MAX9773 [MAXIM]
1.8W, Filterless, Ultra-Low EMI, Stereo Class D Audio Power Amplifier;
| 型号： | MAX9773 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 1.8W, Filterless, Ultra-Low EMI, Stereo Class D Audio Power Amplifier |
| 文件： | 总21页 (文件大小：603K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3976; Rev 0; 1/06
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
General Description
Features
♦ Filterless Amplifier Passes FCC-Radiation
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 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. 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.
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, V
= 5V, THD+N = 1%,
DD
P
OUT
= 1.8W)
♦ No LC Output Filter Required
♦ 85% Efficiency (R = 8Ω, P = 600mW)
L
♦ Less Than 0.1% THD+N
♦ High 80dB PSRR
O
♦ 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
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.
♦ 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
PIN-
PKG
PART
TEMP RANGE
PACKAGE
CODE
MAX9773EBP-T -40°C to +85°C 20 UCSP-20
MAX9773ETG+ -40°C to +85°C 24 TQFN-EP*
B20-1
T2444-4
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.
+Denotes lead-free package.
*EP = Exposed paddle.
Block Diagram
V
DD
MAX9773
INR+
INR-
RIGHT
MODULATOR
AND H-BRIDGE
Applications
GAIN1
GAIN2
GAIN
Cellular/Multimedia Phones
Notebooks
INL+
LEFT
MODULATOR
AND H-BRIDGE
Handheld Gaming Consoles
MP3 Players
INL-
Pin Configurations and Gain Selection appear at end of
data sheet.
OSCILLATOR
SYNC
SYNC_OUT
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
ABSOLUTE MAXIMUM RATINGS
V
V
to GND..............................................................................6V
Duration of Short Circuit Between OUT+ and OUT- ......Continuous
DD
DD
to PV ..........................................................-0.3V to +0.3V
Continuous Power Dissipation (T = +70°C)
DD
A
PV
to PGND .........................................................................6V
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
DD
GND to PGND .......................................................-0.3V to +0.3V
All Other Pins to GND.................................-0.3V to (V + 0.3V)
Continuous Current In/Out of PV , PGND, OUT_......... 800mA
Continuous Input Current (all other pins).......................... 20mA
Duration of OUT_ Short Circuit to
V
DD
DD
/GND/PV /PGND...........................................Continuous
DD
DD
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= V
= V
= 3.3V, V
= V
= 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), R connected between
PGND
L
, unless otherwise noted. Typical values are at T = +25°C.) (Notes 1, 2)
PV
SHDN
L
GND
DD
DD
OUT+ and OUT-, R = ∞, T = T
to T
A
MIN
MAX A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Supply Voltage Range
Quiescent Current
Shutdown Current
V
Inferred from PSRR test
Per channel
2.6
5.5
7.5
10
V
DD
I
5.5
0.1
66
mA
µA
dB
V
DD
I
SHDN
Common-Mode Rejection Ratio
Input Bias Voltage
CMRR
f
= 1kHz
IN
V
1.125
1.25
80
1.375
50
BIAS
Turn-On Time
t
ms
mV
ON
Output Offset Voltage
V
T
= +25oC
A
10
OS
V
= 2.5V to 5.5V, V = 0V, T = +25oC
59
56
80
DD
IN
A
T
MIN
< T < T
A MAX
Power-Supply Rejection Ratio
Output Power (Note 3)
PSRR
dB
f
= 217Hz
= 20kHz
72
50
RIPPLE
f
RIPPLE
100mV
ripple,
P-P
V
= 0V
IN
R = 8Ω
500
750
1300
1800
0.04
0.08
86
L
V
V
= 3.3V
= 5V
DD
DD
R = 4Ω
L
THD+N = 1%,
= +25oC
P
mW
%
OUT
T
A
R = 8Ω
L
R = 4Ω
L
R = 8Ω (P
L
= 400mW), f = 1kHz
= 600mW), f = 1kHz
OUT
Total Harmonic Distortion Plus
Noise (Note 3)
THD+N
SNR
R = 4Ω (P
L
OUT
FFM
SSM
FFM
SSM
BW = 22Hz
to 22kHz
86
Signal-to-Noise Ratio
Oscillator Frequency
V
= 1V
dB
OUT
RMS
88.5
88.5
1100
1400
A-weighted
SYNC = GND, T = +25oC
A
SYNC = unconnected, T = +25oC
950
1250
1600
1200
A
f
kHz
OSC
1200
60
SYNC = V , T = +25oC
DD
A
Minimum On-Time
t
200
ns
MIN
SYNC Frequency Lock Range
f
1000
2000
kHz
SYNC
2
_______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
= V
= 3.3V, V
= V
= 0V, SYNC = 0V (FFM), gain = 12dB (GAIN1 = 1, GAIN2 = 1), R connected between
PGND
L
, unless otherwise noted. Typical values are at T = +25°C.) (Notes 1, 2)
PV
SHDN
L
GND
DD
DD
OUT+ and OUT-, R = ∞, T = T
to T
A
MIN
MAX A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
100
200
400
-50
MAX
UNITS
SYNC_OUT Capacitance Drive
C
pF
SYNC_OUT
Bridge-tied capacitance
Capacitive Drive
C
pF
dBV
%
L
Single ended
Into shutdown
Peak reading, A-weighted,
32 samples per second
(Note 4)
Click-and-Pop Level
Efficiency
K
CP
Out of
shutdown
-50
85
P
= 600mW per channel,
= 1kHz, R = 8Ω
L
OUT
η
f
IN
GAIN1 = 0, GAIN2 = 0
GAIN1 = 1, GAIN2 = 0
GAIN1 = 0, GAIN2 = 1
GAIN1 = 1, GAIN2 = 1
GAIN1 = 0, GAIN2 = 0
GAIN1 = 1, GAIN2 = 0
GAIN1 = 0, GAIN2 = 1
GAIN1 = 1, GAIN2 = 1
10
16
30
Input Resistance
R
kΩ
IN
45
60
26
20
Gain
A
dB
V
15.6
12
Channel-to-Channel Gain
Tracking
1
%
L to R, R to L, f = 10kHz, R = 8Ω,
L
Crosstalk
80
dB
P
= 300mW
OUT
DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)
Input-Voltage High
Input-Voltage Low
V
2
V
V
INH
V
0.8
1
INL
Input Leakage Current
(SHDN, GAIN1, GAIN2)
µA
µA
V
V
= GND, normal operation
-15
2.4
-7
SYNC
SYNC
Input Leakage Current (SYNC)
= V , normal operation
12
25
DD
DIGITAL OUTPUTS (SYNC_OUT)
Output-Voltage High
V
I
I
= 3mA, V = 3.3V
DD
V
V
OH
OH
Output-Voltage Low
V
= 3mA
0.4
OL
OL
Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Note 2: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For R = 4Ω, L = 33µH.
L
For R = 8Ω, L = 68µH.
L
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 transi-
tions are controlled by SHDN. K
level is calculated as: 20 x log[(peak voltage during mode transition, no input signal)].
CP
Units are expressed in dBV.
_______________________________________________________________________________________
3
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Typical Operating Characteristics
(V
= V
= V
= 3.3V, V
= V = 0V, SYNC = V
PGND
(SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
DD
PV
SHDN
GND
DD
DD
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
10
10
1
10
1
V
= 5V
V
= 5V
V
= 3.3V
DD
DD
DD
R = 8Ω
R = 4Ω
R = 4Ω
L
L
L
1
0.1
OUTPUT POWER = 100mW
OUTPUT POWER = 600mW
OUTPUT POWER = 100mW
OUTPUT POWER = 250mW
OUTPUT POWER = 500mW
0.1
0.1
OUTPUT POWER = 100mW
OUTPUT POWER = 300mW
OUTPUT POWER = 300mW
0.01
0.001
0.01
0.001
0.01
0.001
OUTPUT POWER = 600mW
10
100
1k
10k
100k
10
100
1k
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
10
1
100
10
1
10
1
V
= 3.3V
V
= 5V
V
= 5V
DD
R = 4Ω
L
DD
DD
R = 8Ω
R = 8Ω
L
L
P
= 800mW
OUT
OUTPUT POWER = 400mW
FFM
SSM
f
= 1kHz
IN
0.1
0.1
0.1
OUTPUT POWER = 100mW
0.01
0.001
0.01
0.001
0.01
f
= 20Hz
1.0
f
= 20kHz
2.0
IN
IN
OUTPUT POWER = 250mW
0.001
10
100
1k
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
0
0.5
1.5
2.5
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
100
10
100
10
100
10
V
= 3.3V
V
= 5V
V
= 3.3V
DD
L
DD
L
DD
L
R = 4Ω
R = 8Ω
R = 8Ω
f
= 20Hz
IN
1.0
1
1
f
= 1kHz
IN
f
= 1kHz
IN
0.1
0.1
0.1
0.01
0.001
0.01
0.001
0.01
0.001
f
= 1kHz
f = 20kHz
IN
IN
f
= 20kHz
1.5
f
= 20Hz
0.6
IN
f = 20Hz
IN
IN
f = 20kHz
IN
0
0.3
0.9
1.2
1.8
0
0.2
0.4
0.6
0.8
1.0
0
0.2
0.4
OUTPUT POWER (W)
0.6
0.8
OUTPUT POWER (W)
OUTPUT POWER (W)
4
_______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Typical Operating Characteristics (continued)
(V
= V
= V
= 3.3V, V
= V = 0V, SYNC = V
PGND
(SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
DD
PV
SHDN
GND
DD
DD
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
EFFICIENCY vs. OUTPUT POWER
EFFICIENCY vs. OUTPUT POWER
100
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
V
= 5V
DD
R = 8Ω
L
R = 8Ω
L
R = 8Ω
L
f
= 1kHz
IN
10
1
R = 4Ω
L
R = 4Ω
L
FFM
0.1
V
= 5V
DD
0.01
0.001
V
f
= 3.3V
= 1kHz
SSM
DD
IN
f
IN
= 1kHz
OUTPUT POWER PER CHANNEL
OUTPUT POWER PER CHANNEL
0
0.4
0.8
1.2
1.6
2.0
0
0.5
1.0
1.5
2.0
2.5
3.0
0
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER vs. SUPPLY VOLTAGE
OUTPUT POWER vs. SUPPLY VOLTAGE
OUTPUT POWER vs. LOAD RESISTANCE
2.0
1.5
1.0
0.5
0
3.0
2.5
2.0
1.5
1.0
0.5
0
3.0
2.5
2.0
1.5
1.0
0.5
0
R = 4Ω
IN
R = 8Ω
L
L
V
Z
= 5V, f = 1kHz,
DD
f
= 1kHz
f
= 1kHz
IN
= 33µH
LOAD
IN SERIES WITH R
L
THD+N = 10%
THD+N = 10%
THD+N = 10%
THD+N = 1%
THD+N = 1%
THD+N = 1%
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
1
10
LOAD RESISTANCE (Ω)
100
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Typical Operating Characteristics (continued)
(V
= V
= V
= 3.3V, V
= V = 0V, SYNC = V
PGND
(SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
DD
PV
SHDN
GND
DD
DD
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
OUTPUT POWER vs. LOAD RESISTANCE
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
100
90
80
70
60
50
40
30
20
10
0
1.2
V
= 100mV
P-P
V
= 100mV
P-P
V
Z
= 3.3V, f = 1kHz,
RIPPLE
RIPPLE
DD
R = 8Ω
L
R = 8Ω
L
= 33µH
LOAD
1.0
0.8
0.6
0.4
0.2
0
V
= 3.3V
DD
IN SERIES WITH R
L
THD+N = 10%
V
= 5V
DD
THD+N = 1%
10
10
100
1k
FREQUENCY (Hz)
10k
0
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
1
100
LOAD RESISTANCE (Ω)
CROSSTALK vs. FREQUENCY
CROSSTALK vs. INPUT AMPLITUDE
-40
-50
P
= 300mW
f = 1kHz
IN
R = 8Ω
L
OUT
L
-10
R = 8Ω
-20
-30
-40
-50
-60
-70
-80
-90
ONE CHANNEL DRIVEN
-60
-70
-80
RIGHT TO LEFT
-90
-100
-110
-120
-130
-140
LEFT TO RIGHT
-100
-110
-120
10
100
1k
10k
100k
-94
-74
-54
-34
-14
6
FREQUENCY (Hz)
INPUT AMPLITUDE (dB)
OUTPUT FREQUENCY SPECTRUM
OUTPUT FREQUENCY SPECTRUM
0
-20
0
-20
FFM MODE
SSM MODE
V
= -60dBV
V
= -60dB
OUT
OUT
f = 1kHz
f = 1kHz
R = 8Ω
R = 8Ω
L
L
-40
-40
UNWEIGHTED
UNWEIGHTED
-60
-60
-80
-80
-100
-120
-140
-100
-120
-140
0
5
10
15
20
0
5
10
15
20
FREQUENCY (kHz)
FREQUENCY (kHz)
6
_______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Typical Operating Characteristics (continued)
(V
= V
= V
= 3.3V, V
= V = 0V, SYNC = V
PGND
(SSM), gain = 12dB (GAIN1 = 1, GAIN2 = 1)).
DD
PV
SHDN
GND
DD
DD
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
WIDEBAND OUTPUT SPECTRUM
(SSM MODE (SPEAKER MODE))
0
0
R = 8Ω,
DD
INPUTS
AC-GROUNDED
L
R = 8Ω,
DD
INPUTS
AC-GROUNDED
L
-10
-10
V
= 5V
V
= 5V
-20
-30
-40
-50
-60
-70
-80
-90
-100
-20
-30
-40
-50
-60
-70
-80
-90
-100
0.1
1
10
100
0.1
1
10
100
FREQUENCY (MHz)
FREQUENCY (MHz)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
TURN-ON/TURN-OFF RESPONSE
MAX9773 toc25
20
17
14
11
8
BOTH CHANNELS DRIVEN
SHDN
2V/div
1V/div
SSM
FFM
MAX9773
DIFFERENTIAL
OUTPUT
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
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
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Pin Description
PIN
NAME
FUNCTION
TQFN
UCSP
1
A2
SHDN
Active-Low Shutdown. Connect to V
for normal operation.
DD
Frequency Select and External Clock Input:
SYNC = GND: Fixed-frequency mode with f = 1100kHz.
S
2
B3
SYNC
SYNC = Unconnected: Fixed-frequency mode with f = 1400kHz.
S
SYNC = V : Spread-spectrum mode with f = 1200kHz 60kHz.
DD
S
SYNC = Clocked: Fixed-frequency mode with f = external clock frequency.
S
3, 8, 11, 16
—
A3
N.C.
No Connection. Not internally connected.
Left-Channel Amplifier Output Positive Phase
4
5, 14
6, 13
7
OUTL+
A4, D4
B4, C4
A5
PV
H-Bridge Power Supply. Connect to V . Bypass with a 0.1µF capacitor to PGND.
DD
DD
PGND
OUTL-
GND
Power Ground
Left-Channel Amplifier Output Negative Phase
Analog Ground
9, 22
10
B1, B5
C5
SYNC_OUT Clock Signal Output
12
D5
OUTR-
OUTR+
GAIN1
GAIN2
INR-
Right-Channel Amplifier Output Negative Phase
15
D3
Right-Channel Amplifier Output Positive Phase
Gain-Select Input 1
17
C3
18
D2
Gain-Select Input 2
19
D1
Right-Channel Inverting Input
Right-Channel Noninverting Input
20
C2
INR+
21
C1
V
Analog Power Supply. Connect to PV . Bypass with a 10µF capacitor to GND.
DD
DD
23
B2
INL+
INL-
Left-Channel Noninverting Input
Left-Channel Inverting Input
24
A1
Exposed Pad. Connect the exposed thermal pad to the GND plane (see the Supply
Bypassing, Layout, and Grounding section).
EP
—
EP
8
_______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Functional Diagram
V
DD
0.1µF
10µF*
V
DD
PV
DD
SYNC_OUT
OSCILLATOR
AND
SYNC
SAWTOOTH
V
BIAS
470nF
470nF
R
R
IN
OUTL+
INL+
INL-
CLASS D
MODULATOR
AND H-BRIDGE
OUTL-
IN
470nF
470nF
R
R
IN
INR+
INR-
OUTR+
OUTR-
CLASS D
MODULATOR
AND H-BRIDGE
IN
V
BIAS
V
BIAS
BIAS
GENERATOR
GAIN1
GAIN2
SHDN
GAIN
CONTROL
MAX9773
GND
PGND
*BULK CAPACITANCE.
_______________________________________________________________________________________
9
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
t
SW
V
IN-
V
IN+
OUT-
OUT+
t
ON(MIN)
V
- V
OUT-
OUT+
Figure 1. MAX9773 Outputs with an Input Signal Applied
input-coupling capacitors. The inputs can also be config-
ured to accept a single-ended input signal.
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
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 (t ) at the output of the sec-
ON(MIN)
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
(V
- V
) to change. The minimum-width pulse
OUT-
OUT+
helps the device to achieve high levels of linearity.
10 ______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
t
t
t
t
SW
SW
SW
SW
V
IN_-
V
IN_+
OUT_-
OUT_+
t
ON(MIN)
V
- V
OUT_-
OUT_+
Figure 2. MAX9773 Outputs with an Input Signal Applied (SSM Mode)
Operating Modes
Table 1. 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.
SYNC
MODE
GND
FFM with f
FFM with f
= 1100kHz
OSC
OSC
Unconnected
= 1400kHz
V
SSM with f
= 1200kHz 60kHz
= external clock frequency
DD
OSC
OSC
Clocked
FFM with f
______________________________________________________________________________________ 11
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
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-
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.
ing SYNC to V
(Table 1). In SSM mode, the switching
DD
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.
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.
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
40
35
30
25
20
15
10
5
30
60
80
100
120
140
160
180
200
220
240
260
280
300
FREQUENCY (MHz)
Figure 3. EMI Spectrum of MAX9773 with 6in of Twisted-Pair Speaker Cable with TDK Ferrite Beads MPZ1608S300A
12 ______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
EFFICIENCY vs. OUTPUT POWER
100
V
= 0V
IN_
MAX9773
90
80
70
60
50
40
OUT_-
OUT_+
30
CLASS AB
20
10
0
V
= 3.3V
DD
f = 1kHz
R - 8Ω
L
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7
OUTPUT POWER (W)
V
- V = 0V
OUT_+ OUT_-
Figure 4. MAX9773 Outputs with No Input Signal
Figure 5. MAX9773 Efficiency vs. Class AB Efficiency
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
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.
V
) and causes large ripple currents. Any parasitic
DD(P-P)
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.
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).
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 8Ω speakers, for portable
audio applications, exhibit series inductances in the
range of 20µH to 100µH.
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 V for normal operation.
DD
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.
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
Applications Information
Filterless Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM output.
current draw of: 8µW/(V
order of a few µA.
/ 100 x η), which is on the
DD
______________________________________________________________________________________ 13
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
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
Table 2. Gain Settings (V
THD+N = 10%)
= 3.3V,
DD
GAIN
(dB)
INPUT
(V
R
P
OUT
L
GAIN1
GAIN2
)
(Ω)
(mW)
950
950
950
950
650
650
650
650
RMS
0.097699
0.194936
0.323513
0.489657
0.114288
0.228035
0.378444
0.572798
0
1
0
1
0
1
0
1
0
0
1
1
0
0
1
1
+26
+20
+15.6
12
4
4
4
4
8
8
8
8
at V
= 3.3V and THD+N = 10%.
DD
Custom Gain Settings
+26
+20
+15.6
12
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.
Table 3. Custom Gain Components
GAIN_ SETTINGS
GAIN (dB)
R1 (Ω)
R2 (Ω)
C
(µF)
GAIN TOLERANCE (dB)
IN
GAIN1
GAIN2
0
0
0
0
0
0
1
1
1
1
1
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
—
750
1k
—
1
—
20k
10k
6k
1
+0.12/-0.07
+0.14/-0.08
+0.13/-0.08
+0.16/-0.1
+0.19/-0.12
—
1.5
2.2
1k
1.5k
2k
6k
2.2
6k
2
—
—
1
1.2k
2k
30k
20k
10k
10k
40k
40k
20k
—
1
+0.1/-0.06
+0.15/-0.09
+0.12/-0.07
+0.15/-0.09
+0.06/-0.03
+0.15/-0.09
+0.14/-0.08
—
1
2k
1.2
2.5k
1k
1.2
0.86
0.68
0.86
1
2.8k
2.8k
—
1.8k
4k
40k
40k
30k
20k
16k
16k
14k
12k
12k
10k
10k
10k
0.86
0.68
0.68
0.68
0.68
0.68
0.68
0.68
0.68
0.68
0.58
0.47
+0.08/-0.05
+0.15/-0.09
+0.17/-0.1
+0.15/-0.09
+0.15/-0.09
+0.17/-0.1
+0.17/-0.1
+0.16/-0.1
+0.17/-0.1
+0.16/-0.1
+0.16/-0.1
+0.17/-0.1
5k
8
5k
7
5.5k
7k
6
5
8k
4
8k
3
10k
11k
12k
14k
2
1
0
14 ______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
0.47µF
SINGLE-ENDED
INL+
LEFT AUDIO INPUT
OUTL+
MAX9773
0.47µF
SINGLE-ENDED
INR+
C
C
IN
R
R1
R1
IN
MAX9773
RIGHT AUDIO INPUT
INL+
INL-
OUTL-
OUTR+
INL-
INR-
R2
0.47µF
IN
R
R
IN
0.47µF
OUTR-
GAIN1
GAIN2
SHDN
C
C
IN
R1
R1
IN
INR+
INR-
R2
GND
PGND
SYNC
IN
2.5V TO 5.5V
V
DD
R
IN
PV
DD
10µF
0.1µF
FFM MODE WITH f
= 1100kHz, GAIN = 15.6dB.
OSC
Figure 6. Custom Gain Setting
Figure 7. Single-Ended Input
The internal input resistance, R , changes with each
IN
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:
gain setting. The R1 resistors attenuate the gain and
resistors R2 compensate for R ’s tolerance, which can
IN
be as high as 25%. C must be adjusted to compen-
IN
sate for the total change in input impedance or the low-
frequency roll-off point shifts.
1
f
=
−3dB
2πR C
IN IN
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.
Choose C so f
is well below the lowest frequency
IN
-3dB
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.
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 conjunction with the
IN
MAX9773 input impedance (R ) forms a highpass filter
IN
that removes the DC bias from an incoming signal. The
______________________________________________________________________________________ 15
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
5V
C
IN
2200pF
10µF
INL+
INR+
INL-
OUTL+
C
IN
2200pF
8Ω
8Ω
MAX9773
OUTL-
OUTR+
C
IN
2200pF
10µF
C
IN
2200pF
INR-
OUTR-
SYNC
SYNC_OUT
R3
10kΩ
5V
R1
20kΩ
V
DD
R4
39kΩ
SYNC
IN+
C2
1nF
1µF
R2
20kΩ
MAX9705
C1
OUT+
OUT-
0.01µF
4Ω
MAX4238
1µF
1.25V
IN-
NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V.
FFM MODE WITH f = 1100kHz.
OSC
Figure 8. 2.1 Channel Application Circuit
Output Filter
2.1 Channel Configuration
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.
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 (C ) set the highpass cutoff
IN
frequency according to the following equation:
1
f =
2π × R × C
IN
IN
where R
is the typical input resistance of the
IN
MAX9773. The 10µF capacitors on the output of the
MAX9773 ensure a two-pole highpass filter.
16 ______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
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:
Bypass V
with a 0.1µF capacitor to GND and PV
DD DD
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.
−2 × R3
A
=
VLP
R1
where R1 = R2 and R3 = R1//R2. The cutoff frequency
of the lowpass filter is set by the following equation:
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.
1
2π
1
f
LP
=
×
C1 × C2 × R3 × 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 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.
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
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
System Diagram
18 ______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Pin Configurations
TOP VIEW
TOP VIEW
(BUMPS ON BOTTOM)
MAX9773
1
2
3
4
5
18 17 16 15 14 13
A
B
C
D
INL-
GND
SHDN
OUTL+
SYNC
PV
OUTL-
DD
INR- 19
INR+ 20
21
12 OUTR-
11 N.C.
INL+
INR+
PGND
PGND
GND
V
DD
10 SYNC_OUT
MAX9773
GND 22
INL+ 23
INL- 24
9
8
7
GND
SYNC
_OUT
V
DD
GAIN1
N.C.
+
OUTL-
INR-
GAIN2
OUTR+
UCSP
PV
DD
OUTR-
1
2
3
4
5
6
TQFN
Gain Selection
Chip Information
PROCESS: BiCMOS
GAIN SELECTION
GAIN (dB)
GAIN1 = 0, GAIN2 = 0
GAIN1 = 1, GAIN2 = 0
GAIN1 = 0, GAIN2 = 1
GAIN1 = 1, GAIN2 = 1
26
20
15.6
12
______________________________________________________________________________________ 19
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
1
E
21-0139
2
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
2
E
21-0139
2
MAX9773 Package Code: T2444-4
20 ______________________________________________________________________________________
1.8W, Filterless, Ultra-Low EMI,
Stereo Class D Audio Power Amplifier
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE, 5x4 UCSP
1
21-0095
I
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.
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