19-5189; Rev 0; 5/10
Boosted 2.2W Class D Amplifier
with Automatic Level Control
Features
S Boosted Class D Output
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 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
A2
VCCOUT
MAX98500
CONTROL
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
2.5
VBAT
UVLO
VBAT falling
VVCCOUT ILOAD = 0mA
IMAX
VBAT R = 3.6V
Input Current Limit
ILIMIT
Startup, VCCOUT = 0V
nMOS Current Limit
ILX,MAX
Output Current Limit
2.1
2.2
2.3
5.5
5.65
1.5
fS
0.3
Efficiency
E
2
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
1.8
V
A
10
Switching Frequency
V
ms
5.45
pMOS Turn-Off Current Limit
Startup Short-Circuit Time
5.5
5.6
tON
NC
165
VLX = 0V or 5.5V,
VCCOUT = 5.5V
TA = +25NC
-40NC P TA P +85NC
-1.0
+0.1
0.1
______________________________________________________________________________________
+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
V
0.4
10
TA = +25NC
UNITS
kI
1.4
-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
MAX
______________________________________________________________________________________
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
3.0
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
5.5
5.0
2ms/div
BATTERY VOLTAGE (V)
EFFICIENCY vs. OUTPUT POWER
MAX98500 toc05
100
90
80
EFFICIENCY (%)
BATTERY CURRENT (μA)
2.5
5.5
5.0
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
THD+N vs. OUTPUT POWER
MAX98500 toc06
100
ZLOAD = 8I + 68μH
ZLOAD = 8I + 68μH
10
1
POUT = 1.4W
THD+N (%)
THD+N (%)
MAX98500 toc07
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
0
100
0.4
OUTPUT POWER vs. LOAD RESISTANCE
fIN = 1kHz
ZSPRK = LOAD + 68μF
2.5
1.2
1.6
2.0
fIN = 1kHz
ZSPRK = 8I + 68μH
2.5
OUTPUT POWER (W)
THD+N = 10%
2.0
1.5
THD+N = 1%
1.0
0.5
THD+N = 10%
2.0
1.5
THD+N = 1%
1.0
0.5
0
0
1
10
100
1000
2.5
3.0
LOAD RESISTANCE (I)
3.5
4.0
4.5
5.0
BATTERY VOLTAGE (V)
ZLOAD = 8I + 68μH
AV = 20dB
GAIN (dB)
20
10
AV = 15.5dB
0
AV = 6dB
MAX98500 toc10
GAIN vs. FREQUENCY
30
-10
-20
-30
-40
0.1
1
10
100
1000
FREQUENCY (kHz)
6
2.4
OUTPUT POWER vs. BATTERY VOLTAGE
3.0
MAX98500 toc08
3.0
0.8
OUTPUT POWER (W)
FREQUENCY (kHz)
MAX98500 toc09
0.01
OUTPUT POWER (W)
MAX98500
Boosted 2.2W Class D Amplifier
with Automatic Level Control
______________________________________________________________________________________
5.5
Boosted 2.2W Class D Amplifier
with Automatic Level Control
0
MAX98500 toc11
0
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
VRIPPLE AT PVDD = 200mVP-P
INPUTS AC-COUPLED AGND
-20
SHUTDOWN RESPONSE
MAX98500 toc13
MAX98500 toc12
SPEAKER POWER-SUPPLY REJECTION
RATIO vs. FREQUENCY
ZLOAD = 8I + 68μH
-20
SDSPK
2V/div
CMRR (dB)
-60
-40
0V
AV = 6dB
-60
-80
-80
-100
-100
SPKR
OUTPUT
1V/div
0V
AV = 20dB
0.1
1
100
10
0.01
0.1
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
MAX98500 toc19
VBAT = 5V
VBAT = 3.3V
VBAT = 3V
-1.2
0
200 400 600 800 1000 1200 1400 1600
0
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
SWITCHING FREQUENCY (MHz)
MAX98500 toc20
5.52
5.50
5.49
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 0.1PF capacitor.
Boost Converter Output. Connect a 22PF (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 10PF (0805) capacitor between VBAT and BSTPGND.
Include at least 22PF 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 (VPEAK)
PEAK AMPLIFIER OUTPUT VOLTAGE
vs. BATTERY VOLTAGE
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
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
0
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
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
Click-and-Pop Suppression
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.
Shutdown
The MAX98500 features two active-low shutdown inputs
(SDSPK and SDBST). Table 2 shows the different shutdown configurations.
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 (O) in meters is given by:
O = 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
2SRINCIN
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
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
MAX98500
CONTROL
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
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.
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.
14
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
16 WLP
W162B2+1
21-0200
_____________________________________________________________________________________
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
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