19-1743; Rev 1; 2/01 Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator The MAX4298 and MAX4299 are audio system ICs designed for single +5V applications. The MAX4299 features a stereo headphone driver, a microphone amplifier, and a +3.3V linear regulator; the MAX4298 features the stereo headphone driver only. The MAX4298/ MAX4299 are designed specifically for harsh digital environments where board space is at a premium and the digital power supply is noisy. The design uses innovative design techniques to achieve ultra-high power-supply rejection across the audio signal band while, at the same time, delivering a high-current Railto-Rail® output drive capability. The chip is designed to drive highly capacitive loads that may be encountered when driving long cables to a remote load such as desktop/notebook headphones or speakers. These devices are fully compliant with PC99 standards. The amplifiers exhibit 115dB of DC power-supply rejection and 80dB at 100kHz. The output amplifiers are capable of driving a 1.5VRMS signal into a 10kΩ load with 0.0008% THD+N. They can also drive 32Ω headphones to 1.2VRMS with 0.02% distortion. At +3.3V, the linear regulator can output 100mA of current. The MAX4298 is available in a tiny 10-pin µMAX while the MAX4299 is available in the space-saving 16-pin TSSOP package. Features ♦ Audio System IC (MAX4299) Ultra-High PSRR Stereo Headphone Driver Ultra-High PSRR Microphone Amp 100mA, 3.3V Linear Regulator ♦ 93dB typ PSRR at 20kHz Operates Directly from Noisy Digital Supplies ♦ Clickless/Popless Power-Up, Power-Down, Mute and Unmute ♦ PC99-Compliant Output Drivers: Better than 1VRMS Output into 16Ω Load and 1.5VRMS and 0.0008% THD+N into 10kΩ Load ♦ PC99-Compliant Microphone Amplifier: 0.005% THD+N into 10kΩ Load ♦ 22nF Capacitive Load Drive Capability ♦ 4.5V to 5.5V Single-Supply Operation ♦ Internally Generated Bias Voltage ♦ All Gains Externally Adjustable ♦ Available in Space-Saving Packages 10-Pin µMAX (MAX4298) 16-Pin TSSOP (MAX4299) Ordering Information ________________________Applications Notebook and Desktop Audio Hands-Free Headsets USB Audio Peripherals IP Telephones Wireless Internet Devices MP3 Players/Recorders PART TEMP. RANGE PIN-PACKAGE MAX4298EUB -40ºC to +85°C 10 µMAX MAX4298ESD -40ºC to +85°C 14 SO MAX4299EWP -40ºC to +85°C 20 SO MAX4299EUE -40ºC to +85°C 16 TSSOP Typical Operating Circuit appears at end of data sheet. Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd. PSRR vs. Frequency MAX4298/9-13 -50 -60 -70 TOP VIEW OUT1 1 -80 PSRR (dB) Pin Configurations -90 GND 10 VCC 2 -100 MAX4298 9 OUT2 IN1 3 8 IN2 -120 BIAS 4 7 CBYPASS -130 SVCC 5 6 MUTE -110 -140 -150 100 1k 10k FREQUENCY (Hz) 100k µMAX Pin Configurations continued at end of data sheet. ________________________________________________________________ Maxim Integrated Products 1 For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX4298/MAX4299 General Description MAX4298/MAX4299 Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator ABSOLUTE MAXIMUM RATINGS Supply Voltage (VCC) to GND ...............................................+6V Standby Supply Voltage (SVCC) to GND ...............................+6V REG, FB, REGON to GND ..........................-0.3V to (VCC + 0.3V) BIAS, CBYPASS, MUTE, IN_, MICIN to GND ..............-0.3V to the Larger of (VCC +0.3V) or (SVCC +0.3V) OUT_, MICOUT to GND ................................-0.3V to the Smaller of +5.5V, or (VCC + 0.3V) Duration of Output Short-Circuit to GND or VCC ................10min Continuous Power Dissipation 10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW 14-Pin SO (derate 8.3mW/°C above +70°C)................667mW 20-Pin SO (derate 10.0mW/°C above +70°C)..............800mW 16-Pin TSSOP (derate 9.4mW/°C above +70°C) .........755mW Operating Temperature Range ..........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = SVCC = +5V, RL = ∞ on all outputs, CBYPASS = 1µF, CBIAS = 1µF, CREG = 10µF (MAX4299), TA = TMIN to TMAX, unless otherwise noted. Load resistors (RL) are terminated to 2.25V. Typical values are at TA = +25°C. Specifications apply to both MAX4298 and MAX4299, unless otherwise noted.) (Note 1) PARAMETER SYMBOL Supply Voltage Range VCC Quiescent Current ICC Mute Quiescent Current SVCC Current (Note 2) ISVCC CONDITIONS Inferred from PSRR test MIN TYP 4.5 MAX UNITS 5.5 V MAX4298 10.2 17.5 MAX4299 10.6 18.0 MAX4298 10.2 17.5 MAX4299 10.6 18.0 VBIAS = 1.125V, VCC = 0 300 500 VBIAS = 2.25V, VCC = 5.0V 7 mA mA µA DRIVER AMPLIFIERS Input Offset Voltage VOS Input Bias Current IBIAS Power-Supply Rejection Ratio PSRR ±1 0.2 DC, VCC = 4.5V to 5.5V 115 f = 20kHz 93 f = 100kHz Output Drive VOUT 1.45 1.59 RL = 32Ω 1.2 1.53 RL = 16Ω 1.0 1.48 0.02 AV = -1V/V, f = 1kHz, RL = 16Ω, VOUT = 1.0VRMS 0.04 SNR RL = 10kΩ, VOUT = 1.06VRMS, AV = -1V/V 105 Open-Loop Voltage Gain AVOL RL = 32Ω, 0.55V ≤ VOUT ≤ VCC - 0.55V Unity-Gain Bandwidth GBW Capacitive Drive 2 nA dB VRMS 0.0008 AV = -1V/V, f = 1kHz, RL = 32Ω, VOUT = 1.2VRMS, (Notes 3, 4) Full-Scale Signal-to-Noise Ratio (Note 4) mV 80 RL = 10kΩ AV = -1V/V, f = 1kHz, RL = 10kΩ, VOUT = 1.5VRMS THD + Noise ±10 76 0.1 % dB 22 nF 87 dB 1.3 MHz _______________________________________________________________________________________ Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator (VCC = SVCC = +5V, RL = ∞ on all outputs, CBYPASS = 1µF, CBIAS = 1µF, CREG = 10µF (MAX4299), TA = TMIN to TMAX, unless otherwise noted. Load resistors (RL) are terminated to 2.25V. Typical values are at TA = +25°C. Specifications apply to both MAX4298 and MAX4299, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX 2.13 2.25 2.37 UNITS BIAS VOLTAGE OUTPUT DC BIAS Voltage VBIAS IL = 0 Line Regulation Load Regulation IL = 0 to 1µA V 120 dB 50 mV DIGITAL INPUTS (MUTE for MAX4298/MAX4299, and REGON for MAX4299) Input Voltage High VINH Input Voltage Low VINL Input Leakage Current IIN 2.4 V VIN = 0 or VCC 0.8 V ±1 µA ±10 mV MICROPHONE AMPLIFIER (MAX4299 only) Input Offset Voltage VOS ±2 Input Bias Current IBIAS 0.2 Power-Supply Rejection Ratio PSRR DC, VCC = 4.5V to 5.5V 115 f = 20kHz 93 f = 100kHz 80 Voltage Gain AVOL RL = 10kΩ, 0.13V ≤ VMICOUT ≤ VCC - 0.13V 80 Output Drive VOUT RL = 10kΩ 1.4 THD + Noise (Note 4) Full-Scale Signal-to-Noise Ratio (Note 4) THD+N SNR All-Hostile Crosstalk Unity Gain Bandwidth f = 1kHz, RL = 10kΩ, VMICOUT = 1.5VRMS nA dB 100 dB 1.58 VRMS AV = -1V/V 0.005 AV = -10V/V 0.03 % RL = 10kΩ, VMICOUT = 1.06VRMS, AV = -10V/V 80 dB f = 10kHz (Note 5) 80 dB 1 MHz GBW REGULATOR (MAX4299 only) Regulator Output Voltage VREG Line Regulation Load Regulation FB Voltage Note 1: Note 2: Note 3: Note 4: Note 5: VCC = 4.5V to 5.5V. IL = 0 to 100mA, using internal feedback 3.3 3.45 V VCC = 4.5V to 5.5V, IL = 50mA 0.2 mV IL = 10mA to 100mA 30 mV 50 mV 1.233 V IL = 0 to 100mA VFB 3.15 Reference for regulator adjustment All devices are 100% production tested at TA = +25°C. All temperature limits are guaranteed by design. Current drawn from SVCC when VCC < 4V. Guaranteed by design. Measurement bandwidth is 20Hz to 22kHz. Voltage at MICOUT with OUT1 = OUT2 = 1VRMS into 32Ω. _______________________________________________________________________________________ 3 MAX4298/MAX4299 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = SVCC = +5V, typical operating circuit, TA = +25°C, unless otherwise noted.) 10.0 2.0 TA = +25°C 9.5 OUT 1.5 1.0 SPEAKER 0.5 OUT 3 OUTPUT VOLTAGE (V) ICC (mA) 10.5 RL = 32Ω OUTPUT VOLTAGE (V) TA = +85°C 4 MAX4298/9-02 11.0 MUTE PERFORMANCE POWER-UP/POWER-DOWN 2.5 MAX4298/99-01 11.5 MAX4298/9-03 MAX4298 SUPPLY CURRENT vs. SUPPLY VOLTAGE 2 1 0 TA = -40°C 9.0 0 -1 8.5 -0.5 -2 RL = 32Ω CAC = 220µF SPEAKER 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 1.0 0 2.0 1.0 1.5 TIME (s) POWER-DOWN/POWER-UP with SCHOTTKY DIODE AND RESERVOIR CAPACITOR DRIVER OUT THD+N vs. FREQUENCY DRIVER OUT THD+N vs. FREQUENCY 1 BW = 80kHz BW = 22kHz 0.001 RL = 32Ω CAC = 22OµF -1 0 0.5 1.0 TIME (s) 1.5 0.0001 100 2.0 DRIVER OUT THD+N vs. FREQUENCY 10 MAX4298/99-07 1 0.1 1k 10k MAX4298/99-06 RL = 32Ω AV = -1 VOUT = 1.2VRMS 0.0001 100 100k RL = 16Ω AV = -1 VOUT = 1VRMS 0.0001 DRIVER OUT THD+N vs. AMPLITUDE BW = 22kHz 0.1 0.01 0.001 10 BW = 22kHz 1 1k 10k INPUT FREQUENCY (Hz) 100k fIN = 1kHz 0.1 0.01 0.001 AV = -1 RL = 10kΩ fIN = 1kHz 0.0001 100 100k DRIVER OUT THD+N vs. AMPLITUDE THD+N (%) THD+N (%) 0.001 10k INPUT FREQUENCY (Hz) BW = 22kHz 0.01 1k INPUT FREQUENCY (Hz) 1 BW = 80kHz BW = 22kHz 0.01 0.001 RL = 10kΩ AV = -1 VOUT = 1.5VRMS MAX4298/99toc08 0 BW = 80kHz MAX4298/99toc09 VOUT 0.01 THD+N (%) THD+N (%) 3 2 0.1 0.1 SVCC 2.0 1 MAX4298/99-05 1 MAX4298/99-04 VCC = 5V VCC = 0 4 4 0.5 TIME (s) 5 VOLTAGE (V) 0 VCC (V) 6 THD+N (%) MAX4298/MAX4299 Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator RL = 32Ω AV = -1 0.0001 0 0.5 1 1.5 OUTPUT VOLTAGE (VRMS) 2 0 0.5 1 1.5 OUTPUT VOLTAGE (VRMS) _______________________________________________________________________________________ 2 Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator MAX4298/MAX4299 Typical Operating Characteristics (continued) (VCC = SVCC = +5V, typical operating circuit, TA = +25°C, unless otherwise noted.) DRIVER OUT CHANNEL SEPARATION vs. INPUT FREQUENCY 0.001 0 0.5 1 1.5 OUT1 TO OUT2 RL = 10kΩ AV = -1 VOUT = 1VRMS -120 100 2 1k 10k -90 B C A -95 -100 -105 RL = 16Ω A = RI = 20kΩ, RF = 20kΩ B = RI = 10kΩ, RF = 10kΩ C = RI = 10kΩ, RF = 20kΩ -110 -115 -120 100k 100 1k 10k 100k OUTPUT VOLTAGE (VRMS) INPUT FREQUENCY (Hz) INPUT FREQUENCY (Hz) DRIVER OUT POWER-SUPPLY REJECTION RATIO vs. FREQUENCY DRIVER OUT OPEN-LOOP FREQUENCY RESPONSE DRIVER OUT OPEN-LOOP FREQUENCY RESPONSE MAX4298/9-14 MAX4298/9-15 80 180 80 180 70 160 70 160 -80 60 140 60 -90 50 120 50 MAX4298/9-13 -60 GAIN (dB) -70 PHASE GAIN (dB) 90 90 PHASE (deg) 200 -50 80 80 -120 20 60 20 -130 10 40 10 -140 0 20 0 1k 10k 32Ω || 15pF -10 0.01 -150 100 GAIN 100k 0.1 1 10 100 60 GAIN 40 20 32Ω || 1.5nF -10 0.01 0 1000 10,000 120 100 30 -110 140 PHASE 30 100 -100 0.1 1 10 100 0 1000 10,000 FREQUENCY (Hz) INPUT FREQUENCY (kHz) INPUT FREQUENCY (kHz) DRIVER OUT OPEN-LOOP FREQUENCY RESPONSE DRIVER OUT OPEN-LOOP FREQUENCY RESPONSE DRIVER OUT OPEN-LOOP FREQUENCY RESPONSE MAX4298/9-16 180 70 MAX4298/9-18 200 90 80 180 80 180 160 70 160 70 160 60 140 60 140 60 140 50 120 50 120 50 PHASE PHASE GAIN (dB) 80 MAX4298/9-17 PHASE (deg) 90 90 PHASE (deg) 200 200 40 40 GAIN (dB) PSRR (dB) -100 -110 RL = 16Ω AV = -1 0.0001 -90 -85 40 100 30 80 60 20 60 20 10 40 10 40 10 0 20 0 20 0 40 100 30 80 20 -10 0.01 GAIN 32kΩ || 22nF 0.1 1 10 100 INPUT FREQUENCY (kHz) 0 1000 10,000 -10 0.01 GAIN 10kΩ || 15pF 0.1 1 10 100 INPUT FREQUENCY (kHz) 0 1000 10,000 PHASE (deg) 0.01 -80 GAIN (dB) THD+N (%) 0.1 OUT2 TO OUT1 200 120 PHASE 40 100 30 80 -10 0.01 60 GAIN 40 20 10kΩ || 1.5nF 0.1 1 10 100 0 1000 10,000 INPUT FREQUENCY (kHz) _______________________________________________________________________________________ 5 PHASE (deg) -70 fIN = 1kHz -80 MUTED OUTPUT ATTENUATION (dB) 1 CHANNEL SEPARATION (dB) BW = 22kHz MAX4298/9-11 -60 MAX4298/99toc10 10 DRIVER OUT MUTED OUTPUT ATTENUATION vs. INPUT FREQUENCY MAX4298/9-12 DRIVER OUT THD+N vs. AMPLITUDE Typical Operating Characteristics (continued) (VCC = SVCC = +5V, typical operating circuit, TA = +25°C, unless otherwise noted.) 60 140 120 PHASE 40 100 30 80 20 60 GAIN 10 40 0 20 10kΩ || 22nF 1 10 180 70 160 60 140 50 120 40 80 30 60 GAIN 0.1 1 10 20 0 10kΩ || 15pF -10 0.01 0.1 1 100 40 10 100 0 1000 10,000 INPUT FREQUENCY (kHz) INPUT FREQUENCY (kHz) INPUT FREQUENCY (kHz) MICOUT OPEN LOOP FREQUENCY RESPONSE MICOUT THD+N vs. AMPLITUDE REGOUT OUTPUT VOLTAGE vs. LOAD CURRENT 10 200 180 80 70 160 60 140 120 50 40 PHASE 100 30 80 20 60 GAIN 10 0 10kΩ || 150pF -10 0.01 0.1 1 10 100 1 0.1 0.01 40 0.001 20 0 1000 10,000 0.0001 3.5 RL = 10kΩ AV = -1 fIN = 1kHz BW = 22kHz MAX4298/99 toc24 MAX4298/99 toc22 90 3.4 3.3 3.2 3.1 3.0 0 0.5 1.0 1.5 2.0 0 20 AMPLITUDE (VRMS) INPUT FREQUENCY (kHz) REGOUT TRANSIENT RESPONSE 40 REGOUT TRANSIENT RESPONSE MAX4298/99 toc26 VOUT 30mV/div 200µs/div 60 LOAD CURRENT (mA) MAX4298/99 toc25 6 100 PHASE 10 -120 0.01 200 80 20 -100 0 1000 10,000 100 -80 OUTPUT VOLTAGE (V) 0.1 -60 MAX4298/99 toc23 -10 0.01 -40 GAIN (dB) 160 AV = -100 MAX4298/99 toc21 90 MAX4298/99 toc20 70 ALL HOSTILE CROSSTALK (dB) 180 THD+N (%) GAIN (dB) 80 50 -20 200 PHASE (deg) MAX4298/99 toc19 90 MICOUT OPEN LOOP FREQUENCY RESPONSE MICOUT ALL HOSTILE CROSSTLAK (INPUT REFERRED) VOUT 30mV/div 100mA IL 100mA 0 10mA IL 200µs/div _______________________________________________________________________________________ 80 100 PHASE (deg) DRIVER OUT OPEN-LOOP FREQUENCY RESPONSE GAIN (dB) MAX4298/MAX4299 Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator PIN MAX4298 MAX4299 MAX4299 10-PIN µMAX 14-PIN SO 16-PIN TSSOP 20-PIN SO — — 16 1 MAX4298 NAME REG FUNCTION Regulator Output. Bypass REG to GND with a 10µF capacitor. Regulator Feedback. Internal resistors from this point to REG and GND define the regulator output value. Adjustments can be made to the output value by adding resistors in the same place externally. — — 1 2 FB 1 2 2 4 OUT1 Driver Amplifier Output — — 3 5 PGND Power Ground for Driver Outputs GND 2 3 4 6 3 4 5 7 IN1 4 5 6 8 BIAS Bias Point for Amplifiers. Bypass BIAS to GND with a 1µF capacitor. Standby Power Supply. Connect to a standby +5V supply that is always on, or bypass with 220µF and connect a Schottky diode from VCC to SVCC. Short to VCC if clickless power-down is not essential. Ground Inverting Input for Driver Amplifier 5 6 7 9 SVCC — — 8 10 MICOUT — — 9 11 MICIN Inverting Input for Microphone Amplifier Mute Digital Input. Connect to GND for normal operation. When MUTE is connected to VCC, OUT1 and OUT2 are muted, REG stays on, and MICOUT stays on. Microphone Amplifier Output 6 9 10 13 MUTE 7 10 11 14 CBYPASS 8 11 12 15 IN2 9 12 13 16 OUT2 10 13 14 17 VCC Power Supply. Connect to +5V. — 1, 7, 8, 14 — 3, 12, 18, 19 N.C. No Connection. Not internally connected. — — 15 20 REGON Detailed Description The MAX4298/MAX4299 are audio system ICs designed for single +5V applications. The MAX4299 has a stereo headphone driver, a microphone amplifier, and a 100mA +3.3V linear regulator; the MAX4298 has the stereo headphone driver only. The MAX4298/MAX4299 are designed specifically for harsh digital environments where board space is at a premium and the digital Bypass to GND with a 1µF Capacitor Inverting Input for Driver Amplifier Driver Amplifier Output Regulator Control. Connect to VCC for normal operation. Connect to GND to shut off the regulator. power supply is noisy. The design uses innovative design techniques to achieve ultra-high power-supply rejection across the audio signal band while, at the same time, delivering a high current rail-to-rail output drive capability. These devices are designed to drive highly capacitive loads that may be encountered when driving long cables to a remote load such as desktop/notebook headphones or speakers. They are fully compliant to PC99 standards. Figure 1 is the _______________________________________________________________________________________ 7 MAX4298/MAX4299 Pin Description MAX4298/MAX4299 Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator VCC VCC REG MAX4298 SVCC IN1 BIAS _ SVCC 18.4kΩ REGON FB OUT1 + 50kΩ 1.233V + _ 11kΩ 2.25V MUTE MAX4299 IN2 + _ OUT2 IN1 CBYPASS _ OUT1 + GND BIAS 2.25V 50kΩ IN2 Figure 1. MAX4298 Block Diagram + _ OUT2 N.C. MUTE MAX4298 block diagram and Figure 2 is the MAX4299 block diagram. The amplifiers exhibit better than 115dB of DC powersupply rejection and 93dB at 20kHz. The output amplifiers are capable of driving a 1.5VRMS signal into 10kΩ load with 0.0008% distortion. They can also drive 32Ω headphones to 1.2V RMS with 0.02% distortion. At +3.3V, the linear regulator can output 100mA of current. BIAS The common-mode bias point for the amplifiers is set to 2.25V by internal circuitry that has two functions. It provides a clickless/popless power-up/power-down waveform for the amplifiers. Also, it generates a groundreferenced bias voltage with ultra-high power-supply rejection ratio (PSRR). BIAS should be bypassed with 1µF to GND.The output impedance of the BIAS pin is 50kΩ. Clickless/Popless Function The MAX4298/MAX4299 are designed for high-fidelity audio performance into AC-coupled loads. Patented design techniques achieve a clickless/popless power-up sequence, and the use of a low-current standby supply (SVCC) or external Schottky diode/reservoir capacitor combination allows clickless/popless power-down. A clickless/popless mute function is also provided to maintain a low impedance output when the input signal is switched off. Mute Function The MAX4298/MAX4299 have a MUTE pin that allows the user to mute the outputs of the device. This feature disconnects the input signal from the power amplifiers when a logic high is present at the MUTE pin. To ensure proper functionality, the MUTE pin should always be tied to either VCC or GND. MUTE only affects the headphone driver outputs. REG, BIAS, and MICOUT are unaffected. OUT1 8 MICOUT + _ MICIN GND CBYPASS PGND Figure 2. MAX4299 Block Diagram and OUT2 are muted, but remain in a low-impedance state to ensure clickless/popless operation. SVCC The MAX4298/MAX4299 provide a fully clickless powerdown sequence. SVCC can either be connected to a lowcurrent +5V power source or alternatively can be connected with a reservoir capacitor to ground and a Schottky diode to VCC. A reservoir capacitor of 220µF or higher provides enough charge for the clickless powerdown sequence when CBIAS = 1µF. For larger values of CBIAS, increase the reservoir capacitor accordingly. Short to VCC if clickless power-down is not needed. Driver Amplifier The headphone driver amplifier is a class AB amplifier designed to drive 16Ω loads. The amplifiers have innovative architectures for both the input and output stages to achieve ultra-high PSRR while maintaining rail-to-rail output drive capability. The output stage can drive high capacitive loads encountered when driving long cables used for desktop speakers or headphones. Microphone Preamplifier (MAX4299) The MAX4299 provides a microphone preamplifier that is a low-power version of the audio amplifier. It is intended to be used for low-level signal amplification. This microphone preamplifier provides rail-to-rail output with very high PSRR. _______________________________________________________________________________________ Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator Layout Good layout improves performance by decreasing the amount of stray capacitance and noise at the power amplifier’s inputs and output. To decrease stray capacitance, minimize PC board trace lengths and resistor leads, and place external components as close to the pins as possible. Applications Information Capacitor Selection and Regulator Stability Normally, use a 10µF capacitor on REG (MAX4299 only) and a 1µF capacitor on CBYPASS. Larger capacitor values and lower ESRs provide better supply-noise rejection and line-transient response. Reduce noise and improve load-transient response, stability, and powersupply rejection by using larger capacitors. For stable operation over the full temperature range and load currents up to 100mA, a minimum of 10µF (REG) and 1µF (CBYPASS) is recommended. Use a 1µF bypass capacitor on BIAS to ensure a fully clickless/popless power-up sequence. Smaller capacitor values may be used here to decrease the power-up time, but may cause the power-up transient to become audible. Larger bypass capacitors are not necessary to reduce noise and/or improve AC power-supply rejection. SVCC is the standby power supply. If using an external diode for charging, a 220µF reservoir capacitor on SVCC provides standby power for the clickless powerdown sequence. Smaller capacitors here may cause an audible output transient on power-down; 220µF or higher provides enough energy when CBIAS = 1µF. For larger values of C BIAS, increase the reservoir capacitor accordingly. Mic Biasing (MAX4299) Common microphone elements require resistive biasing to power their internal circuitry. A 2kΩ resistor is typically used, and the microphone is AC-coupled to the microphone amplifier. If the microphone element allows low-voltage operation, biasing to the REG output provides excellent power-supply rejection. Power Supply and Bypassing The excellent PSRR of the MAX4298/MAX4299 allows them to operate from noisy power supplies. In most applications, a 0.1µF capacitor from VCC to GND is sufficient. This bypass capacitor should be placed close to the VCC pin. Power Dissipation The first equation below indicates the maximum power dissipation point for a package that has two power amplifiers operating at identical known supply voltages and loads with sine wave inputs: PIC(DISS) = (VCC)2 / (π2RL) [W] For example, with a 5V power supply and a load of 16Ω, the maximum power dissipation of the amplifiers alone is 317mW. The additional power dissipation due to the 100mA regulator operating at maximum current is nominally 170mW, but will increase if the output is reduced externally from its nominal 3.3V. The regulator power consumption is given by: PREG = (VCC - VREG) x 100mA [W] To avoid thermal shutdown the sum of the regulator and amplifier power dissipation must not exceed the absolute maximum power-dissipation rating of the package. Short-Circuit Protection and Thermal Shutdown The MAX4298/MAX4299 have short-circuit current protection on all outputs. They also have a thermal shutdown function designed to protect the chip from junction temperatures in excess of +150°C that may arise from temporary short circuits or operation beyond the power dissipation limit of the package. The driver amplifier outputs limit at around ±220mA, the regulator at 150mA, and the microphone amplifier at +1.5mA/-12mA. USB Applications Universal serial bus (USB) interfaces are an increasingly popular method of interfacing medium-speed (up to 12Mbps) PC peripherals. One of the great benefits of the USB interface is the inclusion of a +5V supply. While this supply works well for a mouse or keyboard, its susceptibility for noise pickup can be unsuitable for highfidelity audio applications. The MAX4298/MAX4299s’ excellent PSRR make them ideal candidates for USB applications due to their insensitivity to the supply noise. Of particular interest is an Internet-Protocol (IP) phone. This PC peripheral uses the local internet service provider as a free long-distance phone. The MAX4299, with its integral microphone amp, headphone driver, and linear regulator, can be a key element in the implementation of an IP phone that interfaces to the PC through the USB. _______________________________________________________________________________________ 9 MAX4298/MAX4299 Regulator (MAX4299) The MAX4299 also has an additional 100mA lowdropout (LDO) regulator to provide clean analog power for other sensitive analog circuitry on the PC board, such as a typical PC99 audio codec or microphone biasing. It is designed to provide good AC line regulation. The nominal output voltage of REG is 3.3V, and is adjustable between 1.2V and 4.5V by connecting a resistor-divider from REG to GND. Connect FB to the junction of the resistor-divider. The input impedance at FB is typically 7kΩ, which should be considered in output voltage calculations. REG should be bypassed to GND with at least 10µF. Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator MAX4298/MAX4299 Typical Operating Circuits RF 10kΩ VCC OPTIONAL VCC MAX4298 SVCC 220µF RI 10kΩ LEFT _ + IN1 OUT1 MUTE BIAS 1µF RI 10kΩ VCC CAC 220µF 2.25V RIGHT IN2 + _ OUT2 1µF CAC 220µF GND CBYPASS RF 10kΩ 20kΩ VCC REGON 10µF AVDD 3.3V REG FB LDO MAX4299 IN1 LEFT AUDIO CODEC 0.33µF 20kΩ BIAS _ + VCC OPTIONAL SVCC 220µF CAC 220µF OUT MUTE VCC 2.25V 1µF IN2 RIGHT + _ CAC 220µF 0.33µF 20kΩ MIC AVDD OUT2 MICOUT CBYPASS + _ MICIN GND 1µF 20kΩ 0.33µF RBIAS ELECTRET MIC PGND 20kΩ 200kΩ 10 ______________________________________________________________________________________ Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator TOP VIEW REG 1 20 REGON 16 REG FB 1 FB 2 19 N.C. OUT1 2 15 REGON N.C. 3 18 N.C. PGND 3 14 VCC OUT1 4 17 VCC GND 4 16 OUT2 IN1 5 PGND 5 MAX4299 GND 6 IN1 7 13 OUT2 12 IN2 15 IN2 BIAS 6 11 CBYPASS 14 CBYPASS SVCC 7 10 MUTE BIAS 8 13 MUTE SVCC 9 12 N.C. MICOUT 10 MAX4299 MICOUT 8 9 TSSOP N.C. 1 14 N.C. OUT1 2 13 VCC GND 3 IN1 4 12 OUT2 MAX4298 BIAS 5 11 IN2 10 CBYPASS SVCC 6 9 MUTE N.C. 7 8 N.C. MICIN SO 11 MICIN WIDE SO Chip Information MAX4298 TRANSISTOR COUNT: 760 MAX4299 TRANSISTOR COUNT: 905 PROCESS: BiCMOS 10LUMAX.EPS Package Information ______________________________________________________________________________________ 11 MAX4298/MAX4299 Pin Configurations (continued) MAX4298/MAX4299 Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator SOICW.EPS Package Information (continued) 12 ______________________________________________________________________________________ Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator SOICN.EPS ______________________________________________________________________________________ 13 MAX4298/MAX4299 Package Information (continued) Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator TSSOP,NO PADS.EPS MAX4298/MAX4299 Package Information (continued) 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 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.