19-3465; Rev 0; 11/04 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown Features The MAX9725 fixed-gain, stereo headphone amplifier is ideal for portable equipment where board space is at a premium. The MAX9725 uses a unique, patented DirectDriveTM architecture to produce a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors, saving cost, board space, and component height. Fixed gains of -2V/V (MAX9725A), 1.5V/V (MAX9725B), -1V/V (MAX9725C), and -4V/V (MAX9725D) further reduce external component count. The MAX9725 delivers up to 20mW per channel into a 32Ω load and achieves 0.006% THD+N. An 80dB at 1kHz power-supply rejection ratio (PSRR) allows the MAX9725 to operate from noisy digital supplies without an additional linear regulator. The MAX9725 includes ±8kV ESD protection on the headphone output. Comprehensive click-andpop circuitry suppresses audible clicks and pops at startup and shutdown. A low-power shutdown mode reduces supply current to 0.6µA (typ). ♦ Low Quiescent Current (2.1mA) ♦ Single-Cell, 0.9V to 1.8V Single-Supply Operation ♦ Fixed Gain Eliminates External Feedback Network MAX9725A: -2V/V MAX9725B: -1.5V/V MAX9725C: -1V/V MAX9725D: -4V/V ♦ Ground-Referenced Outputs Eliminate DC Bias ♦ No Degradation of Low-Frequency Response Due to Output Capacitors ♦ 20mW per Channel into 32Ω ♦ Low 0.006% THD+N ♦ High PSRR (80dB at 1kHz) ♦ Integrated Click-and-Pop Suppression ♦ Low-Power Shutdown Control ♦ Short-Circuit Protection ♦ ±8kV ESD-Protected Amplifier Outputs ♦ Available in Space-Saving Packages 12-Bump UCSP (1.54mm x 2.02mm x 0.6mm) 12-Pin Thin QFN (4mm x 4mm x 0.8mm) The MAX9725 operates from a single 0.9V to 1.8V supply, allowing the device to be powered directly from a single AA or AAA battery. The MAX9725 consumes only 2.1mA of supply current, provides short-circuit protection, and is specified over the extended -40°C to +85°C temperature range. The MAX9725 is available in a tiny (1.54mm x 2.02mm x 0.6mm) 12-bump chip-scale package (UCSP™) and a 12-pin thin QFN package (4mm x 4mm x 0.8mm). Block Diagram Applications MP3 Players Smart Phones Cellular Phones Portable Audio Equipment PDAs SINGLE 1.5V CELL AA OR AAA BATTERY VDD MAX9725 DirectDrive OUTPUTS ELIMINATE DC-BLOCKING CAPACITORS. INL Ordering Information PART PINTEMP RANGE PACKAGE TOP GAIN MARK (V/V) MAX9725AEBC-T* -40°C to +85°C 12 UCSP-12 MAX9725AETC -40°C to +85°C 12 TQFN-EP** AAEW MAX9725BEBC-T* -40°C to +85°C 12 UCSP-12 ACL -1.5 MAX9725BETC -40°C to +85°C 12 TQFN-EP** AAEX -1.5 MAX9725CEBC-T* -40°C to +85°C 12 UCSP-12 ACM -1 MAX9725CETC -40°C to +85°C 12 TQFN-EP** AAEY -1 MAX9725DEBC-T* -40°C to +85°C 12 UCSP-12 ACN -4 MAX9725DETC -40°C to +85°C 12 TQFN-EP** AAEZ -4 ACK OUTL C1P INVERTING CHARGE PUMP -2 -2 C1N PVSS VSS OUTR INR SGND PGND *Future product—contact factory for availability. **EP = Exposed paddle. UCSP is a trademark of Maxim Integrated Products, Inc. Pin Configurations appear at end of data sheet. ________________________________________________________________ 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. 1 MAX9725 General Description MAX9725 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown ABSOLUTE MAXIMUM RATINGS SGND to PGND .....................................................-0.3V to +0.3V VDD to SGND or PGND ............................................-0.3V to +2V VSS to PVSS ...........................................................-0.3V to +0.3V C1P to PGND..............................................-0.3V to (VDD + 0.3V) C1N to PGND............................................(PVSS - 0.3V) to +0.3V VSS, PVSS to GND ....................................................+0.3V to -2V OUTR, OUTL, INR, INL to SGND .....(VSS - 0.3V) to (VDD + 0.3V) SHDN to SGND or PGND .........................................-0.3V to +4V Output Short-Circuit Current ......................................Continuous Continuous Power Dissipation (TA = +70°C) 12-Bump UCSP (derate 6.5mW/°C above +70°C)....518.8mW 12-Pin Thin QFN (derate 16.9mW/°C above +70°C) ..1349.1mW Junction Temperature ......................................................+150°C Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Bump Temperature (soldering) Reflow............................+230°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (See the Functional Diagram.) PARAMETER Supply Voltage Range Quiescent Supply Current Shutdown Current Shutdown to Full Operation SHDN Thresholds SYMBOL VDD IDD ISHDN CONDITIONS Guaranteed by PSRR test Both channels active VDD = 0.9V to 1.8V VIL VDD = 0.9V to 1.8V SHDN Input Leakage Current ILEAK CHARGE PUMP Oscillator Frequency fOSC TYP MAX UNITS 2.1 1.8 3.3 V mA 0.9 TA = +25°C VSHDN = 0V tON VIH MIN 0.6 10 TA = -40°C to +85°C 30 180 µA µs 0.7 x VDD 0.3 x VDD VDD = 0.9V to 1.8V (Note 1) V ±1 µA 667 kHz 493 580 MAX9725A -2.04 -2.00 -1.96 MAX9725B MAX9725C -1.53 -1.02 -1.5 -1.00 -1.47 -0.98 MAX9725D -4.08 -4.00 -3.92 AMPLIFIERS Voltage Gain Gain Match Total Output Offset Voltage Input Resistance Power-Supply Rejection Ratio AV ∆AV VOS ±0.5 Input AC-coupled, RL = 32Ω to GND, TA = +25°C PSRR Output Power (Note 2) Total Harmonic Distortion Plus Noise Signal-to-Noise Ratio 2 ±0.3 ±0.45 ±1.05 ±1.58 MAX9725C ±0.6 ±2.1 15 25 35 60 80 70 VDD = 0.9V to 1.8V, TA = +25°C fIN = 1kHz 100mVP-P ripple fIN = 20kHz VDD = 1.5V POUT THD+N SNR % MAX9725A/MAX9725D MAX9725B RIN RL = 32Ω RL = 16Ω V/V mV kΩ dB 62 10 20 VDD = 1.0V, RL = 32Ω 25 7 VDD = 0.9V, RL = 32Ω 6 RL = 32Ω, POUT = 12mW, f = 1kHz 0.006 RL = 16Ω, POUT = 15mW, f = 1kHz BW = 22Hz to 22kHz RL = 32Ω, POUT = 12mW A-weighted filter 0.015 89 92 _______________________________________________________________________________________ mW % dB 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown (VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (See the Functional Diagram.) PARAMETER SYMBOL Slew Rate Maximum Capacitive Load Crosstalk MIN TYP CL KCP ESD Protection MAX UNITS 0.2 XTALK Click/Pop Level Note 1: Note 2: Note 3: CONDITIONS SR VESD V/µs No sustained oscillations 150 pF fIN = 1.0kHz, RL = 32Ω, POUT = 5mW 100 dB RL = 32Ω, peak voltage, Aweighted, 32 samples per second (Note 3) Into shutdown 72.8 Out of shutdown 72.8 dB Human Body Model (OUTR, OUTL) ±8 kV Input leakage current measurements limited by automated test equipment. fIN = 1kHz, TA = +25°C, THD+N < 1%, both channels driven in-phase. Testing performed with 32Ω resistive load connected to outputs. Mode transitions controlled by SHDN. KCP level calculated as 20 log [peak voltage under normal operation at rated power level / peak voltage during mode transition]. Inputs are ACgrounded. Typical Operating Characteristics VDD = 1.5V RL = 16Ω AV = -2V/V 1 MAX9725 toc02 1 MAX9725 toc01 VDD = 1.5V RL = 32Ω AV = -2V/V 0.1 POUT = 15mW THD+N (%) 0.1 THD+N (%) 0.1 POUT = 2mW 0.01 0.01 VDD = 1V RL = 16Ω AV = -2V/V POUT = 0.7mW THD+N (%) 1 MAX9725 toc03 (VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25°C, unless otherwise noted.) (See the Functional Diagram.) TOTAL HARMONIC DISTORTION PLUS TOTAL HARMONIC DISTORTION PLUS TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY NOISE vs. FREQUENCY NOISE vs. FREQUENCY 0.01 POUT = 2mW POUT = 4mW POUT = 12mW 0.001 0.001 10 1k 10k 0.001 10 100k 100 1k 10k 100k 10 100 1k 10k 100k FREQUENCY (Hz) FREQUENCY (Hz) FREQUENCY (Hz) TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER VDD = 1.5V RL = 16Ω AV = -2V/V 10 fIN = 20Hz fIN = 1kHz 100 VDD = 1.5V RL = 32Ω AV = -2V/V 10 MAX9725 toc06 VDD = 1V RL = 32Ω AV = -2V/V MAX9725 toc05 100 MAX9725 toc04 1 100 fIN = 20Hz fIN = 1kHz THD+N (%) POUT = 0.7mW THD+N (%) THD+N (%) 0.1 1 fIN = 10kHz 0.1 1 fIN = 10kHz 0.1 0.01 0.01 0.01 POUT = 4mW 0.001 0.001 0.001 10 100 1k FREQUENCY (Hz) 10k 100k 0 10 20 30 OUTPUT POWER (mW) 40 0 10 20 30 40 OUTPUT POWER (mW) _______________________________________________________________________________________ 3 MAX9725 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25°C, unless otherwise noted.) (See the Functional Diagram.) 10 fIN = 20Hz fIN = 1kHz POWER-SUPPLY REJECTION RATIO vs. FREQUENCY 100 VDD = 1V RL = 32Ω AV = -2V/V 10 -10 MAX9725 toc08 VDD = 1V RL = 16Ω AV = -2V/V MAX9725 toc07 100 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER fIN = 20Hz fIN = 1kHz MAX9725 toc09 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER VDD = 1.5V RL = 32Ω -20 -30 THD+N (%) fIN = 10kHz 0.1 1 -50 PSRR (dB) THD+N (%) -40 1 fIN = 10kHz 0.1 -60 -70 -80 0.01 -90 0.01 -100 10 0.001 15 -110 0 5 OUTPUT POWER (mW) -20 1k -40 -50 -60 LEFT TO RIGHT -60 -80 -70 10k 100k OUTPUT POWER vs. SUPPLY VOLTAGE -40 PSRR (dB) 80 fIN = 1kHz RL = 16Ω BOTH INPUTS DRIVEN IN-PHASE 70 60 50 THD+N = 10% 40 30 20 -80 -100 -90 10 RIGHT TO LEFT 100 1k 10k 10k 1.1 1.3 OUTPUT POWER vs. LOAD RESISTANCE OUTPUT POWER vs. LOAD RESISTANCE 30 MAX9725 toc13 80 VDD = 1.5V fIN = 1kHz BOTH INPUTS DRIVEN IN-PHASE 70 60 25 20 15 THD+N = 10% 50 THD+N = 1% 40 30 20 10 THD+N = 1% 5 10 1.1 1.3 SUPPLY VOLTAGE (V) 1.5 VDD = 1V fIN = 1kHz BOTH INPUTS DRIVEN IN-PHASE 70 60 50 40 THD+N = 10% 30 THD+N = 1% 20 10 0 0 80 1.5 MAX9725 toc15 OUTPUT POWER vs. SUPPLY VOLTAGE THD+N = 10% 0.9 0.9 100k OUTPUT POWER (mW) 35 1k SUPPLY VOLTAGE (V) fIN = 1kHz RL = 32Ω BOTH INPUTS DRIVEN IN-PHASE 40 100 FREQUENCY (Hz) 50 45 10 100k FREQUENCY (Hz) OUTPUT POWER (mW) 10 THD+N = 1% 0 -120 -100 MAX9725 toc14 PSRR (dB) 100 FREQUENCY (Hz) VDD = 1.5V POUT = 5mW RL = 32Ω -20 -30 4 10 CROSSTALK vs. FREQUENCY 0 MAX9725 toc10 VDD = 1V RL = 32Ω -10 15 OUTPUT POWER (mW) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY 0 10 OUTPUT POWER (mW) 5 MAX9725 toc11 0 MAX9725 toc12 0.001 OUTPUT POWER (mW) MAX9725 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown 0 10 100 LOAD RESISTANCE (Ω) 1k 10 100 LOAD RESISTANCE (Ω) _______________________________________________________________________________________ 1k 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown POWER DISSIPATION vs. OUTPUT POWER POWER DISSIPATION vs. OUTPUT POWER 40 30 VDD = 1.5V fIN = 1kHz POUT = POUTL + POUTR OUTPUTS IN-PHASE RL = 32Ω 10 10 VDD = 1V fIN = 1kHz POUT = POUTL + POUTR OUTPUTS IN-PHASE RL = 32Ω 10 20 30 40 50 2 1 0 -1 -2 MAX9725 toc18 MAX9725 toc17 15 0 0 -3 -4 -5 -6 -7 -8 -9 -10 0 5 10 15 20 10 100 1k 10k OUTPUT POWER (mW) OUTPUT POWER (mW) FREQUENCY (Hz) OUTPUT POWER vs. CHARGE-PUMP CAPACITANCE AND LOAD RESISTANCE OUTPUT SPECTRUM vs. FREQUENCY SUPPLY CURRENT vs. SUPPLY VOLTAGE AMPLITUDE (dB) -40 25 20 15 10 VDD = 1.5V fIN = 1kHz THD+N = 1% C1 = C2 = 0.47µF -80 -100 -120 C1 = C2 = 0.68µF 5 -60 20 30 40 5 10 15 LOAD RESISTANCE (Ω) FREQUENCY (kHz) SHUTDOWN CURRENT vs. SUPPLY VOLTAGE EXITING SHUTDOWN 0.6 4.0 3.5 3.0 2.5 2.0 1.5 20 0.9 1.0 1.1 1.2 1.3 1.4 POWER-UP/-DOWN WAVEFORM MAX9725toc24 VDD 1V/div OUT_ 1V/div 0.5 1.5 SUPPLY VOLTAGE (V) MAX9725 toc23 MAX9725 toc22 0.7 NO LOAD 0 0 50 4.5 0.5 -160 10 5.0 1.0 -140 0 100k MAX9725 toc21 -20 C1 = C2 = 1µF 30 fIN = 1kHz RL = 32Ω VOUT = -60dBV VDD = 1.5V SUPPLY CURRENT (mA) C1 = C2 = 2.2µF 35 0 MAX9725 toc19 40 OUTPUT POWER (mW) RL = 16Ω 20 5 0 SHUTDOWN CURRENT (µA) 25 AMPLITUDE (dB) 50 MAX9725 toc20 POWER DISSIPATION (mW) 60 20 30 POWER DISSIPATION (mW) RL = 16Ω 70 35 MAX9725 toc16 80 GAIN FLATNESS vs. FREQUENCY MAX9725 Typical Operating Characteristics (continued) (VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25°C, unless otherwise noted.) (See the Functional Diagram.) 0.4 SHDN 500mV/div 0.3 0.2 OUT_ 10mV/div 0.1 0 0.9 1.1 1.3 1.5 200µs/div 200ms/div SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 5 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725 Pin Description PIN BUMP THIN QFN UCSP 1 A1 C1N Flying Capacitor Negative Terminal. Connect a 1µF capacitor from C1P to C1N. 2 A2 PVSS Inverting Charge-Pump Output. Bypass with 1µF from PVSS to PGND. PVSS must be connected to VSS. 3 A3 INL Left-Channel Audio Input 4 A4 INR Right-Channel Audio Input 5 B4 VSS Amplifier Negative Power Supply. Must be connected to PVSS. 6 B3 SGND Signal Ground. SGND must be connected to PGND. SGND is the ground reference for the input and output signal. 7 C4 OUTR Right-Channel Output 8 C3 OUTL Left-Channel Output 9 C2 VDD Positive Power-Supply Input. Bypass with a 1µF capacitor to PGND. 10 C1 C1P Flying Capacitor Positive Terminal. Connect a 1µF capacitor from C1P to C1N. 11 B1 PGND Power Ground. Ground reference for the internal charge pump. PGND must be connected to SGND. 12 B2 SHDN Active-Low Shutdown. Connect to VDD for normal operation. Pull low to disable the amplifier and charge pump. EP — EP NAME FUNCTION Exposed Paddle. Internally connected to VSS. Leave paddle unconnected or solder to VSS. Detailed Description The MAX9725 stereo headphone driver features Maxim’s patented DirectDrive architecture, eliminating the large output-coupling capacitors required by conventional single-supply headphone drivers. The MAX9725 consists of two 20mW class AB headphone drivers, shutdown control, inverting charge pump, internal gain-setting resistors, and comprehensive click-and-pop suppression circuitry (see the Functional Diagram). A negative power supply (PVSS) is created by inverting the positive supply (VDD). Powering the drivers from VDD and PVSS increases the dynamic range of the drivers to almost twice that of other 1V single-supply drivers. This increase in dynamic range allows for higher output power. The outputs of the MAX9725 are biased about GND (Figure 1). The benefit of this GND bias is that the driver outputs do not have a DC component, thus large DCblocking capacitors are unnecessary. Eliminating the DC-blocking capacitors on the output saves board space, system cost, and improves frequency response. 6 DirectDrive Conventional single-supply headphone drivers have their outputs biased about a nominal DC voltage (typically half the supply) for maximum dynamic range. Large coupling capacitors are needed to block the DC bias from the headphones. Without these capacitors, a significant amount of DC current flows to the headphone, resulting in unnecessary power dissipation and possible damage to both headphone and headphone driver. Maxim’s DirectDrive architecture uses a charge pump to create an internal negative supply voltage. This allows the MAX9725 outputs to be biased about GND, increasing the dynamic range while operating from a single supply. A conventional amplifier powered from 1.5V ideally provides 18mW to a 16Ω load. The MAX9725 provides 25mW to a 16Ω load. The DirectDrive architecture eliminates the need for two large (220µF, typ) DC-blocking capacitors on the output. The MAX9725 charge pump requires two small ceramic capacitors, conserving board space, reducing cost, and improving the frequency response of the headphone driver. See the Output Power vs. Charge- _______________________________________________________________________________________ 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown VDD VOUT 1) The impedance of the headphone load and the DCblocking capacitor forms a highpass filter with the -3dB point set by: VDD / 2 GND CONVENTIONAL DRIVER-BIASING SCHEME VDD VOUT GND -VDD DirectDrive BIASING SCHEME Figure 1. Traditional Driver Output Waveform vs. MAX9725 Output Waveform (Ideal Case) Pump Capacitance and Load Resistance graph in the Typical Operating Characteristics for details of the possible capacitor sizes. Previous attempts to eliminate the output-coupling capacitors involved biasing the headphone return (sleeve) to the DC-bias voltage of the headphone amplifiers. This method raises some issues: • The sleeve is typically grounded to the chassis. Using this biasing approach, the sleeve must be isolated from system ground, complicating product design. • During an ESD strike, the driver’s ESD structures are the only path to system ground. The driver must be able to withstand the full ESD strike. • When using the headphone jack as a line out to other equipment, the bias voltage on the sleeve may conflict with the ground potential from other equipment, resulting in possible damage to the drivers. f-3dB = 1 2πRLCOUT where RL is the impedance of the headphone and COUT is the value of the DC-blocking capacitor. The highpass filter is required by conventional singleended, single power-supply headphone drivers to block the midrail DC-bias component of the audio signal from the headphones. The drawback to the filter is that it can attenuate low-frequency signals. Larger values of COUT reduce this effect but result in physically larger, more expensive capacitors. Figure 2 shows the relationship between the size of COUT and the resulting low-frequency attenuation. Note that the -3dB point for a 16Ω headphone with a 100µF blocking capacitor is 100Hz, well within the normal audio band, resulting in low-frequency attenuation of the reproduced signal. 2) The voltage coefficient of the DC-blocking capacitor contributes distortion to the reproduced audio signal as the capacitance value varies when the function of the voltage across the capacitor changes. At low frequencies, the reactance of the capacitor dominates at frequencies below the -3dB point and the voltage coefficient appears as frequency-dependent distortion. Figure 3 shows the THD+N introduced by two different capacitor dielectric types. Note that below 100Hz, THD+N increases rapidly. The combination of low-frequency attenuation and frequency-dependent distortion compromises audio reproduction in portable audio equipment that emphasizes low-frequency effects such as multimedia laptops, as well as MP3, CD, and DVD players. These low-frequency, capacitor-related deficiencies are eliminated by using DirectDrive technology. Charge Pump The MAX9725 features a low-noise charge pump. The 580kHz switching frequency is well beyond the audio range, and does not interfere with the audio signals. The switch drivers feature a controlled switching speed that minimizes noise generated by turn-on and turn-off transients. The di/dt noise caused by the parasitic bond wire and trace inductance is minimized by limiting the turn-on/off speed of the charge pump. Additional high- _______________________________________________________________________________________ 7 MAX9725 Low-Frequency Response Large DC-blocking capacitors limit the amplifier’s lowfrequency response and can distort the audio signal: MAX9725 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown ADDITIONAL THD+N DUE TO DC-BLOCKING CAPACITORS LF ROLLOFF (16Ω LOAD) 0 10 -3 -5 330µF 1 100µF -15 -3dB CORNER FOR 100µF IS 100Hz THD+N (%) ATTENUATION (dB) 220µF -10 33µF -20 0.1 TANTALUM 0.01 -25 0.001 -30 ALUM/ELEC -35 0.0001 10 100 FREQUENCY (Hz) 1k 10 100 1k 10k 100k FREQUENCY (Hz) Figure 2. Low-Frequency Attenuation for Common DC-Blocking Capacitor Values Figure 3. Distortion Contributed By DC-Blocking Capacitors frequency noise attenuation can be achieved by increasing the size of C2 (see the Functional Diagram). Extra noise attenuation is not typically required. the internal input resistor (25kΩ, typ) causing an audible click and pop. Delaying the rise of SHDN 4 or 5 time constants, based on RIN x CIN, relative to the startup of the preamplifier eliminates any click and pop caused by the input filter (see the Functional Diagram). Shutdown The MAX9725’s low-power shutdown mode reduces supply current to 0.6µA. Driving SHDN low disables the amplifiers and charge pump. The driver’s output impedance is typically 50kΩ (MAX9725A), 37.5kΩ (MAX9725B), 25kΩ (MAX9725), or 100kΩ (MAX9725D) when in shutdown mode. Click-and-Pop Suppression In conventional single-supply audio drivers, the outputcoupling capacitor is a major contributor of audible clicks and pops. Upon startup, the driver charges the coupling capacitor to its bias voltage, typically half the supply. Likewise, on shutdown, the capacitor is discharged to GND. This results in a DC shift across the capacitor that appears as an audible transient at the speaker. The MAX9725’s DirectDrive technology eliminates the need for output-coupling capacitors. The MAX9725 also features extensive click-and-pop suppression that eliminates any audible transient sources internal to the device. The Power-Up/Down Waveform in the Typical Operating Characteristics shows minimal DC shift and no spurious transients at the output upon startup or shutdown. In most applications, the output of the preamplifier driving the MAX9725 has a DC bias of typically half the supply. At startup, the input-coupling capacitor is charged to the preamplifier’s DC bias voltage through 8 Applications Information Power Dissipation 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: PDISSPKG(MAX) = TJ(MAX) - TA θ JA where TJ(MAX) is +150°C, TA is the ambient temperature, and θJA is the reciprocal of the derating factor in °C/W as specified in the Absolute Maximum Ratings section. For example, θJA for the thin QFN package is +59.3°C/W. The MAX9725 has two power dissipation sources, the charge pump and the two amplifiers. If the power dissipation exceeds the rated package dissipation, reduce VDD, increase load impedance, decrease the ambient temperature, or add heatsinking to the device. Large output, supply, and ground traces decrease θJA, allowing more heat to be transferred from the package to surrounding air. _______________________________________________________________________________________ 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown 50 45 OUTPUT POWER (mW) 40 fIN = 1kHz RL = 16Ω THD+N = 1% 35 INPUTS 180° OUT-OF-PHASE 30 Input Filtering The AC-coupling capacitor (CIN) and an internal gainsetting resistor form a highpass filter that removes any DC bias from an input signal (see the Functional Diagram). CIN allows the MAX9725 to bias the signal to an optimum DC level. The -3dB point of the highpass filter, assuming zero source impedance, is given by: 25 f-3dB = 20 15 10 INPUTS IN-PHASE 5 0 0.9 1.1 1.3 1.5 SUPPLY VOLTAGE (V) Figure 4. Output Power vs. Supply Voltage with Inputs In-/Outof-Phase Output Power The MAX9725’s output power increases when the left and right audio signals differ in magnitude and/or phase. Figure 4 shows the two extreme cases for inand out-of-phase input signals. The output power of a typical stereo application lies between the two extremes shown in Figure 4. The MAX9725 is specified to output 20mW per channel when both inputs are in-phase. Powering Other Circuits from the Negative Supply The MAX9725 internally generates a negative supply voltage (PVSS) to provide the ground-referenced output signal. Other devices can be powered from PVSS provided the current drawn from the charge pump does not exceed 1mA. Headphone driver output power and THD+N will be adversely affected if more than 1mA is drawn from PVSS. Using PVSS as an LCD bias is a typical application for the negative supply. PVSS is unregulated and proportional to VDD. Connect a 1µF capacitor from C1P to C1N for best charge-pump operation. 1 2π × 25kΩ × CIN Choose CIN so f-3dB is well below the lowest frequency of interest. Setting f-3dB too high affects the amplifier’s lowfrequency response. Use capacitors with low-voltage coefficient dielectrics. Film or C0G dielectric capacitors are good choices for AC-coupling capacitors. Capacitors with high-voltage coefficients, such as ceramics, can result in increased distortion at low frequencies. Charge-Pump Capacitor Selection Use capacitors with less than 100mΩ of ESR. Low-ESR ceramic capacitors minimize the output impedance of the charge pump. Capacitors with an X7R dielectric provide the best performance over the extended temperature range. Table 1 lists suggested capacitor manufacturers. Flying Capacitor (C1) The value of C1 affects the charge pump’s load regulation and output impedance. Choosing C1 too small degrades the MAX9725’s ability to provide sufficient current drive and leads to a loss of output voltage. Increasing the value of C1 improves load regulation and reduces the charge-pump output impedance. See the Output Power vs. Charge-Pump Capacitance and Load Impedance graph in the Typical Operating Characteristics. Hold Capacitor (C2) The hold capacitor’s value and ESR directly affect the ripple at PVSS. Increasing the value of C2 reduces ripple. 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 Impedance graph in the Typical Operating Characteristics. _______________________________________________________________________________________ 9 MAX9725 Component Selection OUTPUT POWER vs. SUPPLY VOLTAGE WITH INPUTS IN- AND OUT-OF-PHASE MAX9725 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown Table 1. Suggested Capacitor Manufacturers PHONE FAX Taiyo Yuden SUPPLIER 800-348-2496 847-925-0899 www.t-yuden.com TDK 847-803-6100 847-390-4405 www.component.tdk.com Power-Supply Bypass Capacitor (C3) The power-supply bypass capacitor (C3) lowers the output impedance of the power supply and reduces the impact of the MAX9725’s charge-pump switching transients. Bypass VDD to PGND with the same value as C1. Place C3 as close to VDD as possible. Layout and Grounding Proper layout and grounding are essential for optimum performance. Connect PGND and SGND together at a single point on the PC board. Connect PVSS to SVSS and bypass with C2 to PGND. Bypass VDD to PGND with C3. Place capacitors C2 and C3 as close to the MAX9725 as possible. Route PGND, and all traces that carry switching transients, away from SGND and the audio signal path. The MAX9725 does not require additional heatsinking. The thin QFN package features an exposed paddle that improves thermal efficiency of the package. Ensure the exposed paddle is electrically isolated from GND and VDD. Connect the exposed paddle to VSS if necessary. 10 WEBSITE UCSP Applications Information For the latest application details on UCSP construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout , and recommended reflow temperature profile, as well as the latest information on reliability testing results, go to Maxim’s website at www.maxim-ic.com/ucsp for the Application Note: UCSP—A Wafer-Level Chip-Scale Package. Chip Information TRANSISTOR COUNT: 2559 PROCESS: BiCMOS ______________________________________________________________________________________ 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown 0.9V TO 1.8V 1µF 0.47µF MP3 DECODER SHDN VDD INR STEREO DAC INL 0.47µF C1P MAX9725 OUTR 1µF C1N OUTL VSS PVSS 1µF SGND PGND Pin Configurations MAX9725 TOP VIEW (BUMP-SIDE DOWN) 1 2 3 4 TOP VIEW A C1N PVSS INL SHDN PGND C1P 12 11 10 INR C1N 1 PVSS 2 INL 3 9 VDD 8 OUTL 7 OUTR B PGND SHDN SGND C C1P VDD OUTL UCSP VSS OUTR MAX9725 4 5 6 INR VSS SGND THIN QFN ______________________________________________________________________________________ 11 MAX9725 System Diagram 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725 Functional Diagram LEFTCHANNEL AUDIO IN 0.9V TO 1.8V CIN 0.47µF C3 1µF 9 (C2) 12 (B2) 3 (A3) VDD SHDN INL RF* VDD RIN 25kΩ 8 OUTL (C3) VSS CHARGE PUMP C1 1µF HEADPHONE JACK SGND UVLO/ SHUTDOWN CONTROL 10 (C1) C1P CLICK-AND-POP SUPPRESSION 1 (A1) C1N VDD SGND OUTR MAX9725 RIN 25kΩ 7 (C4) VSS RF* PVSS VSS PGND SGND 2 (A2) C2 1µF 5 (B4) 11 (B1) 6 (B3) INR 4 (A4) CIN 0.47µF RIGHTCHANNEL AUDIO IN *MAX9725A = 50kΩ. MAX9725B = 37.5kΩ. MAX9725C = 25kΩ. MAX9725D = 100kΩ. ( ) DENOTE BUMPS FOR UCSP. 12 ______________________________________________________________________________________ 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown 12L, UCSP 4x3.EPS PACKAGE OUTLINE, 4x3 UCSP 21-0104 F 1 1 ______________________________________________________________________________________ 13 MAX9725 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.) 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.) 24L QFN THIN.EPS MAX9725 1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm 21-0139 C 1 2 PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm 21-0139 C 2 2 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. 14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.