Rainbow Electronics MAX98500 User Manual

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.

Features

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

Wide 2.5V to 5.5V Supply Voltage Range

S

S

Undervoltage Lockout Protection

S

High Total Efficiency of 87%

S

High Step-Up Switching Frequency (2MHz)

S

Active Emission Limiting for Low EMI

MAX98500

Applications

Cell Phones

Smartphones

GPS Devices

Ordering Information

PART TEMP RANGE PIN-PACKAGE

MAX98500EWE+

+Denotes a lead(Pb)-free/RoHS-compliant package.

-40NC to +85NC

16 WLP

Mobile Internet Devices

Active Speaker Accessories

Typical Application Circuit appears at end of data sheet.

Simplified Block Diagram

BATTERY

LXV

OUTPUT

STAGE

V

CCOUT

A2

A1

PVDD

B1

SPKP

C1

SPKN

SDBST

SDSPK

GAIN

RKNEE B3

INP D2

INN

BAT

B4 A3

D4

C3

B2

D3

CONTROL

DIFFERENTIAL

INPUT

C4 A4 D1, C2

AGND SPKPGNDBSTPGND

BOOST CONVERTER

MAX98500

GAIN

_______________________________________________________________ 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

ABSOLUTE MAXIMUM RATINGS

V

to AGND .........................................................-0.3V to +6V

BAT

V

to BSTPGND, AGND .................................-0.3V to +6V

CCOUT

PVDD to SPKPGND .................................................-0.3V to +6V

BSTPGND, SPKPGND to AGND ......................... -0.3V to +0.3V

GAIN to AGND ........................................-0.3V to (V

SDBST, SDSPK to AGND ...................................... -0.3V to V

BAT

+ 0.3V)

BAT

All Other Pins (excluding LX) to AGND ..................-0.3V to +6V

Current Into/Out of LX, V
Continuous Current Into/Out of SPK_, PVDD,

MAX98500

, BSTPGND ..................... Q3.9A

CCOUT

SPKPGND .................................................................. Q800mA

Continuous Input Current (all other pins) ........................ Q20mA

Duration of Short Circuit Between V

CCOUT

and BSTPGND ...................................................... Continuous

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-

layer 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

(V

= 3.6V, RL = J between SPKP and SPKN, AV = +6dB, CIN = 1FF, 20Hz to 22kHz AC measurement bandwidth, TA = T

BAT

T

, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2)

MAX

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Power-Supply Rejection Ratio
(Note 3)

Quiescent Current

Combined Efficiency
Shutdown Current I
Turn-On Time t

BOOST CONVERTER

Battery Supply Voltage Range V
Soft-Start Interval t
Undervoltage Lockout UVLO V
Boost Converter Output Voltage V
Output Current Limit I
Input Current Limit I
nMOS Current Limit I
pMOS Turn-Off Current Limit 10 mA
Switching Frequency f
Efficiency
Startup Short-Circuit Time Converter latch off 50 ms
Thermal Shutdown 165

LX Leakage Current

PSRR

I

VBAT

I

PVDD

SHDN

ON

BAT

ON

VCCOUTILOAD

MAX

LIMIT

LX,MAX

T

= +25NC, V

A

TA = +25NC, SDSPK = SDBST = V
T

= +25NC, V

A

TA = +25NC, PVDD = 5.55V, SDSPK =
SDBST = V

E P

OUT

V

SDSPK

Time from power-on to full operation 10 12 ms

BAT

V

BAT

Startup, V

S

E 0.1A P I

= 0V or 5.5V,

V

LX

V

CCOUT

BAT

= 1.7W, f = 1kHz, Z

= V

SDBST

falling 2.1 2.2 2.3 V

= 0mA 5.45 5.5 5.65 V

R = 3.6V

CCOUT

P 0.75A

OUT

= 5.5V

Duration of SPK_ Short Circuit to PVDD or

SPKPGND .............................................................. Continuous

Duration of Short Circuit Between SPKP

and SPKN ..............................................................Continuous

Continuous Power Dissipation, Multilayer Board (T

WLP (derate 20.4mW/NC above +70NC)........................1.33W

θ

(Note 1).................................................................49NC/W

JA

= +70NC)

A

Junction Temperature .....................................................+150NC

Operating Temperature Range .......................... -40NC to +85NC

Storage Temperature Range ............................ -65NC to +150NC

Soldering Temperature (reflow) ......................................+260NC

= 2.5V to 5.5V

BAT

= 0V, SDBST = V

SDSPK

BAT

BAT

95 dB

3.05

0.09 0.15

1.7 2.7

= 8I + 68FH

SPK

= 0V, TA = +25NC

87 %

0.04 1.5

2.5 5.5 V

5.6 ms

1.5 A

= 0V 0.3 0.5 A

3.3 A

1.8 2.0 2.2 MHz
93 %

= +25NC

T

A

-40NC P T

P +85NC

A

-1.0 +0.1 +1.0

0.1

MIN

mA

FA

NC

FA

to

2 ______________________________________________________________________________________

Boosted 2.2W Class D Amplifier

with Automatic Level Control

ELECTRICAL CHARACTERISTICS (continued)

(V

= 3.6V, RL = J between SPKP and SPKN, AV = +6dB, CIN = 1FF, 20Hz to 22kHz AC measurement bandwidth, TA = T

BAT

T

, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2)

MAX

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

SPEAKER AMPLIFIER

Output Offset Voltage V

Click-and-Pop Level K

Output Power (Note 5) P

Total Harmonic Distortion Plus
Noise

Output Switching Frequency 300 kHz

Gain A

Output Current Limit 2 A
Efficiency
Output Noise A-weighted 43

Input Resistance R

Common-Mode Rejection Ratio CMRR f = 1kHz 60 dB
Bias Voltage V

ALC

Attack Time 20
Release Time 1.6 s/dB
Maximum Attenuation 8 dB
Attenuation Resolution 0.5 dB

Knee Voltage V

OUT

THD+N

BIAS

KNEE

TA = +25NC

OS

Peak voltage, TA =
+25NC, A-weighted, 32
samples per second,

CP

Z

= 8I + 68FH,

SPK

(Notes 3, 4)

Z

= 8I + 68FH

SPK

f = 1kHz, P
Z

= 8I + 68FH

SPK

GAIN = AGND 5.5 6 6.5

V

GAIN = V

E P

IN

= 1.7W, f = 1kHz, Z

OUT

SDBST = SDSPK =
V

BAT

V

SDBST

TA = +25NC

= 850mW, TA = +25NC,

OUT

BAT

= V

SDSPK

Into shutdown -56

Out of shutdown -56

THD+N P 1%
THD+N P 10%

= 8I + 68FH

SPK

AV = 6dB
(GAIN = AGND)

= 15.5dB

A

V

(GAIN =
unconnected)

A

= 20dB

V

= 0V

(GAIN = V

All gain settings 110

R

= 154kI

KNEE

= 40.5kI

R

KNEE

R

= 13kI

KNEE

BAT

)

19.5 20 20.5

36 54 72

12 18 26

6.5 11 16

1.3 1.4 1.5 V

2.19 2.3 2.42

3.14 3.3 3.47

3.71 3.9 4.10

1 3 mV

1.7

2.2

0.05 %

92 %

MIN

dBV

W

dBGAIN = unconnected 15 15.5 16

FV

RMS

kI

Fs/dB

V

MAX98500

to

_______________________________________________________________________________________ 3

Boosted 2.2W Class D Amplifier
with Automatic Level Control

ELECTRICAL CHARACTERISTICS (continued)

(V

= 3.6V, RL = J between SPKP and SPKN, AV = +6dB, CIN = 1FF, 20Hz to 22kHz AC measurement bandwidth, TA = T

BAT

T

, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2)

MAX

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

= 3.25V 43.2

V

KNEE

V

= 3.35V 37.4

KNEE

= 3.45V 32.4

V

KNEE

= 3.55V 27.4

V

KNEE

= 3.65V 23.2

V

KNEE

= 3.75V 18.7

V

KNEE

= 3.85V 15.0

V

KNEE

Knee Resistor R

KNEE

MAX98500

DIGITAL INPUTS (SDBST, SDSPK)

Input Voltage High V
Input Voltage Low V
Input Capacitance C
Input Leakage Current I

Note 2: 100% production tested at T
Note 3: Amplifier inputs are AC-coupled to AGND.
Note 4: Mode transitions are controlled by SDSPK.

IN

= +25NC. Specifications over temperature limits are guaranteed by design.

A

iH

IL

IN

TA = +25NC,
A

= 15.5dB

V

TA = +25NC

1.4 V

0.4 V

10 pF

-1.0 +1.0

MIN

kI

FA

to

4 ______________________________________________________________________________________

Boosted 2.2W Class D Amplifier

with Automatic Level Control

Typical Operating Characteristics

(V

= 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = V

BAT

otherwise noted.)

General

BATTERY CURRENT

vs. BATTERY VOLTAGE

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

BATTERY CURRENT (mA)

1.0

0.5

0

2.5 5.5

INPUTS AC-COUPLED TO AGND
SDSPK = SDBST = V

BATTERY VOLTAGE (V)

BAT

MAX98500 toc01

5.04.54.03.53.0

, 20Hz to 22kHz AC measurement bandwidth, unless

BAT

BATTERY CURRENT

vs. BATTERY VOLTAGE

140

120

100

BATTERY CURRENT (µA)

80

60

2.5 5.5

INPUTS AC-COUPLED TO AGND
SDSPK = GND, SDBST = V

BATTERY VOLTAGE (V)

BAT

MAX98500 toc02

5.04.54.03.53.0

MAX98500

BATTERY CURRENT

vs. BATTERY VOLTAGE

10

INPUTS AC-COUPLED TO AGND

9

SDSPK = V

8

7

6

5

4

3

BATTERY CURRENT (µA)

2

1

0

2.5 5.5

, SDBST = AGND

BAT

BATTERY VOLTAGE (V)

MAX98500 toc03

5.04.54.03.53.0

EFFICIENCY vs. OUTPUT POWER

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0 2.5

V

BAT

V

= 3.0V

BAT

Z

LOAD

fIN = 1kHz

P

(W)

OUT

OV

OV

OV

V

= 4.2V

BAT

= 3.6V

= 8I + 68µH

2.01.51.00.5

TURN-ON RESPONSE

2ms/div

MAX98500 toc05

MAX98500 toc04

SDBST
2V/div

V

CCOUT

2V/div

SPKR
OUTPUT
1V/div

_______________________________________________________________________________________ 5

Boosted 2.2W Class D Amplifier
with Automatic Level Control

Typical Operating Characteristics (continued)

(V

= 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = V

BAT

otherwise noted.)

Speaker

, 20Hz to 22kHz AC measurement bandwidth, unless

BAT

10

MAX98500

1

0.1

THD+N (%)

0.01

0.001

0.01 100

OUTPUT POWER vs. LOAD RESISTANCE

3.0

2.5

2.0

1.5

1.0

OUTPUT POWER (W)

THD+N vs. FREQUENCY

Z

= 8I + 68µH

LOAD

P

= 1.4W

OUT

FREQUENCY (kHz)

THD+N = 1%

P

= 400mW

OUT

fIN = 1kHz
Z

SPRK

THD+N = 10%

1010.1

= LOAD + 68µF

MAX98500 toc06

MAX98500 toc08

100

Z

= 8I + 68µH

LOAD

10

1

THD+N (%)

0.1

0.01

0.001
0 2.4

f = 6kHz

f = 1kHz

f = 100Hz

OUTPUT POWER (W)

OUTPUT POWER vs. BATTERY VOLTAGE

3.0
fIN = 1kHz

= 8I + 68µH

Z

SPRK

2.5

2.0

THD+N vs. OUTPUT POWER

1.5

1.0

OUTPUT POWER (W)

THD+N = 1%

2.01.61.20.80.4

THD+N = 10%

MAX98500 toc07

MAX98500 toc09

0.5

0

1 1000

LOAD RESISTANCE (I)

10010

0.5

0

2.5 5.5
BATTERY VOLTAGE (V)

5.04.54.03.53.0

GAIN vs. FREQUENCY

30

Z

= 8I + 68µH

LOAD

20

10

0

GAIN (dB)

-10

-20

-30

-40

0.1 1000

AV = 20dB

MAX98500 toc10

AV = 15.5dB

AV = 6dB

100101

FREQUENCY (kHz)

6 ______________________________________________________________________________________

Boosted 2.2W Class D Amplifier

with Automatic Level Control

Typical Operating Characteristics (continued)

(V

= 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = V

BAT

otherwise noted.)

, 20Hz to 22kHz AC measurement bandwidth, unless

BAT

MAX98500

SPEAKER POWER-SUPPLY REJECTION

RATIO vs. FREQUENCY

0

V

AT PVDD = 200mV

RIPPLE

INPUTS AC-COUPLED AGND

-20

-40

PSRR (dB)

-60

-80

-100

0.01 100
FREQUENCY (kHz)

P-P

TURN-ON RESPONSE

SDBST = V

BAT

0V

COMMON-MODE REJECTION RATIO

0

vs. FREQUENCY

Z

= 8I + 68µH

LOAD

MAX98500 toc11

-20

-40

CMRR (dB)

-60

-80

1010.1

-100

0.01 100

MAX98500 toc14

SDSPK
2V/div

AV = 15.5dB

AV = 6dB

AV = 20dB

1010.1

FREQUENCY (kHz)

THD+N = 10%

0V

MAX98500 toc12

0V

0V

CLIPPING RESPONSE

SHUTDOWN RESPONSE

40µs/div

MAX98500 toc15

SPKR
OUTPUT
500mV/div

MAX98500 toc13

SDSPK
2V/div

SPKR
OUTPUT
1V/div

0V

1ms/div

WIDEBAND OUTPUT SPECTRUM

20

0

-20

-40

AMPLITUDE (dBV)

-60

-80

-100

0.1 1000

RBW = 100Hz
AUDIO INPUTS AC-GROUNDED

FREQUENCY (MHz)

100101

SPKR
OUTPUT
1V/div

MAX98500 toc16

200µs/div

INBAND OUTPUT SPECTRUM

0

fIN = 1kHz
OUTPUT = -60dBV

-20

-40

-60

AMPLITUDE (dBV)

-80

-100

-120
0 20

FREQUENCY (kHz)

MAX98500 toc17

15105

_______________________________________________________________________________________ 7

Boosted 2.2W Class D Amplifier
with Automatic Level Control

Typical Operating Characteristics (continued)

(V

= 3.6V, RL = ∞ between SPKP and SPKN, AV = +15.5dB, RKNEE = V

BAT

otherwise noted.)

Boost Converter

, 20Hz to 22kHz AC measurement bandwidth, unless

BAT

100

98

MAX98500

96

94

92

90

88

EFFICIENCY (%)

86

84

82

80

0 1600

OUTPUT VOLTAGE vs. OUTPUT CURRENT

5.52

5.51

5.50

5.49

5.48

5.47

OUTPUT VOLTAGE (V)

5.46

5.45

5.44
0 1600

EFFICIENCY vs. OUTPUT CURRENT

V

= 4.2V

BAT

V

= 4V

BAT

V

= 3.6V

BAT

V

= 3V

BAT

I

OUT

V

BAT

V

= 3V

BAT

V

= 3.3V

BAT

V

= 3.6V

BAT

I

OUT

(mA)

= 4.2V

(A)

V

= 5V

BAT

V

= 3.3V

BAT

14001200800 1000400 600200

V

= 5V

BAT

14001200200 400 600 800 1000

MAX98500 toc18

MAX98500 toc20

LOAD REGULATION vs. OUTPUT CURRENT

0.2

0

V

= 5V

BAT

-0.2

-0.4

-0.6

LOAD REGULATION (%)

-0.8
V

-1.0

-1.2

0 1600

BAT

= 3.6V

V

= 4.2V

BAT

V

= 4V

BAT

V

= 3.3V

BAT

V

= 3V

BAT

I

(mA)

OUT

SWITCHING FREQUENCY

vs. BATTERY VOLTAGE

2.04

2.02

I

= 100mA

OUT

2.00

I

= 500mA

1.98

SWITCHING FREQUENCY (MHz)

1.96

OUT

2.5 4.5
BATTERY VOLTAGE (V)

MAX98500 toc19

140012001000800600400200

MAX98500 toc21

4.34.13.93.73.53.33.12.92.7

SOFT-START

1ms/div

MAX98500 toc22

SDBST
2V/div

0V

V

CCOUT

2V/div

0V

8 ______________________________________________________________________________________

Boosted 2.2W Class D Amplifier

with Automatic Level Control

Pin Configuration

TOP VIEW

(BUMP SIDE DOWN)

MAX98500

V

2 3 41

CCOUT

LX BSTPGNDPVDD

+

A

MAX98500

B

SPKP

C

D

GAIN RKNEE V

SPKPGND

SDSPK

INP INNSPKPGND

WLP

BAT

AGNDSPKN

SDBST

Pin Description

BUMP NAME FUNCTION

A1 PVDD

A2 V

CCOUT

A3 LX Boost Switch Input
A4 BSTPGND Boost Power Ground
B1 SPKP Positive Speaker Output

B2 GAIN

B3 RKNEE ALC Knee Voltage Set Input. Set the ALC knee voltage with a resistor to AGND.

B4 V

BAT

C1 SPKN Negative Speaker Output

C2, D1 SPKPGND Speaker Ground

C3

SDSPK Speaker Output Shutdown. Drive SDSPK low to shutdown the speaker output.

C4 AGND Analog Ground
D2 INP Positive Audio Input
D3 INN Negative Audio Input

D4 SDBST

Speaker Amplifier Power Supply. Bypass to SPKPGND with a 0.1mF capacitor.

Boost Converter Output. Connect a 22mF (0805) capacitor between V

CCOUT

and

BSTPGND.

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 V

to set the speaker

BAT

gain to 20dB.

Battery Voltage Input. Connect a 10mF (0805) capacitor between V

and BSTPGND.

BAT

Include at least 22mF of system bulk capacitance.

Boost Converter Shutdown. Drive SDBST low to shutdown the boost converter and the
speaker output.

_______________________________________________________________________________________ 9

Boosted 2.2W Class D Amplifier
with Automatic Level Control

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.

MAX98500

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

5

4

3

2

1

PEAK AMPLIFIER OUTPUT VOLTAGE (V

0

Figure 1. Typical Tracking Function

4.0

3.9

3.8

3.7

3.6

(V)

3.5

KNEE

3.4

V

3.3

3.2

3.1

3.0

2.9

Figure 2. The Relationship of R

SLOPE

KNEE VOLTAGE

06

BATTERY VOLTAGE (V)

V

vs. R

KNEE

10 70

R

(kI)

KNEE

and V

KNEE

52341

KNEE

6050403020

KNEE

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

2

the I

R loss of the MOSFET on-resistance and quiescent

current overhead.

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.

Automatic Level Control

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 V

-swing is reduced by 3V/V.

PEAK

The knee voltage can be changed by applying different
resistors between RKNEE and AGND. The typical track­ing function is shifted horizontally with different R

KNEE

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.

GAIN Select

The MAX98500 features three internal gain settings that
are selectable with the GAIN input. Table 1 shows the
gain settings.

Table 1. Gain Settings

GAIN AMPLIFIER GAIN (dB)

AGND 6

Unconnected 15.5

V

BAT

20

10 _____________________________________________________________________________________

Boosted 2.2W Class D Amplifier

with Automatic Level Control

Table 2. Shutdown Configurations

SDBST SDSPK

Low Low Off Off

Low High Off Off
High Low On Off
High High On On

The MAX98500 features two active-low shutdown inputs
(SDSPK and SDBST). Table 2 shows the different shut­down configurations.

BOOST

STATUS

Click-and-Pop Suppression

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.

Current-Limit and Thermal Protection

The IC features overcurrent and thermal protection.
The IC shuts down when the V
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.

CCOUT

Boost Converter

The MAX98500 features a two-stage, soft-start, power­up sequence. When SDBST is taken high and V
above UVLO the soft-start first ramps V
to V
Once the V
switching turns on and ramps the V
(typ), see the Soft-Start graph in the Typical Operating
Characteristics. The maximum load current is available
after the soft-start is completed.

The undervoltage lockout (UVLO) circuit compares the
voltage at V
ensure that the input voltage is high enough for reliable
operation. Once the V

voltage with a battery current of 300mA (typ).

BAT

CCOUT

reaches the V

Undervoltage Lockout (UVLO)

with the UVLO threshold (2.2V typ) to

BAT

voltage exceeds the UVLO

BAT

voltage, the internal

BAT

CCOUT

SPEAKER

STATUS

Shutdown

output decreases

Soft-Start

is

BAT

quickly

CCOUT

to 5.5V in 5ms

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 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.

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 10
of interest.

8

m/s, and f = the RF frequency

MAX98500

______________________________________________________________________________________ 11

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

MAX98500

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 (C

An input capacitor, C
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:

Choose C
quency 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.

such that f

IN

, in conjunction with the input

IN

f

-3dB

-3dB

1

=

2 R C

π

IN IN

is well below the lowest fre-

IN

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 V

where f
factor given by D = 1 - (V
equation above results in a peak-to-peak inductor cur­rent ripple of 0.5 x I
current of 1.25 x I
tion) 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.

An output capacitor, C
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.

An input capacitor, C
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.

is the switching frequency, and D is the duty

SW

MAX98500

x D x (1-D))/(I

BATT

OUT

/(1 - D). Ensure the peak (satura-

OUT

VBAT

SPKP

SPKN

OUT(MAX

BAT/VOUT

/(1 - D), and a peak inductor

Output Capacitor (C

VCCOUT

, reduces the current peaks

). Using L from the

, is required to keep the

Input Capacitor (C

)

x fSW)

VCCOUT

VBAT

)

)

Figure 3. Optional Class D Ferrite Bead Filter

12 _____________________________________________________________________________________

Boosted 2.2W Class D Amplifier

with Automatic Level Control

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.

0.25mm

0.22mm

Figure 4. Recommended PCB Footprint

Bypass V

with a 10FF capacitor and a system

BAT

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.

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: Wafer-
Level 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

Typical Application Circuit

2.2µH

BATTERY

C

VBAT

C
1µF

C
1µF

IN

IN

10µF
0805
10%

SDBST

SDSPK

GAIN

RKNEE B3

INP D2

INN

D4

C3

B2

D3

CONTROL

DIFFERENTIAL

INPUT

C4 A4 D1, C2

AGND SPKPGNDBSTPGND

GAIN

22µF*

27.4kI
1%

*SYSTEM LEVEL REQUIREMENT

______________________________________________________________________________________ 13

20%

V

BAT

B4 A3

BOOST CONVERTER

MAX98500

OUTPUT

STAGE

LX

V

CCOUT

A2

A1

PVDD

B1

SPKP

C1

SPKN

0.1µF
10%

8I

C

VCCOUT

22µF
0805
10%

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

MAX98500

14 _____________________________________________________________________________________

Boosted 2.2W Class D Amplifier

with Automatic Level Control

Revision History

MAX98500

REVISION

NUMBER

0 5/10 Initial release —

REVISION

DATE

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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©

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