19-3976; Rev 0; 1/06
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
The MAX9773 3rd-generation, ultra-low EMI, stereo,
Class D audio power amplifier provides Class AB performance with Class D efficiency. The MAX9773 delivers 1.8W per channel into a 4Ω load, 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. Zerodead-time (ZDT) technology maintains state-of-the-art
efficiency and THD+N performance by allowing the output FETs to switch simultaneously without cross conduction. A spread-spectrum modulation scheme
eliminates the need for output filtering found in traditional Class D devices. These design concepts reduce
component count and extend battery life.
The MAX9773 offers two modulation schemes: a fixedfrequency (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 synchronization 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 internally set gains of 12dB, 15.6dB, 20dB, and 26dB
selected through two gain-select inputs, further reducing 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
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)
Ordering Information
PART
TEMP RANGE
PINPACKAGE
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
+Denotes lead-free package.
*EP = Exposed paddle.
Block Diagram
VDD
MAX9773
INR+
RIGHT
MODULATOR
AND H-BRIDGE
INR-
GAIN1
GAIN2
GAIN
Notebooks
Handheld Gaming Consoles
MP3 Players
Pin Configurations and Gain Selection appear at end of
data sheet.
INL+
LEFT
MODULATOR
AND H-BRIDGE
INL-
SYNC
OSCILLATOR
SYNC_OUT
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ 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
MAX9773
General Description
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
ABSOLUTE MAXIMUM RATINGS
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
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
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), RL connected between
OUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
5.5
V
5.5
7.5
mA
0.1
10
GENERAL
Supply Voltage Range
VDD
Inferred from PSRR test
Quiescent Current
IDD
Per channel
Shutdown Current
ISHDN
Common-Mode Rejection Ratio
CMRR
Input Bias Voltage
VBIAS
Turn-On Time
tON
Output Offset Voltage
VOS
2.6
fIN = 1kHz
66
1.125
PSRR
±10
TA = +25oC
VDD = 2.5V to 5.5V, VIN = 0V, TA = +25 C
59
TMIN < TA < TMAX
56
100mVP-P ripple,
VIN = 0V
Output Power (Note 3)
Total Harmonic Distortion Plus
Noise (Note 3)
POUT
THD+N
THD+N = 1%,
TA = +25oC
fRIPPLE = 217Hz
VDD = 3.3V
VDD = 5V
SNR
Oscillator Frequency
fOSC
50
RL = 8Ω
500
RL = 4Ω
750
RL = 8Ω
1300
RL = 4Ω
1800
0.04
0.08
FFM
SSM
86
88.5
SSM
88.5
SYNC Frequency Lock Range
2
dB
950
1100
1250
SYNC = unconnected, TA = +25oC
1200
1400
1600
kHz
1200
±60
tMIN
fSYNC
%
SYNC = GND, TA = +25 C
SYNC = VDD, TA = +25oC
Minimum On-Time
mW
86
FFM
o
mV
dB
RL = 4Ω (POUT = 600mW), f = 1kHz
A-weighted
±50
80
RL = 8Ω (POUT = 400mW), f = 1kHz
VOUT = 1VRMS
V
ms
72
fRIPPLE = 20kHz
BW = 22Hz
to 22kHz
Signal-to-Noise Ratio
1.375
80
o
Power-Supply Rejection Ratio
1.25
µA
dB
200
1000
_______________________________________________________________________________________
ns
2000
kHz
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), RL connected between
OUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYNC_OUT Capacitance Drive
Capacitive Drive
SYMBOL
CL
Click-and-Pop Level
KCP
η
Efficiency
CONDITIONS
MIN
CSYNC_OUT
RIN
Gain
AV
Bridge-tied capacitance
200
Single ended
400
Peak reading, A-weighted,
32 samples per second
(Note 4)
Into shutdown
-50
Out of
shutdown
-50
POUT = 600mW per channel,
fIN = 1kHz, RL = 8Ω
10
pF
dBV
%
16
GAIN1 = 1, GAIN2 = 0
30
GAIN1 = 0, GAIN2 = 1
45
GAIN1 = 1, GAIN2 = 1
60
GAIN1 = 0, GAIN2 = 0
26
GAIN1 = 1, GAIN2 = 0
20
GAIN1 = 0, GAIN2 = 1
15.6
GAIN1 = 1, GAIN2 = 1
12
L to R, R to L, f = 10kHz, RL = 8Ω,
POUT = 300mW
UNITS
pF
85
Channel-to-Channel Gain
Tracking
Crosstalk
MAX
100
GAIN1 = 0, GAIN2 = 0
Input Resistance
TYP
kΩ
dB
1
%
80
dB
DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)
Input-Voltage High
VINH
Input-Voltage Low
VINL
2
V
Input Leakage Current
(SHDN, GAIN1, GAIN2)
VSYNC = GND, normal operation
Input Leakage Current (SYNC)
-15
VSYNC = VDD, normal operation
0.8
V
±1
µA
-7
12
25
µA
DIGITAL OUTPUTS (SYNC_OUT)
Output-Voltage High
VOH
IOH = 3mA, VDD = 3.3V
Output-Voltage Low
VOL
IOL = 3mA
2.4
V
0.4
V
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 = 4Ω, L = 33µH.
For RL = 8Ω, L = 68µH.
Note 3: When driving speakers below 4Ω with large signals, exercise care to avoid violating the absolute maximum rating for continuous
output current.
Note 4: Testing performed with 8Ω resistive load in series with 68µH inductive load connected across the BTL output. Mode transitions 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.
_______________________________________________________________________________________
3
MAX9773
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
VDD = 5V
RL = 4Ω
VDD = 5V
RL = 8Ω
10
1
1
VDD = 3.3V
RL = 4Ω
1
0.1
OUTPUT POWER = 600mW
THD+N (%)
THD+N (%)
THD+N (%)
OUTPUT POWER = 100mW
OUTPUT POWER = 100mW
OUTPUT POWER = 250mW
0.1
OUTPUT POWER = 300mW
0.1
OUTPUT POWER = 100mW
OUTPUT POWER = 500mW
0.01
0.01
MAX9773 toc03
10
MAX9773 toc01
10
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9773 toc02
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
OUTPUT POWER = 300mW
0.01
OUTPUT POWER = 600mW
0.001
0.001
10
100
10k
100k
0.001
10
100
1k
10k
100k
10
10k
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
VDD = 5V
RL = 8Ω
POUT = 800mW
VDD = 5V
RL = 4Ω
10
1
OUTPUT POWER = 400mW
THD+N (%)
THD+N (%)
FFM
0.1
0.1
0.01
0.1
10k
100k
fIN = 20Hz
fIN = 20kHz
0.001
0.001
0.001
1k
fIN = 1kHz
0.01
OUTPUT POWER = 250mW
100
1
SSM
0.01
10
10
100
1k
10k
0
100k
0.5
1.0
1.5
2.0
FREQUENCY (Hz)
FREQUENCY (Hz)
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
1
fIN = 1kHz
0.1
1.0
0.1
0.01
0.01
0.6
0.9
1.2
OUTPUT POWER (W)
1.5
1.8
10
1
fIN = 1kHz
0.1
fIN = 20Hz
0.001
0.3
VDD = 3.3V
RL = 8Ω
0.01
fIN = 20kHz
fIN = 1kHz
fIN = 20kHz
0.001
100
2.5
MAX9773 toc09
fIN = 20Hz
10
THD+N (%)
10
VDD = 3.3V
RL = 4Ω
THD+N (%)
VDD = 5V
RL = 8Ω
MAX9773 toc08
100
MAX9773 toc07
100
fIN = 20Hz
100k
MAX9773 toc06
100
MAX9773 toc05
10
OUTPUT POWER = 100mW
4
1k
FREQUENCY (Hz)
VDD = 3.3V
RL = 8Ω
0
100
FREQUENCY (Hz)
1
THD+N (%)
1k
MAX9773 toc04
10
THD+N (%)
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
fIN = 20kHz
0.001
0
0.2
0.4
0.6
OUTPUT POWER (W)
0.8
1.0
0
0.2
0.4
OUTPUT POWER (W)
_______________________________________________________________________________________
0.6
0.8
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
EFFICIENCY vs. OUTPUT POWER
FFM
0.1
MAX9773 toc11
80
70
60
90
RL = 4Ω
50
40
30
0.01
10
0.001
1.2
1.6
2.0
0.5
OUTPUT POWER (W)
1.5
2.0
2.5
3.0
0
THD+N = 10%
1.5
1.0
THD+N = 1%
RL = 8Ω
fIN = 1kHz
3.0
1.0
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
1.0
1.2
2.0
THD+N = 10%
1.5
1.0
THD+N = 1%
0
3.5
0.8
VDD = 5V, f = 1kHz,
ZLOAD = 33µH
IN SERIES WITH RL
2.5
0.5
3.0
0.6
OUTPUT POWER vs. LOAD RESISTANCE
THD+N = 10%
0.5
2.5
0.4
1.5
0.5
0
0.2
OUTPUT POWER (W)
OUTPUT POWER vs. SUPPLY VOLTAGE
OUTPUT POWER (W)
OUTPUT POWER (W)
2.0
1.0
2.0
MAX9773 toc13
RL = 4Ω
fIN = 1kHz
2.5
VDD = 3.3V
fIN = 1kHz
OUTPUT POWER PER CHANNEL
OUTPUT POWER (W)
OUTPUT POWER vs. SUPPLY VOLTAGE
3.0
40
0
0
OUTPUT POWER (W)
0.8
RL = 4Ω
50
10
MAX9773 toc14
0.4
60
20
0
0
70
30
VDD = 5V
fIN = 1kHz
OUTPUT POWER PER CHANNEL
20
SSM
RL = 8Ω
80
MAX9773 toc15
1
100
EFFICIENCY (%)
THD+N (%)
10
RL = 8Ω
90
EFFICIENCY (%)
VDD = 5V
RL = 8Ω
fIN = 1kHz
EFFICIENCY vs. OUTPUT POWER
100
MAX9773 toc10
100
MAX9773 toc12
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
THD+N = 1%
0
1
10
100
LOAD RESISTANCE (Ω)
_______________________________________________________________________________________
5
MAX9773
Typical Operating Characteristics (continued)
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
Typical Operating Characteristics (continued)
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
VRIPPLE = 100mVP-P
RL = 8Ω
-10
-20
70
-40
PSRR (dB)
THD+N = 10%
0.6
-50
-60
0.4
THD+N = 1%
10
-80
20
-90
10
0
10
100
1k
-70
CROSSTALK (dBV)
CROSSTALK (dB)
-60
RIGHT TO LEFT
-90
-100
-110
LEFT TO RIGHT
-120
-140
1k
10k
fIN = 1kHz
RL = 8Ω
ONE CHANNEL DRIVEN
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
100
100k
-94
FREQUENCY (Hz)
OUTPUT FREQUENCY SPECTRUM
-34
-14
6
OUTPUT FREQUENCY SPECTRUM
-60
-80
-100
-120
SSM MODE
VOUT = -60dB
f = 1kHz
RL = 8Ω
UNWEIGHTED
-20
OUTPUT MAGNITUDE (dBV)
OUTPUT MAGNITUDE (dBV)
-54
0
MAX9773 toc21
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
-40
-74
INPUT AMPLITUDE (dB)
0
-20
1k
CROSSTALK vs. INPUT AMPLITUDE
0
-10
-20
-30
MAX9773 toc19
POUT = 300mW
RL = 8Ω
10
100
FREQUENCY (Hz)
CROSSTALK vs. FREQUENCY
-40
-80
10
100k
10k
FREQUENCY (Hz)
LOAD RESISTANCE (Ω)
-50
40
30
100
VDD = 5V
50
MAX9773 toc22
1
60
-70
-100
0
VDD = 3.3V
80
CMRR (dB)
0.8
VRIPPLE = 100mVP-P
RL = 8Ω
90
-30
0.2
-40
-60
-80
-100
-120
-140
-140
0
5
10
FREQUENCY (kHz)
6
100
MAX9773 toc20
1.0
0
MAX9773 toc17
VDD = 3.3V, f = 1kHz,
ZLOAD = 33µH
IN SERIES WITH RL
MAX9773 toc16
1.2
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
15
MAX9773 toc18
OUTPUT POWER vs. LOAD RESISTANCE
OUTPUT POWER (W)
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
20
0
5
10
15
20
FREQUENCY (kHz)
_______________________________________________________________________________________
10k
100k
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
WIDEBAND OUTPUT SPECTRUM
(SSM MODE (SPEAKER MODE))
-30
-40
-50
-60
-70
MAX9773 toc24
-20
-30
-40
-50
-60
-70
-80
-80
-90
-90
-100
-100
0.1
1
100
10
0.1
1
10
FREQUENCY (MHz)
FREQUENCY (MHz)
TURN-ON/TURN-OFF RESPONSE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9773 toc25
100
20
MAX9773 toc26
OUTPUT AMPLITUDE (dBV)
RL = 8Ω,
VDD = 5V
INPUTS
AC-GROUNDED
-10
OUTPUT AMPLITUDE (dBV)
RL = 8Ω,
VDD = 5V
INPUTS
AC-GROUNDED
-20
0
MAX9773 toc23
0
-10
BOTH CHANNELS DRIVEN
SHDN
17
MAX9773
DIFFERENTIAL
OUTPUT
SUPPLY CURRENT (mA)
2V/div
1V/div
SSM
14
FFM
11
8
5
20ms/div
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN CURRENT (µA)
MAX9773 toc27
0.16
0.14
0.12
0.10
0.08
0.06
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
7
MAX9773
Typical Operating Characteristics (continued)
(VDD = VPVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = VDD (SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
MAX9773
Pin Description
PIN
TQFN
UCSP
1
A2
2
8
B3
NAME
FUNCTION
SHDN
Active-Low Shutdown. Connect to VDD for normal operation.
SYNC
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.
4
A3
OUTL+
No Connection. Not internally connected.
5, 14
A4, D4
PVDD
6, 13
B4, C4
PGND
Power Ground
7
A5
OUTL-
Left-Channel Amplifier Output Negative Phase
9, 22
B1, B5
GND
10
C5
SYNC_OUT
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
19
D1
INR-
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
Left-Channel Amplifier Output Positive Phase
H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1µF capacitor to PGND.
Analog Ground
Clock Signal Output
Gain-Select Input 2
Right-Channel Inverting Input
Exposed Pad. Connect the exposed thermal pad to the GND plane (see the Supply
Bypassing, Layout, and Grounding section).
_______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
VDD
0.1µF
10µF*
VDD
INL+
470nF
CLASS D
MODULATOR
AND H-BRIDGE
INL-
INR+
RIN
INR-
RIN
470nF
VBIAS
RIN
RIN
470nF
SYNC_OUT
OSCILLATOR
AND
SAWTOOTH
SYNC
470nF
PVDD
CLASS D
MODULATOR
AND H-BRIDGE
VBIAS
OUTL+
OUTL-
OUTR+
OUTR-
VBIAS
BIAS
GENERATOR
GAIN1
GAIN2
GAIN
CONTROL
MAX9773
SHDN
GND
PGND
*BULK CAPACITANCE.
_______________________________________________________________________________________
9
MAX9773
Functional Diagram
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9773 Outputs with an Input Signal Applied
Detailed Description
The MAX9773 ultra-low EMI, filterless, stereo Class D
audio power amplifier incorporates several improvements to switch-mode amplifier topology. The MAX9773
features output-driver AEL circuitry to reduce EMI. Zero
dead time technology maintains state-of-the art efficiency and THD+N performance by allowing the output FETs
to switch simultaneously without cross conduction. The
MAX9773 offers Class AB performance with Class D efficiency, 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
10
input-coupling capacitors. The inputs can also be configured to accept a single-ended input signal.
Comparators monitor the MAX9773 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 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
tSW
tSW
MAX9773
tSW
tSW
VIN_-
VIN_+
OUT_-
OUT_+
tON(MIN)
VOUT_+ - VOUT_-
Figure 2. MAX9773 Outputs with an Input Signal Applied (SSM Mode)
Operating Modes
Fixed-Frequency (FFM) Mode
The MAX9773 features two fixed-frequency modes.
Connect SYNC to GND to select a 1.1MHz switching frequency. Leave SYNC unconnected to select a 1.4MHz
switching frequency. The frequency spectrum of the
MAX9773 consists of the fundamental switching frequency 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 reproduction is not affected by changing the switching frequency.
Table 1. Operating Modes
SYNC
MODE
GND
FFM with fOSC = 1100kHz
Unconnected
FFM with fOSC = 1400kHz
VDD
Clocked
SSM with fOSC = 1200kHz ±60kHz
FFM with fOSC = external clock frequency
______________________________________________________________________________________
11
the MAX9773 to be synchronized to another Maxim Class
D amplifier operating in SSM mode.
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 connecting SYNC to VDD (Table 1). In SSM mode, the switching
frequency varies randomly by ±60kHz around the center frequency (1.2MHz). 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 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.
SYNC_OUT
SYNC_OUT allows several MAX9773s as well as other
Class D amplifiers (such as the MAX9700) to be cascaded. The synchronized output minimizes interference 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 present. 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.
Synchronous Switching Mode
SYNC
The SYNC input allows the MAX9773 to be synchronized
to a user-defined clock, or another Maxim Class D amplifier, creating a fully synchronous system, minimizing
clock intermodulation, and allocating spectral components 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
40
35
AMPLITUDE (dBμV/m)
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
30
25
20
15
10
5
30
60
80
100
120
140
160
180
200
220
240
260
280
FREQUENCY (MHz)
Figure 3. EMI Spectrum of MAX9773 with 6in of Twisted-Pair Speaker Cable with TDK Ferrite Beads MPZ1608S300A
12
______________________________________________________________________________________
300
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
MAX9773
EFFICIENCY vs. OUTPUT POWER
VIN_ = 0V
MAX9773 fig05
100
MAX9773
90
EFFICIENCY (%)
80
OUT_-
70
60
50
40
30
CLASS AB
20
OUT_+
VDD = 3.3V
f = 1kHz
RL - 8Ω
10
0
0
VOUT_+ - VOUT_- = 0V
0.1
0.2
0.3
0.4
0.5
0.6
0.7
OUTPUT POWER (W)
Figure 5. MAX9773 Efficiency vs. Class AB Efficiency
Figure 4. MAX9773 Outputs with No Input Signal
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 onresistance, 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 damaged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8Ω speakers, 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 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 / 100 x η), which is on the
order of a few µA.
______________________________________________________________________________________
13
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Selectable Gain
Table 2. Gain Settings (VDD = 3.3V,
THD+N = 10%)
GAIN1
GAIN2
GAIN
(dB)
INPUT
(VRMS)
RL
(Ω)
POUT
(mW)
0
0
+26
0.097699
4
950
4
950
1
0
+20
0.194936
0
1
+15.6
0.323513
4
950
1
1
12
0.489657
4
950
+26
0.114288
8
650
0
0
1
0
+20
0.228035
8
650
0
1
+15.6
0.378444
8
650
12
0.572798
8
650
1
1
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 several gain settings.
Table 3. Custom Gain Components
GAIN_ SETTINGS
14
GAIN (dB)
R1 (Ω)
R2 (Ω)
CIN (µF)
—
—
1
—
750
20k
1
+0.12/-0.07
GAIN TOLERANCE (dB)
GAIN1
GAIN2
0
0
26
0
0
25
0
0
24
1k
10k
1.5
+0.14/-0.08
0
0
23
1k
6k
2.2
+0.13/-0.08
0
0
22
1.5k
6k
2.2
+0.16/-0.1
0
0
21
2k
6k
2
+0.19/-0.12
1
0
20
—
—
1
—
1
0
19
1.2k
30k
1
+0.1/-0.06
1
0
18
2k
20k
1
+0.15/-0.09
1
0
17
2k
10k
1.2
+0.12/-0.07
1
0
16
2.5k
10k
1.2
+0.15/-0.09
0
1
15
1k
40k
0.86
+0.06/-0.03
0
1
14
2.8k
40k
0.68
+0.15/-0.09
0
1
13
2.8k
20k
0.86
+0.14/-0.08
1
1
12
—
—
1
—
1
1
11
1.8k
40k
0.86
+0.08/-0.05
1
1
10
4k
40k
0.68
+0.15/-0.09
1
1
9
5k
30k
0.68
+0.17/-0.1
1
1
8
5k
20k
0.68
+0.15/-0.09
1
1
7
5.5k
16k
0.68
+0.15/-0.09
1
1
6
7k
16k
0.68
+0.17/-0.1
1
1
5
8k
14k
0.68
+0.17/-0.1
1
1
4
8k
12k
0.68
+0.16/-0.1
1
1
3
10k
12k
0.68
+0.17/-0.1
1
1
2
11k
10k
0.68
+0.16/-0.1
1
1
1
12k
10k
0.58
+0.16/-0.1
1
1
0
14k
10k
0.47
+0.17/-0.1
______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
MAX9773
0.47µF
SINGLE-ENDED
LEFT AUDIO INPUT
INL+
OUTL+
MAX9773
CIN
R1
INL+
0.47µF
SINGLE-ENDED
RIGHT AUDIO INPUT
RIN
INR+
MAX9773
INLR2
CIN
R1
INL-
0.47µF
RIN
INR-
OUTLOUTR+
0.47µF
OUTR-
CIN
GAIN2
R1
INR+
RIN
GAIN1
SHDN
R2
CIN
R1
INR-
2.5V TO 5.5V
RIN
VDD
PVDD
10µF
GND
PGND
0.1µF
SYNC
FFM MODE WITH fOSC = 1100kHz, GAIN = 15.6dB.
Figure 6. Custom Gain Setting
Figure 7. Single-Ended Input
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 compensate for the total change in input impedance or the lowfrequency roll-off point shifts.
AC-coupling capacitor allows the amplifier to automatically bias the signal to an optimum DC level. Assuming
zero-source impedance, the -3dB point of the highpass
filter is given by:
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-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 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, C IN , in conjunction with the
MAX9773 input impedance (RIN) forms a highpass filter
that removes the DC bias from an incoming signal. The
f−3dB =
1
2πRINCIN
Choose CIN so f-3dB is well below the lowest frequency
of interest. Use capacitors whose dielectrics have lowvoltage 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 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 300Hz. 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.
______________________________________________________________________________________
15
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
5V
CIN
2200pF
10µF
INL+
OUTL+
CIN
2200pF
8Ω
MAX9773
INR+
OUTL-
CIN
2200pF
10µF
INLOUTR+
CIN
2200pF
8Ω
INROUTRSYNC
SYNC_OUT
R3
10kΩ
5V
R1
20kΩ
VDD
R4
39kΩ
R2
20kΩ
SYNC
C2
1nF
1µF
IN+
C1
0.01µF
1.25V
MAX4238
MAX9705
OUT+
4Ω
1µF
IN-
OUT-
NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V.
FFM MODE WITH fOSC = 1100kHz.
Figure 8. 2.1 Channel Application Circuit
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.
16
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:
f=
1
2π × RIN × CIN
where R IN is the typical input resistance of the
MAX9773. The 10µF capacitors on the output of the
MAX9773 ensure a two-pole highpass filter.
______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
A VLP =
−2 × R3
R1
where R1 = R2 and R3 = R1//R2. The cutoff frequency
of the lowpass filter is set by the following equation:
fLP =
1
×
2π
1
C1 × C2 × R 3 × R4
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 channels, 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/components 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 delivered 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.
______________________________________________________________________________________
17
MAX9773
Low frequencies are summed through a two-pole lowpass filter and sent to the MAX9705 mono speaker
amplifier. The passband gain of the lowpass filter is
unity for in-phase stereo signals:
18
DVDD
10kΩ
APPLICATIONS
PROCESSOR
FM
RECEIVER
10kΩ
0.47µF
0.47µF
DGND PGND AGND
2.2µF
C1N
C1P
HPS
HPR
GPIO
REF
OUTL
OUTR
HPL
SVSS
AVDD
1µF
SCL
PVSS
MAX9850
PVDD
1µF
SDA
LRCLK
SDIN
BCLK
MCLK
INR
INL
DVDD
1µF
1.8V TO 3.6V
0.47µF
1µF
0.47µF
0.47µF
0.47µF
0.47µF
INL-
INL+
INR-
INR+
GAIN2
GAIN1
SYNC
SHDN
VDD
GND
MAX9773
PGND
OUTL-
OUTL+
OUTR-
OUTR+
SYNC_OUT
PVDD
4.2V BATTERY
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
System Diagram
______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
TOP VIEW
(BUMPS ON BOTTOM)
GAIN2
GAIN1
N.C.
OUTR+
PVDD
PGND
TOP VIEW
18
17
16
15
14
13
INR- 19
12 OUTR-
INR+ 20
11 N.C.
VDD 21
10 SYNC_OUT
MAX9773
GND 22
INL+ 23
5
6
PVDD
4
PGND
3
N.C.
2
OUTL+
1
SYNC
+
SHDN
INL- 24
9
GND
8
N.C.
7
OUTL-
MAX9773
1
2
3
4
5
A
INL-
SHDN
OUTL+
PVDD
OUTL-
B
GND
INL+
SYNC
PGND
GND
C
VDD
INR+
GAIN1
PGND
SYNC
_OUT
D
INR-
GAIN2
OUTR+
PVDD
OUTR-
UCSP
TQFN
Gain Selection
GAIN SELECTION
GAIN1 = 0, GAIN2 = 0
GAIN (dB)
Chip Information
PROCESS: BiCMOS
26
GAIN1 = 1, GAIN2 = 0
20
GAIN1 = 0, GAIN2 = 1
15.6
GAIN1 = 1, GAIN2 = 1
12
______________________________________________________________________________________
19
MAX9773
Pin Configurations
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.)
24L QFN THIN.EPS
MAX9773
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
E
1
2
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
E
2
2
MAX9773 Package Code: T2444-4
20
______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
5x4 UCSP.EPS
PACKAGE OUTLINE, 5x4 UCSP
21-0095
I
1
1
MAX9773 Package Code: B20-1
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21
© 2006 Maxim Integrated Products
Heaney
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
MAX9773
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.)
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