19-4536; Rev 0; 3/09
KIT
ATION
EVALU
E
L
B
A
AVAIL
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
Features
The MAX9875 combines a high-efficiency Class D
audio power amplifier with a stereo Class AB capacitorless DirectDrive® headphone amplifier. Maxim’s 3rd
generation, filterless Class D amplifier with active emissions limiting technology provides Class AB performance with Class D efficiency.
The MAX9875 delivers up to 725mW from a 3.7V supply
into an 8Ω load with 87% efficiency to extend battery life.
The filterless modulation scheme combined with active
emissions limiting circuitry and spread-spectrum modulation greatly reduces EMI while eliminating the need for
output filtering used in traditional Class D devices.
The stereo Class AB headphone amplifier in the
MAX9875 uses Maxim’s DirectDrive architecture, that
produces a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors, saving cost, space, and component height.
The device utilizes a user-defined input architecture,
three preamplifier gain settings, an input mixer, volume
control, comprehensive click-and-pop suppression, and
I2C control.
The MAX9875 is available in a thermally efficient,
space-saving 20-bump WLP package.
♦ Low Emissions, Filterless Class D Amplifier
Achieves Better than 10dB Margin Under EN55022
Class B Limits
♦ Low RF Susceptibility Design Rejects TDMA
Noise from GSM Radios
♦ Input Mixer with User-Defined Input Mode
♦ 725mW Speaker Output (RSPK = 8Ω, PVDD = 3.7V)
♦ 53mW Headphone Output (RHP = 16Ω, VDD = 3.7V)
♦ Low 0.05% THD+N at 1kHz (Class D Power
Amplifier)
♦ Low 0.016% THD+N at 1kHz (Headphone
Amplifier)
♦ 87% Efficiency (RSPK = 8Ω, POUT = 750mW)
♦ High Speaker Amplifier PSRR (72dB at 217Hz)
♦ High Headphone Amplifier PSRR (84dB at 217Hz)
♦ I2C Control
♦ Hardware and Software Shutdown Mode
♦ Click-and-Pop Suppression
♦ Current-Limit and Thermal Protection
♦ Available in a Space-Saving, 2.5mm x 2.0mm WLP
Package
Applications
Cell Phones
Portable Multimedia Players
DirectDrive is a registered trademark of Maxim Integrated
Products, Inc.
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX9875ERP+TG45
-40°C to +85°C
20 WLP (5x4)
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
G45 indicates protective die coating.
Simplified Block Diagram
SINGLE SUPPLY
2.7V TO 5.25V
VOLUME
CONTROL
PREAMPLIFIER
MIXER/MUX
TOP VIEW
(BUMP SIDE DOWN)
1
2
3
4
5
HPR
HPL
VSS
C1N
C1P
VDD
BIAS
SDA
N.C.
OUT+
INB2
INB1
SCL
PGND
PVDD
INA2
INA1
GND
N.C.
OUT-
A
B
VOLUME
CONTROL
I2C
INTERFACE
Pin Configuration
C
D
MAX9875
WLP
________________________________________________________________ Maxim Integrated Products
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.
1
MAX9875
General Description
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
ABSOLUTE MAXIMUM RATINGS
VDD, PVDD to PGND .............................................-0.3V to +5.5V
VDD to PVDD .........................................................-0.3V to +0.3V
VSS to PGND .........................................................-5.5V to +0.3V
C1N to PGND..............................................(VSS - 0.3V) to +0.3V
C1P to PGND...........................................-0.3V to (PVDD + 0.3V)
HPL, HPR to VSS
(Note 1)......-0.3V to the lower of (PVDD - (VSS + 0.3V)) or +9V
HPL, HPR to PVDD
(Note 2) .....+0.3V to the higher of (VSS - (PVDD - 0.3V)) or -9V
GND to PGND.....................................................................±0.3V
INA1, INA2, INB1, INB2, BIAS..................................-0.3V to +4V
SDA, SCL...............................................................-0.3V to +5.5V
All Other Pins to GND..............................-0.3V to (PVDD + 0.3V)
Continuous Current In/Out of PVDD, PGND, OUT_........±800mA
Continuous Current In/Out of HPR and HPL .....................140mA
Continuous Input Current VSS ...........................................100mA
Continuous Input Current (all other pins) .........................±20mA
Duration of OUT_ Short Circuit to GND or PVDD .......Continuous
Duration of Short Circuit Between OUT+ and OUT- ..Continuous
Duration of HP_ Short Circuit to GND or PVDD..........Continuous
Continuous Power Dissipation (TA = +70°C)
20-Bump WLP, 5 x 4, Multilayer Board
(derate 13.0mW/°C above +70°C) ..................................1.04W
Junction Temperature ......................................................+150°C
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: HPR and HPL should be limited to no more than 9V above VSS, or above PVDD + 0.3V, whichever limits first.
Note 2: HPR and HPL should be limited to no more than 9V below PVDD, or below VSS - 0.3V, whichever limits first.
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
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. ZSPK = ∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 3)
PARAMETER
Supply Voltage Range
SYMBOL
CONDITIONS
VDD, PVDD Guaranteed by PSRR test
HP mode,
OUTMODE = 2
Quiescent Current
Shutdown Current
IDD
ISHDN
MIN
OSC = 00
5.6
OSC = 10
5.5
SPK mode,
OUTMODE = 7
OSC = 00
6.6
OSC = 10
5.7
SPK + HP mode,
OUTMODE = 9
OSC = 00
10.4
OSC = 10
9.3
ISHDN = IVDD + IPVDD; SHDN = 0; VSDA =
VSCL = logic-high; TA = +25°C
10
OSC = 00
Turn-On Time
tON
BIAS Release Time
tBR
Input Resistance
RIN
Maximum Input Signal Swing
2
TYP
2.7
Time from shutdown to
full operation
MAX
UNITS
5.25
V
9.0
11.0
mA
16.0
22
µA
10
OSC = 01
10
OSC = 10
17.5
After forcing BIAS low, time from BIAS
released to I2C reset
ms
25
80
TA = +25°C, preamp gain = 0dB or +9dB
11
21
31
TA = +25°C, preamp gain = +20dB
3
5.5
8
Preamp = 0dB
2.30
Preamp = +9dB
0.820
Preamp = +20dB
0.230
_______________________________________________________________________________________
ms
kΩ
VP-P
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. ZSPK = ∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 3)
PARAMETER
Common-Mode Rejection Ratio
SYMBOL
CMRR
Input DC Voltage
CONDITIONS
fIN = 1kHz (differential
input mode)
TYP
Preamp = 0dB
47
Preamp = +9dB
49
Preamp = +20dB
42
IN__ inputs
Bias Voltage
MIN
MAX
UNITS
dB
1.22
1.3
1.38
V
1.13
1.2
1.27
V
TA = +25°C (volume at mute)
±0.5
±4
TA = +25°C (volume at 0dB,
OUTMODE = 1, ∆IN_ = 0)
±1.5
VBIAS
SPEAKER AMPLIFIER (OUTMODE = 1)
Output Offset Voltage
Click-and-Pop Level
VOS
KCP
Peak voltage, TA =
+25°C, A-weighted, 32
samples per second,
volume at mute (Note 4)
Into shutdown
-70
Out of shutdown
-70
dBV
PVDD = VDD =
2.7V to 5.5V
Power-Supply Rejection Ratio
(Note 4)
Output Power (Note 5)
Total Harmonic Distortion Plus
Noise
PSRR
POUT
THD+N
TA = +25°C, PVDD =
VDD
THD+N ≤ 1%
Signal-to-Noise Ratio
SNR
A-weighted,
OUTMODE = 7, 9
50
76
f = 217Hz,
100mVP-P ripple
72
f = 1kHz,
100mVP-P ripple
68
f = 20kHz,
100mVP-P ripple
55
ZSPK = 8Ω +
68µH, VDD = 3.7V
725
ZSPK = 8Ω +
68µH, VDD = 3.3V
560
ZSPK = 8Ω +
68µH, VDD = 3.0V
465
ZSPK = 4Ω +
33µH, VDD = 3.7V
825
ZSPK = 4Ω +
33µH, VDD = 3.0V
770
f = 1kHz, POUT = 350mW, TA = +25°C,
ZSPK = 8Ω + 68µH
A-weighted,
OUTMODE = 1, 3,
4, 6
mV
dB
0.05
∆IN_ = 0
(single-ended)
92
∆IN_ = 1 (differential)
94
∆IN_ = 0
(single-ended)
88
∆IN_ = 1 (differential)
92
mW
%
dB
_______________________________________________________________________________________
3
MAX9875
ELECTRICAL CHARACTERISTICS (continued)
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. ZSPK = ∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 3)
PARAMETER
SYMBOL
Output Frequency
CONDITIONS
MIN
Spread-spectrum modulation mode,
OSC = 00
1176
±60
Fixed-frequency mode, OSC = 01
1100
Fixed-frequency mode, OSC = 10
700
Current Limit
Efficiency
Speaker Gain
η
POUT = 600mW, f = 1kHz
AV
11.5
A-weighted, OUTMODE = 1, ∆IN_ = 0
(Note 4)
Output Noise
TYP
MAX
UNITS
kHz
1.5
A
87
%
12.0
12.5
63
dB
µVRMS
HEADPHONE AMPLIFIERS (OUTMODE = 2)
Output Offset Voltage
Click-and-Pop Level
VOS
KCP
TA = +25°C (volume at mute)
±0.15
TA = +25°C (volume at 0dB)
±1.6
Peak voltage, TA =
+25°C, A-weighted,
32 samples per
second. volume at
mute (Note 4)
Into shutdown
-80
Out of shutdown
-80
Output Power
Headphone Gain
PSRR
POUT
THD+N ≤ 1%
THD+N
f = 1kHz,
VRIPPLE = 100mVP-P
80
f = 20kHz,
VRIPPLE = 100mVP-P
62
RHP = 16Ω
53
RHP = 32Ω
27
dB
mW
0
+0.4
dB
TA = +25°C, HPL to HPR, volume at 0dB,
OUTMODE = 2, 5; ∆IN_ = 0
±0.3
±2.5
%
RHP = 32Ω (POUT = 10mW, f = 1kHz)
0.016
RHP = 16Ω (POUT = 10mW, f = 1kHz),
TA = +25°C
0.03
SNR
A-weighted, RHP =
16Ω, OUTMODE =
8, 9
4
85
84
-0.4
A-weighted,
OUTMODE = 2, 3,
5, 6; RHP = 16Ω
Signal-to-Noise Ratio
70
f = 217Hz,
VRIPPLE = 100mVP-P
AV
Channel-to-Channel Gain
Tracking
Total Harmonic Distortion Plus
Noise
TA = +25°C, PVDD =
VDD
mV
dBV
PVDD = VDD = 2.7V
to 5.25V
Power-Supply Rejection Ratio
(Note 4)
±0.6
∆IN_ = 0
(single-ended)
98
∆IN_ = 1 (differential)
98
∆IN_ = 0
(single-ended)
96
∆IN_ = 1 (differential)
96
_______________________________________________________________________________________
%
dB
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. ZSPK = ∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Slew Rate
SR
0.35
Capacitive Drive
CL
100
pF
65
dB
Crosstalk
HPL to HPR, HPR to HPL, f = 20Hz to 20kHz
Spread-spectrum modulation mode,
OSC = 00
Charge-Pump Frequency
V/µs
588
±30
Fixed-frequency mode, OSC = 01
430
550
670
Fixed-frequency mode, OSC = 10
220
350
500
kHz
VOLUME CONTROL
Minimum Setting
_VOL = 1
-75
dB
Maximum Setting
_VOL = 31
0
dB
PGAIN_ = 00
Preamp Gain
Input A or B
Mute Attenuation
f = 1kHz, _VOL = 0
Zero-Crossing Detection Timeout
ZCD = 1
0
PGAIN_ = 01
9
PGAIN_ = 10
20
Speaker
100
Headphone
110
dB
dB
60
ms
DIGITAL INPUTS
Input-Voltage High (SDA, SCL)
VH
Input-Voltage Low (SDA, SCL)
VL
1.4
0.4
V
V
Input-Voltage Low (BIAS)
VBL
0.15
V
Input Hysteresis (SDA, SCL)
VHYS
80
SDA, SCL Input Capacitance
CIN
4
Input Leakage Current
IIN
BIAS Pullup Current
SDA, SCL; TA = +25°C
mV
pF
±1.0
IBIAS
94
µA
µA
DIGITAL OUTPUTS (SDA Open Drain)
Output Low Voltage SDA
Output Fall Time SDA
VOL
ISINK = 3mA
0.4
V
tOF
VH(MIN) to VL(MAX) bus capacitance = 10pF
to 400pF, ISINK = 3mA
250
ns
1.7
3.6
V
400
kHz
2-WIRE INTERFACE TIMING
External Pullup Voltage Range:
SDA and SCL
Serial Clock Frequency
fSCL
DC
Bus Free Time Between STOP
and START Conditions
tBUF
1.3
µs
START Condition Hold
tHD:STA
0.6
µs
START Condition Setup Time
tSU:STA
0.6
µs
Clock Low Period
tLOW
1.3
µs
Clock High Period
tHIGH
0.6
µs
_______________________________________________________________________________________
5
MAX9875
ELECTRICAL CHARACTERISTICS (continued)
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. ZSPK = ∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
Data Setup Time
tSU:DAT
100
Data Hold Time
tHD:DAT
0
TYP
MAX
UNITS
900
ns
ns
Maximum Receive SCL/SDA Rise
Time
tR
300
ns
Maximum Receive SCL/SDA Fall
Time
tF
300
ns
Setup Time for STOP Condition
tSU:STO
Capacitive Load for Each Bus
Line
Cb
0.6
µs
400
pF
Note 3: All devices are 100% production tested at room temperature. All temperature limits are guaranteed by design.
Note 4: Amplifier inputs are AC-coupled to GND.
Note 5: Output levels higher than 825mW are not recommended for extended durations. Production tested with ZSPK = 8Ω + 68µH only.
6
_______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
GENERAL
6
8
7
6
11
10
fOSC = 700kHz
9
4
8
4
3.0
3.5
4.0
4.5
5.0
5.5
fOSC = 1100kHz
7
2.5
SUPPLY VOLTAGE (V)
3.0
3.5
4.0
4.5
5.0
2.5
5.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
VOLUME ATTENUATION
vs. _VOL CONTROL CODE
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
12
11
10
9
20
MAX9875 toc05
INPUTS AC-COUPLED TO GND
VSDA = VSCL = 3.3V
0
VOLUME ATTENUATION (dB)
MAX9875 toc04
14
13
fOSC = 1176kHz
SPREAD-SPECTRUM MODE
fOSC = 700kHz
fOSC = 1100kHz
5
fOSC = 700kHz
2.5
HEADPHONE AND SPEAKER
INPUTS AC-COUPLED TO GND
OUTMODE = 9
VSDA = VSCL = 3.3V
12
fOSC = 1176kHz
SPREAD-SPECTRUM MODE
fOSC = 1100kHz
5
13
MAX9875 toc02
SPEAKER ONLY
INPUTS AC-COUPLED TO GND
OUTMODE = 7
VSDA = VSCL = 3.3V
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
9
fOSC = 1176kHz SREAD-SPECTRUM MODE
SHUTDOWN CURRENT (µA)
SUPPLY CURRENT (mA)
HEADPHONE ONLY
INPUTS AC-COUPLED TO GND
OUTMODE = 8
VSDA = VSCL = 3.3V
7
10
MAX9875 toc01
9
8
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9875 toc03
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
-20
-40
-60
-80
fIN = 1kHz
MEASURED AT HPL
AND HPR
-100
8
-120
7
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
35
30
25
20
15
10
5
0
_VOL CONTROL CODE
_______________________________________________________________________________________
7
MAX9875
Typical Operating Characteristics
Typical Operating Characteristics (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
SPEAKER AMPLIFIER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
VDD = VPVDD = 3.7V
ZSPK = 8Ω + 68µH
VDD = VPVDD = 3.7V
ZSPK = 4Ω + 33µH
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
10
1
POUT = 675mW
THD+N (%)
POUT = 200mW
POUT = 1100mW
0.1
0.1
VDD = VPVDD = 3V
ZSPK = 8Ω + 68µH
1
THD+N (%)
THD+N (%)
1
MAX9875 toc08
10
MAX9875 toc06
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc07
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
POUT = 425mW
0.1
POUT = 650mW
POUT = 200mW
0.01
0.01
10
100
1k
0.01
10
100k
10k
100
1k
100k
10k
100
10
1k
10k
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
1
10
MAX9875 toc10
VDD = VPVDD = 3V
ZSPK = 4Ω + 33µH
VDD = VPVDD = 3.7V
POUT = 200mW
ZSPK = 8Ω + 68µH
fOSC = 700kHz
MAX9875 toc11
FREQUENCY (Hz)
1
VDD = VPVDD = 5V
ZSPK = 8Ω + 68µH
fIN = 6kHz
POUT = 700mW
THD+N (%)
THD+N (%)
1
0.1
fOSC = 1176kHz
0.1
fIN = 20Hz
0.1
POUT = 250mW
fOSC = 1100kHz
0.01
1k
10k
100k
10
FREQUENCY (Hz)
100
1k
10k
0.5
1.5
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
MAX9875 toc12
VDD = VPVDD = 5V
ZSPK = 4Ω + 33µH
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
1.0
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
0
100k
FREQUENCY (Hz)
1
MAX9875 toc13
100
fIN = 1kHz
0.01
0.01
10
VDD = VPVDD = 3.7V
ZSPK = 8Ω + 68µH
THD+N (%)
THD+N (%)
1
fIN = 20Hz
fIN = 6kHz
0.1
fIN = 20Hz
0.1
fIN = 6kHz
fIN = 1kHz
fIN = 1kHz
0.01
0.01
0
0.5
1.0
1.5
2.0
OUTPUT POWER (W)
8
100k
FREQUENCY (Hz)
MAX9875 toc09
10
THD+N (%)
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
2.5
3.0
0
200
400
600
800
OUTPUT POWER (mW)
_______________________________________________________________________________________
1000
2.0
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
VDD = VPVDD = 3.7V
ZSPK = 4Ω + 33µH
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
1
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
MAX9875 toc15
10
MAX9875 toc14
VDD = VPVDD = 3V
ZSPK = 8Ω + 68µH
fIN = 6kHz
0.1
THD+N (%)
1
THD+N (%)
fIN = 20Hz
0.1
fIN = 1kHz
fIN = 1kHz
0.01
0.01
0.5
1.0
1.5
0.01
0
200
400
600
0
0.4
0.6
0.8
1.0
OUTPUT POWER (mW)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
EFFICIENCY
vs. OUTPUT POWER
1
100
MAX9875 toc18
VDD = VPVDD = 3.7V
fIN = 1kHz
ZSPK = 8Ω + 68µH
fOSC = 1100kHz
90
80
fOSC = 1176kHz SSM
0.1
EFFICIENCY (%)
THD+N (%)
fOSC = 700kHz
0.1
fOSC = 1176kHz SSM
VDD = VPVDD = 3.7V
fIN = 6kHz
ZSPK = 8Ω + 68µH
fOSC = 1100kHz
0.01
200
400
600
60
800
40
10
200
400
600
0
800
80
100
ZSPK = 4Ω + 33µH
50
40
2.0
2.5
3.0
80
70
60
fOSC = 1176kHz AND 1100kHz
50
40
30
VDD = VPVDD = 3.7V
fIN = 1kHz
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
10
1.5
fOSC = 700kHz
90
EFFICIENCY (%)
70
ZSPK = 8Ω + 68µH
1.0
EFFICIENCY
vs. OUTPUT POWER
MAX9875 toc20
90
20
0.5
OUTPUT POWER (W)
EFFICIENCY
vs. OUTPUT POWER
30
VDD = VPVDD = 5V
fIN = 1kHz
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
OUTPUT POWER (mW)
100
ZSPK = 4Ω + 33µH
0
0
OUTPUT POWER (mW)
60
ZSPK = 8Ω + 68µH
50
20
0.01
0
1.2
70
30
fOSC = 700kHz
EFFICIENCY (%)
THD+N (%)
0.2
OUTPUT POWER (W)
MAX9875 toc17
1
fIN = 6kHz
0.1
fIN = 6kHz
fIN = 1kHz
0
fIN = 20Hz
MAX9875 toc19
THD+N (%)
1
fIN = 20Hz
VDD = VPVDD = 3V
ZSPK = 4Ω + 33µH
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
MAX9875 toc21
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9875 toc16
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
VDD = VPVDD = 3.7V
fIN = 1kHz
ZSPK = 8Ω + 68µH
20
10
0
0
0
0.5
1.0
OUTPUT POWER (W)
1.5
2.0
0
200
400
600
800
1000
OUTPUT POWER (mW)
_______________________________________________________________________________________
9
MAX9875
Typical Operating Characteristics (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
OUTPUT POWER
vs. SUPPLY VOLTAGE
ZSPK = 4Ω + 33µH
ZSPK = 8Ω + 68µH
50
40
30
10
1.5
1.0
VDD = VPVDD = 3V
fIN = 1kHz
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
20
10% THD+N
2.0
1% THD+N
200
400
600
800
10% THD+N
1.0
0.8
0.6
1% THD+N
0
2.5
1000
3.0
3.5
4.0
4.5
5.0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
OUTPUT POWER (mW)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
OUTPUT POWER
vs. LOAD RESISTANCE
OUTPUT POWER
vs. LOAD RESISTANCE
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
1.0
OUTPUT POWER (W)
1.4
1.2
1.0
10% THD+N
0.6
VDD = VPVDD = 3V
fIN = 1kHz
ZSPK = LOAD + 68µH
0
VDD = VPVDD = 3.7V
VRIPPLE = 100mVP-P
INPUTS AC-COUPLED TO GND
-10
-20
5.5
-30
0.8
0.6
PSRR (dB)
1.6
1.2
MAX9875 toc26
VDD = VPVDD = 3.7V
fIN = 1kHz
ZSPK = LOAD + 68µH
MAX9875 toc25
1.8
0.8
1.2
0.2
0
0
1.4
0.4
0.5
0
10% THD+N
0.4
1% THD+N
-40
-50
-60
-70
1% THD+N
0.4
-80
0.2
0.2
-90
0
-100
0
10 20 30 40 50 60 70 80 90 100
0
LOAD RESISTANCE (Ω)
-40
-60
-80
fOSC = 700kHz
fIN = 1kHz
-20
AMPLITUDE (dBV)
AMPLITUDE (dBV)
10k
IN-BAND OUTPUT SPECTRUM
0
MAX9875 toc28
fOSC = 1100kHz
fIN = 1kHz
-20
1k
FREQUENCY (Hz)
LOAD RESISTANCE (Ω)
IN-BAND OUTPUT SPECTRUM
0
100
10
10 20 30 40 50 60 70 80 90 100
MAX9875 toc29
0
-40
-60
-80
-100
-100
-120
-120
-140
-140
0
5
10
FREQUENCY (kHz)
10
1.6
MAX9875 toc27
60
2.5
VDD = VPVDD
ZSPK = 8Ω + 68µH
1.8
OUTPUT POWER (W)
70
2.0
MAX9875 toc23
80
VDD = VPVDD
ZSPK = 4Ω + 33µH
DASHED LINES ARE LIMITED
BY THE ABS. MAX RATINGS
3.0
OUTPUT POWER (W)
90
EFFICIENCY (%)
3.5
MAX9875 toc22
100
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9875 toc24
EFFICIENCY
vs. OUTPUT POWER
OUTPUT POWER (W)
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
15
20
0
5
10
15
FREQUENCY (kHz)
______________________________________________________________________________________
20
100k
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
IN-BAND OUTPUT SPECTRUM
-20
AMPLITUDE (dBV)
AMPLITUDE (dBV)
-40
-60
-80
fOSC = 1100kHz
INPUTS AC-COUPLED TO GND
-10
MAX9875 toc31
fOSC = 1176kHz
fIN = 1kHz
-20
WIDEBAND OUTPUT SPECTRUM
0
MAX9875 toc30
0
-30
-40
-50
-60
-70
-100
-80
-120
-90
-140
-100
10
15
20
0.1
FREQUENCY (kHz)
WIDEBAND OUTPUT SPECTRUM
-10
fOSC = 700kHz
INPUTS AC-COUPLED TO GND
-10
-40
-50
-60
-40
-50
-60
-70
-80
-80
-90
-90
-100
-100
1
10
100
0.1
1
10
FREQUENCY (MHz)
FREQUENCY (MHz)
HARDWARE SHUTDOWN RESPONSE
SOFTWARE SHUTDOWN
ON- AND OFF-RESPONSE
VBIAS
500mV/div
OUT+ - OUT1V/div
100
-30
-70
0.1
fOSC = 1176kHz
INPUTS AC-COUPLED TO GND
-20
AMPLITUDE (dBV)
-30
MAX9875 toc34
AMPLITUDE (dBV)
-20
10
WIDEBAND OUTPUT SPECTRUM
0
MAX9875 toc32
0
1
FREQUENCY (MHz)
MAX9875 toc33
5
100
MAX9875 toc35
0
VSDA
2V/div
OUT+ - OUT1V/div
20ms/div
20ms/div
______________________________________________________________________________________
11
MAX9875
Typical Operating Characteristics (continued)
Typical Operating Characteristics (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
HEADPHONE AMPLIFIER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
VDD = VPVDD = 3.7V
RHP = 32Ω
VDD = VPVDD = 3.7V
RHP = 16Ω
1
0.1
THD+N (%)
POUT = 10mW
POUT = 20mW
POUT = 10mW
0.01
0.01
POUT = 20mW
0.001
10
100
1k
10k
0.01
POUT = 20mW
POUT = 40mW
0.001
10
100k
VDD = VPVDD = 3V
RHP = 32Ω
0.1
THD+N (%)
THD+N (%)
0.1
MAX9875 toc38
1
MAX9875 toc36
0
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc37
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
100
1k
0.001
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
VDD = VPVDD = 3V
RHP = 16Ω
10
MAX9875 toc40
10
MAX9875 toc39
1
VDD = VPVDD = 3.7V
RHP = 32Ω
MAX9875 toc41
FREQUENCY (Hz)
VDD = VPVDD = 3.7V
RHP = 16Ω
1
1
POUT = 15mW
THD+N (%)
THD+N (%)
0.1
THD+N (%)
fIN = 20Hz
0.1
fIN = 20Hz AND 1kHz
0.1
0.01
0.01
0.01
0.001
0.001
0.001
100
1k
10k
100k
0
FREQUENCY (Hz)
10
20
30
0
40
10
MAX9875 toc42
VDD = VPVDD = 3V
RHP = 32Ω
30
40
50
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
1
VDD = VPVDD = 3V
RHP = 16Ω
THD+N (%)
1
fIN = 20Hz
0.1
0.01
fIN = 20Hz AND 1kHz
0.1
0.01
fIN = 6kHz
fIN = 6kHz
fIN = 1kHz
0.001
0.001
0
10
20
OUTPUT POWER (mW)
12
20
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
10
OUTPUT POWER (mW)
MAX9875 toc43
10
fIN = 6kHz
fIN = 1kHz fIN = 6kHz
POUT = 30mW
THD+N (%)
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
30
40
0
10
20
30
40
OUTPUT POWER (mW)
______________________________________________________________________________________
50
60
60
70
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
RHP = 16Ω
200
150
100
VDD = VPVDD = 3.7V
fIN = 1kHz
POUT = PHPL + PHPR
RHP = 32Ω
MAX9875 toc45
100
35
30
25
20
10
5
0
0
0
50
100
150
0
50
100
3.0
3.5
4.0
4.5
5.0
OUTPUT POWER (mW)
SUPPLY VOLTAGE (V)
OUTPUT POWER
vs. SUPPLY VOLTAGE
OUTPUT POWER
vs. LOAD RESISTANCE
OUTPUT POWER
vs. LOAD RESISTANCE
1% THD+N
30
50
40
30
20
20
10
10
0
0
3.0
3.5
4.0
4.5
5.0
10% THD+N
5.5
70
20
30
40
50
60
70
80
10
90 100
20
30
40
50
60
70
80
90 100
LOAD RESISTANCE (Ω)
0
-10
40
30
VDD = VPVDD = 3.7V
VRIPPLE = 100mVP-P
RHP = 32Ω
INPUTS AC-COUPLED TO GND
-20
-30
-40
PSRR (dB)
C1 = C2 = 2.2µF
-50
-60
-70
-80
HPR
-90
-100
20
C1 = C2 = 0.47µF
-110
-120
0
40
1% THD+N
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
50
30
30
10
MAX9875 toc50
80
20
40
LOAD RESISTANCE (Ω)
VDD = VPVDD = 3V
OSC = 10
fIN = 1kHz
1% THD+N
10
10% THD+N
50
0
10
100
10
60
20
OUTPUT POWER
vs. LOAD RESISTANCE
60
70
1% THD+N
SUPPLY VOLTAGE (V)
90
5.5
MAX9875 toc51
50
80
70
60
VDD = VPVDD = 3V
fIN = 1kHz
90
OUTPUT POWER (mW)
60
100
MAX9875 toc48
80
70
40
VDD = VPVDD = 3.7V
fIN = 1kHz
90
OUTPUT POWER (mW)
10% THD+N
80
100
MAX9875 toc47
fIN = 1kHz
RHP = 16Ω
90
OUTPUT POWER (mW)
2.5
150
OUTPUT POWER (mW)
100
2.5
1% THD+N
15
VDD = VPVDD = 3V
fIN = 1kHz
POUT = PHPL + PHPR
RHP = 32Ω
10% THD+N
40
RHP = 16Ω
150
50
0
OUTPUT POWER (mW)
200
fIN = 1kHz
RHP = 32Ω
45
MAX9875 toc49
250
50
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
300
POWER DISSIPATION (mW)
250
MAX9875 toc44
350
50
OUTPUT POWER
vs. SUPPLY VOLTAGE
POWER DISSIPATION
vs. OUTPUT POWER
MAX9875 toc46
POWER DISSIPATION
vs. OUTPUT POWER
50
60
70
LOAD RESISTANCE (Ω)
80
90 100
HPL
10
100
1k
10k
100k
FREQUENCY (Hz)
______________________________________________________________________________________
13
MAX9875
Typical Operating Characteristics (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VDD = VPVDD = 3.7V, VGND = VPGND = 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (ZSPK) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. ZSPK =
∞, RHP = ∞. C1 = C2 = CBIAS = 1µF. TA = +25°C, unless otherwise noted.)
OUTPUT SPECTRUM
-40
-60
-80
-40
-60
-80
-100
-100
-120
-120
-140
-140
5
10
15
20
5
10
15
FREQUENCY (kHz)
CROSSTALK vs. FREQUENCY
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
VDD = VPVDD = 3.7V
VINA_ = 1VP-P
RHP = 16Ω
20
80
MAX9875 toc55
0
-10
-20
-30
-40
-50
-60
0
FREQUENCY (kHz)
MAX9875 toc54
0
70
+9dB
60
CMRR (dB)
HPR TO HPL
-70
-80
-90
0dB
50
40
30
+20dB
20
HPL TO HPR
-100
-110
-120
VDD = VPVDD = 3.7V
CMRR = 20log(ADM/ACM)
10
0
100
1k
10k
100k
10
100
1k
10k
FREQUENCY (Hz)
HARDWARE SHUTDOWN RESPONSE
SOFTWARE SHUTDOWN
ON- AND OFF-REPSONSE
VBIAS
500mV/div
VBIAS
500mV/div
HPL
500mV/div
HPL
500mV/div
HPR
500mV/div
HPR
500mV/div
20ms/div
100k
MAX9875 toc57
FREQUENCY (Hz)
MAX9875 toc56
10
14
VDD = VPVDD = 3.7V
fIN = 1kHz
RHP = 16Ω
-20
AMPLITUDE (dBV)
AMPLITUDE (dBV)
MAX9875 toc52
VDD = VPVDD = 3.7V
fIN = 1kHz
RHP = 32Ω
-20
0
MAX9875 toc53
OUTPUT SPECTRUM
0
CROSSTALK (dB)
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
20ms/div
______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
PIN
NAME
FUNCTION
A1
HPR
A2
HPL
Left Headphone Output
A3
VSS
Headphone Amplifier Negative Power Supply. Bypass with a 1µF capacitor to PGND.
A4
C1N
Charge-Pump Flying Capacitor Negative Terminal. Connect a 1µF capacitor between C1P and C1N.
A5
C1P
Charge-Pump Flying Capacitor Positive Terminal. Connect a 1µF capacitor between C1P and C1N.
B1
VDD
Analog Supply. Connect to PVDD. Bypass with a 1µF capacitor to GND.
B2
BIAS
Common-Mode Bias. Bypass to GND with a 1µF capacitor. Pulse low to reset the part and place in
shutdown (see the Typical Application Circuit).
B3
SDA
Serial-Data Input. Connect a pullup resistor from SDA to a 1.7V to 3.6V supply.
B4
N.C.
No Connection
B5
OUT+
Positive Speaker Output
C1
INB2
Input B2. Right input or positive input (see the Differential Input Configuration (∆IN_) section).
C2
INB1
Input B1. Left input or negative input (see the Differential Input Configuration (∆IN_) section).
C3
SCL
Serial-Clock Input. Connect a pullup resistor from SCL to a 1.7V to 3.6V supply.
C4
PGND
Power Ground
C5
PVDD
Class D and Charge-Pump Power Supply. Bypass with a 1µF capacitor to PGND.
D1
INA2
Input A2. Right input or positive input (see the Differential Input Configuration (∆IN_) section).
D2
INA1
Input A1. Left input or negative input (see the Differential Input Configuration (∆IN_) section).
D3
GND
Analog Ground
D4
N.C.
No Connection
D5
OUT-
Negative Speaker Output
Right Headphone Output
Detailed Description
Signal Path
The MAX9875 signal path consists of flexible inputs,
signal mixing, volume control, and output amplifiers
(Figure 1).
The inputs can be configured for single-ended or differential signals (Figure 2). The internal preamplifiers feature three programmable gain settings of 0dB, +9dB,
and +20dB. Following preamplification, the input signals are mixed, volume adjusted, and routed to the
headphone and speaker amplifiers based on the output mode configuration (see Table 7). The volume control stages provide up to 75dB attenuation. The
headphone amplifier is configured as a unity-gain
buffer while the speaker amplifier provides +12dB of
additional gain.
When an input is configured as mono differential it can
be routed to the speaker or to both headphones. When
an input is stereo, it is mixed to mono without attenuation
for the speaker and kept stereo for the headphones.
When the application does not require the use of both
INA_ and INB_, the SNR of the MAX9875 is improved
by deselecting the unused input through the I2C output
mode register and AC-coupling the unused inputs to
ground with a 330pF capacitor. The 330pF capacitor
and the input resistance to the MAX9875 form a highpass filter preventing audible noise from coupling into
the outputs.
______________________________________________________________________________________
15
MAX9875
Pin Description
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
INA2
INA1
INB2
INB1
INPUT A
0dB/+9dB/+20dB
0dB
HPR
0dB
HPL
-75dB TO 0dB
MIXER
AND
MUX
INPUT B
0dB/+9dB/+20dB
-75dB TO 0dB
OUT+
+12dB
OUT-75dB TO 0dB
Figure 1. Signal Path
STEREO SINGLE-ENDED
IN_2 (R)
R
TO MIXER
IN_1 (L)
L
DIFFERENTIAL
IN_2 (+)
IN_1 (-)
TO MIXER
Figure 2. Differential and Stereo Single-Ended Input Configurations
16
______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
dV/dt normally results in decreased efficiency. Maxim’s
active emissions limiting circuitry actively limits the
dV/dt of the rising and falling edge transitions, providing reduced EMI emissions, while maintaining up to
87% efficiency.
In addition to active emission limiting, the MAX9875
features a spread-spectrum modulation mode that flattens the wideband spectral components. Proprietary
techniques ensure that the cycle-to-cycle variation of
the switching period does not degrade audio reproduction or efficiency (see the Typical Operating
Characteristics). Select spread-spectrum modulation
mode through the I2C interface (Table 6). In spreadspectrum modulation mode, the switching frequency
varies randomly by ±60kHz around the center frequency (1.176MHz). The effect is to reduce the peak energy
at harmonics of the switching frequency. Above
10MHz, the wideband spectrum looks like white noise
for EMI purposes (see Figure 4).
Class D Speaker Amplifier
The MAX9875 integrates a filterless Class D amplifier
that offers much higher efficiency than Class AB without the typical disadvantages.
The high efficiency of a Class D amplifier is due to the
switching operation of the output stage transistors. In a
Class D amplifier, the output transistors act as currentsteering switches and consume negligible additional
power. 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.
The theoretical best efficiency of a linear amplifier is
78%, however, that efficiency is only exhibited at peak
output power. Under normal operating levels (typical
music reproduction levels), efficiency falls below 30%,
whereas the MAX9875 still exhibits 70% efficiency
under the same conditions (Figure 3).
Speaker Current Limit
Most applications will not enter current limit unless the
output is short circuited or connected incorrectly.
When the output current of the speaker amplifier
exceeds the current limit (1.5A, typ) the MAX9875 disables the outputs for approximately 250µs. At the end of
250µs, the outputs are re-enabled, if the fault condition
still exists, the MAX9875 will continue to disable and reenable the outputs until the fault condition is removed.
Ultra-Low EMI Filterless Output Stage
In traditional Class D amplifiers, the high dV/dt of the
rising and falling edge transitions results in increased
EMI emissions, which requires the use of external LC
filters or shielding to meet EN55022 electromagneticinterference (EMI) regulation standards. Limiting the
MAX9875 EFFICIENCY
vs. IDEAL CLASS EFFICIENCY
MAX9875 fig03
100
90
EFFICIENCY (%)
80
70
MAX9875
60
50
IDEAL CLASS AB
40
30
20
VDD = VPVDD = 3.7V (MAX9875)
VSUPPLY = 3.7V (IDEAL CLASS AB)
10
0
0
0.25
0.50
0.75
1.00
OUTPUT POWER (W)
Figure 3. MAX9875 Efficiency vs. Class AB Efficiency
______________________________________________________________________________________
17
MAX9875
Volume Control and Mute
The MAX9875 features three volume control registers
(see Table 4) allowing independent volume control of
mono speaker and stereo headphone amplifier outputs.
Each volume control register has 31 steps providing 0 to
75dB (typ) of attenuation and a mute function.
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
40
TEST LIMIT
AMPLITUDE (dB∝V/m)
35
30
25
20
MAX9875 OUTPUT
15
10
5
30
60
80
100
120
140
160
180
200
220
240
260
280
300
FREQUENCY (MHz)
TEST LIMIT
AMPLITUDE (dB∝V/m)
40
35
25
MAX9875 OUTPUT
20
15
10
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
FREQUENCY (MHz)
Figure 4. EMI with 152mm of Speaker Cable
DirectDrive Headphone Amplifier
Traditional single-supply headphone amplifiers have
outputs biased at a nominal DC voltage (typically half
the supply). Large coupling capacitors are needed to
block this DC bias from the headphone. Without these
capacitors, a significant amount of DC current flows to
the headphone, resulting in unnecessary power dissipation and possible damage to both the headphone
and headphone amplifier.
Maxim’s DirectDrive architecture uses a charge pump to
create an internal negative supply voltage. This allows
the headphone outputs of the MAX9875 to be biased at
GND while operating from a single supply (Figure 5).
Without a DC component, there is no need for the large
DC-blocking capacitors. Instead of two large (220µF,
typ) capacitors, the MAX9875 charge pump requires
two small ceramic capacitors, conserving board space,
18
reducing cost, and improving the frequency response of
the headphone amplifier. See the Output Power vs.
Load Resistance graph in the Typical Operating
Characteristics for details of the possible capacitor
sizes. There is a low DC voltage on the amplifier outputs
due to amplifier offset. However, the offset of the
MAX9875 is typically ±0.15mV, which, when combined
with a 32Ω load, results in less than 10µA of DC current
flow to the headphones.
In addition to the cost and size disadvantages of the
DC-blocking capacitors required by conventional headphone amplifiers, these capacitors limit the amplifier’s
low-frequency response and can distort the audio signal. Previous attempts at eliminating the output-coupling capacitors involved biasing the headphone return
(sleeve) to the DC bias voltage of the headphone
amplifiers. This method raises some issues:
______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
VDD
Headphone Current Limit
The headphone amplifier current is limited to 140mA (typ).
The current limit clamps the output current, which appears
as clipping when the maximum current is exceeded.
Shutdown Mode
The MAX9875 features two ways of entering low-power
shutdown. The hardware shutdown function is controlled
by pulsing BIAS low for 1ms. While BIAS is low the amplifiers are shut down. Following an 80ms reset period, the
MAX9875 reverts to its power-on-reset condition. Pull
BIAS low using an open-drain output that is not pulled up
with a resistor (see the Typical Application Circuit). The
open-drain output leakage must not exceed 100nA and
must be able to sink at least 1mA.
The device can also be placed in shutdown mode by
writing to the SHDN bit in the Output Mode Control
Register.
Click-and-Pop Suppression
The MAX9875 features click-and-pop suppression that
eliminates audible transients from occurring at startup
and shutdown.
Use the following procedure to start up the MAX9875:
1) Configure the desired output mode and preamplifier gain.
VDD/2
2) Set the SHDN bit to 1 to start up the amplifier.
3) Wait 10ms for the startup time to pass.
4) Increase the output volume to the desired level.
GND
To disable the device simply set SHDN to 0.
During the startup period, the MAX9875 precharges the
input capacitors to prevent clicks and pops. If the output
amplifiers have been programmed to be active they are
held in shutdown until the precharge period is complete.
When power is initially applied to the MAX9875, the
power-on-reset state of all three volume control registers
is mute. For most applications, the volume can be set to
the desired level once the device is active. If the clickand-pop is too high, step through intermediate volume
settings with zero-crossing detection disabled. Stepping
through higher volume settings has a greater impact on
click-and-pop than lower volume settings.
For the lowest possible click-and-pop, start up the device
at minimum volume and then step through each volume
setting until the desired setting is reached. Disable zerocrossing detection if no input signal is expected.
CONVENTIONAL AMPLIFIER BIASING SCHEME
+VDD
GND
DirectDrive AMPLIFIER BIASING SCHEME
Although not typically required, additional high-frequency noise attenuation can be achieved by increasing the
size of C2 (see the Typical Application Circuit). The
charge pump is active only in headphone modes.
-VDD
(VSS)
Figure 5. Traditional Amplifier Output vs. MAX9875 DirectDrive
Output
______________________________________________________________________________________
19
MAX9875
1) The sleeve is typically grounded to the chassis.
Using the midrail biasing approach, the sleeve must
be isolated from system ground, complicating product design.
2) During an ESD strike, the amplifier’s ESD structures
are the only path to system ground. Thus, the amplifier must be able to withstand the full energy from an
ESD strike.
3) When using the headphone jack as a line out to
other equipment, the bias voltage on the sleeve may
conflict with the ground potential from other equipment, resulting in possible damage to the amplifiers.
The MAX9875 features a low-noise charge pump. The
switching frequency of the charge pump is 1/2 of the
Class D switching frequency, regardless of the operating
mode. When the Class D amplifiers are operated in
spread-spectrum mode, the charge pump also switches
with a spread-spectrum pattern. The nominal switching
frequency is well beyond the audio range, and thus does
not interfere with audio signals. The switch drivers feature a controlled switching speed that minimizes noise
generated by turn-on and turn-off transients. By limiting
the switching speed of the charge pump, the di/dt noise
caused by the parasitic trace inductance is minimized.
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
I2C Interface
The MAX9875 is controlled through five I2C programmable registers. Table 1 shows the MAX9875’s complete register map. Tables 2, 3, and 5 show the
individual registers.
I2C Address
The slave address of the MAX9875 is 1001101R/(W).
Table 1. Register Map
REGISTER
ADDRESS
POR STATE
B7
B6
B5
B4
Input Mode
Control
0x00
0x40
0
ZCD
∆INA
∆INB
Speaker
Volume
Control
0x01
0x00
0
0
0
SVOL (Table 4)
Left
Headphone
Volume
Control
0x02
0x00
0
0
0
HPLVOL (Table 4)
Right
Headphone
Volume
Control
0x03
0x00
0
0
0
HPRVOL (Table 4)
Output Mode
Control
0x04
0x49
SHDN
0
REGISTER
OSC (Table 6)
B3
B2
B1
PGAINA
B0
PGAINB
OUTMODE (Table 7)
Table 2. Input Mode Control
REGISTER
0x00
B7
B6
B5
B4
0
ZCD
∆INA
∆INB
I2C Register Description
Zero-Crossing Detection (ZCD)
Zero-crossing detection limits distortion in the output
signal during volume transitions by delaying the transition until the mixer output crosses the internal bias voltage. A timeout period (typically 60ms) forces the
volume transition if the mixer output signal does not
cross the bias voltage.
1 = Zero-crossing detection is enabled.
0 = Zero-crossing detection is disabled.
Differential Input Configuration (∆IN_)
The inputs INA_ and INB_ can be configured for mono
differential or stereo single-ended operation.
20
B3
B2
PGAINA
B1
B0
PGAINB
1 = IN__ is configured as a mono differential input with
IN_2 as the positive and IN_1 as the negative input.
0 = IN__ is configured as a stereo single-ended input
with IN_2 as the right and IN_1 as the left input.
Preamplifier Gain (PGAIN_)
The preamplifier gain of INA_ and INB_ can be programmed by writing to PGAIN_.
00 = 0dB
01 = +9dB
10 = +20dB
11 = Reserved
______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
REGISTER
B7
B6
B5
0x01
0
0
0
B4
B3
B2
B1
0x02
0
0
0
HPLVOL (Table 4)
0x03
0
0
0
HPRVOL (Table 4)
B0
SVOL (Table 4)
Volume Control
The device has a separate volume control for left headphone, right headphone, and speaker amplifiers. The
total system gain is a combination of the input gain, the
volume control, and the output amplifier gain. Table 4
shows the volume settings for each volume control.
Table 4. Volume Control Settings
CODE
_VOL
GAIN (dB)
CODE
_VOL
B4
B3
B2
B1
B0
GAIN (dB)
B4
B3
B2
B1
B0
0
0
0
0
0
0
MUTE
16
1
0
0
0
0
-23
1
0
0
0
0
1
-75
17
1
0
0
0
1
-21
1
0
0
1
0
-19
2
0
0
0
1
0
-71
18
3
0
0
0
1
1
-67
19
1
0
0
1
1
-17
4
0
0
1
0
0
-63
20
1
0
1
0
0
-15
1
0
1
0
1
-13
5
0
0
1
0
1
-59
21
6
0
0
1
1
0
-55
22
1
0
1
1
0
-11
7
0
0
1
1
1
-51
23
1
0
1
1
1
-9
1
1
0
0
0
-7
8
0
1
0
0
0
-47
24
9
0
1
0
0
1
-44
25
1
1
0
0
1
-6
10
0
1
0
1
0
-41
26
1
1
0
1
0
-5
11
0
1
0
1
1
-38
27
1
1
0
1
1
-4
12
0
1
1
0
0
-35
28
1
1
1
0
0
-3
13
0
1
1
0
1
-32
29
1
1
1
0
1
-2
14
0
1
1
1
0
-29
30
1
1
1
1
0
-1
15
0
1
1
1
1
-26
31
1
1
1
1
1
0
Table 5. Output Mode Control
REGISTER
0x04
B7
B6
SHDN
0
B5
B4
OSC (Table 6 )
SHDN)
Shutdown (S
1 = MAX9875 operational.
0 = MAX9875 in low-power shutdown mode.
B3
B2
B1
B0
OUTMODE (Table 7)
SHDN is an active-low shutdown bit that overrides all
settings and places the entire device in low-power shutdown mode. The I2C interface is fully active in this shutdown mode. All register settings are preserved while in
shutdown.
______________________________________________________________________________________
21
MAX9875
Table 3. Speaker/Left Headphone/Right Headphone Volume Control
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
Output Configuration (OUTMODE)
The MAX9875 has a stereo DirectDrive headphone amplifier and a mono Class D amplifier. Table 7 shows how
each of the output amplifiers can be configured and connected to the input signals. For simplicity, not all possible
combinations of ∆INA and ∆INB are shown.
Table 6. Oscillator Modes
OSC
CLASS D OSCILLATOR MODE (kHz)
CHARGE-PUMP OSCILLATOR MODE (kHz)
0
1176, spread spectrum
588, spread spectrum
0
1
1100, fixed frequency
550, fixed frequency
1
0
700, fixed frequency
1
1
B5
B4
0
350, fixed frequency
Reserved
Table 7. Output Modes
∆IN_ = 0
(THE SINGLE-ENDED INPUT SIGNALS
ARE DEFINED AS IN_1 = LEFT AND
IN_2 = RIGHT)
OUTMODE
MODE
B3
B2
B1
B0
0
0
0
0
0
1
0
0
0
1
2
0
0
1
3
0
0
1
4
0
1
5
0
6
0
7
SPK
LEFT HP
RIGHT HP
∆IN_ = 1
(THE DIFFERENTIAL INPUT SIGNAL IS
DEFINED AS IN_∆ = IN_2 - IN_1)
SPK
Reserved
LEFT HP
INA1+INA2
—
—
0
—
INA1
INA2
—
INA∆
INA∆
1
INA1+INA2
INA1
INA2
INA∆
INA∆
INA∆
0
0
INB1+INB2
—
—
INB∆
—
—
1
0
1
—
INB1
INB2
—
INB∆
INB∆
1
1
0
INB1+INB2
INB1
INB2
INB∆
INB∆
INB∆
0
1
1
1
INA1+INA2
+INB1+INB2
—
—
INA∆+INB∆
—
—
8
1
0
0
0
—
INA1+INB1
INA2+INB2
—
INA∆
+INB∆
INA∆ +INB∆
9
1
0
0
1
INA1+INA2
+INB1+INB2
INA1+INB1
INA2+INB2
INA∆+INB∆
INA∆
+INB∆
INA∆ +INB∆
10–15
Reserved
INA∆
—
Reserved
— = Amplifier Off
22
RIGHT HP
Reserved
______________________________________________________________________________________
—
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
than 500Ω, is required on SCL if there are multiple masters on the bus, or if the single master has an opendrain SCL output. Series resistors in line with SDA and
SCL are optional. Series resistors protect the digital
inputs of the MAX9875 from high voltage spikes on the
bus lines, and minimize crosstalk and undershoot of the
bus signals.
Bit Transfer
One data bit is transferred during each SCL cycle. The
data on SDA must remain stable during the high period
of the SCL pulse. Changes in SDA while SCL is high
are control signals (see the START and STOP
Conditions section).
START and STOP Conditions
SDA and SCL idle high when the bus is not in use. A
master initiates communication by issuing a START condition. A START condition is a high-to-low transition on
SDA with SCL high. A STOP condition is a low-to-high
transition on SDA while SCL is high (Figure 7). A START
condition from the master signals the beginning of a
transmission to the MAX9875. The master terminates
transmission, and frees the bus, by issuing a STOP condition. The bus remains active if a REPEATED START
condition is generated instead of a STOP condition.
SDA
tBUF
tSU:STA
tSU:DAT
tSU:STA
tHD:DAT
tLOW
tSU:STO
SCL
tHIGH
tHD:STA
tR
tF
REPEATED
START CONDITION
START
CONDITION
STOP
CONDITION
START
CONDITION
Figure 6. 2-Wire Interface Timing Diagram
S
Sr
P
SCL
SDA
Figure 7. START, STOP, and REPEATED START Conditions
SMBus is a trademark of Intel Corp.
______________________________________________________________________________________
23
MAX9875
I2C Interface Specification
The MAX9875 features an I2C/SMBus™-compatible, 2wire serial interface consisting of a serial-data line
(SDA) and a serial-clock line (SCL). SDA and SCL facilitate communication between the MAX9875 and the
master at clock rates up to 400kHz. Figure 6 shows the
2-wire interface timing diagram. The master generates
SCL and initiates data transfer on the bus. The master
device writes data to the MAX9875 by transmitting the
proper slave address followed by the register address
and then the data word. Each transmit sequence is
framed by a START (S) or REPEATED START (Sr) condition and a STOP (P) condition. Each word transmitted
to the MAX9875 is 8 bits long and is followed by an
acknowledge clock pulse. A master reading data from
the MAX9875 transmits the proper slave address followed by a series of nine SCL pulses. The MAX9875
transmits data on SDA in sync with the master-generated SCL pulses. The master acknowledges receipt of
each byte of data. Each read sequence is framed by a
START or REPEATED START condition, a not acknowledge, and a STOP condition. SDA operates as both an
input and an open-drain output. A pullup resistor, typically greater than 500Ω, is required on SDA. SCL operates only as an input. A pullup resistor, typically greater
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
Early STOP Conditions
The MAX9875 recognizes a STOP condition at any
point during data transmission except if the STOP condition occurs in the same high pulse as a START condition. For proper operation, do not send a STOP
condition during the same SCL high pulse as the
START condition.
Slave Address
The MAX9875 is preprogrammed with a slave address
of 1001101R/(W). The address is defined as the seven
most significant bits (MSBs) followed by the Read/Write
bit. Setting the Read/Write bit to 1 configures the
MAX9875 for read mode. Setting the Read/Write bit to 0
configures the MAX9875 for write mode. The address is
the first byte of information sent to the MAX9875 after
the START condition.
Acknowledge
The acknowledge bit (ACK) is a clocked 9th bit that the
MAX9875 uses to handshake receipt each byte of data
when in write mode (see Figure 8). The MAX9875 pulls
down SDA during the entire master-generated 9th
clock pulse if the previous byte is successfully
received. Monitoring ACK allows for detection of unsuccessful data transfers. An unsuccessful data transfer
occurs if a receiving device is busy or if a system fault
has occurred. In the event of an unsuccessful data
transfer, the bus master may retry communication.
The master pulls down SDA during the ninth clock
cycle to acknowledge receipt of data when the
MAX9875 is in read mode. An acknowledge is sent by
the master after each read byte to allow data transfer to
continue. A not acknowledge is sent when the master
reads the final byte of data from the MAX9875, followed
by a STOP condition.
Write Data Format
A write to the MAX9875 includes transmission of a
START condition, the slave address with the R/W bit set
to 0, one byte of data to configure the internal register
address pointer, one or more bytes of data, and a
STOP condition. Figure 9 illustrates the proper frame
format for writing one byte of data to the MAX9875.
Figure 10 illustrates the frame format for writing n-bytes
of data to the MAX9875.
The slave address with the R/W bit set to 0 indicates
that the master intends to write data to the MAX9875.
The MAX9875 acknowledges receipt of the address
byte during the master-generated 9th SCL pulse.
CLOCK PULSE FOR
ACKNOWLEDGMENT
START
CONDITION
SCL
1
2
8
9
NOT ACKNOWLEDGE
SDA
ACKNOWLEDGE
Figure 8. Acknowledge
ACKNOWLEDGE FROM MAX9875
B7
ACKNOWLEDGE FROM MAX9875
S
SLAVE ADDRESS
0
B6
B5
B4
B3
B2
B1
B0
ACKNOWLEDGE FROM MAX9875
A
R/W
REGISTER ADDRESS
A
A
DATA BYTE
P
1 BYTE
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
Figure 9. Writing One Byte of Data to the MAX9875
24
______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
contents of register 0x00. Transmitted data is valid on the
rising edge of SCL. The address pointer autoincrements
after each read data byte. This autoincrement feature
allows all registers to be read sequentially within one
continuous frame. A STOP condition can be issued after
any number of read data bytes. If a STOP condition is
issued followed by another read operation, the first data
byte to be read will be from register 0x00.
The address pointer can be preset to a specific register
before a read command is issued. The master presets
the address pointer by first sending the MAX9875‘s
slave address with the R/W bit set to 0 followed by the
register address. A REPEATED START condition is then
sent followed by the slave address with the R/W bit set
to 1. The MAX9875 then transmits the contents of the
specified register. The address pointer autoincrements
after transmitting the first byte. The master acknowledges receipt of each read byte during the acknowledge clock pulse. The master must acknowledge all
correctly received bytes except the last byte. The final
byte must be followed by a not acknowledge from the
master and then a STOP condition. Figure 11 illustrates
the frame format for reading one byte from the
MAX9875. Figure 12 illustrates the frame format for
reading multiple bytes from the MAX9875.
Register addresses greater than 0x04 are reserved. Do
not write to these addresses.
Read Data Format
Send the slave address with the R/W bit set to 1 to initiate
a read operation. The MAX9875 acknowledges receipt of
its slave address by pulling SDA low during the 9th SCL
clock pulse. A START command followed by a read
command resets the address pointer to register 0x00.
The first byte transmitted from the MAX9875 will be the
ACKNOWLEDGE FROM MAX9875
ACKNOWLEDGE FROM MAX9875
S
SLAVE ADDRESS
B7 B6 B5 B4 B3 B2 B1 B0
ACKNOWLEDGE FROM MAX9875
0
A
REGISTER ADDRESS
ACKNOWLEDGE FROM MAX9875
A
A
DATA BYTE 1
R/W
B7 B6 B5 B4 B3 B2 B1 B0
DATA BYTE n
1 BYTE
A
P
1 BYTE
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
Figure 10. Writing n-Bytes of Data to the MAX9875
NOT ACKNOWLEDGE FROM MASTER
ACKNOWLEDGE FROM MAX9875
ACKNOWLEDGE FROM MAX9875
S
SLAVE ADDRESS
0
R/W
A
REGISTER ADDRESS
ACKNOWLEDGE FROM MAX9875
A
REPEATED START
Sr
SLAVE ADDRESS
1
R/W
A
DATA BYTE
A
P
1 BYTE
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
Figure 11. Reading One Indexed Byte of Data from the MAX9875
______________________________________________________________________________________
25
MAX9875
The second byte transmitted from the master configures the MAX9875’s internal register address pointer.
The pointer tells the MAX9875 where to write the next
byte of data. An acknowledge pulse is sent by the
MAX9875 upon receipt of the address pointer data.
The third byte sent to the MAX9875 contains the data
that will be written to the chosen register. An acknowledge pulse from the MAX9875 signals receipt of the
data byte. The address pointer autoincrements to the
next register address after each received data byte.
This autoincrement feature allows a master to write to
sequential registers within one continuous frame. Figure
10 illustrates how to write to multiple registers with one
frame. The master signals the end of transmission by
issuing a STOP condition.
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
S
SLAVE ADDRESS
0
R/W
ACKNOWLEDGE FROM MAX9875
ACKNOWLEDGE FROM MAX9875
ACKNOWLEDGE FROM MAX9875
A
REGISTER ADDRESS
A
Sr
REPEATED START
SLAVE ADDRESS
1
DATA BYTE
A
R/W
A
P
1 BYTE
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
Figure 12. Reading n-Bytes of Indexed Data from the MAX9875
Applications Information
OUT+
Filterless Class D Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s output. The
filters add cost, increase 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 VDD(P-P)) and causes large ripple currents. Any parasitic resistance in the filter components
results in a loss of power, lowering the efficiency.
The MAX9875 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, more efficient solution.
Because the frequency of the MAX9875 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 > 10µH. Typical 8Ω speakers exhibit series
inductances in the 20µH to 100µH range.
Component Selection
Optional Ferrite Bead Filter
In applications where speaker leads exceed 20mm,
additional EMI suppression can be achieved by using a
filter constructed from a ferrite bead and a capacitor to
ground. A ferrite bead with low DC resistance, highfrequency (> 1.176MHz) impedance of 100Ω to 600Ω,
and rated for at least 1A should be used. 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
An input capacitor, CIN, in conjunction with the input
impedance of the MAX9875 forms a highpass filter that
removes the DC bias from an incoming signal. The AC26
MAX9875
OUT-
Figure 13. Optional Ferrite Bead Filter
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:
1
f−3dB =
2πRINCIN
Choose CIN so that f-3dB is well below the lowest frequency of interest. Use capacitors whose dielectrics
have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as ceramics, may result in increased
distortion at low frequencies.
BIAS Capacitor
BIAS is the output of the internally generated DC bias voltage. The BIAS bypass capacitor, CBIAS, reduces power
supply and other noise sources at the common-mode
bias node. Bypass BIAS with a 1µF capacitor to GND.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩ for optimum
performance. Low-ESR ceramic capacitors minimize the
output resistance of the charge pump. Most surfacemount ceramic capacitors satisfy the ESR requirement.
For best performance over the extended temperature
range, select capacitors with an X7R dielectric.
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the output
resistance of the charge pump. A C1 value that is too
small degrades the device’s ability to provide sufficient
current drive, which leads to a loss of output voltage.
______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
PVDD Bulk Capacitor (C3)
In addition to the recommended PVDD bypass capacitance, bulk capacitance equal to C3 should be used.
Place the bulk capacitor as close to the device as possible.
MAX9875 fig14
RF SUSCEPTIBILITY
-10
-30
EFFICIENCY (dBµ)
Output Holding Capacitor (C2)
The output capacitor value and ESR directly affect the
ripple at VSS. Increasing the value of C2 reduces output
ripple. Likewise, decreasing the ESR of C2 reduces both
ripple and output resistance. Lower capacitance values
can be used in systems with low maximum output power
levels. See the Output Power vs. Load Resistance graph
in the Typical Operating Characteristics.
-50
THRESHOLD OF HEARING
-70
MAX9875
-90
-110
-130
NOISE FLOOR
-150
10
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
that is easily demodulated by audio amplifiers. Figure
14 shows the susceptibility of the MAX9875 to a transmitting GSM radio placed in close proximity. Although
there is measurable noise at 217Hz and its harmonics,
the noise is well below the threshold of hearing using
typical headphones.
In RF applications, improvements to both layout and
component selection decreases the MAX9875’s sus-
100
1k
10k
100k
FREQUENCY (Hz)
Supply Bypassing,
Layout, and Grounding
Proper layout and grounding are essential for optimum
performance. Use wide traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance. Wide traces also aid in moving heat away from the package. Proper grounding
improves audio performance, minimizes crosstalk
between channels, and prevents any switching noise
from coupling into the audio signal. Connect PGND and
GND together at a single point on the PCB. Route all
traces that carry switching transients away from GND
and the traces/components in the audio signal path.
Connect PVDD to a 2.7V to 5.25V source. Bypass
PVDD to the PGND pin with a 1µF ceramic capacitor.
Additional bulk capacitance should be used to prevent
power-supply pumping. Place the bypass capacitors
as close to the MAX9875 as possible.
Connect VDD to PVDD. Bypass VDD to GND with a 1µF
capacitor. Place the bypass capacitors as close to the
MAX9875 as possible.
MAX9875
Increasing the value of C1 reduces the charge-pump output resistance to an extent. Above 1µF, the on-resistance
of the switches and the ESR of C1 and C2 dominate.
Figure 14. MAX9875 Susceptibility to a GSM Cell Phone Radio
ceptibility to RF noise and prevent RF signals from
being demodulated into audible noise. Trace lengths
should be kept below 1/4 the wavelength of the RF frequency of interest. Minimizing the trace lengths prevents them from functioning as antennas and coupling
RF signals into the MAX9875. The wavelength λ in
meters is given by:
108m/s,
λ = c/f
and f = the RF frequency of inter-
where c = 3 x
est.
Route audio signals on middle layers of the PCB to
allow ground planes above and below 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
MAX9875. For these capacitors to be effective, they
must have a low-impedance, 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.
______________________________________________________________________________________
27
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
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: UCSP—A
Wafer-Level Chip-Scale Package on Maxim’s website
at www.maxim-ic.com/ucsp. See Figure 15 for the
recommended PCB footprint for the MAX9875.
45±5µm
250µm
Figure 15. PCB Footprint Recommendation Diagram
28
______________________________________________________________________________________
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
VBATT
C2
1µF
VSS
A3
VBATT
C3
1µF
1µF
VDD
B1
PVDD
C5
C1N A4
C1
1µF
MAX9875
CHARGE
PUMP
C1P A5
1µF
-75dB TO 0dB
0dB
INPUT A
0dB/+9dB/+20dB
1µF
0dB
MIXER
AND
MUX
INA1 D2
A2
HPL
B5
OUT+
D5
OUT-
-75dB TO 0dB
INB2 C1
INPUT B
0dB/+9dB/+20dB
INPUT B
1µF
HPR
INA2 D1
INPUT A
1µF
A1
CLASS D
MODULATOR
+12dB
INB1 C2
-75dB TO 0dB
OPEN-DRAIN GPIO
BIAS
B2
1µF
SDA
SCL
B3
I2C
CONTROL
C3
D3
C4
GND
PGND
Chip Information
PROCESS: BiCMOS
______________________________________________________________________________________
29
MAX9875
Typical Application Circuit
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
20 WLP
R202A2+2
21-0059
20L WLP.EPS
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
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.
30 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
工商网监
湘ICP备2023018690号
