General Description
The MAX9773 3rd-generation, ultra-low EMI, stereo,
Class D audio power amplifier provides Class AB per-
formance with Class D efficiency. The MAX9773 deliv-
ers 1.8W per channel into a 4Ωload, and offers
efficiencies above 90%. Active emissions limiting (AEL)
circuitry greatly reduces EMI by actively controlling the
output FET gate transitions under all possible transient
conditions. AEL controls high-frequency emissions
resulting from conventional Class D free-wheeling
behavior in the presence of an inductive load. Zero-
dead-time (ZDT) technology maintains state-of-the-art
efficiency and THD+N performance by allowing the out-
put FETs to switch simultaneously without cross con-
duction. A spread-spectrum modulation scheme
eliminates the need for output filtering found in tradition-
al Class D devices. These design concepts reduce
component count and extend battery life.
The MAX9773 offers two modulation schemes: a fixed-
frequency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions. The
MAX9773 oscillator can be synchronized to an external
clock through the SYNC input, allowing synchroniza-
tion of multiple Maxim Class D amplifiers. The sync
output (SYNC_OUT) can be used for a master-slave
application where more channels are required. The
MAX9773 features a fully differential architecture, a full
bridge-tied load (BTL) output, and comprehensive
click-and-pop suppression. The device features inter-
nally set gains of 12dB, 15.6dB, 20dB, and 26dB
selected through two gain-select inputs, further reduc-
ing external component count.
The MAX9773 features high 80dB PSRR, less than
0.1% THD+N, and SNR in excess of 88dB. Short-circuit
and thermal-overload protection prevent the device
from being damaged during a fault condition. The
MAX9773 is available in 24-pin thin QFN-EP (4mm x
4mm x 0.8mm), and 20-bump UCSP™ (2mm x 2.5mm x
0.6mm) packages. The MAX9773 is specified over the
extended -40°C to +85°C temperature range.
Applications
Cellular/Multimedia Phones
Notebooks
Handheld Gaming Consoles
MP3 Players
Features
Filterless Amplifier Passes FCC-Radiation
Emissions Standards with 6in of Cable
Unique Spread-Spectrum Mode and Active
Emissions Limiting Achieves Better than 15dB
Margin Under FCC Limit
Zero Dead Time (ZDT) H-Bridge Maintains Good
THD+N Performance
Single-Supply Operation (2.5V to 5.5V)
Stereo Output (4Ω, VDD = 5V, THD+N = 1%,
POUT = 1.8W)
No LC Output Filter Required
85% Efficiency (RL= 8Ω, PO= 600mW)
Less Than 0.1% THD+N
High 80dB PSRR
Fully Differential Inputs
Integrated Click-and-Pop Suppression
Low-Power Shutdown Mode (0.1µA)
Short-Circuit and Thermal-Overload Protection
Pin-for-Pin Compatible with the MAX9701
Available in Thermally Efficient, Space-Saving
Packages
24-Pin TQFN-EP (4mm x 4mm x 0.8mm)
20-Bump UCSP (2mm x 2.5mm x 0.6mm)
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
________________________________________________________________ Maxim Integrated Products 1
MAX9773
GAIN2
GAIN1
VDD
GAIN
RIGHT
MODULATOR
AND H-BRIDGE
SYNC OSCILLATOR
LEFT
MODULATOR
AND H-BRIDGE
INR+
INR-
INL+
INL-
SYNC_OUT
Block Diagram
Ordering Information
19-3976; Rev 0; 1/06
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.
PART
TEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX9773EBP-T -40°C to +85°C 20 UCSP-20
B20-1
MAX9773ETG+ -40°C to +85°C 24 TQFN-EP*
T2444-4
Pin Configurations and Gain Selection appear at end of
data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
+Denotes lead-free package.
*EP = Exposed paddle.
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), RLconnected between
OUT+ and OUT-, RL= , TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
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.
VDD to GND..............................................................................6V
VDD to PVDD ..........................................................-0.3V to +0.3V
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 In/Out of PVDD, PGND, OUT_.........±800mA
Continuous Input Current (all other pins)..........................±20mA
Duration of OUT_ Short Circuit to
VDD/GND/PVDD/PGND...........................................Continuous
Duration of Short Circuit Between OUT+ and OUT- ......Continuous
Continuous Power Dissipation (TA= +70°C)
20-Bump UCSP (derate 10mW/°C above +70°C) ...........800mW
24-Pin Thin QFN (derate 20.8mW/°C above +70°C) ..1666.7mW
Junction Temperature......................................................+150°C
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Bump Temperature (soldering) Reflow............................+235°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
GENERAL
Supply Voltage Range VDD Inferred from PSRR test 2.6 5.5 V
Quiescent Current IDD Per channel 5.5 7.5 mA
Shutdown Current ISHDN 0.1 10 µA
Common-Mode Rejection Ratio CMRR fIN = 1kHz 66 dB
Input Bias Voltage VBIAS
1.125 1.25 1.375
V
Turn-On Time tON 80 ms
Output Offset Voltage VOS TA = +25oC±10
±50
mV
VDD = 2.5V to 5.5V, VIN = 0V, TA = +25oC5980
TMIN < TA < TMAX 56
fRIPPLE = 217Hz 72
Power-Supply Rejection Ratio PSRR
100mVP-P ripple,
VIN = 0V fRIPPLE = 20kHz 50
dB
RL = 8
500
VDD = 3.3V RL = 4
750
RL = 81300
Output Power (Note 3) POUT THD+N = 1%,
TA = +25oCVDD = 5V
RL = 41800
mW
RL = 8 (POUT = 400mW), f = 1kHz
0.04
Total Harmonic Distortion Plus
Noise (Note 3)
THD+N
RL = 4 (POUT = 600mW), f = 1kHz
0.08
%
FFM 86
BW = 22Hz
to 22kHz SSM 86
FFM
88.5
Signal-to-Noise Ratio SNR VOUT = 1VRMS
A-weighted
SSM
88.5
dB
SYNC = GND, TA = +25oC
950 1100 1250
SYNC = unconnected, TA = +25oC
1200 1400 1600
Oscillator Frequency fOSC
SYNC = VDD, TA = +25oC
1200
±60
kHz
Minimum On-Time tMIN 200 ns
SYNC Frequency Lock Range fSYNC
1000 2000
kHz
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
_______________________________________________________________________________________ 3
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= 4, L = 33µH.
For RL= 8, L = 68µH.
Note 3: When driving speakers below 4with large signals, exercise care to avoid violating the absolute maximum rating for continuous
output current.
Note 4: Testing performed with 8resistive load in series with 68µH inductive load connected across the BTL output. Mode transi-
tions are controlled by SHDN. KCP level is calculated as: 20 x log[(peak voltage during mode transition, no input signal)].
Units are expressed in dBV.
ELECTRICAL CHARACTERISTICS (continued)
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), RLconnected between
OUT+ and OUT-, RL= , TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SYNC_OUT Capacitance Drive
CSYNC_OUT
100 pF
Bridge-tied capacitance 200
Capacitive Drive CLSingle ended 400 pF
Into shutdown
-50
Click-and-Pop Level KCP
Peak reading, A-weighted,
32 samples per second
(Note 4)
Out of
shutdown -50 dBV
Efficiency ηPOUT = 600mW per channel,
fIN = 1kHz, RL = 885 %
GAIN1 = 0, GAIN2 = 0 10 16
GAIN1 = 1, GAIN2 = 0 30
GAIN1 = 0, GAIN2 = 1 45
Input Resistance RIN
GAIN1 = 1, GAIN2 = 1 60
k
GAIN1 = 0, GAIN2 = 0 26
GAIN1 = 1, GAIN2 = 0 20
GAIN1 = 0, GAIN2 = 1
15.6
Gain AV
GAIN1 = 1, GAIN2 = 1 12
dB
Channel-to-Channel Gain
Tracking 1%
Crosstalk L to R, R to L, f = 10kHz, RL = 8,
POUT = 300mW 80 dB
DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)
Input-Voltage High VINH 2V
Input-Voltage Low VINL 0.8 V
Input Leakage Current
(SHDN, GAIN1, GAIN2) ±A
VSYNC = GND, normal operation -15 -7
Input Leakage Current (SYNC) VSYNC = VDD, normal operation 12 25 µA
DIGITAL OUTPUTS (SYNC_OUT)
Output-Voltage High VOH IOH = 3mA, VDD = 3.3V 2.4 V
Output-Voltage Low VOL IOL = 3mA 0.4 V
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
4_______________________________________________________________________________________
Typical Operating Characteristics
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9773 toc01
FREQUENCY (Hz)
THD+N (%)
10k1k10010 100k
VDD = 5V
RL = 4
OUTPUT POWER = 600mW
OUTPUT POWER = 300mW
OUTPUT POWER = 100mW
0.1
0.01
1
10
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9773 toc02
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
0.01
1
10
0.001
10 100k
VDD = 5V
RL = 8
OUTPUT POWER = 250mW
OUTPUT POWER = 100mW
OUTPUT POWER = 500mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9773 toc03
FREQUENCY (Hz)
THD+N (%)
10k1k10010 100k
VDD = 3.3V
RL = 4
OUTPUT POWER = 100mW
OUTPUT POWER = 600mW
OUTPUT POWER = 300mW
0.1
0.01
1
10
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9773 toc04
FREQUENCY (Hz)
THD+N (%)
10k1k10010 100k
VDD = 3.3V
RL = 8
OUTPUT POWER = 100mW
OUTPUT POWER = 400mW
OUTPUT POWER = 250mW
0.1
0.01
1
10
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9773 toc05
FREQUENCY (Hz)
THD+N (%)
10k1k10010 100k
VDD = 5V
RL = 8
POUT = 800mW
FFM
SSM
0.1
0.01
1
10
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9773 toc06
OUTPUT POWER (W)
THD+N (%)
2.52.01.51.00.5
0.1
0.01
10
1
100
0.001
0
VDD = 5V
RL = 4
fIN = 20Hz fIN = 20kHz
fIN = 1kHz
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9773 toc07
OUTPUT POWER (W)
THD+N (%)
1.51.20.90.60.3
0.01
0.1
1
10
100
0.001
01.8
VDD = 5V
RL = 8
fIN = 1kHz
fIN = 20Hz fIN = 20kHz
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9773 toc08
OUTPUT POWER (W)
THD+N (%)
1.00.80.60.40.2
0.1
0.01
10
1.0
100
0.001
0
VDD = 3.3V
RL = 4
fIN = 20Hz
fIN = 1kHz fIN = 20kHz
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9773 toc09
OUTPUT POWER (W)
THD+N (%)
0.60.40.2
0.1
0.01
1
10
100
0.001
00.8
VDD = 3.3V
RL = 8
fIN = 1kHz
fIN = 20Hz fIN = 20kHz
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
_______________________________________________________________________________________ 5
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9773 toc10
OUTPUT POWER (W)
THD+N (%)
1.61.20.80.4
0.01
0.1
1
10
100
0.001
02.0
VDD = 5V
RL = 8
fIN = 1kHz
FFM
SSM
EFFICIENCY vs. OUTPUT POWER
MAX9773 toc11
OUTPUT POWER (W)
EFFICIENCY (%)
2.52.01.51.00.5
10
20
30
40
50
60
70
80
90
100
0
0 3.0
RL = 8
RL = 4
VDD = 5V
fIN = 1kHz
OUTPUT POWER PER CHANNEL
EFFICIENCY vs. OUTPUT POWER
MAX9773 toc12
OUTPUT POWER (W)
EFFICIENCY (%)
1.00.80.60.40.2
10
20
30
40
50
60
70
80
90
100
0
01.2
RL = 8
RL = 4
VDD = 3.3V
fIN = 1kHz
OUTPUT POWER PER CHANNEL
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9773 toc13
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
5.04.54.03.53.0
0.5
1.0
1.5
2.0
2.5
3.0
0
2.5 5.5
RL = 4
fIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9773 toc14
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
5.04.54.03.53.0
0.5
1.0
1.5
2.0
0
2.5 5.5
RL = 8
fIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER vs. LOAD RESISTANCE
MAX9773 toc15
LOAD RESISTANCE ()
OUTPUT POWER (W)
10
0.5
1.0
1.5
2.0
2.5
3.0
0
1100
VDD = 5V, f = 1kHz,
ZLOAD = 33µH
IN SERIES WITH RL
THD+N = 10%
THD+N = 1%
Typical Operating Characteristics (continued)
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
6_______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
CROSSTALK vs. FREQUENCY
MAX9773 toc19
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-140
10 100k
RIGHT TO LEFT
LEFT TO RIGHT
POUT = 300mW
RL = 8
CROSSTALK vs. INPUT AMPLITUDE
MAX9773 toc20
INPUT AMPLITUDE (dB)
CROSSTALK (dBV)
-14-34-54-74
-90
-100
-110
-80
-70
-60
-50
-40
-30
-20
-10
0
-120
-94 6
fIN = 1kHz
RL = 8
ONE CHANNEL DRIVEN
OUTPUT FREQUENCY SPECTRUM
MAX9773 toc21
FREQUENCY (kHz)
OUTPUT MAGNITUDE (dBV)
15105
-120
-100
-80
-60
-40
-20
0
-140
020
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8
UNWEIGHTED
OUTPUT FREQUENCY SPECTRUM
MAX9773 toc22
FREQUENCY (kHz)
OUTPUT MAGNITUDE (dBV)
15105
-120
-100
-80
-60
-40
-20
0
-140
020
SSM MODE
VOUT = -60dB
f = 1kHz
RL = 8
UNWEIGHTED
OUTPUT POWER vs. LOAD RESISTANCE
MAX9773 toc16
LOAD RESISTANCE ()
OUTPUT POWER (W)
10
0.2
0.4
0.6
0.8
1.0
1.2
0
1100
VDD = 3.3V, f = 1kHz,
ZLOAD = 33µH
IN SERIES WITH RL
THD+N = 10%
THD+N = 1%
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9773 toc17
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
VRIPPLE = 100mVP-P
RL = 8
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9773 toc18
FREQUENCY (Hz)
CMRR (dB)
10k1k100
10
20
30
40
50
60
70
80
90
100
0
10 100k
VRIPPLE = 100mVP-P
RL = 8
VDD = 5V
VDD = 3.3V
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
_______________________________________________________________________________________ 7
TURN-ON/TURN-OFF RESPONSE
MAX9773 toc25
20ms/div
SHDN 2V/div
1V/div
MAX9773
DIFFERENTIAL
OUTPUT
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9773 toc26
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
4.5 5.55.03.0 3.5 4.0
8
11
14
17
20
5
2.5 6.0
SSM
FFM
BOTH CHANNELS DRIVEN
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX9773 toc27
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT (µA)
4.5 5.55.03.0 3.5 4.0
0.08
0.06
0.10
0.12
0.14
0.16
2.5 6.0
Typical Operating Characteristics (continued)
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
MAX9773 toc23
FREQUENCY (MHz)
OUTPUT AMPLITUDE (dBV)
101
-90
-70
-50
-30
-10
-80
-60
-40
-20
0
-100
0.1 100
RL = 8,
VDD = 5V
INPUTS
AC-GROUNDED
WIDEBAND OUTPUT SPECTRUM
(SSM MODE (SPEAKER MODE))
MAX9773 toc24
FREQUENCY (MHz)
OUTPUT AMPLITUDE (dBV)
101
-90
-70
-50
-30
-10
-80
-60
-40
-20
0
-100
0.1 100
RL = 8,
VDD = 5V
INPUTS
AC-GROUNDED
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
8_______________________________________________________________________________________
Pin Description
PIN
TQFN UCSP NAME FUNCTION
1A2SHDN Active-Low Shutdown. Connect to VDD for normal operation.
2B3SYNC
Frequency Select and External Clock Input:
SYNC = GND: Fixed-frequency mode with fS = 1100kHz.
SYNC = Unconnected: Fixed-frequency mode with fS = 1400kHz.
SYNC = VDD: Spread-spectrum mode with fS = 1200kHz ±60kHz.
SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency.
3, 8, 11, 16
—N.C. No Connection. Not internally connected.
4A3OUTL+ Left-Channel Amplifier Output Positive Phase
5, 14 A4, D4 PVDD H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1µF capacitor to PGND.
6, 13 B4, C4 PGND Power Ground
7A5OUTL- Left-Channel Amplifier Output Negative Phase
9, 22 B1, B5 GND Analog Ground
10 C5
SYNC_OUT
Clock Signal Output
12 D5 OUTR- Right-Channel Amplifier Output Negative Phase
15 D3 OUTR+ Right-Channel Amplifier Output Positive Phase
17 C3 GAIN1 Gain-Select Input 1
18 D2 GAIN2 Gain-Select Input 2
19 D1 INR- Right-Channel Inverting Input
20 C2 INR+ Right-Channel Noninverting Input
21 C1 VDD Analog Power Supply. Connect to PVDD. Bypass with a 10µF capacitor to GND.
23 B2 INL+ Left-Channel Noninverting Input
24 A1 INL- Left-Channel Inverting Input
EP EP Exposed Pad. Connect the exposed thermal pad to the GND plane (see the Supply
Bypassing, Layout, and Grounding section).
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
_______________________________________________________________________________________ 9
Functional Diagram
VBIAS
VBIAS
CLASS D
MODULATOR
AND H-BRIDGE
CLASS D
MODULATOR
AND H-BRIDGE
BIAS
GENERATOR
OSCILLATOR
AND
SAWTOOTH
GAIN
CONTROL
OUTL+
VBIAS
MAX9773
GND PGND
OUTR+
OUTL-
OUTR-
SYNC_OUT
PVDD
SYNC
INL+
INL-
INR+
INR-
GAIN1
GAIN2
*BULK CAPACITANCE.
SHDN
RIN
RIN
RIN
RIN
470nF
470nF
470nF
470nF
VDD
VDD
0.1µF10µF*
MAX9773
Detailed Description
The MAX9773 ultra-low EMI, filterless, stereo Class D
audio power amplifier incorporates several improve-
ments to switch-mode amplifier topology. The MAX9773
features output-driver AEL circuitry to reduce EMI. Zero
dead time technology maintains state-of-the art efficien-
cy and THD+N performance by allowing the output FETs
to switch simultaneously without cross conduction. The
MAX9773 offers Class AB performance with Class D effi-
ciency, while occupying minimal board space. A unique,
filterless modulation scheme, synchronizable switching
frequency, and spread-spectrum switching mode create
a compact, flexible, low-noise, efficient audio power
amplifier. The differential input architecture reduces
common-mode noise pickup, and can be used without
input-coupling capacitors. The inputs can also be config-
ured to accept a single-ended input signal.
Comparators monitor the MAX9773 inputs and compare
the complementary input voltages to the sawtooth wave-
form. 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 sec-
ond comparator (Figure 1). As the input voltage increases
or decreases, the duration of the pulse at one output
increases while the other output pulse duration remains
the same. This causes the net voltage across the speaker
(VOUT+ - VOUT-) to change. The minimum-width pulse
helps the device to achieve high levels of linearity.
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
10 ______________________________________________________________________________________
OUT+
OUT-
VIN-
VIN+
VOUT+ - VOUT-
tON(MIN)
tSW
Figure 1. MAX9773 Outputs with an Input Signal Applied
Operating Modes
Fixed-Frequency (FFM) Mode
The MAX9773 features two fixed-frequency modes.
Connect SYNC to GND to select a 1.1MHz switching fre-
quency. Leave SYNC unconnected to select a 1.4MHz
switching frequency. The frequency spectrum of the
MAX9773 consists of the fundamental switching frequen-
cy and its associated harmonics (see the Wideband FFT
graph in the Typical Operating Characteristics). Program
the switching frequency so the harmonics do not fall
within a sensitive frequency band (Table 1). Audio repro-
duction is not affected by changing the switching fre-
quency.
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
______________________________________________________________________________________ 11
VOUT_+ - VOUT_-
tSW tSW tSW tSW
VIN_-
VIN_+
OUT_+
OUT_-
tON(MIN)
Figure 2. MAX9773 Outputs with an Input Signal Applied (SSM Mode)
Table 1. Operating Modes
SYNC MODE
GND FFM with fOSC = 1100kHz
Unconnected FFM with fOSC = 1400kHz
VDD SSM with fOSC = 1200kHz ±60kHz
Clocked FFM with fOSC = external clock frequency
MAX9773
Spread-Spectrum (SSM) Mode
The MAX9773 features a unique spread-spectrum
mode that flattens the wideband spectral components,
improving EMI emissions that may be radiated by the
speaker and cables. This mode is enabled by connect-
ing SYNC to VDD (Table 1). In SSM mode, the switching
frequency varies randomly by ±60kHz around the cen-
ter frequency (1.2MHz). The modulation scheme
remains the same, but the period of the sawtooth wave-
form 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 spread
over a bandwidth that increases with frequency. Above
a few megahertz, the wideband spectrum looks like
white noise for EMI purposes (Figure 3). A proprietary
amplifier topology ensures this does not corrupt the
noise floor in the audio bandwidth.
Synchronous Switching Mode
SYNC
The SYNC input allows the MAX9773 to be synchronized
to a user-defined clock, or another Maxim Class D ampli-
fier, creating a fully synchronous system, minimizing
clock intermodulation, and allocating spectral compo-
nents of the switching harmonics to insensitive frequency
bands. Applying a TTL clock signal between 1000kHz
and 2000kHz to SYNC synchronizes the MAX9773. The
period of the SYNC clock can be randomized, allowing
the MAX9773 to be synchronized to another Maxim Class
D amplifier operating in SSM mode.
SYNC_OUT
SYNC_OUT allows several MAX9773s as well as other
Class D amplifiers (such as the MAX9700) to be cas-
caded. The synchronized output minimizes interfer-
ence due to clock intermodulation caused by the
switching spread between single devices. Using
SYNC_OUT, the modulation scheme remains the same
and audio reproduction is not affected by changing the
switching frequency.
Filterless Modulation/Common-Mode Idle
The MAX9773 uses Maxim’s unique 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,
180°out-of-phase square wave when no signal is pre-
sent. With no filter, the square wave appears across the
load as a DC voltage, resulting in finite load current,
which increases power consumption especially when
idling. When no signal is present at the input of the
MAX9773, the amplifiers output an in-phase square wave
as shown in Figure 4. Because the MAX9773 drives the
speaker differentially, the two outputs cancel each other,
resulting in no net idle mode voltage across the speaker,
minimizing power consumption.
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
12 ______________________________________________________________________________________
FREQUENCY (MHz)
AMPLITUDE (dBμV/m)
280260240200 22080 100 120 140 160 18060
5
10
15
20
25
30
35
40
30 300
Figure 3. EMI Spectrum of MAX9773 with 6in of Twisted-Pair Speaker Cable with TDK Ferrite Beads MPZ1608S300A
Efficiency
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 current-steering
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.
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 MAX9773 still exhibits >80% efficiencies
under the same conditions (Figure 5).
Shutdown
The MAX9773 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9773 in a low-power (0.1µA) shutdown
mode. Connect SHDN to VDD for normal operation.
Click-and-Pop Suppression
The MAX9773 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 80ms following startup, a soft-start function
gradually unmutes the input amplifiers.
Applications Information
Filterless Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM 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(P-P)) and causes large ripple currents. Any parasitic
resistance in the filter components results in a loss of
power, lowering the efficiency.
The MAX9773 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 MAX9773 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 dam-
aged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8speakers, for portable
audio applications, exhibit series inductances in the
range of 20µH to 100µH.
Output Offset
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 the
power conversion of the Class D amplifier. For example,
an 8mV DC offset across an 8load results in 1mA extra
current consumption in a Class AB device. In the Class D
case, an 8mV offset into 8equates 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 / 100 x η), which is on the
order of a few µA.
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
______________________________________________________________________________________ 13
VIN_ = 0V
OUT_-
OUT_+
VOUT_+ - VOUT_- = 0V
Figure 4. MAX9773 Outputs with No Input Signal
EFFICIENCY vs. OUTPUT POWER
MAX9773 fig05
OUTPUT POWER (W)
EFFICIENCY (%)
0.60.50.3 0.40.20.1
10
20
30
40
50
60
70
80
90
100
0
00.7
MAX9773
CLASS AB VDD = 3.3V
f = 1kHz
RL - 8
Figure 5. MAX9773 Efficiency vs. Class AB Efficiency
MAX9773
Selectable Gain
The MAX9773 features four selectable gain settings,
minimizing external component count. Gains of 12dB,
15.6dB, 20dB, and 26dB are set through gain-select
inputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can be
hardwired or digitally controlled. Table 2 shows the
suggested gain settings to attain a maximum output
power from a given peak input voltage and given load
at VDD = 3.3V and THD+N = 10%.
Custom Gain Settings
The MAX9773 can be set up with any gain setting by
adding three external resistors per amplifier. Figure 6
shows the required circuit for setting up custom gain.
Table 3 displays a list of the components to use for sev-
eral gain settings.
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
14 ______________________________________________________________________________________
GAIN1
GAIN2
GAIN
(dB)
INPUT
(VRMS)
RL
()
POUT
(mW)
00+26
0.097699
4950
10+20
0.194936
4950
01
+15.6 0.323513
4950
1112
0.489657
4950
00+26
0.114288
8650
10+20
0.228035
8650
01
+15.6 0.378444
8650
1112
0.572798
8650
Table 2. Gain Settings (VDD = 3.3V,
THD+N = 10%)
GAIN_ SETTINGS
GAIN1 GAIN2 GAIN (dB) R1 () R2 ()C
IN (µF)
GAIN TOLERANCE (dB)
0026—— 1
0025 750 20k 1 +0.12/-0.07
0024 1k 10k 1.5 +0.14/-0.08
0023 1k 6k 2.2 +0.13/-0.08
0022 1.5k 6k 2.2 +0.16/-0.1
0021 2k 6k 2 +0.19/-0.12
1020—— 1
1019 1.2k 30k 1 +0.1/-0.06
1018 2k 20k 1 +0.15/-0.09
1017 2k 10k 1.2 +0.12/-0.07
1016 2.5k 10k 1.2 +0.15/-0.09
0115 1k 40k 0.86 +0.06/-0.03
0114 2.8k 40k 0.68 +0.15/-0.09
0113 2.8k 20k 0.86 +0.14/-0.08
1112—— 1
1111 1.8k 40k 0.86 +0.08/-0.05
1110 4k 40k 0.68 +0.15/-0.09
11 95k30k 0.68 +0.17/-0.1
11 85k20k 0.68 +0.15/-0.09
11 75.5k 16k 0.68 +0.15/-0.09
11 67k16k 0.68 +0.17/-0.1
11 58k14k 0.68 +0.17/-0.1
11 48k12k 0.68 +0.16/-0.1
11 310k 12k 0.68 +0.17/-0.1
11 211k 10k 0.68 +0.16/-0.1
11 112k 10k 0.58 +0.16/-0.1
11 014k 10k 0.47 +0.17/-0.1
Table 3. Custom Gain Components
The internal input resistance, RIN, changes with each
gain setting. The R1 resistors attenuate the gain and
resistors R2 compensate for RIN’s tolerance, which can
be as high as 25%. CIN must be adjusted to compen-
sate for the total change in input impedance or the low-
frequency roll-off point shifts.
Input Amplifier
Differential Input
The MAX9773 features a differential input structure,
making it compatible with many CODECs and offers
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.
Single-Ended Input
The MAX9773 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND, and driving the other input (Figure 7).
Component Selection
Input Filter
An input capacitor, CIN, in conjunction with the
MAX9773 input impedance (RIN) forms a highpass filter
that removes the DC bias from an incoming signal. The
AC-coupling capacitor allows the amplifier to automati-
cally bias the signal to an optimum DC level. Assuming
zero-source impedance, the -3dB point of the highpass
filter is given by:
Choose CIN so 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.
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 300Hz. 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.
fRC
dB IN IN
=
3
1
2π
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
______________________________________________________________________________________ 15
MAX9773
0.1µF10µF
2.5V TO 5.5V
0.47µF
0.47µF
0.47µF
0.47µF
SINGLE-ENDED
LEFT AUDIO INPUT
SINGLE-ENDED
RIGHT AUDIO INPUT
OUTL+
OUTL-
OUTR+
OUTR-
GAIN1
GND
PGND
SYNC
INL+
INR+
INL-
INR-
GAIN2
SHDN
VDD
PVDD
FFM MODE WITH fOSC = 1100kHz, GAIN = 15.6dB.
Figure 7. Single-Ended Input
MAX9773
INL+
INL-
R1
R2
CIN
CIN R1
RIN
RIN
INR+
INR-
R1
R2
CIN
CIN R1
RIN
RIN
Figure 6. Custom Gain Setting
MAX9773
Output Filter
The MAX9773 does not require an output filter. The
device passes FCC emissions standards with 6in 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 if the circuit is near
EMI-sensitive devices. Use a ferrite bead filter when
radiated frequencies above 10MHz are of concern. Use
an LC filter or a common-mode choke when radiated
emissions below 10MHz are of concern, or when long
leads (>6in) connect the amplifier to the speaker.
2.1 Channel Configuration
The typical 2.1 channel application circuit (Figure 8)
shows the MAX9773 configured as a mid/high-frequency
amplifier and the MAX9705 configured as a mono bass
amplifier. Input capacitors (CIN) set the highpass cutoff
frequency according to the following equation:
where RIN is the typical input resistance of the
MAX9773. The 10µF capacitors on the output of the
MAX9773 ensure a two-pole highpass filter.
fRC
IN IN
=××
1
2π
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
16 ______________________________________________________________________________________
MAX9773
MAX9705
MAX4238
INR+
INL+
INL-
INR-
SYNC
5V
OUTL+
OUTL-
OUTR+
OUTR-
8
8
SYNC_OUT
10µF
10µF
CIN
2200pF
1µF
1µF
5V
NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V.
FFM MODE WITH fOSC = 1100kHz.
OUT+
OUT-
SYNC
IN+
IN-
1.25V
R3
10k
C2
1nF
R1
20k
R2
20k
R4
39k
C1
0.01µF
VDD
CIN
2200pF
CIN
2200pF
CIN
2200pF
4
Figure 8. 2.1 Channel Application Circuit
Low frequencies are summed through a two-pole low-
pass filter and sent to the MAX9705 mono speaker
amplifier. The passband gain of the lowpass filter is
unity for in-phase stereo signals:
where R1 = R2 and R3 = R1//R2. The cutoff frequency
of the lowpass filter is set by the following equation:
Supply Bypassing, Layout, and Grounding
Proper layout and grounding are essential for optimum
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance. Large traces also aid in moving
heat away from the package. Proper grounding improves
audio performance, minimizes crosstalk between chan-
nels, and prevents any switching noise from coupling into
the audio signal. Connect PGND and GND together at a
single point on the PC board. Route all traces that carry
switching transients away from GND and the traces/com-
ponents in the audio signal path.
Bypass VDD with a 0.1µF capacitor to GND and PVDD
with a 10µF capacitor to PGND. Place the bypass
capacitors as close to the MAX9773 as possible. Use
large, low-resistance output traces. Current drawn from
the outputs increases as load impedance decreases.
High-output trace resistance decreases the power deliv-
ered to the load. Large output, supply, and GND traces
allow more heat to move from the MAX9773 to the air,
decreasing the thermal impedance of the circuit.
The MAX9773 thin QFN-EP package features an
exposed thermal pad on its underside. This pad lowers
the package’s thermal impedance by providing a direct
heat conduction path from the die to the PC board.
Connect the exposed thermal pad to the GND plane.
UCSP Applications Information
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 Application Note:
UCSP—A Wafer-Level Chip-Scale Package available on
Maxim’s website at www.maxim-ic.com/ucsp.
fCC R R
LP ×××
1
2
1
12 34π
AR
R
VLP
=−×23
1
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
______________________________________________________________________________________ 17
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
18 ______________________________________________________________________________________
MAX9773
GAIN1
GAIN2
SYNC SYNC_OUT
INR+
INR-
GND
SHDN PGND
OUTR+
OUTR-
0.47µF
0.47µF
0.47µF
1µF
OUTL+
OUTL-
PVDD
INL+
INL-
0.47µF
0.47µF
1µF
VDD
1.8V TO 3.6V 4.2V BATTERY
MAX9850
INL OUTR
AGND
DGND
10k
DVDD
10k
PVSS SVSS
OUTL
REF
FM
RECEIVER
INR
0.47µF
0.47µF
GPIO
HPL
HPR
AVDD
PVDD
DVDD
HPS
C1P
2.2µF
C1N
PGND
MCLK
SDIN
APPLICATIONS
PROCESSOR
1µF1µF
BCLK
LRCLK
SDA
SCL
System Diagram
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
______________________________________________________________________________________ 19
Chip Information
PROCESS: BiCMOS
GND INL+ SYNC PGND GND
VDD INR+ GAIN1 PGND SYNC
_OUT
INR- GAIN2 OUTR+ PVDD OUTR-
INL- SHDN OUTL+ PVDD OUTL-A
B
C
D
12345
MAX9773
UCSP
TOP VIEW
(BUMPS ON BOTTOM)
MAX9773
18 17 16 15 14
19
TQFN
TOP VIEW
13
1 2 3 4 5 6
24 +
23
22
21
20
12
7
8
9
10
11
INL+
VDD
INR+
INR-
INL-
GND
N.C.
SYNC_OUT
N.C.
OUTR-
OUTL-
GND
SHDN
SYNC
N.C.
OUTL+
PVDD
PGND
GAIN2
GAIN1
N.C.
OUTR+
PVDD
PGND
Pin Configurations
Gain Selection
GAIN SELECTION GAIN (dB)
GAIN1 = 0, GAIN2 = 0 26
GAIN1 = 1, GAIN2 = 0 20
GAIN1 = 0, GAIN2 = 1 15.6
GAIN1 = 1, GAIN2 = 1 12