MAXIM MAX9875 Technical data

General Description
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 I
2
C control.
The MAX9875 is available in a thermally efficient, space-saving 20-bump WLP package.
Applications
Cell Phones
Portable Multimedia Players
Features
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 Mode725mW Speaker Output (R
SPK
= 8Ω, PVDD = 3.7V)
53mW Headphone Output (R
HP
= 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 (R
SPK
= 8Ω, P
OUT
= 750mW)
High Speaker Amplifier PSRR (72dB at 217Hz)High Headphone Amplifier PSRR (84dB at 217Hz)I
2
C Control
Hardware and Software Shutdown ModeClick-and-Pop SuppressionCurrent-Limit and Thermal ProtectionAvailable in a Space-Saving, 2.5mm x 2.0mm WLP
Package
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
________________________________________________________________
Maxim Integrated Products
1
Simplified Block Diagram
WLP
HPL V
SS
C1N
HPR
1
A
B
C
D
2
3
4
C1P
BIAS SDA
N.C.
V
DD
OUT+
INB1 SCL
PGND
INB2
PVDD
INA1 GND
N.C.
INA2
OUT-
5
TOP VIEW
(BUMP SIDE DOWN)
Pin Configuration
19-4536; Rev 0; 3/09
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.
EVALUATION KIT
AVAILABLE
Ordering Information
PART
PIN - PA C K A G E
MAX9875ERP+TG45
20 WLP (5x4)
+
Denotes a lead(Pb)-free/RoHS-compliant package. T = Tape and reel. G45 indicates protective die coating.
DirectDrive is a registered trademark of Maxim Integrated Products, Inc.
TEMP RANGE
-40°C to +85°C
PREAMPLIFIER
I2C
INTERFACE
SINGLE SUPPLY
2.7V TO 5.25V
VOLUME
CONTROL
MIXER/MUX
VOLUME
CONTROL
MAX9875
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD= V
PVDD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. Z
SPK
= , RHP= . C1 = C2 = C
BIAS
= 1µF. TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are
at T
A
= +25°C.) (Note 3)
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.
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 V
SS
- 0.3V, whichever limits first.
V
DD
, PVDD to PGND .............................................-0.3V to +5.5V
V
DD
to PVDD .........................................................-0.3V to +0.3V
V
SS
to PGND .........................................................-5.5V to +0.3V
C1N to PGND..............................................(V
SS
- 0.3V) to +0.3V
C1P to PGND...........................................-0.3V to (PVDD + 0.3V)
HPL, HPR to V
SS
(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 (V
SS
- (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 V
SS
...........................................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 (T
A
= +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
Supply Voltage Range VDD, PVDD Guaranteed by PSRR test 2.7 5.25 V
Quiescent Current I
Shutdown Current I
Turn-On Time t
BIAS Release Time t
Input Resistance R
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
DD
SHDN
ON
BR
IN
HP mode, OUTMODE = 2
SPK mode, OUTMODE = 7
SPK + HP mode, OUTMODE = 9
I
= I
SHDN
V
Time from shutdown to full operation
After forcing BIAS low, time from BIAS released to I
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 0.820Maximum Input Signal Swing
Preamp = +20dB 0.230
VDD
= logic-high; TA = +25°C
SCL
+ I
2
C reset
; SHDN = 0; V
PVDD
OSC = 00 5.6 9.0
OSC = 10 5.5
OSC = 00 6.6 11.0
OSC = 10 5.7
OSC = 00 10.4 16.0
OSC = 10 9.3
OSC = 00 10
OSC = 01 10
OSC = 10 17.5
=
SDA
10 22 µA
25 80 ms
mA
ms
V
k
P-P
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD= V
PVDD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. Z
SPK
= , RHP= . C1 = C2 = C
BIAS
= 1µF. TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are
at T
A
= +25°C.) (Note 3)
Common-Mode Rejection Ratio CMRR
Input DC Voltage IN__ inputs 1.22 1.3 1.38 V
Bias Voltage V
SPEAKER AMPLIFIER (OUTMODE = 1)
Output Offset Voltage V
Click-and-Pop Level K
Power-Supply Rejection Ratio (Note 4)
Output Power (Note 5) P
Total Harmonic Distortion Plus Noise
Signal-to-Noise Ratio SNR
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
BIAS
OS
CP
PSRR
OUT
THD+N
f
= 1kHz (differential
IN
input mode)
TA = +25°C (volume at mute) ±0.5 ±4
TA = +25°C (volume at 0dB, OUTMODE = 1, IN_ = 0)
Peak voltage, TA = +25°C, A-weighted, 32 samples per second, volume at mute (Note 4)
T
= +25°C, PVDD =
A
V
DD
THD+N 1%
f = 1kHz, P Z
= 8 + 68µH
SPK
A-weighted, OUTMODE = 1, 3, 4, 6
A-weighted, OUTMODE = 7, 9
= 350mW, TA = +25°C,
OUT
IN_ = 0 (single-ended)
IN_ = 1 (differential) 94
IN_ = 0
(single-ended)
IN_ = 1 (differential) 92
Preamp = 0dB 47
Preamp = +9dB 49
Preamp = +20dB 42
Into shutdown -70
Out of shutdown -70
PVDD = VDD =
2.7V to 5.5V
f = 217Hz, 100mV
f = 1kHz, 100mV
f = 20kHz, 100mV
Z
= 8Ω +
SPK
68µH, V
Z
= 8Ω +
SPK
68µH, V
Z
= 8Ω +
SPK
68µH, V
Z
= 4Ω +
SPK
33µH, V
= 4Ω +
Z
SPK
33µH, V
1.13 1.2 1.27 V
±1.5
50 76
P-P
P-P
P-P
DD
DD
DD
DD
DD
ripple
ripple
ripple
= 3.7V
= 3.3V
= 3.0V
= 3.7V
= 3.0V
72
68
55
725
560
465
825
770
0.05 %
92
88
dB
mV
dBV
dB
mW
dB
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VDD= V
PVDD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. Z
SPK
= , RHP= . C1 = C2 = C
BIAS
= 1µF. TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are
at T
A
= +25°C.) (Note 3)
Output Frequency
Current Limit 1.5 A
Efficiency η P
Speaker Gain A
Output Noise
HEADPHONE AMPLIFIERS (OUTMODE = 2)
Output Offset Voltage V
Click-and-Pop Level K
Power-Supply Rejection Ratio (Note 4)
Output Power P
Headphone Gain A
Channel-to-Channel Gain Tracking
Total Harmonic Distortion Plus Noise
Signal-to-Noise Ratio SNR
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
V
OS
CP
PSRR
OUT
V
THD+N
Spread-spectrum modulation mode, OSC = 00
Fixed-frequency mode, OSC = 01 1100
Fixed-frequency mode, OSC = 10 700
= 600mW, f = 1kHz 87 %
OUT
A-weighted, OUTMODE = 1, IN_ = 0 (Note 4)
TA = +25°C (volume at mute) ±0.15 ±0.6
TA = +25°C (volume at 0dB) ±1.6
Peak voltage, TA = +25°C, A-weighted, 32 samples per second. volume at mute (Note 4)
TA = +25°C, PVDD = V
DD
THD+N 1%
TA = +25°C, HPL to HPR, volume at 0dB, OUTMODE = 2, 5; IN_ = 0
RHP = 32 (P
R
= 16 (P
HP
= +25°C
T
A
A-weighted, OUTMODE = 2, 3, 5, 6; R
A-weighted, R 16Ω, OUTMODE = 8, 9
HP
OUT
OUT
= 16
HP
Into shutdown -80
Out of shutdown -80
PVDD = VDD = 2.7V to 5.25V
f = 217Hz, V
f = 1kHz, V
f = 20kHz, V
RHP = 16 53
R
= 10mW, f = 1kHz) 0.016
= 10mW, f = 1kHz),
IN_ = 0 (single-ended)
IN_ = 1 (differential) 98
IN_ = 0
=
(single-ended)
IN_ = 1 (differential) 96
= 100mV
RIPPLE
= 100mV
RIPPLE
= 100mV
RIPPLE
= 32 27
HP
11.5 12.0 12.5 dB
70 85
P-P
P-P
P-P
-0.4 0 +0.4 dB
1176
±60
63 µV
84
80
62
±0.3 ±2.5 %
0.03
98
96
kHz
RMS
mV
dBV
dB
mW
%
dB
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(VDD= V
PVDD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. Z
SPK
= , RHP= . C1 = C2 = C
BIAS
= 1µF. TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are
at T
A
= +25°C.) (Note 3)
Slew Rate SR 0.35 V/µs
Capacitive Drive C
Crosstalk HPL to HPR, HPR to HPL, f = 20Hz to 20kHz 65 dB
Charge-Pump Frequency
VOLUME CONTROL
Minimum Setting _VOL = 1 -75 dB
Maximum Setting _VOL = 31 0 dB
Mute Attenuation f = 1kHz, _VOL = 0
Zero-Crossing Detection Timeout ZCD = 1 60 ms
DIGITAL INPUTS
Input-Voltage High (SDA, SCL) V
Input-Voltage Low (SDA, SCL) V
Input-Voltage Low (BIAS) V
Input Hysteresis (SDA, SCL) V
SDA, SCL Input Capacitance C
Input Leakage Current I
BIAS Pullup Current I
DIGITAL OUTPUTS (SDA Open Drain)
Output Low Voltage SDA V
Output Fall Time SDA t
2-WIRE INTERFACE TIMING
External Pullup Voltage Range: SDA and SCL
Serial Clock Frequency f
Bus Free Time Between STOP and START Conditions
START Condition Hold t
START Condition Setup Time t
Clock Low Period t
Clock High Period t
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
L
H
L
BL
HYS
IN
IN
BIAS
OL
OF
SCL
t
BUF
HD:STA
SU:STA
LOW
HIGH
Spread-spectrum modulation mode, OSC = 00
Fixed-frequency mode, OSC = 01 430 550 670
Fixed-frequency mode, OSC = 10 220 350 500
SDA, SCL; TA = +25°C ±1.0 µA
I
= 3mA 0.4 V
SINK
V
to V
H(MIN)
to 400pF, I
bus capacitance = 10pF
L(MAX)
= 3mA
SINK
PGAIN_ = 00 0
PGAIN_ = 01 9Preamp Gain Input A or B
PGAIN_ = 10 20
Speaker 100
Headphone 110
100 pF
588
±30
1.4 V
80 mV
4pF
94 µA
1.7 3.6 V
DC 400 kHz
1.3 µs
0.6 µs
0.6 µs
1.3 µs
0.6 µs
0.4 V
0.15 V
250 ns
kHz
dB
dB
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
6 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VDD= V
PVDD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. SDA and
SCL pullup voltage = 3.3V. Z
SPK
= , RHP= . C1 = C2 = C
BIAS
= 1µF. TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are
at T
A
= +25°C.) (Note 3)
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 Z
SPK
= 8+ 68µH only.
Data Setup Time t
Data Hold Time t
Maximum Receive SCL/SDA Rise Time
Maximum Receive SCL/SDA Fall Time
Setup Time for STOP Condition t
Capacitive Load for Each Bus Line
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SU:DAT
HD:DAT
t
R
t
F
SU:STO
C
b
100 ns
0 900 ns
0.6 µs
300 ns
300 ns
400 pF
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
_______________________________________________________________________________________ 7
Typical Operating Characteristics
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, RHP= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
GENERAL
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
9
HEADPHONE ONLY INPUTS AC-COUPLED TO GND OUTMODE = 8
8
= V
V
7
6
SUPPLY CURRENT (mA)
5
4
2.5 5.5
= 3.3V
SDA
SCL
f
= 1176kHz SREAD-SPECTRUM MODE
OSC
f
= 700kHz
OSC
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT
14
INPUTS AC-COUPLED TO GND
= V
V
SDA
13
12
SCL
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
10
SPEAKER ONLY INPUTS AC-COUPLED TO GND
9
OUTMODE = 7
= V
= 3.3V
V
SDA
8
7
6
SUPPLY CURRENT (mA)
5
4
MAX9875 toc04
SCL
f
OSC
SPREAD-SPECTRUM MODE
f
OSC
2.5 5.5 SUPPLY VOLTAGE (V)
f
= 1100kHz
OSC
5.04.54.03.53.0
vs. SUPPLY VOLTAGE
= 3.3V
MAX9875 toc01
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
HEADPHONE AND SPEAKER INPUTS AC-COUPLED TO GND OUTMODE = 9
= V
SDA
f
SCL
OSC
= 3.3V
f
OSC
SPREAD-SPECTRUM MODE
= 1100kHz
SUPPLY VOLTAGE (V)
V
= 1176kHz
= 1100kHz
f
OSC
= 700kHz
5.04.54.03.53.0
MAX9875 toc02
20
0
-20
13
12
11
10
9
SUPPLY CURRENT (mA)
8
7
2.5 5.5
VOLUME ATTENUATION
vs. _VOL CONTROL CODE
f
OSC
= 1176kHz
= 700kHz
5.04.54.03.53.0
MAX9875 toc05
MAX9875 toc03
11
10
9
SHUTDOWN CURRENT (µA)
8
7
2.5 5.5 SUPPLY VOLTAGE (V)
-40
-60
-80
VOLUME ATTENUATION (dB)
fIN = 1kHz
-100
MEASURED AT HPL AND HPR
-120
5.04.54.03.53.0
35 0
_VOL CONTROL CODE
15
5
10202530
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, RHP= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
SPEAKER AMPLIFIER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc06
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01 10 100k
VDD = V
PVDD
= 3.7V
Z
SPK
= 8Ω + 68µH
P
OUT
= 200mW
P
OUT
= 675mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc07
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01 10 100k
VDD = V
PVDD
= 3.7V
Z
SPK
= 4Ω + 33µH DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
P
OUT
= 1100mW
P
OUT
= 650mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc08
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01 10 100k
P
OUT
= 425mW
P
OUT
= 200mW
VDD = V
PVDD
= 3V
Z
SPK
= 8Ω + 68µH
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc09
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01 10 100k
P
OUT
= 700mW
P
OUT
= 250mW
VDD = V
PVDD
= 3V
Z
SPK
= 4Ω + 33µH
THD+N (%)
0.01
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
VDD = V Z DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
1
fIN = 20Hz
0.1
02.51.0 3.00.5 2.0
PVDD
= 4Ω + 33µH
SPK
= 5V
fIN = 6kHz
fIN = 1kHz
1.5
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
1
VDD = V P Z
0.1
f
THD+N (%)
0.01 10 100k
MAX9875 toc12
PVDD
= 200mW
OUT
= 8Ω + 68µH
SPK
= 1176kHz
OSC
= 3.7V
f
= 700kHz
OSC
f
= 1100kHz
OSC
FREQUENCY (Hz)
10k1k100
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
VDD = V
= 8Ω + 68µH
Z
MAX9875 toc10
SPK
1
fIN = 20Hz
THD+N (%)
0.1
0.01
02.0
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
1
THD+N (%)
0.1
0.01 0 1000600400 800200
VDD = V Z
PVDD
= 8Ω + 68µH
SPK
= 3.7V
fIN = 20Hz
fIN = 1kHz
OUTPUT POWER (mW)
= 5V
PVDD
fIN = 1kHz
OUTPUT POWER (W)
MAX9875 toc11
fIN = 6kHz
1.51.00.5
MAX9875 toc13
fIN = 6kHz
MAX9875
EFFICIENCY
vs. OUTPUT POWER
MAX9875 toc19
OUTPUT POWER (W)
EFFICIENCY (%)
1.5
100
0
50
60
10
80
30
70
20
90
40
03.00.5 2.01.0 2.5
VDD = V
PVDD
= 5V
f
IN
= 1kHz DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
Z
SPK
= 8Ω + 68µH
Z
SPK
= 4Ω + 33µH
EFFICIENCY
vs. OUTPUT POWER
MAX9875 toc20
OUTPUT POWER (W)
EFFICIENCY (%)
100
0
50
60
10
80
30
70
20
90
40
02.01.51.00.5
VDD = V
PVDD
= 3.7V
f
IN
= 1kHz DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
Z
SPK
= 8Ω + 68µH
Z
SPK
= 4Ω + 33µH
EFFICIENCY
vs. OUTPUT POWER
MAX9875 toc21
OUTPUT POWER (mW)
EFFICIENCY (%)
100
0
50
60
10
80
30
70
20
90
40
0 1000600200 800400
VDD = V
PVDD
= 3.7V
f
IN
= 1kHz
Z
SPK
= 8Ω + 68µH
f
OSC
= 700kHz
f
OSC
= 1176kHz AND 1100kHz
Typical Operating Characteristics (continued)
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, R
HP
= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
_______________________________________________________________________________________ 9
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
VDD = V
PVDD
= 4Ω + 33µH
Z
SPK
DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
1
fIN = 20Hz
THD+N (%)
0.1
0.01 0 1.51.00.5
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
1
VDD = V
PVDD
= 1kHz
f
IN
= 8Ω + 68µH
Z
SPK
= 3.7V
fIN = 6kHz
fIN = 1kHz
OUTPUT POWER (W)
= 3.7V
MAX9875 toc14
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
1
THD+N (%)
0.1
0.01
VDD = V Z
0600400200
PVDD
= 8Ω + 68µH
SPK
= 3V
fIN = 20Hz
fIN = 1kHz
OUTPUT POWER (mW)
MAX9875 toc15
fIN = 6kHz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
VDD = V Z DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
1
THD+N (%)
0.1
0.01 0 1.20.80.4 1.00.60.2
PVDD
= 4Ω + 33µH
SPK
fIN = 20Hz
= 3V
fIN = 1kHz
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
1
f
= 1100kHz
MAX9875 toc17
OSC
f
OSC
MAX9875 toc18
= 700kHz
fIN = 6kHz
MAX9875 toc16
0.1
THD+N (%)
0.01 0800
f
= 1176kHz SSM
OSC
f
= 1100kHz
OSC
OUTPUT POWER (mW)
f
= 700kHz
OSC
600400200
0.1
f
THD+N (%)
0.01
= 1176kHz SSM
OSC
VDD = V f
IN
Z
0800
OUTPUT POWER (mW)
= 6kHz
= 8Ω + 68µH
SPK
PVDD
600400200
= 3.7V
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
10 ______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, RHP= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
IN-BAND OUTPUT SPECTRUM
MAX9875 toc28
FREQUENCY (kHz)
AMPLITUDE (dBV)
15105
0
-140
-80
-40
-120
-20
-60
-100
020
f
OSC
= 1100kHz
f
IN
= 1kHz
IN-BAND OUTPUT SPECTRUM
MAX9875 toc29
FREQUENCY (kHz)
AMPLITUDE (dBV)
15105
0
-140
-80
-40
-120
-20
-60
-100
020
f
OSC
= 700kHz
f
IN
= 1kHz
EFFICIENCY
vs. OUTPUT POWER
MAX9875 toc22
OUTPUT POWER (mW)
EFFICIENCY (%)
100
0
50
60
10
80
30
70
20
90
40
01000600400 800200
VDD = V
PVDD
= 3V
f
IN
= 1kHz DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
Z
SPK
= 8Ω + 68µH
Z
SPK
= 4Ω + 33µH
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9875 toc23
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
5.04.54.03.53.0
2.0
2.5
0.5
1.0
1.5
3.0
3.5
0
2.5 5.5
10% THD+N
1% THD+N
VDD = V
PVDD
Z
SPK
= 4Ω + 33µH DASHED LINES ARE LIMITED BY THE ABS. MAX RATINGS
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9875 toc24
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
5.04.54.03.53.0
2.0
0.2
0.8
0.6
1.2
1.0
1.6
0.4
1.8
1.4
0
2.5 5.5
VDD = V
PVDD
Z
SPK
= 8Ω + 68µH
10% THD+N
1% THD+N
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9875 toc25
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
1.8
0.2
0.8
0.6
1.2
1.0
1.6
0.4
1.4
0
0100704010 805020 906030
VDD = V
PVDD
= 3.7V
f
IN
= 1kHz
Z
SPK
= LOAD + 68µH
10% THD+N
1% THD+N
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9875 toc26
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
1.2
0.2
0.8
0.6
1.0
0.4
0
0100704010 805020 906030
VDD = V
PVDD
= 3V
f
IN
= 1kHz
Z
SPK
= LOAD + 68µH
10% THD+N
1% THD+N
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9875 toc27
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-90
-70
-60
-40
-30
-10
-80
-50
-20
0
-100 10 100k
VDD = V
PVDD
= 3.7V
V
RIPPLE
= 100mV
P-P
INPUTS AC-COUPLED TO GND
MAX9875
Typical Operating Characteristics (continued)
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, RHP= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 11
0
f
OSC
= 1kHz
f
IN
-20
-40
-60
-80
AMPLITUDE (dBV)
-100
-120
-140 020
WIDEBAND OUTPUT SPECTRUM
0
f
OSC
-10
INPUTS AC-COUPLED TO GND
-20
-30
-40
-50
-60
AMPLITUDE (dBV)
-70
-80
-90
-100
0.1 10 1001
IN-BAND OUTPUT SPECTRUM
= 1176kHz
FREQUENCY (kHz)
= 700kHz
FREQUENCY (MHz)
MAX9875 toc30
15105
MAX9875 toc32
WIDEBAND OUTPUT SPECTRUM
0
f
= 1100kHz
OSC
-10
INPUTS AC-COUPLED TO GND
-20
-30
-40
-50
-60
AMPLITUDE (dBV)
-70
-80
-90
-100
0.1 10 1001
WIDEBAND OUTPUT SPECTRUM
0
f
= 1176kHz
OSC
-10
INPUTS AC-COUPLED TO GND
-20
-30
-40
-50
-60
AMPLITUDE (dBV)
-70
-80
-90
-100
0.1 10 1001
FREQUENCY (MHz)
FREQUENCY (MHz)
MAX9875 toc31
MAX9875 toc33
V
BIAS
500mV/div
OUT+ - OUT-
1V/div
HARDWARE SHUTDOWN RESPONSE
20ms/div
MAX9875 toc34
V
SDA
2V/div
OUT+ - OUT-
1V/div
ON- AND OFF-RESPONSE
MAX9875 toc35
20ms/div
SOFTWARE SHUTDOWN
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
12 ______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, RHP= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
HEADPHONE AMPLIFIER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc36
FREQUENCY (Hz)
THD+N (%)
0
0.001
0.01
0.1
10 100 1k 10k 100k
VDD = V
PVDD
= 3.7V
R
HP
= 32
P
OUT
= 10mW
P
OUT
= 20mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc37
FREQUENCY (Hz)
THD+N (%)
1
0.001
0.01
0.1
10 100 1k 10k 100k
VDD = V
PVDD
= 3.7V
R
HP
= 16
P
OUT
= 20mW
P
OUT
= 40mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc38
FREQUENCY (Hz)
THD+N (%)
1
0.001
0.01
0.1
10 100 1k 10k 100k
VDD = V
PVDD
= 3V
R
HP
= 32
P
OUT
= 10mW
P
OUT
= 20mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9875 toc39
FREQUENCY (Hz)
THD+N (%)
1
0.001
0.01
0.1
10 100 1k 10k 100k
VDD = V
PVDD
= 3V
R
HP
= 16
P
OUT
= 15mW
P
OUT
= 30mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9875 toc40
OUTPUT POWER (mW)
THD+N (%)
302010
0.01
0.1
1
10
0.001 040
VDD = V
PVDD
= 3.7V
R
HP
= 32
fIN = 20Hz
fIN = 1kHz
fIN = 6kHz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9875 toc41
OUTPUT POWER (mW)
THD+N (%)
0.01
0.1
1
10
0.001 0 20406010 30 50 70
VDD = V
PVDD
= 3.7V
R
HP
= 16
fIN = 20Hz AND 1kHz
fIN = 6kHz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9875 toc42
OUTPUT POWER (mW)
THD+N (%)
302010
0.01
0.1
1
10
0.001 040
VDD = V
PVDD
= 3V
R
HP
= 32
fIN = 20Hz
fIN = 1kHz
fIN = 6kHz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9875 toc43
OUTPUT POWER (mW)
THD+N (%)
0.01
0.1
1
10
0.001 0204010 30 50 60
VDD = V
PVDD
= 3V
R
HP
= 16
fIN = 20Hz AND 1kHz
fIN = 6kHz
MAX9875
Typical Operating Characteristics (continued)
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, RHP= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 13
350
300
250
200
150
100
POWER DISSIPATION (mW)
50
0
100
90
80
70
60
50
40
OUTPUT POWER (mW)
30
20
10
0
POWER DISSIPATION
vs. OUTPUT POWER
RHP = 16
RHP = 32
015010050
OUTPUT POWER (mW)
VDD = V
f P
= 1kHz
IN
OUT
= P
PVDD
HPL
= 3.7V
+ P
HPR
OUTPUT POWER
vs. SUPPLY VOLTAGE
fIN = 1kHz
= 16
R
10% THD+N
1% THD+N
2.5 5.5 SUPPLY VOLTAGE (V)
HP
5.04.54.03.53.0
250
MAX9875 toc44
200
150
100
POWER DISSIPATION (mW)
50
0
0 15010050
100
90
MAX9875 toc47
80
70
60
50
40
OUTPUT POWER (mW)
30
20
10
0
10 40 70 10020 50 8030 60 90
POWER DISSIPATION
vs. OUTPUT POWER
RHP = 32
OUTPUT POWER (mW)
OUTPUT POWER
vs. LOAD RESISTANCE
10% THD+N
1% THD+N
LOAD RESISTANCE (Ω)
RHP = 16
VDD = V
= 1kHz
f
IN
P
OUT
VDD = V
= 1kHz
f
IN
= P
PVDD
HPL
PVDD
= 3V
+ P
= 3.7V
HPR
MAX9875 toc45
OUTPUT POWER (mW)
100
MAX9875 toc48
OUTPUT POWER (mW)
OUTPUT POWER
vs. SUPPLY VOLTAGE
50
45
40
35
30
25
20
15
10
5
0
2.5 5.5
10% THD+N
1% THD+N
SUPPLY VOLTAGE (V)
fIN = 1kHz
= 32
R
HP
5.04.54.03.53.0
OUTPUT POWER
vs. LOAD RESISTANCE
VDD = V
90
80
70
60
10% THD+N
50
40
30
20
1% THD+N
10
0
10 40 70 10020 50 8030 60 90
LOAD RESISTANCE (Ω)
f
IN
= 1kHz
PVDD
= 3V
MAX9875 toc46
MAX9875 toc49
OUTPUT POWER
vs. LOAD RESISTANCE
100
90
80
70
60
C1 = C2 = 2.2µF
50
40
OUTPUT POWER (mW)
30
20
C1 = C2 = 0.47µF
10
0
10 40 70 10020 50 8030 60 90
LOAD RESISTANCE (Ω)
VDD = V
PVDD
OSC = 10
= 1kHz
f
IN
1% THD+N
= 3V
MAX9875 toc50
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
0
-10
-20
-30
-40
-50
-60
PSRR (dB)
-70
-80
-90
-100
-110
-120 10 100 1k 10k 100k
VDD = V V
RIPPLE
RHP = 32 INPUTS AC-COUPLED TO GND
HPR
HPL
FREQUENCY (Hz)
= 3.7V
PVDD
= 100mV
P-P
MAX9875 toc51
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
14 ______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= V
PV
DD
= 3.7V, V
GND
= V
PGND
= 0V. Single-ended inputs, preamp gain = 0dB, volume controls = 0dB, OSC = 00, SHDN = 1.
Speaker loads (Z
SPK
) connected between OUT+ and OUT-. Headphone loads (RHP) connected from HPL or HPR to GND. Z
SPK
=
, RHP= . C1 = C2 = C
BIAS
= 1µF. TA= +25°C, unless otherwise noted.)
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9875 toc55
FREQUENCY (Hz)
CMRR (dB)
80
0
20
40
60
10
70
30
50
10 100k10k1k100
VDD = V
PVDD
= 3.7V
CMRR = 20log(A
DM/ACM
)
+9dB
+20dB
0dB
OUTPUT SPECTRUM
MAX9875 toc52
FREQUENCY (kHz)
AMPLITUDE (dBV)
0
-140
-100
-60
-20
-120
-80
-40
02015105
VDD = V
PVDD
= 3.7V
f
IN
= 1kHz
R
HP
= 32
OUTPUT SPECTRUM
MAX9875 toc53
FREQUENCY (kHz)
AMPLITUDE (dBV)
0
-140
-100
-60
-20
-120
-80
-40
02015105
VDD = V
PVDD
= 3.7V
f
IN
= 1kHz
R
HP
= 16
CROSSTALK vs. FREQUENCY
MAX9875 toc54
FREQUENCY (Hz)
CROSSTALK (dB)
0
-120
-30
-10
-50
-90
-60
-100
-110
-70
-20
-40
-80
10 100k10k1k100
VDD = V
PVDD
= 3.7V
V
INA_
= 1V
P-P
R
HP
= 16
HPR TO HPL
HPL TO HPR
HARDWARE SHUTDOWN RESPONSE
V
BIAS
500mV/div
HPL
500mV/div
500mV/div
HPR
20ms/div
MAX9875 toc56
V
BIAS
500mV/div
HPL
500mV/div
HPR
500mV/div
ON- AND OFF-REPSONSE
20ms/div
SOFTWARE SHUTDOWN
MAX9875 toc57
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 15
Pin Description
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.
PIN NAME FUNCTION
A1 HPR Right Headphone Output
A2 HPL Left Headphone Output
A3 V
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 V
B2 BIAS
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
SS
DD
Headphone Amplifier Negative Power Supply. Bypass with a 1µF capacitor to PGND.
Analog Supply. Connect to PVDD. Bypass with a 1µF capacitor to GND.
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).
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
16 ______________________________________________________________________________________
Figure 1. Signal Path
IN_2 (R)
R
L
IN_1 (L)
STEREO SINGLE-ENDED
TO MIXER
IN_2 (+)
IN_1 (-)
DIFFERENTIAL
TO MIXER
Figure 2. Differential and Stereo Single-Ended Input Configurations
0dB HPR
INA2
INA1
INB2
INB1
INPUT A
0dB/+9dB/+20dB
INPUT B
0dB/+9dB/+20dB
MIXER
AND MUX
-75dB TO 0dB
-75dB TO 0dB
-75dB TO 0dB
0dB HPL
OUT+
+12dB
OUT-
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 17
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.
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).
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
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 I
2
C 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).
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.
MAX9875 EFFICIENCY
vs. IDEAL CLASS EFFICIENCY
MAX9875 fig03
OUTPUT POWER (W)
EFFICIENCY (%)
0.750.500.25
10
20
30
40
50
60
70
80
90
100
0
0 1.00
MAX9875
IDEAL CLASS AB
VDD = V
PVDD
= 3.7V (MAX9875)
V
SUPPLY
= 3.7V (IDEAL CLASS AB)
Figure 3. MAX9875 Efficiency vs. Class AB Efficiency
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
18 ______________________________________________________________________________________
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,
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:
FREQUENCY (MHz)
AMPLITUDE (dB∝V/m)
1601401201008060
10
15
20
25
30
35
40
TEST LIMIT
MAX9875 OUTPUT
MAX9875 OUTPUT
TEST LIMIT
5
30
180 200 240 260 280 300220
FREQUENCY (MHz)
AMPLITUDE (dB∝V/m)
600
550
500
450
400350
15
20
25
35
40
10
300
650
700 800
850 900
1000950
750
Figure 4. EMI with 152mm of Speaker Cable
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 19
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 1/2of 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.
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.
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.
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. 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.
V
DD
VDD/2
GND
CONVENTIONAL AMPLIFIER BIASING SCHEME
DirectDrive AMPLIFIER BIASING SCHEME
+V
DD
GND
-V
DD
(VSS)
Figure 5. Traditional Amplifier Output vs. MAX9875 DirectDrive Output
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
20 ______________________________________________________________________________________
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.
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
The MAX9875 is controlled through five I
2
C 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
Table 2. Input Mode Control
I2C Interface
REGISTER
Input Mode Control
Speaker Volume Control
Left Headphone Volume Control
Right Headphone Volume Control
Output Mode Control
REGISTER
ADDRESS
0x00 0x40 0 ZCD INA INB PGAINA PGAINB
0x01 0x00 0 0 0 SVOL (Table 4)
0x02 0x00 0 0 0 HPLVOL (Table 4)
0x03 0x00 0 0 0 HPRVOL (Table 4)
0x04 0x49 SHDN 0 OSC (Table 6) OUTMODE (Table 7)
POR STATE B7 B6 B5 B4 B3 B2 B1 B0
REGISTER B7 B6 B5 B4 B3 B2 B1 B0
0x00 0 ZCD INA INB PGAINA PGAINB
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 21
Shutdown (
SSHHDDNN
)
1 = MAX9875 operational.
0 = MAX9875 in low-power shutdown mode.
SHDN is an active-low shutdown bit that overrides all settings and places the entire device in low-power shut­down mode. The I
2
C interface is fully active in this shut­down mode. All register settings are preserved while in shutdown.
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
Table 5. Output Mode Control
Table 3. Speaker/Left Headphone/Right Headphone Volume Control
REGISTER B7 B6 B5 B4 B3 B2 B1 B0
0x01 0 0 0 SVOL (Table 4)
0x02 0 0 0 HPLVOL (Table 4)
0x03 0 0 0 HPRVOL (Table 4)
CODE
0 0 0 0 0 0 MUTE
1 0 0 0 0 1 -75
2 0 0 0 1 0 -71
3 0 0 0 1 1 -67
4 0 0 1 0 0 -63
5 0 0 1 0 1 -59
6 0 0 1 1 0 -55
7 0 0 1 1 1 -51
8 0 1 0 0 0 -47
9 0 1 0 0 1 -44
10 0 1 0 1 0 -41
11 0 1 0 1 1 -38
12 0 1 1 0 0 -35
13 0 1 1 0 1 -32
14 0 1 1 1 0 -29
15 0 1 1 1 1 -26
B4 B3 B2 B1 B0
_VOL
GAIN (dB)
CODE
16 1 0 0 0 0 -23
17 1 0 0 0 1 -21
18 1 0 0 1 0 -19
19 1 0 0 1 1 -17
20 1 0 1 0 0 -15
21 1 0 1 0 1 -13
22 1 0 1 1 0 -11
23 1 0 1 1 1 -9
24 1 1 0 0 0 -7
25 1 1 0 0 1 -6
26 1 1 0 1 0 -5
27 1 1 0 1 1 -4
28 1 1 1 0 0 -3
29 1 1 1 0 1 -2
30 1 1 1 1 0 -1
31 1 1 1 1 1 0
B4 B3 B2 B1 B0
_VOL
GAIN (dB)
REGISTER B7 B6 B5 B4 B3 B2 B1 B0
0x04 SHDN 0 OSC (Table 6 ) OUTMODE (Table 7)
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
22 ______________________________________________________________________________________
Table 6. Oscillator Modes
Table 7. Output Modes
— = Amplifier Off
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.
OSC
B5 B4
0 0 1176, spread spectrum 588, spread spectrum
0 1 1100, fixed frequency 550, fixed frequency
1 0 700, fixed frequency 350, fixed frequency
1 1 Reserved
CLASS D OSCILLATOR MODE (kHz) CHARGE-PUMP OSCILLATOR MODE (kHz)
IN_ = 0
MODE
B3 B2 B1 B0 SPK LEFT HP RIGHT HP SPK LEFT HP RIGHT HP
0 0000 Reserved Reserved
1 0001INA1+INA2 INA ——
2 0010 INA1 INA2 INA INA∆
3 0011INA1+INA2 INA1 INA2 INA INA∆ INA∆
4 0100INB1+INB2 INB ——
5 0101 INB1 INB2 INB INB∆
6 0110INB1+INB2 INB1 INB2 INB INB∆ INB∆
7 0111
8 1000 — INA1+INB1 INA2+INB2
9 1001
10–15 Reserved Reserved
OUTMODE
(THE SINGLE-ENDED INPUT SIGNALS
ARE DEFINED AS IN_1 = LEFT AND
IN_2 = RIGHT)
INA1+INA2
+INB1+INB2
INA1+INA2
+INB1+INB2
INA+INB ——
INA1+INB1 INA2+INB2 INA+INB
(THE DIFFERENTIAL INPUT SIGNAL IS
DEFINED AS IN_ = IN_2 - IN_1)
IN_ = 1
INA
+INB
INA
+INB
INA +INB
INA +INB
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 23
Figure 6. 2-Wire Interface Timing Diagram
SCL
SDA
SSrP
Figure 7. START, STOP, and REPEATED START Conditions
SMBus is a trademark of Intel Corp.
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 500, is required on SDA. SCL oper­ates only as an input. A pullup resistor, typically greater
than 500, 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
t
t
LOW
SCL
t
HD:STA
START
CONDITION
SU:DAT
t
HIGH
t
R
t
HD:DAT
t
F
t
SU:STA
REPEATED
START CONDITION
t
SU:STA
t
SU:STO
STOP
CONDITION
t
BUF
START
CONDITION
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
24 ______________________________________________________________________________________
Figure 9. Writing One Byte of Data to the MAX9875
1
SCL
START
CONDITION
SDA
289
CLOCK PULSE FOR
ACKNOWLEDGMENT
ACKNOWLEDGE
NOT ACKNOWLEDGE
Figure 8. Acknowledge
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.
ACKNOWLEDGE FROM MAX9875
ACKNOWLEDGE FROM MAX9875
S AA
0SLAVE ADDRESS REGISTER ADDRESS DATA BYTE
R/W
ACKNOWLEDGE FROM MAX9875
1 BYTE
B1 B0B3 B2B5 B4B7 B6
A
P
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 25
Figure 11. Reading One Indexed Byte of Data from the MAX9875
1 BYTE
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
ACKNOWLEDGE FROM MAX9875
ACKNOWLEDGE FROM MAX9875
B1 B0B3 B2B5 B4B7 B6
A
A0
ACKNOWLEDGE FROM MAX9875
R/W
S
A
1 BYTE
ACKNOWLEDGE FROM MAX9875
B1 B0B3 B2B5 B4B7 B6
P
A
SLAVE ADDRESS
REGISTER ADDRESS
DATA BYTE 1
DATA BYTE n
Figure 10. Writing n-Bytes of Data to the 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.
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
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.
ACKNOWLEDGE FROM MAX9875
SA
ACKNOWLEDGE FROM MAX9875
0
R/W
ACKNOWLEDGE FROM MAX9875
Sr 1SLAVE ADDRESS REGISTER ADDRESS SLAVE ADDRESS DATA BYTE
NOT ACKNOWLEDGE FROM MASTER
AA
R/WREPEATED START
A
1 BYTE
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
P
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
26 ______________________________________________________________________________________
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 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 V
DD(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 8speakers 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 100to 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 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
IN
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, C
BIAS
, 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 100mfor 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.
Figure 13. Optional Ferrite Bead Filter
ACKNOWLEDGE FROM MAX9875
1 BYTE
AUTOINCREMENT INTERNAL
REGISTER ADDRESS POINTER
ACKNOWLEDGE FROM MAX9875
AA
AP
0
ACKNOWLEDGE FROM MAX9875
R/W
SA
R/W
REPEATED START
Sr 1SLAVE ADDRESS REGISTER ADDRESS SLAVE ADDRESS DATA BYTE
Figure 12. Reading n-Bytes of Indexed Data from the MAX9875
OUT+
MAX9875
OUT-
f
−=3
dB
1
RC
2π
IN IN
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
______________________________________________________________________________________ 27
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.
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
.
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.
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 VDDto PVDD. Bypass VDDto GND with a 1µF capacitor. Place the bypass capacitors as close to the MAX9875 as possible.
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-
ceptibility to RF noise and prevent RF signals from being demodulated into audible noise. Trace lengths should be kept below
1
/4the 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:
λ = c/f
where c = 3 x 108m/s, and f = the RF frequency of inter­est.
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.
RF SUSCEPTIBILITY
MAX9875 fig14
FREQUENCY (Hz)
EFFICIENCY (dBµ)
10k1k100
-130
-110
-90
-70
-50
-30
-10
-150 10 100k
THRESHOLD OF HEARING
MAX9875
NOISE FLOOR
Figure 14. MAX9875 Susceptibility to a GSM Cell Phone Radio
MAX9875
Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier
28 ______________________________________________________________________________________
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.
250µm
45±5µm
Figure 15. PCB Footprint Recommendation Diagram
MAX9875
Low RF Susceptibility, Mono Audio
Subsystem with DirectDrive Headphone Amplifier
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Typical Application Circuit
Chip Information
PROCESS: BiCMOS
INPUT A
INPUT B
OPEN-DRAIN GPIO
1µF
1µF
V
BATT
C2 1µF
V
SS
A3
C1N
C1
C1PA4A5
1µF
INA2
INA1D1D2
1µF
1µF
INB2
INB1C1C2
1µF
BIAS
B2
CHARGE
PUMP
INPUT A
0dB/+9dB/+20dB
INPUT B
0dB/+9dB/+20dB
V
DD
B1
MIXER
AND
MUX
1µF
V
BATT
PVDD
C5
-75dB TO 0dB
-75dB TO 0dB
-75dB TO 0dB
C3 1µF
0dB
0dB
CLASS D
MODULATOR
+12dB
MAX9875
A1 HPR
A2 HPL
B5D5OUT+
OUT-
SDA
SCL
B3
C3
2
I
C
CONTROL
D3
GND
C4
PGND
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.
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
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