MAX9712EUB-T [MAXIM]
Audio Amplifier, 0.7W, 1 Channel(s), 1 Func, BICMOS, PDSO10, MICRO, MAX-10;
| 型号： | MAX9712EUB-T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Audio Amplifier, 0.7W, 1 Channel(s), 1 Func, BICMOS, PDSO10, MICRO, MAX-10 放大器 信息通信管理 光电二极管 商用集成电路 |
| 文件： | 总18页 (文件大小：531K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2917; Rev 1; 1/04
500mW, Low EMI, Filterless,
Class D Audio Amplifier
General Description
Features
The MAX9712 mono class D audio power amplifier pro-
vides class AB amplifier performance with class D effi-
ciency, conserving board space, and extending battery
life. Using a class D architecture, the MAX9712 delivers
up to 500mW into an 8Ω load while offering efficiencies
above 85%. A patented, low EMI modulation scheme
renders the traditional class D output filter unnecessary.
✕ Filterless Amplifier Passes FCC Radiated
Emissions Standards with 100mm of Cable
✕ Unique Spread-Spectrum Mode Offers 5dB
Emissions Improvement Over Conventional
Methods
✕ Optional External SYNC Input
✕ Simple Master-Slave Setup for Stereo Operation
✕ 85% Efficiency
The MAX9712 offers two modulation schemes: a fixed-
frequency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions due to the
modulation frequency. Furthermore, the MAX9712 oscil-
lator can be synchronized to an external clock through
the SYNC input, allowing the switching frequency to be
user defined. The SYNC input also allows multiple
MAX9712s to be cascaded and frequency locked, mini-
mizing interference due to clock intermodulation. The
device utilizes a fully differential architecture, a full-
bridged output, and comprehensive click-and-pop sup-
pression. The gain is internally set to +4V/V, further
reducing external component count.
✕ Up to 500mW into 8Ω
✕ Low 0.01% THD+N
✕ High PSRR (72dB at 217Hz)
✕ Integrated Click-and-Pop Suppression
✕ Low Quiescent Current (4mA)
✕ Low-Power Shutdown Mode (0.1µA)
✕ Short-Circuit and Thermal-Overload Protection
✕ Available in Thermally Efficient, Space-Saving
Packages
The MAX9712 features high 72dB PSRR, a low 0.01%
THD+N, and SNR in excess of 90dB. Short-circuit and
thermal-overload protection prevent the device from
damage during a fault condition. The MAX9712 is avail-
able in 10-pin TDFN (3mm ✕ 3mm ✕ 0.8mm), 10-pin
µMAX, and 12-bump UCSP™ (1.5mm ✕ 2mm ✕ 0.6mm)
packages. The MAX9712 is specified over the extended
-40°C to +85°C temperature range.
10-Pin TDFN (3mm ✕ 3mm ✕ 0.8mm)
10-Pin µMAX
12-Bump UCSP (1.5mm ✕ 2mm ✕ 0.6mm)
Ordering Information
PIN/BUMP-
PACKAGE
TOP
MARK
Applications
PART
TEMP RANGE
Cellular Phones
PDAs
MP3 Players
MAX9712ETB
MAX9712EUB
MAX9712EBC-T
-40°C to +85°C 10 TDFN
-40°C to +85°C 10 µMAX
-40°C to +85°C 12 UCSP-12
AAI
—
Portable Audio
ABN
Simplified Block Diagram
V
DD
Pin Configurations
TOP VIEW
DIFFERENTIAL
AUDIO INPUT
MODULATOR
AND H-BRIDGE
V
1
2
3
4
5
10 PV
DD
DD
IN+
IN-
9
8
7
6
OUT-
OUT+
PGND
SYNC
MAX9712
SYNC
INPUT
OSCILLATOR
GND
SHDN
MAX9712
TDFN/µMAX
Pin Configurations continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
500mW, Low EMI, Filterless,
Class D Audio Amplifier
ABSOLUTE MAXIMUM RATINGS
V
to GND..............................................................................6V
Continuous Power Dissipation (T = +70°C)
A
DD
PV
to PGND .........................................................................6V
10-Pin TDFN (derate 24.4mW/°C above +70°C) .....1951.2mW
DD
o
GND to PGND .......................................................-0.3V to +0.3V
10-Pin µMAX (derate 5.6mW/ C above +70°C).........444.4mW
All Other Pins to GND.................................-0.3V to (V
+ 0.3V)
12-Bump UCSP (derate 6.1mW/°C above +70°C)........484mW
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
Bump Temperature (soldering)
DD
Continuous Current Into/Out of PV /PGND/OUT_........±600mA
DD
Continuous Input Current (all other pins)..........................±20mA
Duration of OUT_ Short Circuit to GND or PV ........Continuous
DD
Duration of Short Circuit Between OUT+ and OUT- ..Continuous
Reflow ..........................................................................+235°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
DD
= PV
= SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), R = 8Ω, R connected between OUT+ and OUT-, T
=
DD
L
L
A
T
MIN
to T
, unless otherwise noted. Typical values are at T = +25°C.) (Notes 1, 2)
MAX A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Supply Voltage Range
Quiescent Current
Shutdown Current
Turn-On Time
V
Inferred from PSRR test
2.5
5.5
5.2
5
V
DD
I
4
0.1
30
mA
µA
ms
kΩ
V
DD
I
SHDN
t
ON
Input Resistance
Input Bias Voltage
Voltage Gain
R
T
A
= +25°C
14
0.73
3.8
20
IN
V
Either input
0.83
4
0.93
4.2
BIAS
A
V/V
V
MAX9712EUB/MAX9712ETB
MAX9712EBC
±11
±15
±40
±65
±65
±95
T
= +25°C
A
Output Offset Voltage
V
mV
OS
MAX9712EUB/MAX9712ETB
MAX9712EBC
T
T
≤ T ≤
A
MIN
MAX
Common-Mode Rejection Ratio
CMRR
PSRR
f
= 1kHz, input referred
72
70
dB
dB
IN
V
= 2.5V to 5.5V
50
DD
Power-Supply Rejection Ratio
(Note 3)
f
f
= 217Hz
= 20kHz
72
RIPPLE
200mV
ripple
P-P
55
RIPPLE
R = 16Ω, V
= 5V
700
450
250
L
DD
Output Power
P
THD+N = 1%
R = 8Ω
L
mW
%
OUT
R = 6Ω
L
R = 8Ω,
L
0.01
0.01
P
= 125mW
OUT
Total Harmonic Distortion Plus
Noise
f
IN
= 1kHz, either
THD+N
FFM or SSM
R = 6Ω,
L
P
= 125mW
OUT
2
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= PV
= SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), R = 8Ω, R connected between OUT+ and OUT-, T
=
DD
L
L
A
T
MIN
to T
, unless otherwise noted. Typical values are at T = +25°C.) (Notes 1, 2)
MAX A
PARAMETER
SYMBOL
CONDITIONS
BW = 22Hz
MIN
TYP
88
MAX
UNITS
FFM
SSM
FFM
SSM
to 22kHz
86
Signal-to-Noise Ratio
Oscillator Frequency
SNR
V
= 1.8V
dB
OUT
RMS
91
A-weighted
89
SYNC = GND
SYNC = float
980
1100
1450
1220
1620
1280
f
kHz
OSC
1220
±120
SYNC = V
(SSM mode)
DD
SYNC Frequency Lock Range
Efficiency
800
2
2000
kHz
%
η
P
= 300mW, f = 1kHz
85
OUT
IN
DIGITAL INPUTS (SHDN, SYNC)
V
V
IH
IL
Input Thresholds
V
0.8
±1
±5
SHDN Input Leakage Current
µA
µA
SYNC Input Current
Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Note 2: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For R = 6Ω, L = 47µH.
L
For R = 8Ω, L = 68µH. For R = 16Ω, L = 136µH.
L
L
Note 3: PSRR is specified with the amplifier inputs connected to GND through C
.
IN
Typical Operating Characteristics
(V
DD
= 3.3V, V
= GND, T = +25°C, unless otherwise noted.)
SYNC
A
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
1
1
1
V
DD
= +3.3V
V
DD
= +5V
V
DD
= +3.3V
R = 8Ω
R = 8Ω
L
R = 8Ω
L
L
P
= 125mW
OUT
0.1
0.1
0.1
P
OUT
= 300mW
P
OUT
= 300mW
SSM MODE
0.01
0.01
0.001
0.01
0.001
P
= 125mW
OUT
P
= 125mW
10k
OUT
FFM MODE
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
FREQUENCY (Hz)
_______________________________________________________________________________________
3
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, V
= GND, T = +25°C, unless otherwise noted.)
SYNC
A
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
100
100
10
1
100
10
1
V
DD
= 3.3V
V
DD
= 5V
V
DD
= 3.3V
R = 8Ω
L
R = 16Ω
L
R = 6Ω
L
10
1
f = 10kHz
f = 10kHz
0.1
0.1
0.1
f = 10kHz
0.01
0.01
0.01
f = 100Hz
0.2
f = 100Hz
0.3
f = 1kHz
f = 100Hz
0.6 0.8
f = 1kHz
0.4
f = 1kHz
0.001
0.001
0.001
0
0.1
0.2
0.4
0.5
0
0.2
1.0
0
0.1
0.3
0.4
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
100
10
1
100
10
1
100
10
1
V
= 2.5V
V
DD
= 3.3V
DD
V
DD
= 3.3V
R = 8Ω
R = 8Ω
SYNC = 3.3V
L
L
R = 8Ω
L
f = 2MHz
SYNC
V
CM
= 1.25V
P-P
NO INPUT CAPACITORS
50% DUTY CYCLE
SQUARE WAVE
f
= 1.4MHz
SYNC
SSM
(SYNC = V
FFM
DIFFERENTIAL
INPUT
)
DD
(SYNC FLOATING)
0.1
0.1
0.1
0.01
0.01
0.01
SINGLE-ENDED
FFM
f
= 800kHz
0.2
SYNC
(SYNC = GND)
0.001
0.001
0.001
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.3
0.4
0.5
0.6
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
EFFICIENCY vs. OUTPUT POWER
EFFICIENCY vs. OUTPUT POWER
10
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
V
DD
= 3.3V
R = 8Ω
L
f = 1kHz
R = 16Ω
L
P
= 300mW
R = 16Ω
L
OUT
DIFFERENTIAL INPUT
R = 8Ω
L
1
R = 8Ω
L
R = 6Ω
L
0.1
V
DD
= 5V
V
DD
= 3.3V
f = 1kHz
f = 1kHz
0.01
0
0.5
1.0
1.5
2.0
2.5
3.0
0
0.1
0.2
0.3
0.4
0.5
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7
OUTPUT POWER (W)
OUTPUT POWER (W)
COMMON-MODE VOLTAGE (V)
4
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, V
= GND, T = +25°C, unless otherwise noted.)
SYNC
A
EFFICIENCY
vs. SYNC INPUT FREQUENCY
OUTPUT POWER
vs. SUPPLY VOLTAGE
EFFICIENCY vs. SUPPLY VOLTAGE
100
90
80
70
60
50
40
30
20
10
0
1000
900
800
700
600
500
400
300
200
100
0
100
f = 1kHz
90
80
70
60
50
40
30
20
10
0
R = 16Ω
L
R = 8Ω
L
R = 6Ω
L
R = 16Ω
L
R = 8Ω
L
V
= 3.3V
DD
f = 1kHz
= 300mW
P
OUT
R = 6Ω
L
R = 8Ω
f = 1kHz
L
800 1000 1200 1400 1600 1800 2000
SYNC FREQUENCY (kHz)
2.5
3.1
3.7
4.3
4.9
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
OUTPUT POWER
vs. LOAD RESISTANCE
0
0
1000
900
800
700
600
500
400
300
200
100
0
f = 1kHz
THD+N = 1%
INPUT REFERRED
OUTPUT REFERRED
INPUTS AC GROUNDED
-10
-20
-30
-40
-50
-60
-70
-80
-10
-20
-30
-40
-50
-60
-70
-80
V
IN
= 200mV
P-P
V
DD
= 3.3V
V
= 5V
DD
V
= 3.3V
DD
-90
-90
-100
-100
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
10k
100k
0
10 20 30 40 50 60 70 80 90 100
FREQUENCY (Hz)
LOAD RESISTANCE (Ω)
GSM POWER-SUPPLY REJECTION
OUTPUT FREQUENCY SPECTRUM
MAX9712TOC19
0
-20
-40
-60
-80
FFM MODE
V
OUT
= -60dBV
f = 1kHz
500mV/div
V
DD
R = 8Ω
L
UNWEIGHTED
-100
-120
-140
MAX9712
OUTPUT
100µV/div
2ms/div
0
5k
10k
15k
20k
f = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
DUTY CYCLE = 88%
R = 8Ω
FREQUENCY (Hz)
L
_______________________________________________________________________________________
5
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, V
= GND, T = +25°C, unless otherwise noted.)
SYNC
A
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
OUTPUT FREQUENCY SPECTRUM
OUTPUT FREQUENCY SPECTRUM
0
0
0
-20
SSM MODE
SSM MODE
RBW = 10kHz
-10
-20
-30
-40
-50
-60
-70
-80
V
= -60dBV
V
= -60dBV
OUT
OUT
-20
-40
f = 1kHz
f = 1kHz
R = 8Ω
R = 8Ω
L
L
-40
UNWEIGHTED
A-WEIGHTED
-60
-60
-80
-80
-100
-120
-140
-100
-120
-140
-90
-100
1M
10M
100M
1G
0
5
10
15
20
0
5
10
15
20
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (Hz)
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
TURN-ON/TURN-OFF RESPONSE
0
RBW = 10kHz
-10
-20
-30
-40
-50
-60
-70
-80
3V
SHDN
0V
MAX9712
OUTPUT
250mV/div
-90
-100
1M
10M
100M
1G
10ms/div
f = 1kHz
R = 8Ω
FREQUENCY (Hz)
L
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
6.0
5.5
5.0
4.5
4.0
3.5
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0
T
= +85°C
A
T
= +85°C
A
T
A
= +25°C
T
A
= +25°C
T
= -40°C
A
T
A
= -40°C
3.0
2.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
6
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Functional Diagram
V
DD
10µF
1µF
1
10
6
(C4)
(B1)
(C2)
V
DD
PV
DD
SYNC
5
(B3)
SHDN
UVLO/POWER
MANAGEMENT
CLICK AND POP
SUPPRESSION
OSCILLATOR
PV
DD
2
(B4)
8
(C1)
IN+
IN-
OUT+
OUT-
PGND
CLASS D
MODULATOR
3
(A4)
PV
DD
9
(A1)
MAX9712
PGND
GND
PGND
7
4
(B2)
(A5)
( ) UCSP BUMP.
_______________________________________________________________________________________
7
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Pin Description
PIN
BUMP
UCSP
C4
NAME
FUNCTION
TDFN/µMAX
1
2
3
4
5
V
Analog Power Supply
Noninverting Audio Input
Inverting Audio Input
Analog Ground
DD
B4
IN+
IN-
A4
A3
GND
SHDN
B3
Active-Low Shutdown Input. Connect to V
for normal operation.
DD
Frequency Select and External Clock Input.
SYNC = GND: Fixed-frequency mode with f = 1100kHz.
S
6
C2
SYNC
SYNC = Float: Fixed-frequency mode with f = 1450kHz.
S
SYNC = V : Spread-spectrum mode with f = 1220kHz ±120kHz.
DD
S
SYNC = Clocked: Fixed-frequency mode with f = external clock frequency.
S
7
8
B2
C1
A1
B1
PGND
OUT+
OUT-
Power Ground
Amplifier Output Positive Phase
Amplifier Output Negative Phase
H-Bridge Power Supply
9
10
PV
DD
Operating Modes
Detailed Description
Fixed-Frequency Modulation (FFM) Mode
The MAX9712 features two FFM modes. The FFM
modes are selected by setting SYNC = GND for a
1.1MHz switching frequency, and SYNC = FLOAT for a
1.45MHz switching frequency. In FFM mode, the fre-
quency spectrum of the class D output consists of the
fundamental switching frequency and its associated
harmonics (see the Wideband FFT graph in the Typical
Operating Characteristics). The MAX9712 allows the
switching frequency to be changed by +32%, should
the frequency of one or more of the harmonics fall in a
sensitive band. This can be done at any time and does
not affect audio reproduction.
The MAX9712 filterless, class D audio power amplifier
features several improvements to switch-mode amplifier
technology. The MAX9712 offers class AB performance
with class D efficiency, while occupying minimal board
space. A unique filterless modulation scheme, synchro-
nizable switching frequency, and SSM mode create a
compact, flexible, low-noise, efficient audio power
amplifier. The differential input architecture reduces
common-mode noise pick-up, and can be used without
input-coupling capacitors. The device can also be con-
figured as a single-ended input amplifier.
Comparators monitor the MAX9712 inputs and com-
pare the complementary input voltages to the sawtooth
waveform. The comparators trip when the input magni-
tude of the sawtooth exceeds their corresponding input
voltage. Both comparators reset at a fixed time after the
rising edge of the second comparator trip point, gener-
Spread-Spectrum Modulation (SSM) Mode
The MAX9712 features a unique, patented spread-spec-
trum mode that flattens the wideband spectral compo-
nents, improving EMI emissions that may be radiated by
the speaker and cables by 5dB. Proprietary techniques
ensure that the cycle-to-cycle variation of the switching
period does not degrade audio reproduction or efficien-
cy (see the Typical Operating Characteristics). Select
ating a minimum-width pulse t
at the output of
ON(min)
the second comparator (Figure 1). As the input voltage
increases or decreases, the duration of the pulse at one
output increases (the first comparator to trip) while the
SSM mode by setting SYNC = V . In SSM mode, the
DD
other output pulse duration remains at t
. This
OUT+
ON(min)
switching frequency varies randomly by ±120kHz
around the center frequency (1.22MHz). The modulation
scheme remains the same, but the period of the saw-
tooth waveform changes from cycle to cycle (Figure 2).
Instead of a large amount of spectral energy present at
multiples of the switching frequency, the energy is now
causes the net voltage across the speaker (V
-
V
) to change.
OUT-
8
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
t
SW
V
IN-
V
IN+
OUT-
OUT+
t
ON(MIN)
V
OUT+
- V
OUT-
Figure 1. MAX9712 Outputs with an Input Signal Applied
system), or allocating the spectral components of the
switching harmonics to insensitive frequency bands.
Applying an external TTL clock of 800kHz to 2MHz to
SYNC synchronizes the switching frequency of the
MAX9712. The period of the SYNC clock can be ran-
domized, enabling the MAX9712 to be synchronized to
another MAX9712 operating in SSM mode.
Table 1. Operating Modes
SYNC INPUT
MODE
GND
FFM with f = 1100kHz
S
FLOAT
FFM with f = 1450kHz
S
V
SSM with f = 1220kHz ±120kHz
S
DD
Clocked
FFM with f = external clock frequency
S
Filterless Modulation/Common-Mode Idle
The MAX9712 uses Maxim’s unique, patented modula-
tion scheme that eliminates the LC filter required by
traditional class D amplifiers, improving efficiency,
reducing component count, conserving board space
and system cost. Conventional class D amplifiers out-
put a 50% duty cycle square wave when no signal is
present. With no filter, the square wave appears across
spread over a bandwidth that increases with frequency.
Above a few MHz, the wideband spectrum looks like
white noise for EMI purposes (Figure 3).
External Clock Mode
The SYNC input allows the MAX9712 to be synchro-
nized to a system clock (allowing a fully synchronous
_______________________________________________________________________________________
9
500mW, Low EMI, Filterless,
Class D Audio Amplifier
t
t
t
t
SW
SW
SW
SW
V
IN-
V
IN+
OUT-
OUT+
t
ON(MIN)
V
OUT+
- V
OUT-
Figure 2. MAX9712 Output with an Input Signal Applied (SSM Mode)
the load as a DC voltage, resulting in finite load current,
increasing power consumption. When no signal is pre-
sent at the input of the MAX9712, the outputs switch as
shown in Figure 4. Because the MAX9712 drives the
speaker differentially, the two outputs cancel each
other, resulting in no net idle mode voltage across the
speaker, minimizing power consumption.
The theoretical best efficiency of a linear amplifier is
78%, however, that efficiency is only exhibited at peak
output powers. Under normal operating levels (typical
music reproduction levels), efficiency falls below 30%,
whereas the MAX9712 still exhibits >80% efficiencies
under the same conditions (Figure 5).
Efficiency
Efficiency of a class D amplifier is attributed to the
region of operation of the output stage transistors. In a
class D amplifier, the output transistors act as current-
steering switches and consume negligible additional
power. Any power loss associated with the class D out-
put stage is mostly due to the I ✕ R loss of the MOSFET
on-resistance, and quiescent current overhead.
10 ______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
V
IN
= 0V
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
OUT-
OUT+
30.0
60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 240.0 260.0 280.0 300.0
FREQUENCY (MHz)
V - V = 0V
OUT+ OUT-
Figure 3. MAX9712 with 76mm of Speaker Cable
Figure 4. MAX9712 Outputs with No Input Signal
Shutdown
The MAX9712 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9712 in a low-power (0.1µA) shutdown
EFFICIENCY vs. OUTPUT POWER
100
90
80
70
mode. Connect SHDN to V
for normal operation.
DD
Click-and-Pop Suppression
The MAX9712 features comprehensive click-and-pop
suppression that eliminates audible transients on start-
up and shutdown. While in shutdown, the H-bridge is in
a high-impedance state. During startup, or power-up,
the input amplifiers are muted and an internal loop sets
the modulator bias voltages to the correct levels, pre-
venting clicks and pops when the H-bridge is subse-
quently enabled. For 35ms following startup, a soft-start
function gradually unmutes the input amplifiers.
MAX9712
60
50
40
CLASS AB
30
V
DD
= 3.3V
20
10
0
f = 1kHz
R - 8Ω
L
0
0.1
0.2
0.3
0.4
0.5
OUTPUT POWER (W)
Applications Information
Figure 5. MAX9712 Efficiency vs. Class AB Efficiency
Filterless 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 amplifi-
er, and can decrease efficiency. The traditional PWM
Because the frequency of the MAX9712 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 may be dam-
aged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8Ω speakers exhibit series
inductances in the range of 20µH to 100µH.
scheme uses large differential output swings (2 x V
DD
peak-to-peak) and causes large ripple currents. Any
parasitic resistance in the filter components results in a
loss of power, lowering the efficiency.
The MAX9712 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.
Power Conversion Efficiency
Unlike a class AB amplifier, the output offset voltage of
a class D amplifier does not noticeably increase quies-
cent current draw when a load is applied. This is due to
______________________________________________________________________________________ 11
500mW, Low EMI, Filterless,
Class D Audio Amplifier
the power conversion of the class D amplifier. For exam-
ple, an 8mV DC offset across an 8Ω load results in 1mA
extra current consumption in a class AB device. In the
class D case, an 8mV offset into 8Ω equates to an addi-
tional power drain of 8µW. Due to the high efficiency of
the class D amplifier, this represents an additional quies-
1µF
SINGLE-ENDED
AUDIO INPUT
IN+
IN-
MAX9712
cent current draw of: 8µW/(V /100η), which is on the
1µF
DD
order of a few microamps.
Input Amplifier
Differential Input
The MAX9712 features a differential input structure,
making it compatible with many CODECs, and offering
improved noise immunity over a single-ended input
amplifier. In devices such as cellular phones, high-fre-
quency signals from the RF transmitter can be picked
up by the amplifier’s input traces. The signals appear at
the amplifier’s inputs as common-mode noise. A differ-
ential input amplifier amplifies the difference of the two
inputs, any signal common to both inputs is canceled.
Figure 6. Single-Ended Input
high-voltage coefficients, such as ceramics, may result
in increased distortion at low frequencies.
Other considerations when designing the input filter
include the constraints of the overall system and the
actual frequency band of interest. Although high-fidelity
audio calls for a flat-gain response between 20Hz and
20kHz, portable voice-reproduction devices such as
cellular phones and two-way radios need only concen-
trate on the frequency range of the spoken human
voice (typically 300Hz to 3.5kHz). In addition, speakers
used in portable devices typically have a poor response
below 150Hz. Taking these two factors into considera-
tion, the input filter may not need to be designed for a
20Hz to 20kHz response, saving both board space and
cost due to the use of smaller capacitors.
Single-Ended Input
The MAX9712 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND, and driving the other input (Figure 6).
DC-Coupled Input
The input amplifier can accept DC-coupled inputs that
are biased within the amplifier’s common-mode range
(see the Typical Operating Characteristics). DC cou-
pling eliminates the input-coupling capacitors, reduc-
ing component count to potentially one external
component (see the System Diagram). However, the
low-frequency rejection of the capacitors is lost, allow-
ing low-frequency signals to feedthrough to the load.
Output Filter
The MAX9712 does not require an output filter. The
device passes FCC emissions standards with 100mm
of unshielded speaker cables. However, output filtering
can be used if a design is failing radiated emissions
due to board layout or cable length, or the circuit is
near EMI sensitive devices. Use an LC filter when radi-
ated emissions are a concern, or when long leads are
used to connect the amplifier to the speaker.
Component Selection
Input Filter
An input capacitor, C , in conjunction with the input
IN
impedance of the MAX9712 forms a highpass filter that
removes the DC bias from an incoming signal. The AC-
coupling capacitor allows the amplifier to bias the sig-
nal to an optimum DC level. Assuming zero-source
impedance, the -3dB point of the highpass filter is
given by:
Supply Bypassing/Layout
Proper power-supply bypassing ensures low distortion
operation. For optimum performance, bypass VDD to
GND and PVDD to PGND with separate 0.1µF capaci-
tors as close to each pin as possible. A low-imped-
ance, high-current power-supply connection to PVDD is
assumed. Additional bulk capacitance should be
added as required depending on the application and
power-supply characteristics. GND and PGND should
be star connected to system ground. Refer to the
MAX9712 Evaluation Kit for layout guidance.
1
f
=
−3dB
2πR C
IN IN
Choose C so f
is well below the lowest frequency
-3dB
IN
-3dB
of interest. Setting f
too high affects the low-fre-
Stereo Configuration
Two MAX9712s can be configured as a stereo amplifier
(Figure 7). Device U1 is the master amplifier; its unfil-
quency response of the amplifier. Use capacitors
whose dielectrics have low-voltage coefficients, such
as tantalum or aluminum electrolytic. Capacitors with
12 ______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
tered output drives the SYNC input of the slave device
(U2), synchronizing the switching frequencies of the two
devices. Synchronizing two MAX9712s ensures that no
beat frequencies occur within the audio spectrum. This
configuration works when the master device is in either
FFM or SSM mode. There is excellent THD+N perfor-
mance and minimal crosstalk between devices due to
the SYNC connection (Figures 8 and 9). U2 locks onto
only the frequency present at SYNC, not the pulse
width. The internal feedback loop of device U2 ensures
that the audio component of U1’s output is rejected.
V
DD
1µF
V
DD
PV
DD
MAX9712
IN+
IN-
OUT+
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
OUT-
UCSP Applications Information
SYNC
For the latest application details on UCSP construction,
dimensions, tape carrier information, printed circuit
board techniques, bump-pad layout, and recommend-
ed 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 available on Maxim’s website at www.maxim-
ic.com/ucsp.
1µF
V
DD
PV
DD
MAX9712
IN+
IN-
OUT+
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
Chip Information
TRANSISTOR COUNT: 3595
OUT-
PROCESS: BiCMOS
SYNC
Figure 7. Master-Slave Stereo Configuration
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
CROSSTALK vs. FREQUENCY
100
0
V
= 3.3V
DD
V
L
= 3.3V
R = 8Ω
f = 1kHz
DD
f = 1kHz
R = 8Ω
L
-20
-40
10
1
SLAVE DEVICE
V
= 500mV
IN
P-P
-60
MASTER-TO-SLAVE
SLAVE-TO-MASTER
0.1
-80
0.01
-100
-120
0.001
0
0.1
0.2
0.3
0.4
0.5
10
100
1k
10k
100k
OUTPUT POWER (W)
FREQUENCY (Hz)
Figure 8. Master-Slave THD
Figure 9. Master-Slave Crosstalk
______________________________________________________________________________________ 13
500mW, Low EMI, Filterless,
Class D Audio Amplifier
System Diagram
V
DD
V
DD
0.1µF
2.2kΩ
AUX_IN
1µF
V
DD
PV
DD
MAX9712
MAX4063
IN+
OUT+
CODEC/
BASEBAND
PROCESSOR
BIAS
IN-
OUT
OUT
2.2kΩ
0.1µF
OUT-
SHDN
SYNC
IN+
IN-
V
DD
0.1µF
100kΩ
1µF
MODE1
MODE2
INL
V
DD
HPS
OUTL
OUTR
1µF
1µF
V
DD
MAX9720
INR
10kΩ
µCONTROLLER
ALERT
TIME
PV
SV
DD
DD
C1P
CIN
220nF
1µF
1µF
Pin Configurations (continued)
TOP VIEW
(BUMP SIDE DOWN)
1
MAX9712
2
3
4
OUT-
GND
IN-
A
B
PV
SHDN
IN+
PGND
SYNC
DD
OUT+
V
DD
C
UCSP
14 ______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE, 4x3 UCSP
1
21-0104
F
1
______________________________________________________________________________________ 15
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
L
A
D2
D
A2
PIN 1 ID
1
N
1
C0.35
b
[(N/2)-1] x e
REF.
E
E2
PIN 1
INDEX
AREA
DETAIL A
e
k
A1
C
L
C
L
L
L
e
e
A
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
1
2
21-0137
D
16 ______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
COMMON DIMENSIONS
SYMBOL
MIN.
0.70
2.90
2.90
0.00
0.20
MAX.
0.80
3.10
3.10
0.05
0.40
A
D
E
A1
L
k
0.25 MIN.
0.20 REF.
A2
PACKAGE VARIATIONS
PKG. CODE
T633-1
N
6
D2
E2
e
JEDEC SPEC
MO229 / WEEA
MO229 / WEEC
b
[(N/2)-1] x e
1.90 REF
1.95 REF
2.00 REF
1.50±0.10 2.30±0.10 0.95 BSC
1.50±0.10 2.30±0.10 0.65 BSC
0.40±0.05
0.30±0.05
T833-1
8
T1033-1
10
1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
2
2
21-0137
D
______________________________________________________________________________________ 17
500mW, Low EMI, Filterless,
Class D Audio Amplifier
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
e
4X S
10
10
INCHES
MAX
MILLIMETERS
MAX
1.10
0.15
0.95
3.05
3.00
3.05
3.00
5.05
0.70
DIM MIN
MIN
-
A
-
0.043
0.006
0.037
0.120
0.118
0.120
0.118
0.199
A1
A2
D1
D2
E1
E2
H
0.002
0.030
0.116
0.114
0.116
0.114
0.187
0.05
0.75
2.95
2.89
2.95
2.89
4.75
0.40
H
ÿ 0.50±0.1
0.6±0.1
L
0.0157 0.0275
0.037 REF
L1
b
0.940 REF
0.007
0.0106
0.177
0.270
0.200
1
1
e
0.0197 BSC
0.500 BSC
0.6±0.1
c
0.0035 0.0078
0.0196 REF
0.090
BOTTOM VIEW
0.498 REF
S
α
TOP VIEW
0∞
6∞
0∞
6∞
D2
E2
GAGE PLANE
A2
c
A
E1
b
L
α
A1
D1
L1
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0061
I
1
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.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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