUPPLY CURRENT (mA) 5.4 5.3 5.2 5.1 5.0 4.9 4.8 2 3 4 SUPPLY VOLTAGE (V) 5 NO LOAD INPUTS AC GROUNDED 10 9 SHUTDOWN CURRENT (A) 8 7 6 5 4 VSHDN 5V/div VIN_ 200mV/div VOUT_ 2V/div 20s/div 6 2 3 4 SUPPLY VOLTAGE (V) 5 6 8 _______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control Pin Description PIN TQFN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 BUMP UCSP A1 A2 A3 A4 A5 B3 C3 C2 B4 B5 C5 C4 D5 D2 D4 NAME VDD C1P PGND C1N PVSS SDA SCL SHDN FBL INL INR FBR SGND NREG BMR FUNCTION Power-Supply Input. Bypass VDD to PGND with a 1F capacitor. Charge-Pump Flying Capacitor Positive Terminal. Connect a 1F capacitor between C1P and C1N. Power Ground. Connect to SGND. Charge-Pump Flying Capacitor Negative Terminal. Connect a 1F capacitor between C1P and C1N. Charge-Pump Output. Connect to SVSS and bypass with a 1F capacitor to PGND. Serial Data Input. Connect a pullup resistor greater than 500 from SDA to VDD. Serial Clock Input. Connect a pullup resistor greater than 500 from SCL to VDD. Active-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). Left-Channel Feedback Output. Connect a feedback resistor between FBL and INL. See the Gain-Setting Components section. Left-Channel Input. Connect an input resistor to INL. See the Gain-Setting Components section. Right-Channel Input. Connect an input resistor to INR. See the Gain-Setting Components section. Right-Channel Feedback Output. Connect a feedback resistor between FBR and INR. See the Gain-Setting Components section. Signal Ground. Connect to PGND. Negative Supply Regulator Voltage. Bypass NREG to PGND with a 1F capacitor. 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. Headphone Amplifier Negative Power-Supply Input. Connect to PVSS and bypass with a 1F capacitor to PGND. Right Headphone Output Left Headphone Output 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. Positive Supply Regulator Voltage. Bypass PREG to PGND with a 1F capacitor. Exposed Pad. Connect EP to SVSS or leave unconnected. MAX9726 16 17 18 19 20 EP D1 C1 B1 D3 B2 -- SVSS OUTR OUTL BML PREG EP _______________________________________________________________________________________ 9 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Detailed Description The MAX9726 stereo headphone amplifier features Maxim's patented DirectDrive architecture, eliminating the large output-coupling capacitors required by conventional single-supply headphone amplifiers. The MAX9726 consists of two 105mW Class AB headphone amplifiers, two adjustable gain preamplifiers, hardware/software shutdown 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 positive supply (VDD). Powering the amplifiers from VDD and PVSS increases 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 communication between the MAX9726 and a microcontroller. The internal command register controls the shutdown status of the MAX9726, enables the BassMax circuitry, and sets the volume level (see the Volume Control section). The MAX9726's BassMax circuitry improves audio reproduction by boosting the bass response of the amplifier, compensating for any lowfrequency attenuation introduced by the headphone. External components set the MAX9726's overall gain allowing for custom gain settings (see the Gain-Setting Components section). Amplifier volume is digitally programmable to any one of 64 levels. Maxim's patented 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 220F) tantalum capacitors, the MAX9726 charge pump requires only two small 1F 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 Characteristics for details of the possible capacitor sizes. VOUT VDD VDD VDD/2 GND CONVENTIONAL DRIVER-BIASING SCHEME VOUT VDD* DirectDrive Traditional single-supply headphone amplifiers have their outputs biased about a nominal DC voltage, typically half the supply, for maximum dynamic range. Large coupling capacitors are needed to block this DC bias from the headphone. Without these capacitors, a significant amount of DC current flows to the headphone, resulting in unnecessary power dissipation and possible damage to both the headphone and headphone amplifier. In addition to the cost and size disadvantages, the DC-blocking capacitors required by conventional headphone amplifiers limit low-frequency response and can distort the audio signal. GND 2VDD* -VDD* DirectDrive BIASING SCHEME *VDD IS INTERNALLY LIMITED TO 2.5V DUE TO ABSOLUTE MAXIMUM RATINGS AND TO LIMIT POWER DISSIPATION. Figure 1. Traditional Amplifier Output vs. MAX9726 DirectDrive Output 10 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control Charge Pump The 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 switching 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. 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 headroom than typical single-supply headphone amplifiers. This additional headroom allows boosting the bass frequencies without the output signal clipping. Program the BassMax gain and cutoff frequency with external components connected between OUT_ and BM_ (see the Gain-Setting Components section and the Functional Diagram/Typical Operating Circuit). Use the I2C-compatible interface to program the command register to enable/disable the BassMax circuit. BM_ is connected to the noninverting input of the output amplifier when BassMax is enabled. BM_ is pulled to SGND when BassMax is disabled. The typical application of the BassMax circuit involves feeding a lowpass 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 implement BassMax. MAX9726 Click-and-Pop Suppression In 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 headphone amplifier does not require output-coupling capacitors, no audible transients occur. Additionally, the MAX9726 features extensive click-andpop suppression that eliminates any audible transient sources internal to the device. The Power-Up/PowerDown 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 preamplifier's bias voltage through the MAX9726's input resistor (R IN ) during startup. The resulting voltage shift across the capacitor creates an audible click-and-pop. Delay the rise of SHDN by at least four time constants (4 x RIN x CIN) relative to the start of the preamplifier to avoid clicks/pops caused by the input filter. MAX9726 R R FROM ATTENUATOR STAGE OUT_ TO HEADPHONE SPEAKER R1 BM_ BassMax ENABLE Shutdown The MAX9726 features a 8A, low-power shutdown mode that reduces quiescent current consumption and extends battery life. Shutdown is controlled by a hardware and software interface. Driving the SHDN input low disables the drive amplifiers, bias circuitry, charge pump, and sets the headphone amplifier output resistance to 50k. Similarly, the MAX9726 enters shutdown when bit seven (B7) in the control register is set to 0 (see the Command Register section). SHDN and 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. R2 C3 Figure 2. BassMax External Connections ______________________________________________________________________________________ 11 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Volume Control The 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 (RIN and RF). Mute attenuation is typically better than 120dB when driving a 32 load. 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. 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 transmitted 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 500, is required on the SDA bus. The MAX9726 SCL line operates as an input only. A pullup resistor, greater than 500, 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 MAX9726 from highvoltage spikes on the bus lines, and minimize crosstalk and undershoot of the bus signals. Serial Interface The MAX9726 features an I 2 C-/SMBus-compatible, 2-wire serial interface consisting of a serial data line (SDA) and a serial clock line (SCL). SDA and SCL facilitate 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 generate the SCL signal. The MAX9726 cannot write to the SDA tSU, DAT tLOW SCL tHD, STA tR START CONDITION tHIGH tF REPEATED START CONDITION STOP CONDITION START CONDITION tHD, DAT tSU, STA tBUF tHD, STA tSP tSU, STO Figure 3. 2-Wire Serial-Interface Timing Diagram 12 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control 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 since changes in SDA while SCL is high are control signals (see the START and STOP Conditions section). SDA and SCL idle high when the I2C bus is not busy. START and STOP Conditions SDA and SCL idle high when the bus is not in use. 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 5). A START condition from the master signals the beginning of a transmission to the MAX9726. The master terminates transmission, and frees the bus, by issuing a STOP condition. The bus remains active if a REPEATED START condition is generated instead of a STOP condition. Early STOP Conditions The MAX9726 recognizes 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 slave address is defined as the seven most significant bits (MSBs) of the serial data transmission. The first byte of information sent to the MAX9726 after the START condition must contain the slave address and R/W bit (see Table 1). The MAX9726 is a slave device only capable of being written to. The sent R/W bit must always be set to zero when configuring the MAX9726. The MAX9726 acknowledges the receipt of its address even if R/W is set to 1. However, the MAX9726 does not drive SDA. Addressing the MAX9726 with R/W set to 1 causes the master to receive all ones regardless of the contents of the command register. Acknowledge The acknowledge bit (ACK) is a clocked 9th bit that the MAX9726 uses to handshake receipt each byte of data (see Figure 6). The MAX9726 pulls down SDA during the master generated 9th clock pulse. The SDA line must remain stable and low during the high period of the acknowledge 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 communication. MAX9726 S Sr P START CONDITION CLOCK PULSE FOR ACKNOWLEDGMENT SCL SCL 1 2 8 NOT ACKNOWLEDGE 9 SDA SDA ACKNOWLEDGE Figure 4. START, STOP, and REPEATED START Conditions Figure 5. Acknowledge Bit Table 1. MAX9726 Slave Address with Read/Write Bit PART MAX9726A MAX9726B A6 (MSB) 1 1 A5 0 0 A4 0 0 A3 1 1 A2 1 1 A1 0 0 A0 0 1 R/W 0 0 ______________________________________________________________________________________ 13 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control COMMAND BYTE IS STORED ON RECEIPT OF STOP CONDITION ACKNOWLEDGE FROM MAX9726 S START CONDITION SLAVE ADDRESS R/W 0 A COMMAND BYTE ACKNOWLEDGE FROM MAX9726 AP STOP CONDITION B7 B6 B5 B4 B3 B2 B1 B0 Figure 6. Write Data Format Example Write Data Format A write to the MAX9726 includes transmission of a START condition, the slave address with the R/W bit set to 0 (see Table 1), one byte of data to configure the command register, and a STOP condition. Figure 6 illustrates the proper format for one frame. The MAX9726 only accepts write data, but it acknowledges the receipt of its address byte with the R/W bit set to 1. The MAX9726 does not write to the SDA bus in the event that the R/W bit is set to 1. Subsequently, the master reads all 1's from the MAX9726. Always set the R/W bit to zero to avoid this situation. Command Register The MAX9726 has one command register that is used to enable/disable shutdown, enable/disable BassMax, and set the volume. Table 2 describes the function of the bits contained in the command register. Set B7 to 0 to shutdown the MAX9726. The MAX9726 wakes up from shutdown when B7 is set to 1 provided SHDN is high. SHDN must be high and B7 must be set to 1 for the MAX9726 to operate normally (see Table 3). Set B6 to 1 to enable BassMax (see Table 4). The output signal's low-frequency response is boosted according to the external components connected between OUT_ and BM_. See the Gain-Setting Components section for details on choosing the external components. MAX9726 ATTENUATION OF MAX. GAIN SETTING (dB) 20 40 60 80 100 120 0 16 32 CODE (DECIMAL) 48 64 MAX9726 fig07 0 Figure 7. Volume-Control Transfer Function Adjust the MAX9726's volume with control bits [5:0]. The volume is adjustable to one of 64 steps ranging from full mute to the maximum gain set by the external components. Table 5 lists all the possible volume settings for the MAX9726. Figure 7 shows the volume-control transfer function for the MAX9726. Table 2. Command Register B7 Shutdown B6 BassMax Enable B5 B4 B3 B2 B1 B0 Volume (See Table 5) Table 3. Shutdown Control, SHDN = VDD MODE Disabled Enabled B7 0 1 Table 4. BassMax Control MODE BassMax Disabled BassMax Enabled B6 0 1 14 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control Table 5. MAX9726 Volume-Control Settings B5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 B4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 B3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 B2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 B1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 B0 (LSB) 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 ATTENUATION OF MAXIMUM GAIN SETTING (dB) 120 116 112 108 104 100 96 92 88 84 80 76 72 68 64 62 60 58 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28 MAX9726 15 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Table 5. MAX9726 Volume-Control Settings (continued) B5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 B4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 B3 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 B2 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 B1 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 B0 (LSB) 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 ATTENUATION OF MAXIMUM GAIN SETTING (dB) 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2.5 2 1.5 1 0.5 0 16 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control Table 6. Initial Power-Up Command Register Status MODE Power-On Reset B7 1 B6 1 B5 1 B4 1 B3 1 B2 1 B1 1 B0 1 MAX9726 Power-On Reset The contents of the MAX9726's command register at power-on are as shown in Table 6. Use the following equation to determine the peak-topeak output voltage that causes 1% THD+N for a given load. VOUT(P -P) = 2 2(POUT _ 1% x RL where POUT_1% is the output power that causes 1% THD+N, RL is the load resistance, and VOUT(P-P) is the peak-to-peak output voltage. Determine the voltage gain (AV) necessary to attain this output voltage based on the maximum peak-to-peak input voltage (VIN(P-P)): AV = VOUT(P -P) VIN(P -P) Applications Information Power Dissipation and Heatsinking Linear power amplifiers can dissipate a significant amount of power under normal operating conditions. The maximum power dissipation for each package is given in the Absolute Maximum Ratings section under Continuous Power Dissipation or can be calculated by the following equation: TJ(MAX) - TA PD(MAX) = JA where TJ(MAX) is +150C, TA is the ambient temperature, and JA is the reciprocal of the derating factor in C/W as specified in the Absolute Maximum Ratings section. For example, JA for the TQFN package is +39C/W. If the power dissipation exceeds the rated package dissipation, reduce VDD, increase load impedance, decrease the ambient temperature, or add heatsinking. Large output, supply, and ground traces decrease JA, allowing more heat to be transferred from the package to surrounding air. The maximum voltage gain setting is determined by external components (see the Gain-Setting Components section). UVLO The MAX9726 features an undervoltage lockout (UVLO) function that prevents the device from operating if the supply voltage is less than 2.7V. This feature ensures proper operation during brownout conditions and prevents deep battery discharge. Once the supply voltage exceeds the UVLO threshold, the MAX9726 charge pump is turned on and the amplifiers are powered, provided that SHDN is high and B7 in the command register is set to 1. Output Dynamic Range Dynamic range is the difference between the noise floor of the system and the output level at 1% THD+N. It is essential that a system's dynamic range be known before setting the maximum output gain. Output clipping occurs if the output signal is greater than the dynamic range of the system. The DirectDrive architecture of the MAX9726 has increased dynamic range (for a given VDD) compared to other single-supply amplifiers. Due to the absolute maximum ratings of the MAX9726 and to limit power dissipation, the MAX9726 includes internal circuitry that limits the output voltage to approximately 2.5V. Use the THD+N vs. Output Power graphs in the Typical Operating Characteristics section to identify the system's dynamic range. Find the output power that causes 1% THD+N for a given load. This point indicates the output power that causes the output to begin to clip. Component Selection Charge-Pump Capacitor Selection Use ceramic capacitors with a low ESR for optimum performance. For optimal performance over the extended temperature range, select capacitors with an X7R dielectric. Charge-Pump Flying Capacitor (C1) The charge-pump flying capacitor connected between C1N and C1P affects the charge pump's load regulation and output impedance. Choosing a flying capacitor that is too small degrades the MAX9726's ability to provide sufficient current drive and leads to a loss of output voltage. Increasing the value of the flying capacitor improves load regulation and reduces the chargepump output impedance. See the Output Power vs. Charge-Pump Capacitance and Load Resistance graphs in the Typical Operating Characteristics. 17 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control Charge-Pump Hold Capacitor (C2) The hold capacitor's value and ESR directly affect the ripple at PVSS. Ripple is reduced by increasing the value of the hold capacitor. Choosing a capacitor with lower ESR reduces ripple and output impedance. Lower capacitance values can be used in systems with low maximum output power levels. See the Output Power vs. Charge-Pump Capacitance and Load Resistance graphs in the Typical Operating Characteristics. C2 should be greater than or equal to the value of C1. Input-Coupling Capacitor The AC-coupling capacitor (C IN) and input resistor (RIN) form a highpass filter that removes any DC bias from an input signal. See the Functional Diagram/ Typical Operating Circuit. CIN prevents any DC components from the input signal source from appearing in the amplifier outputs. The -3dB point of the highpass filter, assuming zero-source impedance due to the input signal source, is given by: f-3dB = 1 (Hz) 2 x RIN x CIN MAX9726 where AV is the maximum voltage gain in dB. The overall voltage gain of the MAX9726 with BassMax disabled is equal to: A TOTAL = A V - ATTENdB _ VOL (dB) where ATTENdB_VOL is the attenuation due to the volume setting in dB and ATOTAL is the overall voltage gain of the MAX9726 in dB. When BassMax is enabled, the bass-boost low-frequency response is set by the ratio of R1 to R2, by the following equation (see Figure 2): R1 + R2 ABOOST = 20 x log (dB) R1 - R2 where ABOOST is the voltage gain boost at low frequencies in dB. ABOOST is added to the gain realized by the volume setting and the gain set by resistors RIN and RF (AV). The overall voltage gain of the MAX9726 at low frequencies with BassMax enabled is equal to: A TOTAL _ BB = A V + ABOOST - ATTENdB _ VOL (dB) where ATOTAL_BB is the overall gain of the MAX9726 at low frequencies in dB. R2 To maintain circuit stability, the ratio R1 + R2 must not exceed one-half. A ratio equal to or less than one-third is recommended. The switch that shorts BM_ to SGND, when BassMax is disabled, can have an onresistance as high as 300. Choose a value for R1 that is greater than 40k to ensure that positive feedback is negligible when BassMax is disabled. Table 7 contains a list of R2 values, with R1 = 47k, and the corresponding low-frequency gain boost. Choose CIN such that f-3dB is well below the lowest frequency of interest. Setting f-3dB too high affects the amplifier's low-frequency response. Use capacitors with low-voltage coefficient dielectrics. Aluminum electrolytic, tantalum, or film dielectric capacitors are good choices for AC-coupling capacitors. Capacitors with high-voltage coefficients, such as ceramics (non-C0G dielectrics), can result in increased distortion at low frequencies. Gain-Setting Components With BassMax disabled, the maximum gain of the MAX9726 is set by the values of the external resistors R IN and R F (see the Functional Diagram/Typical Operating Circuit). When BassMax is disabled, the maximum gain of the MAX9726 is: R A V = 20 x log F (dB) RIN Table 7. BassMax Gain Examples (R1 = 47k) R2 (k) 39 33 27 22 15 10 LOW-FREQUENCY GAIN BOOST (dB) 20.6 15.1 11.3 8.8 5.7 3.7 18 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control The low-frequency boost attained by the BassMax circuit is added to the gain realized by the maximum gain and volume settings. Select the BassMax gain so that the output signal remains within the dynamic range of the MAX9726. Output signal clipping occurs at low frequencies if the BassMax gain boost is excessively large. See the Output Dynamic Range section. Capacitor C3 forms a pole and a zero according to the following equations: R1 - R2 (Hz) 2 x C3 x R1 x R2 R1 + R2 (Hz) fZERO = 2 x C3 x R1 x R2 fPOLE = fPOLE is the frequency at which the gain boost begins to roll off. fZERO is the frequency at which the bassboost gain no longer effects the transfer function. At frequencies greater than or equal to fZERO, the gain set by resistors RIN and RF and the volume control attenuation dominate. Table 8 contains a list of capacitor values and the corresponding poles and zeros for a given DC gain. See Figure 8 for an example of a gain profile using BassMax. The passband gain of the active filter is determined by the external component values described in the GainSetting Components section. To minimize distortion, use capacitors with low-voltage coefficient dielectrics when selecting CF. Film or C0G dielectric capacitors are good choices for feedback capacitors. Capacitors with high-voltage coefficients, such as ceramics (non-C0G dielectrics), can result in increased distortion. MAX9726 BassMax FREQUENCY RESPONSE 8 6 4 GAIN (dB) 2 0 -2 -4 -6 -8 -10 10 100 1k 10k FREQUENCY (Hz) BassMax DISABLED fPOLE BassMax ENABLED fZERO R1 = 47k R2 = 22k C3 = 0.1F RL = 32 MAX9726 fig08 10 Table 8. BassMax Pole and Zero Examples for a Gain Boost of 8.8dB (R1 = 47k, R2 = 22k) C3 (nF) 100 82 68 56 47 22 10 fPOLE (Hz) 38 47 56 68 81 174 384 fZERO (Hz) 106 130 156 190 230 490 1060 Figure 8. BassMax Gain Profile Example CF RF MAX9726 Single-Pole Active Lowpass Filter (LPF) To configure the MAX9726 as an active single-pole lowpass filter (Figure 9), connect a single feedback capacitor (CF) in parallel with the feedback resistor (RF). The -3dB point (below passband) of the active lowpass filter is equal to: f-3dB = 1 (Hz) 2RFCF RIN IN_ FB_ TO ATTENUATOR STAGE f-3dB = 1 2RFCF Figure 9. Single-Pole Active Lowpass Filter ______________________________________________________________________________________ 19 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Summing Amplifier (Audio Mixer) Figure 10 shows the MAX9726 configured as a summing amplifier, which allows multiple audio sources to be linearly mixed together. Using this configuration, the output of the MAX9726 is equal to the weighted sum of the input signals: R R R VOUT _ = - VIN1 F + VIN2 F + VIN3 F RIN1 RIN2 RIN3 As shown in the above equation, the weighting or amount of gain applied to each input signal source is determined by the ratio of RF and the respective input resistor (RIN1, RIN2, RIN3) connected to each signal source. When BassMax is enabled, the low-frequency gain (ABOOST) set by R1, R2, and C3 (see the GainSetting Components section) adds to the gain determined by RF and RIN_. Select RF and RIN_ such that the dynamic range of the MAX9726 is not exceeded when BassMax is enabled and/or when the input signals are at their maximum values and in phase with each other. RF CIN VIN1 CIN VIN2 CIN VIN3 RIN3 RF R R + VIN2 F + VIN3 F ) RIN2 RIN3 RIN1 RIN2 IN_ FB_ TO ATTENUATOR STAGE RIN1 Layout and Grounding Proper layout and grounding are essential for optimum performance. Connect PGND and SGND together at a single point (star ground point) on the PC board. Connect PVSS to SVSS at the device and bypass this connection with a 1F capacitor to PGND. Bypass VDD, PREG, and NREG to PGND with a 1F capacitor. Place the power-supply bypass capacitor and the chargepump hold capacitor as close as possible to the MAX9726. Route PGND, and all traces that carry switching transients, away from SGND and the audio signal path. Route digital signal traces away from the audio signal path. Make traces perpendicular to each other when routing digital signals over or under audio signals. The TQFN package features an exposed pad that improves thermal efficiency. Ensure that the exposed pad is electrically isolated from PGND, SGND, and VDD. Connect the exposed pad to PVSS when the board layout dictates that the exposed pad cannot be left unconnected. UCSP Applications Information For the latest application details on UCSP construction, dimensions, tape carrier information, PC board techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information on reliability testing results, go to Maxim's website at www.maxim-ic.com/ucsp and look up the Application Note: UCSP--A Wafer-Level Chip-Scale Package. MAX9726 VFB_ = -(VIN1 DIAGRAM SHOWN WITH BassMax DISABLED. Figure 10. Summing Amplifier 20 ______________________________________________________________________________________ LEFT AUDIO INPUT CIN 1F 2.7V TO 5.5V RIN 10k ON OFF 9 (D2) VCC FBL SHDN 8 (B3) RF 10k 1F 1 (A1) 10 (E2) INL VCC R VCC 18 OUTL (A2) R1 47k VDD POSITIVE REGULATOR 10k 10k 20 (B2) PREG CPREG 1F TO I2C I2C SCL INTERFACE 6 (C2) SDA VEE 0 TO 120dB ATTENUATOR R MASTER 7 (C3) 14 (B4) NREG VEE NEGATIVE REGULATOR VEE VCC BMR 15 (D4) 19 BML (C4) CNREG 1F C3 0.1F R2 22k 2 (B1) C1P R C1N VEE R VEE SGND PGND PVSS 3 5 13 (C1) (E1) (E4) SVSS INR 16 11 (A4) (E3) FBR 12 (D3) C2 1F RIN 10k CIN 1F RIGHT AUDIO INPUT RF 10k CHARGE PUMP VCC 0 TO 120dB ATTENUATOR C1 1F OUTR 17 (A3) C3 0.1F R2 22k 4 (D1) R1 47k MAX9726 MAX9726 ______________________________________________________________________________________ Functional Diagram/Typical Operating Circuit RF AND RIN ARE CHOSEN FOR A GAIN OF 20dB. BassMax CIRCUIT TUNED FOR +8.8dB AT 106Hz. ( ) UCSP PACKAGE DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control 21 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 System Diagrams 2.7V TO 5.5V CPREG 1F CNREG 1F 10k 10k 1F VDD SDA CONTROLLER SCL SHDN CIN 1F RIN 10k RF 100k FBL FM RADIO IC CIN 1F RIN 10k RF 100k FBR INR C1P C1N SGND PGND INL PREG NREG OUTL R1 47k BML C3 0.1F R2 22k MAX9726 C3 0.1F BMR R1 47k PVSS OUTR SVSS C3 0.1F R2 22k C1 1F 10k 10k 1F 2.7V TO 5.5V CPREG 1F CNREG 1F VDD SDA CONTROLLER SCL SHDN CIN 1F RIN 10k RF 100k FBL FM RADIO IC CIN 1F RIN 10k RF 100k FBR CIN RIN 0.1F 100k AUDIO DAC CIN RIN 0.1F 100k C1 1F INR C1P C1N SGND PGND INL PREG NREG OUTL R1 47k BML C3 0.1F R2 22k MAX9726 C3 0.1F BMR R1 47k PVSS OUTR SVSS C2 0.1F R2 22k 22 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Pin Configurations NREG BMR SGND FBR 15 SVSS 16 OUTR 17 OUTL 18 BML 19 PREG 20 14 13 12 INR TOP VIEW TOP VIEW (BUMP SIDE DOWN) 1 VDD A 2 C1P 3 PGND 4 C1N 5 PVSS 11 10 9 INL OUTL FBL SHDN SCL SDA D 1 VDD 2 C1P 3 PGND 4 C1IN 5 PVSS C SVSS B OUTR PREG SDA FBL INL MAX9726 8 7 SHDN SCL FBR INR + 6 NREG BML BMR SGND UCSP TQFN (4mm x 4mm) Chip Information PROCESS: BiCMOS ______________________________________________________________________________________ 23 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 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.) 24L QFN THIN.EPS PACKAGE OUTLINE, 12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm 21-0139 E 1 2 24 ______________________________________________________________________________________ DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control 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.) MAX9726 PACKAGE OUTLINE, 12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm 21-0139 E 2 2 ______________________________________________________________________________________ 25 DirectDrive, Headphone Amplifier with BassMax, I2C, Volume and Gain Control MAX9726 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) 5x4 UCSP.EPS 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. 26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. |
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