MAXIM MAX9712EUB

19-2917; Rev 1; 1/04
500mW, Low EMI, Filterless,
Class D Audio Amplifier
The MAX9712 mono class D audio power amplifier provides class AB amplifier performance with class D efficiency, 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.
The MAX9712 offers two modulation schemes: a fixedfrequency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions due to the
modulation frequency. Furthermore, the MAX9712 oscillator 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, minimizing interference due to clock intermodulation. The
device utilizes a fully differential architecture, a fullbridged output, and comprehensive click-and-pop suppression. The gain is internally set to +4V/V, further
reducing external component count.
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 available 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.
Applications
Cellular Phones
MP3 Players
PDAs
Portable Audio
Simplified Block Diagram
Features
♦ 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
♦ 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
10-Pin TDFN (3mm ✕ 3mm ✕ 0.8mm)
10-Pin µMAX
12-Bump UCSP (1.5mm ✕ 2mm ✕ 0.6mm)
Ordering Information
TEMP RANGE
PIN/BUMPPACKAGE
MAX9712ETB
-40°C to +85°C
10 TDFN
AAI
MAX9712EUB
-40°C to +85°C
10 µMAX
—
MAX9712EBC-T
-40°C to +85°C
12 UCSP-12
PART
VDD
TOP
MARK
ABN
Pin Configurations
TOP VIEW
DIFFERENTIAL
AUDIO INPUT
MODULATOR
AND H-BRIDGE
VDD 1
IN+
SYNC
INPUT
OSCILLATOR
MAX9712
10 PVDD
2
MAX9712
9
OUT-
IN-
3
8
OUT+
GND
4
7
PGND
SHDN
5
6
SYNC
TDFN/µMAX
UCSP is a trademark of Maxim Integrated Products, Inc.
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX9712
General Description
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
ABSOLUTE MAXIMUM RATINGS
VDD to GND..............................................................................6V
PVDD to PGND .........................................................................6V
GND to PGND .......................................................-0.3V to +0.3V
All Other Pins to GND.................................-0.3V to (VDD + 0.3V)
Continuous Current Into/Out of PVDD/PGND/OUT_ ........±600mA
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
Continuous Power Dissipation (TA = +70°C)
10-Pin TDFN (derate 24.4mW/°C above +70°C) .....1951.2mW
10-Pin µMAX (derate 5.6mW/oC above +70°C) .........444.4mW
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)
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
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), RL = 8Ω, RL connected between OUT+ and OUT-, TA =
TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Supply Voltage Range
VDD
5.5
V
Quiescent Current
IDD
Inferred from PSRR test
2.5
4
5.2
mA
Shutdown Current
ISHDN
0.1
5
µA
Turn-On Time
tON
Input Resistance
RIN
TA = +25°C
14
20
VBIAS
Either input
0.73
0.83
Input Bias Voltage
Voltage Gain
30
AV
3.8
TA = +25°C
Output Offset Voltage
Common-Mode Rejection Ratio
Power-Supply Rejection Ratio
(Note 3)
Output Power
Total Harmonic Distortion Plus
Noise
2
VOS
CMRR
TMIN ≤ TA ≤
TMAX
POUT
THD+N
kΩ
0.93
V
V/V
4
4.2
MAX9712EUB/MAX9712ETB
±11
±40
MAX9712EBC
±15
±65
±65
MAX9712EUB/MAX9712ETB
200mVP-P ripple
THD+N = 1%
fIN = 1kHz, either
FFM or SSM
mV
±95
MAX9712EBC
fIN = 1kHz, input referred
VDD = 2.5V to 5.5V
PSRR
ms
72
50
dB
70
fRIPPLE = 217Hz
72
fRIPPLE = 20kHz
55
RL = 16Ω, VDD = 5V
700
RL = 8Ω
450
RL = 6Ω
250
RL = 8Ω,
POUT = 125mW
0.01
RL = 6Ω,
POUT = 125mW
0.01
dB
mW
%
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), RL = 8Ω, RL connected between OUT+ and OUT-, TA =
TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
BW = 22Hz
to 22kHz
Signal-to-Noise Ratio
SNR
VOUT = 1.8VRMS
A-weighted
Oscillator Frequency
fOSC
MIN
FFM
TYP
MAX
88
SSM
86
FFM
91
SSM
dB
89
SYNC = GND
980
1100
1220
SYNC = float
1280
1450
1620
SYNC Frequency Lock Range
800
η
kHz
1220
±120
SYNC = VDD (SSM mode)
Efficiency
UNITS
POUT = 300mW, fIN = 1kHz
2000
kHz
85
%
DIGITAL INPUTS (SHDN, SYNC)
VIH
Input Thresholds
2
V
0.8
VIL
SHDN Input Leakage Current
±1
µA
SYNC Input Current
±5
µA
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 RL = 6Ω, L = 47µH.
For RL = 8Ω, L = 68µH. For RL = 16Ω, L = 136µH.
Note 3: PSRR is specified with the amplifier inputs connected to GND through CIN.
Typical Operating Characteristics
(VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.)
1
1
1
VDD = +5V
RL = 8Ω
VDD = +3.3V
RL = 8Ω
VDD = +3.3V
RL = 8Ω
POUT = 125mW
0.1
POUT = 300mW
0.01
THD+N (%)
THD+N (%)
0.1
THD+N (%)
0.1
POUT = 300mW
POUT = 125mW
FFM MODE
0.001
0.001
10
100
1k
FREQUENCY (Hz)
SSM MODE
0.01
0.01
POUT = 125mW
0.001
10k
100k
MAX9712 TOC03
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9712 TOC02
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9712 TOC01
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
_______________________________________________________________________________________
3
MAX9712
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.)
1
f = 10kHz
10
1
10
1
0.1
0.1
f = 1kHz
0.3
0.4
0.5
f = 100Hz
f = 1kHz
f = 100Hz
0.001
0.2
f = 10kHz
0.01
f = 100Hz
f = 1kHz
0
0.001
0
0.2
0.4
0.6
0.8
1.0
0
0.1
0.2
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
DIFFERENTIAL
INPUT
FFM
(SYNC FLOATING)
SSM
(SYNC = VDD)
fSYNC = 800kHz
0.4
0.5
0.001
0
0.1
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
0.3
0.4
0.5
0.1
80
RL = 8Ω
60
50
40
2.0
2.5
COMMON-MODE VOLTAGE (V)
3.0
80
0.6
RL = 16Ω
70
RL = 8Ω
60
RL = 6Ω
50
40
VDD = 3.3V
f = 1kHz
10
0
0
1.5
0.5
20
VDD = 5V
f = 1kHz
10
1.0
0.4
30
20
0.01
0.3
90
RL = 16Ω
70
0.2
100
MAX9712TOC11
90
30
0.5
0.1
EFFICIENCY vs. OUTPUT POWER
EFFICIENCY vs. OUTPUT POWER
EFFICIENCY (%)
VDD = 3.3V
RL = 8Ω
f = 1kHz
POUT = 300mW
DIFFERENTIAL INPUT
0
0
OUTPUT POWER (W)
100
MAX9712 TOC10
10
1
0.2
OUTPUT POWER (W)
EFFICIENCY (%)
0.3
0.1
0.01
0.001
0.2
fSYNC = 2MHz
fSYNC = 1.4MHz
FFM
(SYNC = GND)
0.001
0.1
1
0.01
SINGLE-ENDED
0
10
MAX9712 TOC09
MAX9712 TOC08
1
VDD = 3.3V
RL = 8Ω
SYNC = 3.3VP-P
50% DUTY CYCLE
SQUARE WAVE
MAX9712TOC12
0.01
10
0.1
100
THD+N (%)
1
0.1
VDD = 3.3V
RL = 8Ω
THD+N (%)
VDD = 2.5V
RL = 8Ω
VCM = 1.25V
NO INPUT CAPACITORS
10
100
MAX9712 TOC07
100
4
VDD = 3.3V
RL = 6Ω
0.01
0.001
THD+N (%)
f = 10kHz
0.1
0.01
100
MAX9712 TOC05
VDD = 5V
RL = 16Ω
THD+N (%)
THD+N (%)
10
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
THD+N (%)
VDD = 3.3V
RL = 8Ω
0.1
100
MAX9712 TOC04
100
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC06
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
THD+N (%)
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
0
0.1
0.2
0.3
0.4
0.5
OUTPUT POWER (W)
0.6
0.7
0
0.1
0.2
0.3
OUTPUT POWER (W)
_______________________________________________________________________________________
0.4
0.5
500mW, Low EMI, Filterless,
Class D Audio Amplifier
EFFICIENCY
vs. SYNC INPUT FREQUENCY
RL = 16Ω
60
50
40
60
50
40
30
20
20
10
10
f = 1kHz
3.5
4.0
4.5
5.0
1600
RL = 6Ω
0
1800
2000
2.5
3.1
3.7
4.3
4.9
OUTPUT POWER
vs. LOAD RESISTANCE
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
400
0
-20
-20
-30
-30
-40
-40
-50
-60
-50
-60
300
-70
-70
200
-80
-80
100
-90
-90
0
-100
-100
10 20 30 40 50 60 70 80 90 100
10
100
1k
10k
100k
10
FREQUENCY (Hz)
LOAD RESISTANCE (Ω)
1k
10k
100k
OUTPUT FREQUENCY SPECTRUM
MAX9712TOC19
0
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
-20
OUTPUT MAGNITUDE (dBV)
500mV/div
MAX9712
OUTPUT
100
FREQUENCY (Hz)
GSM POWER-SUPPLY REJECTION
VDD
OUTPUT REFERRED
INPUTS AC GROUNDED
VDD = 3.3V
-10
-40
MAX9712TOC20
VDD = 3.3V
INPUT REFERRED
VIN = 200mVP-P
5.5
MAX9712TOC18
0
-10
CMRR (dB)
600
0
RL = 8Ω
300
SUPPLY VOLTAGE (V)
VDD = 5V
500
1400
400
SYNC FREQUENCY (kHz)
800
700
1200
500
SUPPLY VOLTAGE (V)
f = 1kHz
THD+N = 1%
900
1000
600
100
RL = 8Ω
800
5.5
RL = 16Ω
700
200
PSRR (dB)
1000
3.0
MAX9712TOC16
2.5
VDD = 3.3V
f = 1kHz
POUT = 300mW
0
0
OUTPUT POWER (mW)
70
30
800
OUTPUT POWER (mW)
RL = 8Ω
RL = 6Ω
80
f = 1kHz
900
MAX9712TOC17
70
1000
MAX9712TOC14
80
90
EFFICIENCY (%)
90
EFFICIENCY (%)
100
MAX9712TOC13
100
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9712TOC15
EFFICIENCY vs. SUPPLY VOLTAGE
-60
-80
-100
100µV/div
-120
-140
f = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
2ms/div
DUTY CYCLE = 88%
RL = 8Ω
0
5k
10k
15k
FREQUENCY (Hz)
20k
_______________________________________________________________________________________
5
MAX9712
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.)
-40
-60
-80
-100
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
-20
-40
0
RBW = 10kHz
-10
-20
OUTPUT AMPLITUDE (dB)
-20
0
MAX9712TOC22
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
OUTPUT MAGNITUDE (dBV)
MAX9712TOC21
0
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
OUTPUT FREQUENCY SPECTRUM
-60
-80
-100
MAX1972 TOC23
OUTPUT FREQUENCY SPECTRUM
OUTPUT MAGNITUDE (dBV)
-30
-40
-50
-60
-70
-80
-120
-120
-140
-140
0
5
10
15
FREQUENCY (kHz)
20
-90
-100
0
5
10
15
FREQUENCY (kHz)
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
-20
OUTPUT AMPLITUDE (dB)
10M
100M
FREQUENCY (Hz)
MAX9712TOC25
MAX1972TOC24
RBW = 10kHz
-10
1M
20
TURN-ON/TURN-OFF RESPONSE
0
SHDN
3V
-30
-40
-50
0V
-60
-70
MAX9712
OUTPUT
-80
250mV/div
-90
-100
10M
100M
1G
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
TA = +25°C
4.5
TA = -40°C
4.0
TA = +85°C
0.14
SUPPLY CURRENT (µA)
TA = +85°C
5.0
0.16
MAX9712TOC26
6.0
5.5
10ms/div
f = 1kHz
RL = 8Ω
FREQUENCY (Hz)
MAX9712 TOC27
1M
SUPPLY CURRENT (mA)
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
0.12
0.10
TA = +25°C
0.08
0.06
0.04
3.5
0
3.0
2.5
6
TA = -40°C
0.02
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
1G
500mW, Low EMI, Filterless,
Class D Audio Amplifier
VDD
10µF
1µF
5
(B3) SHDN
1
(C4)
10
(B1)
6
(C2)
VDD
PVDD
SYNC
UVLO/POWER
MANAGEMENT
CLICK AND POP
SUPPRESSION
OSCILLATOR
PVDD
2
(B4) IN+
CLASS D
MODULATOR
3
(A4) IN-
8
OUT+ (C1)
PGND
PVDD
OUT- 9
(A1)
MAX9712
PGND
PGND
7
(B2)
GND
4
(A5)
( ) UCSP BUMP.
_______________________________________________________________________________________
7
MAX9712
Functional Diagram
500mW, Low EMI, Filterless,
Class D Audio Amplifier
MAX9712
Pin Description
PIN
BUMP
TDFN/µMAX
UCSP
1
C4
VDD
2
B4
IN+
Noninverting Audio Input
3
A4
IN-
Inverting Audio Input
4
A3
GND
5
B3
SHDN
Active-Low Shutdown Input. Connect to VDD for normal operation.
NAME
FUNCTION
Analog Power Supply
Analog Ground
6
C2
SYNC
Frequency Select and External Clock Input.
SYNC = GND: Fixed-frequency mode with fS = 1100kHz.
SYNC = Float: Fixed-frequency mode with fS = 1450kHz.
SYNC = VDD: Spread-spectrum mode with fS = 1220kHz ±120kHz.
SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency.
7
B2
PGND
Power Ground
8
C1
OUT+
Amplifier Output Positive Phase
9
A1
OUT-
Amplifier Output Negative Phase
10
B1
PVDD
H-Bridge Power Supply
Detailed Description
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, synchronizable 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 configured as a single-ended input amplifier.
Comparators monitor the MAX9712 inputs and compare the complementary input voltages to the sawtooth
waveform. The comparators trip when the input magnitude 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, generating a minimum-width pulse tON(min) at the output of
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
other output pulse duration remains at tON(min). This
causes the net voltage across the speaker (VOUT+ VOUT-) to change.
8
Operating Modes
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 frequency 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.
Spread-Spectrum Modulation (SSM) Mode
The MAX9712 features a unique, patented spread-spectrum mode that flattens the wideband spectral components, 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 efficiency (see the Typical Operating Characteristics). Select
SSM mode by setting SYNC = VDD. In SSM mode, the
switching frequency varies randomly by ±120kHz
around the center frequency (1.22MHz). The modulation
scheme remains the same, but the period of the sawtooth 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
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
MAX9712
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9712 Outputs with an Input Signal Applied
Table 1. Operating Modes
SYNC INPUT
GND
FLOAT
VDD
Clocked
MODE
FFM with fS = 1100kHz
FFM with fS = 1450kHz
SSM with fS = 1220kHz ±120kHz
FFM with fS = external clock frequency
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 synchronized to a system clock (allowing a fully synchronous
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 randomized, enabling the MAX9712 to be synchronized to
another MAX9712 operating in SSM mode.
Filterless Modulation/Common-Mode Idle
The MAX9712 uses Maxim’s unique, patented modulation 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 output a 50% duty cycle square wave when no signal is
present. With no filter, the square wave appears across
_______________________________________________________________________________________
9
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
tSW
tSW
tSW
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
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 present 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 currentsteering switches and consume negligible additional
power. Any power loss associated with the class D output 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
MAX9712
VIN = 0V
50.0
AMPLITUDE (dBµV/m)
45.0
40.0
35.0
30.0
OUT-
25.0
20.0
15.0
10.0
30.0
OUT+
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)
VOUT+ - VOUT- = 0V
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
mode. Connect SHDN to VDD for normal operation.
100
Click-and-Pop Suppression
70
Applications Information
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 amplifier, and can decrease efficiency. The traditional PWM
scheme uses large differential output swings (2 x VDD
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.
90
80
EFFICIENCY (%)
The MAX9712 features comprehensive click-and-pop
suppression that eliminates audible transients on startup 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, preventing clicks and pops when the H-bridge is subsequently enabled. For 35ms following startup, a soft-start
function gradually unmutes the input amplifiers.
EFFICIENCY vs. OUTPUT POWER
MAX9712
60
50
40
CLASS AB
30
VDD = 3.3V
f = 1kHz
RL - 8Ω
20
10
0
0
0.1
0.2
0.3
0.4
0.5
OUTPUT POWER (W)
Figure 5. MAX9712 Efficiency vs. Class AB Efficiency
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 damaged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8Ω speakers exhibit series
inductances in the range of 20µH to 100µH.
Power Conversion Efficiency
Unlike a class AB amplifier, the output offset voltage of
a class D amplifier does not noticeably increase quiescent current draw when a load is applied. This is due to
______________________________________________________________________________________
11
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
the power conversion of the class D amplifier. For example, 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 additional power drain of 8µW. Due to the high efficiency of
the class D amplifier, this represents an additional quiescent current draw of: 8µW/(VDD/100η), which is on the
order of a few microamps.
1µF
SINGLE-ENDED
AUDIO INPUT
IN+
MAX9712
IN1µF
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-frequency 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 differential input amplifier amplifies the difference of the two
inputs, any signal common to both inputs is canceled.
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 coupling eliminates the input-coupling capacitors, reducing component count to potentially one external
component (see the System Diagram). However, the
low-frequency rejection of the capacitors is lost, allowing low-frequency signals to feedthrough to the load.
Component Selection
Input Filter
An input capacitor, CIN, in conjunction with the input
impedance of the MAX9712 forms a highpass filter that
removes the DC bias from an incoming signal. The ACcoupling capacitor allows the amplifier to bias the signal to an optimum DC level. Assuming zero-source
impedance, the -3dB point of the highpass filter is
given by:
f−3dB =
1
2πRINCIN
Choose CIN so f-3dB is well below the lowest frequency
of interest. Setting f-3dB too high affects the low-frequency response of the amplifier. Use capacitors
whose dielectrics have low-voltage coefficients, such
as tantalum or aluminum electrolytic. Capacitors with
12
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 concentrate 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 consideration, 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.
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 radiated emissions are a concern, or when long leads are
used to connect the amplifier to the speaker.
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 capacitors as close to each pin as possible. A low-impedance, 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.
Stereo Configuration
Two MAX9712s can be configured as a stereo amplifier
(Figure 7). Device U1 is the master amplifier; its unfil-
______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
VDD
1µF
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
VDD
PVDD
IN+
MAX9712 OUT+
IN-
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 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 available on Maxim’s website at www.maximic.com/ucsp.
1µF
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
VDD
PVDD
IN+
MAX9712 OUT+
IN-
OUT-
Chip Information
TRANSISTOR COUNT: 3595
PROCESS: BiCMOS
SYNC
Figure 7. Master-Slave Stereo Configuration
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
CROSSTALK vs. FREQUENCY
100
0
VDD = 3.3V
f = 1kHz
RL = 8Ω
SLAVE DEVICE
CROSSTALK (dB)
THD+N (%)
10
VDD = 3.3V
RL = 8Ω
f = 1kHz
VIN = 500mVP-P
-20
1
0.1
0.01
-40
MASTER-TO-SLAVE
-60
-80
-100
0.001
SLAVE-TO-MASTER
-120
0
0.1
0.2
0.3
OUTPUT POWER (W)
Figure 8. Master-Slave THD
0.4
0.5
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 9. Master-Slave Crosstalk
______________________________________________________________________________________
13
MAX9712
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 performance 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.
500mW, Low EMI, Filterless,
Class D Audio Amplifier
MAX9712
System Diagram
VDD
VDD
0.1µF
AUX_IN
1µF
VDD
PVDD
IN+
MAX9712 OUT+
IN-
OUT-
SHDN
SYNC
2.2kΩ
MAX4063
BIAS
OUT
2.2kΩ
CODEC/
BASEBAND
PROCESSOR
0.1µF
OUT
IN+
IN-
100kΩ
0.1µF
1µF
VDD
10kΩ
µCONTROLLER
1µF
1µF
MODE1
VDD
MODE2
HPS
INL
MAX9720 OUTL
INR
OUTR
ALERT
PVDD
TIME
SVDD
C1P
CIN
220nF
1µF
1µF
Pin Configurations (continued)
TOP VIEW
(BUMP SIDE DOWN)
1
MAX9712
2
OUT-
3
4
GND
IN-
SHDN
IN+
A
PVDD
PGND
OUT+
SYNC
B
VDD
C
UCSP
14
VDD
______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
12L, UCSP 4x3.EPS
PACKAGE OUTLINE, 4x3 UCSP
21-0104
F
1
______________________________________________________________________________________
1
15
MAX9712
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 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.)
6, 8, &10L, DFN THIN.EPS
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
L
A
D
D2
A2
PIN 1 ID
1
N
1
C0.35
b
E
PIN 1
INDEX
AREA
[(N/2)-1] x e
REF.
E2
DETAIL A
e
k
A1
CL
CL
L
L
e
e
A
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
16
APPROVAL
DOCUMENT CONTROL NO.
21-0137
______________________________________________________________________________________
REV.
D
1
2
500mW, Low EMI, Filterless,
Class D Audio Amplifier
COMMON DIMENSIONS
SYMBOL
A
MIN.
0.70
MAX.
0.80
D
2.90
3.10
E
2.90
3.10
A1
0.00
0.05
L
k
0.20
0.40
0.25 MIN.
A2
0.20 REF.
PACKAGE VARIATIONS
PKG. CODE
N
D2
E2
e
JEDEC SPEC
b
T633-1
6
1.50±0.10
2.30±0.10
0.95 BSC
MO229 / WEEA
0.40±0.05
1.90 REF
T833-1
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
T1033-1
10
1.50±0.10
2.30±0.10
0.50 BSC
MO229 / WEED-3
0.25±0.05
2.00 REF
[(N/2)-1] x e
DALLAS
SEMICONDUCTOR
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL
DOCUMENT CONTROL NO.
21-0137
REV.
D
2
______________________________________________________________________________________
2
17
MAX9712
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.)
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
10LUMAX.EPS
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
4X S
10
INCHES
10
H
ÿ 0.50±0.1
0.6±0.1
1
1
0.6±0.1
BOTTOM VIEW
TOP VIEW
D2
MILLIMETERS
MAX
DIM MIN
0.043
A
0.006
A1
0.002
A2
0.030
0.037
0.120
D1
0.116
0.118
0.114
D2
0.116
0.120
E1
0.118
E2
0.114
0.199
H
0.187
L
0.0157 0.0275
L1
0.037 REF
b
0.007
0.0106
e
0.0197 BSC
c
0.0035 0.0078
0.0196 REF
S
α
0∞
6∞
MAX
MIN
1.10
0.15
0.05
0.75
0.95
3.05
2.95
3.00
2.89
3.05
2.95
2.89
3.00
4.75
5.05
0.40
0.70
0.940 REF
0.177
0.270
0.500 BSC
0.090
0.200
0.498 REF
0∞
6∞
E2
GAGE PLANE
A2
c
A
b
D1
A1
α
E1
L
L1
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
21-0061
REV.
I
1
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.