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19-5189; Rev 0; 5/10
Boosted 2.2W Class D Amplifier with Automatic Level Control
General 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 wide range of battery supply voltages. The boost converter operates at 2MHz, requiring only a small (2.2FH) external inductor and capacitor. The automatic level control has a battery tracking function that reduces the output swing as the supply voltage drops, preventing collapse of battery voltage. 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. 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. 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 S Wide 2.5V to 5.5V Supply Voltage Range S Undervoltage Lockout Protection S High Total Efficiency of 87% S High Step-Up Switching Frequency (2MHz) S Active Emission Limiting for Low EMI
Features
MAX98500
Applications
Cell Phones Smartphones GPS Devices Mobile Internet Devices Active Speaker Accessories
PART
Ordering Information
TEMP RANGE PIN-PACKAGE MAX98500EWE+ 16 WLP -40NC to +85NC +Denotes a lead(Pb)-free/RoHS-compliant package. Typical Application Circuit appears at end of data sheet.
Simplified Block Diagram
BATTERY VBAT B4 SDBST D4 SDSPK C3 GAIN B2 RKNEE B3 CONTROL A3 BOOST CONVERTER A2 LX VCCOUT
MAX98500
A1 PVDD
INP D2 INN D3
B1 SPKP DIFFERENTIAL INPUT C4 AGND A4 BSTPGND GAIN D1, C2 SPKPGND OUTPUT STAGE C1 SPKN
_______________________________________________________________ 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.
Boosted 2.2W Class D Amplifier with Automatic Level Control MAX98500
ABSOLUTE MAXIMUM RATINGS
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 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 JA (Note 1).................................................................49NC/W Junction Temperature .....................................................+150NC Operating Temperature Range .......................... -40NC to +85NC Storage Temperature Range............................ -65NC to +150NC Soldering Temperature (reflow) ......................................+260NC
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 BOOST CONVERTER Battery Supply Voltage Range Soft-Start Interval Undervoltage Lockout Boost Converter Output Voltage Output Current Limit Input Current Limit nMOS Current Limit pMOS Turn-Off Current Limit Switching Frequency Efficiency Startup Short-Circuit Time Thermal Shutdown LX Leakage Current VLX = 0V or 5.5V, VCCOUT = 5.5V TA = +25NC -40NC P TA P +85NC -1.0 fS E 0.1A P IOUT P 0.75A Converter latch off 1.8 VBAT tON UVLO IMAX ILIMIT ILX,MAX VBAT falling VBAT R = 3.6V Startup, VCCOUT = 0V 2.1 5.45 1.5 0.3 3.3 10 2.0 93 50 165 +0.1 0.1 +1.0 2.2 0.5 VVCCOUT ILOAD = 0mA 2.5 5.6 2.2 5.5 2.3 5.65 5.5 V ms V V A A A mA MHz % ms NC FA E ISHDN tON CONDITIONS TA = +25NC, VBAT = 2.5V to 5.5V TA = +25NC, SDSPK = SDBST = VBAT TA = +25NC, VSDSPK = 0V, SDBST = VBAT TA = +25NC, PVDD = 5.55V, SDSPK = SDBST = VBAT POUT = 1.7W, f = 1kHz, ZSPK = 8I + 68FH VSDSPK = VSDBST = 0V, TA = +25NC Time from power-on to full operation MIN TYP 95 3.05 0.09 1.7 87 0.04 10 1.5 12 0.15 2.7 % FA ms mA MAX UNITS dB
2
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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 SPEAKER AMPLIFIER Output Offset Voltage VOS TA = +25NC Peak voltage, TA = +25NC, A-weighted, 32 samples per second, ZSPK = 8I + 68FH, (Notes 3, 4) ZSPK = 8I + 68FH Into shutdown Out of shutdown THD+N P 1% THD+N P 10% 1 -56 dBV -56 1.7 2.2 0.05 300 GAIN = AGND Gain Output Current Limit Efficiency Output Noise E POUT = 1.7W, f = 1kHz, ZSPK = 8I + 68FH A-weighted AV = 6dB (GAIN = AGND) SDBST = SDSPK = VBAT AV = 15.5dB (GAIN = unconnected) AV = 20dB (GAIN = VBAT) Common-Mode Rejection Ratio Bias Voltage ALC Attack Time Release Time Maximum Attenuation Attenuation Resolution RKNEE = 154kI Knee Voltage VKNEE TA = +25NC RKNEE = 40.5kI RKNEE = 13kI 2.19 3.14 3.71 20 1.6 8 0.5 2.3 3.3 3.9 2.42 3.47 4.10 V Fs/dB s/dB dB dB CMRR VBIAS VSDBST = VSDSPK = 0V f = 1kHz All gain settings 1.3 36 12 6.5 AV GAIN = unconnected GAIN = VBAT 5.5 15 19.5 6 15.5 20 2 92 43 54 18 11 110 60 1.4 1.5 dB V 72 26 16 6.5 16 20.5 A % FVRMS dB W % kHz 3 mV SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX98500
Click-and-Pop Level
KCP
Output Power (Note 5) Total Harmonic Distortion Plus Noise Output Switching Frequency
POUT THD+N
f = 1kHz, POUT = 850mW, TA = +25NC, ZSPK = 8I + 68FH
Input Resistance
RIN
kI
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Boosted 2.2W Class D Amplifier with Automatic Level Control MAX98500
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 SYMBOL CONDITIONS VKNEE = 3.25V VKNEE = 3.35V Knee Resistor RKNEE TA = +25NC, AV = 15.5dB VKNEE = 3.45V VKNEE = 3.55V VKNEE = 3.65V VKNEE = 3.75V VKNEE = 3.85V DIGITAL INPUTS (SDBST, SDSPK) Input Voltage High Input Voltage Low Input Capacitance Input Leakage Current ViH VIL CIN IIN TA = +25NC -1.0 10 +1.0 1.4 0.4 MIN TYP 43.2 37.4 32.4 27.4 23.2 18.7 15.0 V V pF FA kI MAX UNITS
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
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Boosted 2.2W Class D Amplifier with Automatic Level Control
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.)
MAX98500
General
BATTERY CURRENT vs. BATTERY VOLTAGE
4.5 4.0 BATTERY CURRENT (mA) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 BATTERY VOLTAGE (V) 60 2.5 3.0 INPUTS AC-COUPLED TO AGND SDSPK = SDBST = VBAT
MAX98500 toc01
BATTERY CURRENT vs. BATTERY VOLTAGE
INPUTS AC-COUPLED TO AGND SDSPK = GND, SDBST = VBAT BATTERY CURRENT (A) 120
MAX98500 toc02
5.0
140
100
80
3.5
4.0
4.5
5.0
5.5
BATTERY VOLTAGE (V)
BATTERY CURRENT vs. BATTERY VOLTAGE
9 8 BATTERY CURRENT (A) 7 6 5 4 3 2 1 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
OV OV
TURN-ON RESPONSE
MAX98500 toc04 MAX98500 toc03
10 INPUTS AC-COUPLED TO AGND SDSPK = VBAT, SDBST = AGND
SDBST 2V/div OV VCCOUT 2V/div
SPKR OUTPUT 1V/div 2ms/div
BATTERY VOLTAGE (V)
EFFICIENCY vs. OUTPUT POWER
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 0.5 1.0 VBAT = 4.2V VBAT = 3.6V VBAT = 3.0V
MAX98500 toc05
100
ZLOAD = 8I + 68H fIN = 1kHz
1.5 2.0 2.5
POUT (W)
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Boosted 2.2W Class D Amplifier with Automatic Level Control 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.)
Speaker
THD+N vs. FREQUENCY
MAX98500 toc06
THD+N vs. OUTPUT POWER
ZLOAD = 8I + 68H
MAX98500 toc07
10
ZLOAD = 8I + 68H
100 10 THD+N (%) 1 0.1 0.01
1 THD+N (%) POUT = 1.4W 0.1
f = 6kHz f = 1kHz
0.01
POUT = 400mW f = 100Hz
0.001 0.01 0.1 1 FREQUENCY (kHz) 10 100
0.001 0 0.4 0.8 1.2 1.6 2.0 2.4 OUTPUT POWER (W)
OUTPUT POWER vs. LOAD RESISTANCE
MAX98500 toc08
OUTPUT POWER vs. BATTERY VOLTAGE
fIN = 1kHz ZSPRK = 8I + 68H
MAX98500 toc09
3.0 2.5 OUTPUT POWER (W) 2.0 1.5 THD+N = 1% 1.0 0.5 0 1 10
fIN = 1kHz ZSPRK = LOAD + 68F THD+N = 10%
3.0 2.5 OUTPUT POWER (W) 2.0 1.5 1.0 0.5 0 2.5
THD+N = 10%
THD+N = 1%
100
1000
3.0
3.5
4.0
4.5
5.0
5.5
LOAD RESISTANCE (I)
BATTERY VOLTAGE (V)
GAIN vs. FREQUENCY
ZLOAD = 8I + 68H 20 10 GAIN (dB) 0 -10 -20 -30 -40 0.1 1 10 FREQUENCY (kHz) 100 1000 AV = 20dB
MAX98500 toc10
30
AV = 15.5dB AV = 6dB
6
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Boosted 2.2W Class D Amplifier with Automatic Level Control
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 POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX98500 toc11
MAX98500
COMMON-MODE REJECTION RATIO vs. FREQUENCY
ZLOAD = 8I + 68H
MAX98500 toc12
SHUTDOWN RESPONSE
MAX98500 toc13
0 -20 -40 -60 -80 -100
VRIPPLE AT PVDD = 200mVP-P INPUTS AC-COUPLED AGND
0 -20
SDSPK 2V/div 0V
AV = 15.5dB CMRR (dB) PSRR (dB) -40 -60 -80 AV = 20dB -100 0.01 0.1 1 FREQUENCY (kHz) 10 100 0.01 0.1 1 FREQUENCY (kHz) 10 100 AV = 6dB
0V
SPKR OUTPUT 1V/div
40s/div
TURN-ON RESPONSE
MAX98500 toc14
CLIPPING RESPONSE
MAX98500 toc15
SDBST = VBAT SDSPK 2V/div 0V 0V
THD+N = 10%
SPKR OUTPUT 500mV/div
0V
SPKR OUTPUT 1V/div 1ms/div 200s/div
WIDEBAND OUTPUT SPECTRUM
MAX98500 toc16
INBAND OUTPUT SPECTRUM
fIN = 1kHz OUTPUT = -60dBV
MAX98500 toc17
20 0 AMPLITUDE (dBV) -20 -40 -60 -80 -100 0.1 1 10 FREQUENCY (MHz) 100 RBW = 100Hz AUDIO INPUTS AC-GROUNDED
0 -20 AMPLITUDE (dBV) -40 -60 -80 -100 -120
1000
0
5
10 FREQUENCY (kHz)
15
20
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Boosted 2.2W Class D Amplifier with Automatic Level Control 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.)
Boost Converter
EFFICIENCY vs. OUTPUT CURRENT
MAX98500 toc18
LOAD REGULATION vs. OUTPUT CURRENT
0 LOAD REGULATION (%) -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 VBAT = 3.6V VBAT = 3.3V VBAT = 3V
MAX98500 toc19
100 98 96 EFFICIENCY (%) 94 92 90 88 86 84 82 80 0 VBAT = 3.6V VBAT = 3V VBAT = 3.3V VBAT = 4V VBAT = 4.2V VBAT = 5V
0.2 VBAT = 5V VBAT = 4.2V VBAT = 4V
200 400 600 800 1000 1200 1400 1600 IOUT (mA)
0
200 400 600 800 1000 1200 1400 1600 IOUT (mA)
OUTPUT VOLTAGE vs. OUTPUT CURRENT
MAX98500 toc20
SWITCHING FREQUENCY vs. BATTERY VOLTAGE
MAX98500 toc21
5.52 5.51 OUTPUT VOLTAGE (V) 5.50 5.49 5.48 5.47 5.46 5.45 5.44 0 VBAT = 3V VBAT = 4.2V VBAT = 5V
2.04 SWITCHING FREQUENCY (MHz)
2.02 IOUT = 100mA 2.00
1.98
IOUT = 500mA
VBAT = 3.3V VBAT = 3.6V 1.96 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 BATTERY VOLTAGE (V)
200 400 600 800 1000 1200 1400 1600 IOUT (A)
SOFT-START
MAX98500 toc22
SDBST 2V/div 0V
VCCOUT 2V/div 0V 1ms/div
8
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Boosted 2.2W Class D Amplifier with Automatic Level Control
Pin Configuration
TOP VIEW (BUMP SIDE DOWN)
MAX98500
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 A1 A2 A3 A4 B1 B2 B3 B4 C1 C2, D1 C3 C4 D2 D3 D4 NAME PVDD VCCOUT LX BSTPGND SPKP GAIN RKNEE VBAT SPKN SPKPGND SDSPK AGND INP INN SDBST 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 Boost Power Ground Positive Speaker Output 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. 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 Positive Audio Input Negative Audio Input Boost Converter Shutdown. Drive SDBST low to shutdown the boost converter and the speaker output.
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Boosted 2.2W Class D Amplifier with Automatic Level Control MAX98500
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
6 PEAK AMPLIFIER OUTPUT VOLTAGE (VPEAK) 5 SLOPE 4 3 2 1 0 0 1 2 3 4 5 6 BATTERY VOLTAGE (V) KNEE VOLTAGE
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.
Class D Speaker Amplifier
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: U Avoid clipping U Save the battery from collapsing, which could cause a reset of the system The limiter keeps the peak voltage below a value that is a function of battery voltage, as shown in Figure 1. 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. The attack (gain reduction) happens immediately (20Fs/ dB), while the release is set to 1.6s/dB. The MAX98500 features three internal gain settings that are selectable with the GAIN input. Table 1 shows the gain settings.
Automatic Level Control
Figure 1. Typical Tracking Function
VKNEE vs. RKNEE
4.0 3.9 3.8 3.7 VKNEE (V) 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 10 20 30 40 RKNEE (kI) 50 60 70
GAIN Select
Table 1. Gain Settings
GAIN AGND Unconnected VBAT AMPLIFIER GAIN (dB) 6 15.5 20
Figure 2. The Relationship of RKNEE and VKNEE 10
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Boosted 2.2W Class D Amplifier with Automatic Level Control
Table 2. Shutdown Configurations
SDBST Low Low High High SDSPK Low High Low High BOOST STATUS Off Off On On SPEAKER STATUS Off Off Off On
threshold, the soft-start begins. When the input voltage falls below the UVLO threshold, the boost converter and speaker amplifier turn off.
MAX98500
Applications Information
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 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. 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. 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.
Filterless Class D Operation
The MAX98500 features two active-low shutdown inputs (SDSPK and SDBST). Table 2 shows the different shutdown configurations.
Shutdown
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 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.
Click-and-Pop Suppression
Current-Limit and Thermal Protection
RF Susceptibility
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
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.
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11
Boosted 2.2W Class D Amplifier with Automatic Level Control MAX98500
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.
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
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 2RINCIN
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.
SPKN
Figure 3. Optional Class D Ferrite Bead Filter 12 _____________________________________________________________________________________
Boosted 2.2W Class D Amplifier with Automatic Level Control
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.
Supply Bypassing, Layout, and Grounding
0.25mm
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. An evaluation kit (MAX98500 Evaluation Kit) is available to provide an example layout for the MAX98500. 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.
MAX98500
WLP Applications Information
0.22mm
Figure 4. Recommended PCB Footprint
Typical Application Circuit
2.2H 20% CVBAT 10F 0805 10% SDBST D4 SDSPK C3 GAIN B2 RKNEE B3 27.4kI 1% CIN 1F CONTROL VBAT B4 A3 BOOST CONVERTER A2 VCCOUT CVCCOUT 22F 0805 10% 0.1F 10% B1 SPKP DIFFERENTIAL INPUT C4 AGND A4 BSTPGND GAIN OUTPUT STAGE D1, C2 SPKPGND C1 SPKN 8I LX
BATTERY 22F*
MAX98500
A1 PVDD
INP D2 INN D3
CIN 1F
*SYSTEM LEVEL REQUIREMENT
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Boosted 2.2W Class D Amplifier with Automatic Level Control MAX98500
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 16 WLP PACKAGE CODE W162B2+1 DOCUMENT NO. 21-0200
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Boosted 2.2W Class D Amplifier with Automatic Level Control MAX98500
Revision History
REVISION NUMBER 0 REVISION DATE 5/10 Initial release DESCRIPTION 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.
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(c)
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2010 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.

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