19-5189; Rev 0; 5/10 Boosted 2.2W Class D Amplifier with Automatic Level Control Features The MAX98500 is a high-efficiency, Class D audio amplifier that features an integrated boost converter to deliver a constant output power over a wide range of battery supply voltages. S Boosted Class D Output S Integrated Automatic Level Control S Output Power 2.2W into 8I, 10% THD+N 1.7W into 8I, 1% THD+N The boost converter operates at 2MHz, requiring only a small (2.2FH) external inductor and capacitor. S Wide 2.5V to 5.5V Supply Voltage Range The automatic level control has a battery tracking function that reduces the output swing as the supply voltage drops, preventing collapse of battery voltage. S Undervoltage Lockout Protection S High Total Efficiency of 87% S High Step-Up Switching Frequency (2MHz) The amplifier has differential inputs and an internal fully differential design. The MAX98500 also features three gain settings (6dB, 15.5dB, and 20dB) that are selectable with a logic input. S Active Emission Limiting for Low EMI The MAX98500 is available in a small, 0.5mm pitch 16-bump WLP package (2.1mm x 2.1mm). It is specified over the extended -40NC to +85NC temperature range. Ordering Information Applications Cell Phones PART Smartphones TEMP RANGE PIN-PACKAGE MAX98500EWE+ 16 WLP -40NC to +85NC +Denotes a lead(Pb)-free/RoHS-compliant package. GPS Devices Mobile Internet Devices Typical Application Circuit appears at end of data sheet. Active Speaker Accessories Simplified Block Diagram BATTERY VBAT LX B4 SDBST D4 SDSPK C3 GAIN B2 RKNEE A3 BOOST CONVERTER CONTROL MAX98500 A2 VCCOUT A1 PVDD B3 INP D2 INN D3 B1 SPKP DIFFERENTIAL INPUT C4 AGND OUTPUT STAGE GAIN A4 BSTPGND C1 SPKN D1, C2 SPKPGND ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX98500 General Description MAX98500 Boosted 2.2W Class D Amplifier with Automatic Level Control ABSOLUTE MAXIMUM RATINGS Duration of SPK_ Short Circuit to PVDD or SPKPGND...............................................................Continuous Duration of Short Circuit Between SPKP and SPKN...............................................................Continuous Continuous Power Dissipation, Multilayer Board (TA = +70NC) WLP (derate 20.4mW/NC above +70NC)........................1.33W θJA (Note 1).................................................................49NC/W Junction Temperature......................................................+150NC Operating Temperature Range........................... -40NC to +85NC Storage Temperature Range............................. -65NC to +150NC Soldering Temperature (reflow).......................................+260NC VBAT to AGND..........................................................-0.3V to +6V VCCOUT to BSTPGND, AGND..................................-0.3V to +6V PVDD to SPKPGND..................................................-0.3V to +6V BSTPGND, SPKPGND to AGND.......................... -0.3V to +0.3V GAIN to AGND......................................... -0.3V to (VBAT + 0.3V) SDBST, SDSPK to AGND....................................... -0.3V to VBAT All Other Pins (excluding LX) to AGND...................-0.3V to +6V Current Into/Out of LX, VCCOUT, BSTPGND...................... Q3.9A Continuous Current Into/Out of SPK_, PVDD, SPKPGND................................................................... Q800mA Continuous Input Current (all other pins)......................... Q20mA Duration of Short Circuit Between VCCOUT and BSTPGND....................................................... Continuous Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. 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 (VBAT = 3.6V, RL = J between SPKP and SPKN, AV = +6dB, CIN = 1FF, 20Hz to 22kHz AC measurement bandwidth, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER Power-Supply Rejection Ratio (Note 3) SYMBOL PSRR IVBAT Quiescent Current IPVDD Combined Efficiency Shutdown Current Turn-On Time E ISHDN tON CONDITIONS MIN TYP MAX 95 TA = +25NC, VBAT = 2.5V to 5.5V dB TA = +25NC, SDSPK = SDBST = VBAT 3.05 TA = +25NC, VSDSPK = 0V, SDBST = VBAT 0.09 0.15 TA = +25NC, PVDD = 5.55V, SDSPK = SDBST = VBAT 1.7 2.7 87 POUT = 1.7W, f = 1kHz, ZSPK = 8I + 68FH VSDSPK = VSDBST = 0V, TA = +25NC Time from power-on to full operation UNITS mA % 0.04 1.5 FA 10 12 ms BOOST CONVERTER Battery Supply Voltage Range Soft-Start Interval Undervoltage Lockout Boost Converter Output Voltage Output Current Limit 2.5 VBAT UVLO VBAT falling VVCCOUT ILOAD = 0mA VBAT R = 3.6V Input Current Limit ILIMIT Startup, VCCOUT = 0V nMOS Current Limit ILX,MAX 2.1 2.2 2.3 5.45 5.5 5.65 fS Efficiency E 1.8 V 2.0 A A mA 2.2 MHz 0.1A P IOUT P 0.75A 93 % Converter latch off 50 ms Thermal Shutdown LX Leakage Current 0.5 3.3 10 Switching Frequency V A 0.3 pMOS Turn-Off Current Limit V ms 1.5 IMAX Startup Short-Circuit Time 5.5 5.6 tON 165 VLX = 0V or 5.5V, VCCOUT = 5.5V TA = +25NC -40NC P TA P +85NC -1.0 +0.1 0.1 2 _______________________________________________________________________________________ NC +1.0 FA Boosted 2.2W Class D Amplifier with Automatic Level Control (VBAT = 3.6V, RL = J between SPKP and SPKN, AV = +6dB, CIN = 1FF, 20Hz to 22kHz AC measurement bandwidth, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 1 3 mV SPEAKER AMPLIFIER Output Offset Voltage Click-and-Pop Level Output Power (Note 5) Total Harmonic Distortion Plus Noise VOS TA = +25NC KCP Peak voltage, TA = +25NC, A-weighted, 32 samples per second, ZSPK = 8I + 68FH, (Notes 3, 4) POUT THD+N ZSPK = 8I + 68FH Into shutdown -56 Out of shutdown -56 dBV THD+N P 1% 1.7 THD+N P 10% 2.2 f = 1kHz, POUT = 850mW, TA = +25NC, ZSPK = 8I + 68FH Output Switching Frequency Gain AV % 300 kHz GAIN = AGND 5.5 6 15 15.5 16 19.5 20 20.5 Output Current Limit 6.5 2 E Output Noise Input Resistance 0.05 GAIN = unconnected GAIN = VBAT Efficiency W RIN Common-Mode Rejection Ratio CMRR Bias Voltage VBIAS dB A POUT = 1.7W, f = 1kHz, ZSPK = 8I + 68FH 92 % A-weighted 43 FVRMS SDBST = SDSPK = VBAT VSDBST = VSDSPK = 0V f = 1kHz AV = 6dB (GAIN = AGND) 36 54 72 AV = 15.5dB (GAIN = unconnected) 12 18 26 AV = 20dB (GAIN = VBAT) 6.5 11 16 All gain settings kI 110 60 1.3 1.4 dB 1.5 V ALC Attack Time 20 Fs/dB Release Time 1.6 s/dB Maximum Attenuation 8 dB Attenuation Resolution 0.5 Knee Voltage VKNEE TA = +25NC dB RKNEE = 154kI 2.19 2.3 2.42 RKNEE = 40.5kI 3.14 3.3 3.47 RKNEE = 13kI 3.71 3.9 4.10 V _______________________________________________________________________________________ 3 MAX98500 ELECTRICAL CHARACTERISTICS (continued) MAX98500 Boosted 2.2W Class D Amplifier with Automatic Level Control ELECTRICAL CHARACTERISTICS (continued) (VBAT = 3.6V, RL = J between SPKP and SPKN, AV = +6dB, CIN = 1FF, 20Hz to 22kHz AC measurement bandwidth, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER Knee Resistor SYMBOL RKNEE DIGITAL INPUTS (SDBST, SDSPK) Input Voltage High ViH Input Voltage Low VIL Input Capacitance CIN Input Leakage Current IIN CONDITIONS TA = +25NC, AV = 15.5dB MIN TYP VKNEE = 3.25V 43.2 VKNEE = 3.35V 37.4 VKNEE = 3.45V 32.4 VKNEE = 3.55V 27.4 VKNEE = 3.65V 23.2 VKNEE = 3.75V 18.7 VKNEE = 3.85V 15.0 MAX kI 1.4 V 0.4 10 TA = +25NC UNITS -1.0 Note 2: 100% production tested at TA = +25NC. Specifications over temperature limits are guaranteed by design. Note 3: Amplifier inputs are AC-coupled to AGND. Note 4: Mode transitions are controlled by SDSPK. 4 _______________________________________________________________________________________ V pF +1.0 FA Boosted 2.2W Class D Amplifier with Automatic Level Control General BATTERY CURRENT vs. BATTERY VOLTAGE INPUTS AC-COUPLED TO AGND SDSPK = GND, SDBST = VBAT BATTERY CURRENT (µA) BATTERY CURRENT (mA) 4.0 140 MAX98500 toc02 INPUTS AC-COUPLED TO AGND SDSPK = SDBST = VBAT 4.5 MAX98500 toc01 5.0 BATTERY CURRENT vs. BATTERY VOLTAGE 3.5 3.0 2.5 2.0 1.5 1.0 120 100 80 0.5 60 0 2.5 3.0 3.5 4.0 4.5 5.0 3.5 4.0 4.5 BATTERY VOLTAGE (V) BATTERY VOLTAGE (V) BATTERY CURRENT vs. BATTERY VOLTAGE TURN-ON RESPONSE 5.0 5.5 MAX98500 toc04 MAX98500 toc03 10 INPUTS AC-COUPLED TO AGND SDSPK = VBAT, SDBST = AGND 9 8 SDBST 2V/div 7 OV VCCOUT 2V/div 6 5 4 OV 3 2 SPKR OUTPUT 1V/div OV 1 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2ms/div BATTERY VOLTAGE (V) EFFICIENCY vs. OUTPUT POWER MAX98500 toc05 100 90 80 EFFICIENCY (%) BATTERY CURRENT (µA) 3.0 2.5 5.5 VBAT = 4.2V 70 VBAT = 3.6V 60 50 VBAT = 3.0V 40 30 20 ZLOAD = 8I + 68µH fIN = 1kHz 10 0 0 0.5 1.0 1.5 2.0 2.5 POUT (W) _______________________________________________________________________________________ 5 MAX98500 Typical Operating Characteristics (VBAT = 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = VBAT, 20Hz to 22kHz AC measurement bandwidth, unless otherwise noted.) Typical Operating Characteristics (continued) (VBAT = 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = VBAT, 20Hz to 22kHz AC measurement bandwidth, unless otherwise noted.) Speaker MAX98500 toc06 ZLOAD = 8I + 68µH 1 ZLOAD = 8I + 68µH 10 POUT = 1.4W THD+N (%) THD+N (%) 100 MAX98500 toc07 THD+N vs. OUTPUT POWER THD+N vs. FREQUENCY 10 0.1 1 f = 6kHz 0.1 f = 1kHz POUT = 400mW 0.01 0.01 f = 100Hz 0.001 0.001 0.1 1 10 100 0 0.4 OUTPUT POWER vs. LOAD RESISTANCE fIN = 1kHz ZSPRK = LOAD + 68µF 2.5 1.2 1.6 2.0 2.4 fIN = 1kHz ZSPRK = 8I + 68µH 2.5 OUTPUT POWER (W) THD+N = 10% OUTPUT POWER vs. BATTERY VOLTAGE 3.0 MAX98500 toc08 3.0 0.8 OUTPUT POWER (W) FREQUENCY (kHz) 2.0 1.5 THD+N = 1% 1.0 0.5 THD+N = 10% MAX98500 toc09 0.01 OUTPUT POWER (W) 2.0 1.5 THD+N = 1% 1.0 0.5 0 1 10 100 0 1000 2.5 3.0 LOAD RESISTANCE (I) 3.5 4.0 4.5 5.0 BATTERY VOLTAGE (V) ZLOAD = 8I + 68µH AV = 20dB 20 10 AV = 15.5dB 0 AV = 6dB MAX98500 toc10 GAIN vs. FREQUENCY 30 GAIN (dB) MAX98500 Boosted 2.2W Class D Amplifier with Automatic Level Control -10 -20 -30 -40 0.1 1 10 100 1000 FREQUENCY (kHz) 6 _______________________________________________________________________________________ 5.5 Boosted 2.2W Class D Amplifier with Automatic Level Control SPEAKER POWER-SUPPLY REJECTION RATIO vs. FREQUENCY -20 MAX98500 toc12 VRIPPLE AT PVDD = 200mVP-P INPUTS AC-COUPLED AGND SHUTDOWN RESPONSE MAX98500 toc13 0 MAX98500 toc11 0 COMMON-MODE REJECTION RATIO vs. FREQUENCY ZLOAD = 8I + 68µH -20 SDSPK 2V/div -40 CMRR (dB) -60 0V AV = 6dB -60 -80 -80 -100 -100 SPKR OUTPUT 1V/div 0V AV = 20dB 0.1 1 10 100 0.1 0.01 FREQUENCY (kHz) 1 10 100 40µs/div FREQUENCY (kHz) TURN-ON RESPONSE CLIPPING RESPONSE MAX98500 toc14 MAX98500 toc15 SDBST = VBAT THD+N = 10% SDSPK 2V/div 0V SPKR OUTPUT 500mV/div 0V 0V SPKR OUTPUT 1V/div 1ms/div 200µs/div WIDEBAND OUTPUT SPECTRUM RBW = 100Hz AUDIO INPUTS AC-GROUNDED -20 -40 -60 -80 fIN = 1kHz OUTPUT = -60dBV -20 AMPLITUDE (dBV) 0 INBAND OUTPUT SPECTRUM 0 MAX98500 toc17 20 MAX98500 toc16 0.01 AMPLITUDE (dBV) PSRR (dB) AV = 15.5dB -40 -40 -60 -80 -100 -100 -120 0.1 1 10 FREQUENCY (MHz) 100 1000 0 5 10 15 20 FREQUENCY (kHz) _______________________________________________________________________________________ 7 MAX98500 Typical Operating Characteristics (continued) (VBAT = 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = VBAT, 20Hz to 22kHz AC measurement bandwidth, unless otherwise noted.) Typical Operating Characteristics (continued) (VBAT = 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = VBAT, 20Hz to 22kHz AC measurement bandwidth, unless otherwise noted.) Boost Converter EFFICIENCY vs. OUTPUT CURRENT 0 94 92 VBAT = 4V 90 88 VBAT = 3.6V 86 VBAT = 3V 84 82 VBAT = 5V -0.2 VBAT = 4.2V -0.4 VBAT = 4V -0.6 -0.8 VBAT = 3.6V -1.0 VBAT = 3.3V 80 -1.2 0 MAX98500 toc19 VBAT = 5V 200 400 600 800 1000 1200 1400 1600 0 VBAT = 3.3V VBAT = 3V 200 400 600 800 1000 1200 1400 1600 IOUT (mA) IOUT (mA) OUTPUT VOLTAGE vs. OUTPUT CURRENT SWITCHING FREQUENCY vs. BATTERY VOLTAGE 2.04 5.51 5.50 5.49 SWITCHING FREQUENCY (MHz) MAX98500 toc20 5.52 VBAT = 4.2V 5.48 VBAT = 5V 5.47 5.46 VBAT = 3V 5.45 2.02 IOUT = 100mA 2.00 IOUT = 500mA 1.98 VBAT = 3.3V VBAT = 3.6V 5.44 0 MAX98500 toc21 EFFICIENCY (%) 96 LOAD REGULATION (%) VBAT = 4.2V 98 LOAD REGULATION vs. OUTPUT CURRENT 0.2 MAX98500 toc18 100 OUTPUT VOLTAGE (V) MAX98500 Boosted 2.2W Class D Amplifier with Automatic Level Control 1.96 200 400 600 800 1000 1200 1400 1600 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 IOUT (A) BATTERY VOLTAGE (V) SOFT-START MAX98500 toc22 SDBST 2V/div 0V VCCOUT 2V/div 0V 1ms/div 8 _______________________________________________________________________________________ Boosted 2.2W Class D Amplifier with Automatic Level Control TOP VIEW (BUMP SIDE DOWN) MAX98500 1 2 3 4 A PVDD VCCOUT LX BSTPGND B SPKP GAIN RKNEE VBAT C SPKN SPKPGND SDSPK AGND D SPKPGND INP INN SDBST + WLP Pin Description BUMP NAME A1 PVDD A2 VCCOUT FUNCTION Speaker Amplifier Power Supply. Bypass to SPKPGND with a 0.1mF capacitor. Boost Converter Output. Connect a 22mF (0805) capacitor between VCCOUT and BSTPGND. Boost Switch Input A3 LX A4 BSTPGND B1 SPKP Positive Speaker Output B2 GAIN Gain Select Input. Connect GAIN to ground to set the speaker gain to 6dB. Leave GAIN unconnected to set the speaker gain to 15.5dB. Connect GAIN to VBAT to set the speaker gain to 20dB. B3 RKNEE B4 VBAT C1 SPKN C2, D1 SPKPGND C3 SDSPK AGND C4 Boost Power Ground ALC Knee Voltage Set Input. Set the ALC knee voltage with a resistor to AGND. Battery Voltage Input. Connect a 10mF (0805) capacitor between VBAT and BSTPGND. Include at least 22mF of system bulk capacitance. Negative Speaker Output Speaker Ground Speaker Output Shutdown. Drive SDSPK low to shutdown the speaker output. Analog Ground D2 INP Positive Audio Input D3 INN Negative Audio Input D4 SDBST Boost Converter Shutdown. Drive SDBST low to shutdown the boost converter and the speaker output. _______________________________________________________________________________________ 9 MAX98500 Pin Configuration Detailed Description The MAX98500 is a high-efficiency Class D audio amplifier that features an integrated boost converter to deliver a constant output power over a large range of battery supply voltages. The boost converter operates at 2MHz, requiring only a small (2.2FH) external inductor and output capacitor. The amplifier has differential inputs and an internal fully differential design with three gain settings (6dB, 15.5dB, and 20dB) that are selectable with a logic input. The MAX98500 also features automatic level control. The automatic level control reduces the output swing when the battery voltage decreases to prevent the collapse of battery voltage. PEAK AMPLIFIER OUTPUT VOLTAGE vs. BATTERY VOLTAGE PEAK AMPLIFIER OUTPUT VOLTAGE (VPEAK) Low-EMI Filterless Output Stage Traditional Class D amplifiers require the use of external LC filters, or shielding, to meet EN55022B electromagnetic-interference (EMI) regulation standards. Maxim’s active emissions limiting edge-rate control circuitry reduces EMI emissions, while maintaining up to 92% efficiency (speaker only). Above 10MHz, the wideband spectrum looks like noise for EMI purposes. The MAX98500 features an automatic level control circuit that limits the maximum speaker output swing. This helps: 5 U Avoid clipping SLOPE 4 KNEE VOLTAGE U Save the battery from collapsing, which could cause a reset of the system 3 The limiter keeps the peak voltage below a value that is a function of battery voltage, as shown in Figure 1. 2 1 0 0 1 2 3 4 5 6 BATTERY VOLTAGE (V) Figure 1. Typical Tracking Function The full output swing of 5.2V is maintained for battery voltages down to the knee voltage, while for lower battery voltages the maximum VPEAK-swing is reduced by 3V/V. The knee voltage can be changed by applying different resistors between RKNEE and AGND. The typical tracking function is shifted horizontally with different RKNEE resistor values (Figure 2). The preamplifier gain reduces as the automatic level control activates. The maximum gain reduction is 8dB with a resolution of 0.5dB steps. VKNEE vs. RKNEE 4.0 3.9 The attack (gain reduction) happens immediately (20Fs/ dB), while the release is set to 1.6s/dB. 3.8 3.7 3.6 GAIN Select 3.5 The MAX98500 features three internal gain settings that are selectable with the GAIN input. Table 1 shows the gain settings. 3.4 3.3 3.2 3.1 Table 1. Gain Settings 3.0 2.9 10 20 30 40 50 60 RKNEE (kI) Figure 2. The Relationship of RKNEE and VKNEE 10 Class D Speaker Amplifier The MAX98500 filterless Class D amplifier offers much higher efficiency than Class AB amplifiers. The high efficiency of a Class D amplifier is due to the switching operation of the output stage transistors. Any power loss associated with the Class D output stage is mostly due to the I2R loss of the MOSFET on-resistance and quiescent current overhead. Automatic Level Control 6 VKNEE (V) MAX98500 Boosted 2.2W Class D Amplifier with Automatic Level Control 70 GAIN AMPLIFIER GAIN (dB) AGND 6 Unconnected 15.5 VBAT 20 _____________________________________________________________________________________ Boosted 2.2W Class D Amplifier with Automatic Level Control SDSPK BOOST STATUS SPEAKER STATUS Low Low Off Off Low High Off Off High Low On Off High High On On SDBST Shutdown The MAX98500 features two active-low shutdown inputs (SDSPK and SDBST). Table 2 shows the different shutdown configurations. Click-and-Pop Suppression threshold, the soft-start begins. When the input voltage falls below the UVLO threshold, the boost converter and speaker amplifier turn off. Applications Information Filterless Class D Operation Traditional Class D amplifiers require an output filter to recover the audio signal from the amplifier’s output. The filter adds cost, increases the solution size of the amplifier, and can decrease efficiency and THD+N performance. The traditional PWM scheme uses large differential output swings (2 x supply voltage peak-to-peak) and causes large ripple currents. Any parasitic resistance in the filter components results in a loss of power and lowers the efficiency. The MAX98500 speaker amplifier features Maxim’s comprehensive click-and-pop suppression. During startup, the click-and-pop suppression circuitry reduces any audible transient sources internal to the device. When entering shutdown, the differential speaker outputs ramp down to SPKPGND quickly and simultaneously. The MAX98500 does not require an output filter. The device relies on the inherent inductance of the speaker coil and the natural filtering of both the speaker and the human ear to recover the audio component of the square-wave output. Eliminating the output filter results in a smaller, less costly, and more efficient solution. Current-Limit and Thermal Protection Because the frequency of the MAX98500 output is well beyond the bandwidth of most speakers, voice coil movement due to the square-wave frequency is very small. Although this movement is small, a speaker not designed to handle the additional power can be damaged. For optimum results, use a speaker with a series inductance > 10FH. Typical 8I speakers exhibit series inductances in the 20FH to 100FH range. The IC features overcurrent and thermal protection. The IC shuts down when the VCCOUT output decreases to about 80% of the expected output. The IC also enters into shutdown when the die temperature exceeds +165NC. The device remains in shutdown until power is reset or SDBST is toggled low and back high after the fault condition has been removed. The IC speaker amplifier also features a 2A (typ) short-circuit protection scheme. Boost Converter Soft-Start The MAX98500 features a two-stage, soft-start, powerup sequence. When SDBST is taken high and VBAT is above UVLO the soft-start first ramps VCCOUT quickly to VBAT voltage with a battery current of 300mA (typ). Once the VCCOUT reaches the VBAT voltage, the internal switching turns on and ramps the VCCOUT to 5.5V in 5ms (typ), see the Soft-Start graph in the Typical Operating Characteristics. The maximum load current is available after the soft-start is completed. Undervoltage Lockout (UVLO) The undervoltage lockout (UVLO) circuit compares the voltage at VBAT with the UVLO threshold (2.2V typ) to ensure that the input voltage is high enough for reliable operation. Once the VBAT voltage exceeds the UVLO RF Susceptibility GSM radios transmit using time-division multiple access (TDMA) with 217Hz intervals. The result is an RF signal with strong amplitude modulation at 217Hz and its harmonics that is easily demodulated by audio amplifiers. The MAX98500 is designed specifically to reject RF signals; however, PCB layout has a large impact on the susceptibility of the end product. In RF applications, improvements to both layout and component selection decrease the MAX98500’s susceptibility to RF noise and prevent RF signals from being demodulated into audible noise. Trace lengths should be kept below 1/4 of the wavelength of the RF frequency of interest. Minimizing the trace lengths prevents them from functioning as antennas and coupling RF signals into the MAX98500. The wavelength (l) in meters is given by: l = c/f where c = 3 x 108 m/s, and f = the RF frequency of interest. ______________________________________________________________________________________ 11 MAX98500 Table 2. Shutdown Configurations MAX98500 Boosted 2.2W Class D Amplifier with Automatic Level Control Route audio signals on the middle layers of the PCB to allow the ground planes above and below to shield them from RF interference. Ideally the top and bottom layers of the PCB should primarily be ground planes to create effective shielding. Additional RF immunity can also be obtained from relying on the self-resonant frequency of capacitors as it exhibits the frequency response similar to a notch filter. Depending on the manufacturer, 10pF to 20pF capacitors typically exhibit self resonance at RF frequencies. These capacitors, when placed at the input pins, can effectively shunt the RF noise at the inputs of the MAX98500. For these capacitors to be effective, they must have a lowimpedance, low-inductance path to the ground plane. Do not use microvias to connect to the ground plane as these vias do not conduct well at RF frequencies. Speaker Component Selection Optional Ferrite Bead Filter Additional EMI suppression can be achieved using a filter constructed from a ferrite bead and a capacitor to ground (Figure 3). Use a ferrite bead with low DC resistance, high-frequency (> 100MHz) impedance between 100I and 600I, and rated for at least 1A. The capacitor value varies based on the ferrite bead chosen and the actual speaker lead length. Select a capacitor less than 1nF based on EMI performance. Input Capacitor (CIN) An input capacitor, CIN, in conjunction with the input impedance of the MAX98500 speaker inputs forms a highpass filter that removes the DC bias from an incoming analog signal. The AC-coupling capacitor allows the amplifier to automatically bias the signal to an optimum DC level. Assuming zero-source impedance, the -3dB point of the highpass filter is given by: f-3dB = 1 2πRINCIN Choose CIN such that f-3dB is well below the lowest frequency of interest. For best audio quality, use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with highvoltage coefficients, such as ceramics, could result in increased distortion at low frequencies. Boost Converter Component Selection Inductor Selection In most step-up converter designs, a reasonable inductor value can be derived from the following equation. This equation sets peak-to-peak inductor current at 1/2 the DC inductor current: L = (2 x VBATT x D x (1-D))/(IOUT(MAX) x fSW) where fSW is the switching frequency, and D is the duty factor given by D = 1 - (VBAT/VOUT). Using L from the equation above results in a peak-to-peak inductor current ripple of 0.5 x IOUT/(1 - D), and a peak inductor current of 1.25 x IOUT/(1 - D). Ensure the peak (saturation) current rating of the inductor meets or exceeds this requirement. The recommended nominal inductance for the MAX98500 is 2.2FH. Nominal inductance decreases as the inductor current increases. If the decrease from the nominal inductance is severe, the boost converter may become unstable or shut down at lower output power levels than expected. Ensure the minimum inductance at the peak inductor current is 1.0FH. Output Capacitor (CVCCOUT) An output capacitor, CVCCOUT, is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. Ceramic capacitors are highly recommended due to their small size and low ESR. Ceramic capacitors with X5R or X7R temperature characteristics generally perform well. The recommended nominal capacitance for the MAX98500 is 22FF (0805 case size or larger). Ensure the minimum capacitance at 5.5V is 6.8FF. Input Capacitor (CVBAT) An input capacitor, CVBAT, reduces the current peaks drawn from the battery or input power source and reduces switching noise in the IC. The impedance of the input capacitor at the switching frequency should be kept very low. Ceramic capacitors are highly recommended due to their small size and low ESR. Ceramic capacitors with X5R or X7R temperature characteristics generally perform well. One 10FF ceramic capacitor is recommended with a system bulk capacitance of 22FF or larger. SPKP MAX98500 SPKN Figure 3. Optional Class D Ferrite Bead Filter 12 ������������������������������������������������������������������������������������� Boosted 2.2W Class D Amplifier with Automatic Level Control Bypass VBAT with a 10FF capacitor and a system bulk capacitance of 22FF or larger. Bypass PVDD to SPKPGND with a 0.1FF capacitor and with as minimal a loop area as possible. Connect SPKP and SPKN to the speaker using the shortest and widest traces possible. Reducing trace length minimizes radiated EMI. Route SPKP/SPKN as a differential pair on the PCB to minimize loop area, thereby, the inductance of the circuit. If filter components are used on the speaker outputs, be sure to locate them as close as possible to the MAX98500 to ensure maximum effectiveness. Minimize the trace length from any ground-tied passive components to SPKPGND to further minimize radiated EMI. 0.25mm An evaluation kit (MAX98500 Evaluation Kit) is available to provide an example layout for the MAX98500. WLP Applications Information For the latest application details on WLP construction, dimensions, tape carrier information, PCB techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information on reliability testing results, refer to the Application Note 1891: WaferLevel Packaging (WLP) and Its Applications on Maxim’s website at www.maxim-ic.com/ucsp. See Figure 4 for the recommended PCB footprint for the MAX98500. 0.22mm Figure 4. Recommended PCB Footprint Typical Application Circuit 2.2µH 20% BATTERY CVBAT 10µF 0805 10% 22µF* LX VBAT B4 BOOST CONVERTER SDBST D4 SDSPK C3 GAIN B2 A3 CONTROL MAX98500 A2 VCCOUT A1 PVDD RKNEE B3 27.4kI 1% CIN 1µF INP D2 INN D3 CIN 1µF CVCCOUT 22µF 0805 10% 0.1µF 10% B1 SPKP DIFFERENTIAL INPUT C4 AGND GAIN A4 BSTPGND OUTPUT STAGE C1 SPKN 8I D1, C2 SPKPGND *SYSTEM LEVEL REQUIREMENT ______________________________________________________________________________________ 13 MAX98500 Supply Bypassing, Layout, and Grounding Proper layout and grounding are essential for optimum performance. Use a large continuous ground plane on a dedicated layer of the PCB to minimize loop areas. Connect AGND and BSTPGND/SPKPGND directly to the ground plane using the shortest traces length possible. Proper grounding improves audio performance, and prevents any digital noise from coupling into the analog audio signals. MAX98500 Boosted 2.2W Class D Amplifier with Automatic Level Control Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE Document No. 16 WLP W162B2+1 21-0200 14 ������������������������������������������������������������������������������������� Boosted 2.2W Class D Amplifier with Automatic Level Control REVISION NUMBER REVISION DATE 0 5/10 DESCRIPTION Initial release PAGES CHANGED — Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2010 Maxim Integrated Products 15 Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX98500 Revision History