MAX9741ETN+ [MAXIM]
12W12W, Low-EMI, Spread-Spectrum, Stereo, Class D Amplifier;
| 型号： | MAX9741ETN+ |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 12W12W, Low-EMI, Spread-Spectrum, Stereo, Class D Amplifier |
| 文件： | 总16页 (文件大小：1053K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3887; Rev 0; 2/06
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
General Description
Features
The MAX9741 stereo Class D audio power amplifier
provides Class AB amplifier performance with Class D
efficiency, conserving board space and eliminating the
need for a bulky heatsink. Using a high-efficiency Class
D architecture, it delivers 12W continuous output power
into 8Ω loads. Proprietary modulation and switching
schemes render the traditional Class D EMI suppression
output filter unnecessary.
♦ Low-EMI Class D Amplifier
♦ Spread-Spectrum Mode Reduces EMI
♦ Passes FCC EMI Limits with Ferrite Bead Filters
with 0.5m Cables
♦ 12W+12W Continuous Output Power into 8Ω
♦ Low 0.1% THD+N
The MAX9741 offers two modulation schemes: a fixed-fre-
quency mode (FFM), and a spread-spectrum mode (SSM)
that reduces EMI-radiated emissions. The device utilizes a
fully differential architecture, a full bridged output, and
offers comprehensive click-and-pop suppression.
♦ High PSRR (80dB at 1kHz)
♦ 10V to 25V Single-Supply Operation
♦ Differential Inputs Minimize Common-Mode Noise
♦ Pin-Selectable Gain Reduces Component Count
♦ Industry-Leading Click-and-Pop Suppression
♦ Short-Circuit and Thermal-Overload Protection
The MAX9741 features high 80dB PSRR, low 0.1%
THD+N, and SNR in excess of 100dB. Short-circuit and
thermal-overload protection prevent the device from
being damaged during a fault condition. The MAX9741
is available in a 56-pin TQFN (8mm x 8mm x 0.8mm)
package. The MAX9741 is specified over the extended
-40°C to +85°C temperature range.
♦ Available in Thermally Efficient, Space-Saving
56-Pin TQFN (8mm x 8mm x 0.8mm) Package
Applications
Ordering Information
PKG
CODE
T5688-3
LCD/PDP TVs
CRT TVs
PART
TEMP RANGE PIN-PACKAGE
56 TQFN-EP*
MAX9741ETN+ -40°C to +85°C
PC Speakers
+Denotes lead-free package.
*EP = Exposed paddle.
Simplified Block Diagram
INR+
INR-
INL+
INL-
DIFFERENTIAL AUDIO
INPUTS ELIMINATE
NOISE PICKUP
CLASS D
GAIN
CONTROL
OUTPUT
PROTECTION
AMPLIFIERS
DRIVE 2 X 12W
INTO 8Ω LOADS
CLASS D
MODULATOR
G1
G2
PROGRAMMABLE
SWITCHING
2
FS1, FS2
MAX9741
FREQUENCY
Pin Configuration appears at end of data sheet.
________________________________________________________________ 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.
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND.)
Continuous Power Dissipation (T = +70°C)
A
V
to PGND, AGND.............................................................30V
Single-Layer PC Board
56-Pin TQFN (derate 28.6mW/°C above +70°C) ............2.29W
DD
OUTR_, OUTL_, C1N..................................-0.3V to (V
+ 0.3V)
DD
C1P............................................(V
CHOLD........................................................(V
SHDN, FS_, G_ ...........................................................-6.3V to 8V
All Other Pins to GND.............................................-0.3V to +12V
Duration of OUTR_/OUTL_
- 0.3V) to (CHOLD + 0.3V)
θ
................................................................................ 35°C/W
............................................................................... 0.6°C/W
DD
- 0.3V) to +40V
DD
Continuous Power Dissipation (T = +70°C)
Multiple-Layer PC Board
56-Pin TQFN (derate 47.6mW/°C above +70°C) ............3.81W
A
Short Circuit to GND, V ......................................Continuous
Continuous Input Current (V , PGND) ..................................2A
DD
Continuous Input Current (all other pins).......................... 20mA
Thermal Limits (Note 1)
θ
................................................................................ 21°C/W
............................................................................... 0.6°C/W
JA
JC
DD
θ
Junction Temperature......................................................+150°C
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: Thermal performance of this device is highly dependant on PC board layout. See the Applications Information for more
detail.
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
= 18V, GND = PGND = 0V, SHDN ≥ V , A = 16dB, C = C = 0.47µF, C
= 0.01µF, C1 = 100nF, C2 = 1µF, FS1 = FS2 =
REG
DD
IH
V
SS
IN
GND (f = 670kHz), R connected between OUTL+ and OUTL- and OUTR+ and OUTR-, T = T
to T
, unless otherwise noted.
S
L
A
MIN
MAX
Typical values are at T = +25°C.) (Notes 1, 2)
A
PARAMETER
GENERAL
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage Range
Quiescent Current
Shutdown Current
V
Inferred from PSRR test
R = Open
10
25
37
V
DD
I
26
0.2
100
50
mA
µA
DD
L
I
1.5
SHDN
C
C
= 470nF
= 180nF
SS
SS
Turn-On Time
t
ms
ON
Amplifier Output Resistance in
Shutdown
SHDN = GND
A = 13dB
150
320
kΩ
35
30
23
10
53
45
80
65
55
22
V
A = 16dB
V
Input Impedance
Voltage Gain
R
kΩ
IN
A = 19.1dB
V
36
A = 29.6dB
V
14.3
G1 = L, G2 = L
29.4
29.6
29.8
G1 = L, G2 = H
G1 = H, G2 = L
G1 = H, G2 = H
Between channels
18.9
12.8
15.9
19.1
13
16
0.5
5
19.3
13.2
16.3
A
dB
V
Gain Matching
%
Output Offset Voltage
Common-Mode Rejection Ratio
V
30
mV
dB
OS
CMRR
f
= 1kHz, input referred
60
83
80
60
IN
V
= 10V to 25V
48
DD
Power-Supply Rejection Ratio
(Note 3)
PSRR
f
f
= 1kHz
dB
RIPPLE
RIPPLE
200mV
ripple
P-P
= 20kHz
2
_______________________________________________________________________________________
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(V
= 18V, GND = PGND = 0V, SHDN ≥ V , A = 16dB, C = C = 0.47µF, C
= 0.01µF, C1 = 100nF, C2 = 1µF, FS1 = FS2 =
REG
DD
IH
V
SS
IN
GND (f = 670kHz), R connected between OUTL+ and OUTL- and OUTR+ and OUTR-, T = T
to T
, unless otherwise noted.
S
L
A
MIN
MAX
Typical values are at T = +25°C.) (Notes 1, 2)
A
PARAMETER
SYMBOL
CONDITIONS
R = 8Ω
= 18V, THD+N =
MIN
TYP
MAX
UNITS
12
6.5
11
5
L
V
DD
10%, f = 1kHz
R = 4Ω
L
R = 8Ω
L
V
= 24V, THD+N =
Continuous Output Power
(Notes 4, 5)
DD
P
W
CONT
10%, f = 1kHz
R = 4Ω
L
R = 8Ω
L
8
V
= 12V, THD+N =
DD
10%, f = 1kHz
R = 4Ω
L
8.5
Total Harmonic Distortion Plus
Noise
f
P
= 1kHz, either FFM or SSM, R = 8Ω,
IN
L
THD+N
SNR
0.1
%
= 4W
OUT
FFM
SSM
FFM
SSM
95.8
91.8
99.1
95.7
65
R = 8Ω,
P
f = 1kHz
BW = 22Hz to 22kHz
L
Unweighted
A-weighted
= 4W,
OUT
Signal-to-Noise Ratio
Crosstalk
dB
dB
Left to right, right to left, 8Ω load, f = 10kHz
IN
FS1 = L, FS2 = L
FS1 = L, FS2 = H
FS1 = H, FS2 = L
560
670
930
470
800
Oscillator Frequency
Efficiency (Note 4)
f
kHz
OSC
670
7%
FS1 = H, FS2 = H (spread-spectrum mode)
V
V
= 12V, R = 8Ω, P
= 8W
78
DD
DD
L
OUT
η
%
V
= 18V, R = 8Ω, P
= 10W
78
6
L
OUT
Regulator Output
V
REG
DIGITAL INPUTS (SHDN, FS_, G_)
V
V
2.5
IH
IL
Input Thresholds
V
0.8
1
Input Leakage Current
µA
Note 2: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Note 3: PSRR is specified with the amplifier inputs connected to GND through C
.
IN
Note 4: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For R = 8Ω, L = 68µH.
L
For R = 12Ω, L = 100µH. For R = 16Ω, L = 120µH.
L
L
Note 5: Output power measured at T = +25°C, with a soak time of 15 minutes.
A
_______________________________________________________________________________________
3
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Typical Operating Characteristics
(V
= 18V, R = 8Ω, f = 1kHz, 33µH with 4Ω, 68µH with 8Ω, part in SSM mode, 136µH with 16Ω, measurement BW = 22Hz to
L IN
DD
22kHz, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
10
1
10
1
10
1
R = 8Ω
L
R = 4Ω
L
V
DD
= 12V
V
= 18V
DD
V
DD
= 12V
V
= 24V
DD
V
DD
= 24V
V
= 18V
DD
P
= 8W
OUT
0.1
0.1
0.01
0.1
0.01
P
OUT
= 500mW
0.01
0
5
10
OUTPUT POWER (W)
15
20
0
5
10
15
10
100
1k
FREQUENCY (Hz)
10k
100k
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
EFFICIENCY vs. OUTPUT POWER
100
10
1
10
1
R = 8Ω
L
P
OUT
= 8W
V
= 12V
= 18V
90
80
70
60
50
40
30
20
10
0
DD
f = 100Hz
SSM
V
DD
f = 10kHz
V
= 24V
DD
0.1
0.01
0.1
0.01
f = 1kHz
FFM
0
4
8
12
16
0
5
10
15
20
10
100
1k
FREQUENCY (Hz)
10k
100k
OUTPUT POWER (W)
OUTPUT POWER (W)
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
OUTPUT POWER vs. SUPPLY VOLTAGE
OUTPUT POWER vs. LOAD RESISTANCE
20
18
16
14
12
10
8
0
20
18
16
14
12
10
8
-10
THD+N = 10%
-20
-30
-40
-50
-60
-70
-80
R = 8Ω
L
R = 16Ω
L
6
6
THD+N = 1%
4
4
2
2
0
0
10
13
16
19
22
25
10
100
1k
10k
100k
1
10
100
SUPPLY VOLTAGE (V)
FREQUENCY (Hz)
LOAD RESISTANCE (Ω)
4
_______________________________________________________________________________________
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Typical Operating Characteristics (continued)
(V
= 18V, R = 8Ω, f = 1kHz, 33µH with 4Ω, 68µH with 8Ω, part in SSM mode, 136µH with 16Ω, measurement BW = 22Hz to
L IN
DD
22kHz, unless otherwise noted.)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
OUTPUT FREQUENCY SPECTRUM
CROSSTALK vs. FREQUENCY
20
0
0
0
-20
FFM MODE
UNWEIGHTED
200mV INPUT
P-P
-20
-40
f
P
= 1kHz
= 5W
IN
OUT
-20
-40
-60
-80
-100
-120
-140
-40
LEFT TO RIGHT
-60
-60
-80
-80
RIGHT TO LEFT
-100
-100
-120
-120
0
2
4
6
8
10 12 14 16 18 20
10
100
1k
10k
100k
10
100
1k
10k
100k
FREQUENCY (kHz)
FREQUENCY (Hz)
FREQUENCY (Hz)
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
OUTPUT FREQUENCY SPECTRUM
OUTPUT FREQUENCY SPECTRUM
20
0
20
0
0
-20
-40
-60
-80
SSM MODE
UNWEIGHTED
SSM MODE
A-WEIGHTED
RBW = 10kHz
f
P
= 1kHz
= 5W
f
P
= 1kHz
= 5W
IN
OUT
IN
OUT
-20
-40
-60
-80
-100
-120
-140
-20
-40
-60
-80
-100
-120
-140
-100
-120
0
2
4
6
8
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
100k
1M
10M
100M
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (Hz)
_______________________________________________________________________________________
5
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Typical Operating Characteristics (continued)
(V
= 18V, R = 8Ω, f = 1kHz, 33µH with 4Ω, 68µH with 8Ω, part in SSM mode, 136µH with 16Ω, measurement BW = 22Hz to
L IN
DD
22kHz, unless otherwise noted.)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
WITH FERRITE BEAD FILTER
WIDEBAND OUTPUT SPECTRUM
TURN-ON/TURN-OFF RESPONSE
(SSM MODE)
MAX9741 toc17
10
1
0
R = 8Ω
C
SS
= 180pF
L
RBW = 10kHz
V
= 12V
DD
V
DD
= 18V
-20
-40
V
DD
= 24V
SHDN
5V/div
-60
0.1
0.01
-80
OUTPUT
1V/div
-100
-120
f = 1kHz
0
5
10
OUTPUT POWER (W)
15
20
20ms/div
100k
1M
10M
100M
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
WITH FERRITE BEAD FILTER
0.35
0.30
0.25
0.20
0.15
35
30
25
10
1
R = 4Ω
L
V
= 12V
= 18V
DD
V
DD
20
15
10
V
= 24V
DD
0.1
0.10
0.05
5
0
0.01
0
10
12
14
16
18
20
10
13
16
19
22
25
0
5
10
15
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
6
_______________________________________________________________________________________
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Pin Description
PIN
NAME
N.C.
FUNCTION
1, 4, 7, 11–15, 19, 21,
23, 25, 28, 33–36, 39,
42, 43, 44, 49, 50, 55, 56
No Connection. Not internally connected.
2, 3, 40, 41
PGND
Power Ground
5, 6, 37, 38
V
Power-Supply Input
DD
8
C1N
C1P
Charge-Pump Flying Capacitor Negative Terminal
Charge-Pump Flying Capacitor Positive Terminal
Charge-Pump Hold Capacitor. Connect a 1µF capacitor from CHOLD to V
Left-Channel Negative Input
9
10
16
17
CHOLD
INL-
.
DD
INL+
Left-Channel Positive Input
Active-Low Shutdown. Connect SHDN to GND to disable the device. Connect to V
normal operation.
for
DD
18
SHDN
20
22
SS
AGND
REG
INR-
Soft-Start. Connect a 0.47µF capacitor from SS to GND to enable soft-start feature.
Analog Ground
24
Internal Regulator Output. Bypass with a 0.01µF capacitor to PGND.
Right-Channel Negative Input
26
27
INR+
G1
Right-Channel Positive Input
29
Gain-Select Input 1
30
G2
Gain-Select Input 2
31
FS1
Frequency-Select Input 1
32
FS2
Frequency-Select Input 2
45, 46
47, 48
51, 52
53, 54
—
OUTR-
OUTR+
OUTL-
OUTL+
EP
Right-Channel Negative Audio Output
Right-Channel Positive Audio Output
Left-Channel Negative Audio Output
Left-Channel Positive Audio Output
Exposed Paddle. Connect to GND.
and spread-spectrum switching mode create a com-
pact, 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 device can also be
configured as a single-ended input amplifier.
Detailed Description
The MAX9741 low-EMI, Class D audio power amplifier
features several improvements to switch-mode amplifi-
er technology. This device offers Class AB perfor-
mance with Class D efficiency, while occupying
minimal board space. A unique modulation scheme
_______________________________________________________________________________________
7
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
device in low-power (0.2µA) shutdown mode. Connect
SHDN to a logic-high for normal operation.
Operating Modes
Fixed-Frequency Modulation (FFM) Mode
The MAX9741 features three FFM modes with different
switching frequencies (Table 1). In FFM mode, the fre-
quency spectrum of the Class D output consists of the
fundamental switching frequency and its associated
harmonics (see the Wideband Output Spectrum graph
in the Typical Operating Characteristics). The MAX9741
allows the switching frequency to be changed by
35%, should the frequency of one or more of the har-
monics fall in a sensitive band. This can be done at any
time and does not affect audio reproduction.
Click-and-Pop Suppression
Comprehensive click-and-pop suppression eliminates
audible transients on startup and shutdown. While in
shutdown, the H-bridge is pulled to GND through 320kΩ.
During startup, or power-up, the input amplifiers are
muted and an internal loop sets the modulator bias volt-
ages to the correct levels, preventing clicks and pops
when the H-bridge is subsequently enabled. Following
startup, a soft-start function gradually unmutes the input
amplifiers. The value of the soft-start capacitor has an
impact on the click/pop levels. For optimum performance,
Table 1. Operating Modes
C
SS
should be 470nF with a voltage rating of at least 7V.
SWITCHING MODE
Mute Function
FS1
FS2
(kHz)
The MAX9741 features a clickless/popless mute mode.
When the device is muted, the outputs stop switching,
muting the speaker. Mute only affects the output stage
and does not shut down the device. To mute the
MAX9741, drive SS to GND by using a MOSFET pull-
down (Figure 2). Driving SS to GND during the power-
up/down or shutdown/turn-on cycle optimizes
click-and-pop suppression.
L
L
L
H
L
670
930
H
H
470
H
670 7%
Spread-Spectrum Modulation (SSM) Mode
A unique, proprietary spread-spectrum mode flattens
the wideband spectral components, improving EMI
emissions that may be radiated by the speaker and
cables. This mode is enabled by setting FS1 = FS2 =
H. In SSM mode, the switching frequency varies ran-
domly by 7% around the center frequency (670kHz).
The modulation scheme remains the same, but the
period of the triangle waveform changes from cycle to
cycle. Instead of a large amount of spectral energy pre-
sent at multiples of the switching frequency, the energy
is now spread over a bandwidth that increases with fre-
quency. Above a few megahertz, the wideband spec-
trum looks like white noise for EMI purposes.
EFFICIENCY vs. OUTPUT POWER
100
90
MAX9741
80
70
60
50
CLASS AB
40
30
20
10
0
V
DD
= 15V
f = 1kHz
R = 8Ω
L
Efficiency
Efficiency of a Class D amplifier is attributed to the region
of operation of the output stage transistors. In a Class D
amplifier, the output transistors act as current-steering
switches and consume negligible additional power.
2
4
6
8
0
10 12 14 16 18
20
OUTPUT POWER (W)
Figure 1. MAX9741 Efficiency vs. Class AB Efficiency
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 MAX9741 still exhibits > 78% efficiency
under the same conditions (Figure 1).
SS
GPIO
MUTE SIGNAL
0.47µF
MAX9741
Shutdown
A shutdown mode reduces power consumption and
extends battery life. Driving SHDN low places the
Figure 2. MAX9741 Mute Circuit
8
_______________________________________________________________________________________
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
to pure PWM Class D amplifiers. The outputs will contain
both differential and common-mode noise at the switch-
ing frequency and its harmonics. In many applications,
a simple ferrite bead filter (see the Simplified Block
Diagram) will allow the amplifier to pass FCC EMI limits.
Ferrite beads offer significant cost and size reductions
when compared to conventional inductors. The ferrite
bead type and capacitor value can be adjusted to tune
the rejection to match the speaker cable length.
Internal Regulator
The MAX9741 has an internal linear regulator, REG,
used to power the internal analog circuitry. The voltage
at REG is nominally 6V. Bypass REG to AGND with a
10nF capacitor, rated for at least 10V. REG is turned off
in shutdown.
Applications Information
Class D Amplifier Outputs
Class D amplifiers differ from analog amplifiers such as
Class AB in that their output waveform is composed of
high-frequency pulses from ground to the supply rail.
When viewed with an oscilloscope the audio signal will
not be seen; instead, the high-frequency pulses domi-
nate. To evaluate the output of a Class D amplifier
requires taking the difference from the positive and
negative outputs, then lowpass filtering the difference
to recover the amplified audio signal.
Actual EMI test results for the MAX9741 are shown in
Figure 3. This shows the MAX9741, tested in a 10m ane-
choic EMC chamber. The MAX9741 test conditions
were: SSM mode, 0.5m cables on each side, 16dB gain,
18V supply voltage, both channels playing pink noise at
4W per channel into 8Ω shielded speakers.
The graph of Figure 3 indicates peak readings. Actual
quasi peak readings per EN55022B specification will
be lower due to Maxim’s proprietary SSM mode. Table
2 lists select values, indicating the peak reading, the
quasi-peak reading, and the actual margin to
EN55022B specification.
Ferrite Bead Output Filters
The MAX9741’s low-EMI output switching method
reduces the output filtering requirements when compared
40
35
30
25
20
15
10
30
100
200
300
400
500
600
700
800
900
1000
FREQUENCY (MHz)
Figure 3. EMI Measurement of MAX9741 in 10m Anechoic Chamber
Table 2. Peak and Quasi-Peak EMI Readings
FREQUENCY
(MHz)
PRELIMINARY PEAK
READING (dBµV/m)
QUASI PEAK READING
EN55022B LIMIT
(dBµV/m)
ACTUAL MARGIN
(dBµV/m)
(dBµV/m)
75.38
78.57
83.18
28.1
28.0
26.6
18.3
21.9
20.6
30.0
30.0
30.0
11.7
-8.1
-9.4
_______________________________________________________________________________________
9
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Ferrite beads are available from many manufacturers.
Table 3 lists some manufacturers who make ferrite
beads and other products suitable for use with Class D
amplifiers.
converting these into power in the audible frequency
range. Filterless operation requires the Class D amplifi-
er to be very close to the speaker. Distances greater
than a few centimeters must be evaluated for EMC
compliance.
Although they offer a low cost and small size, ferrite
bead filters slightly increase distortion and slightly
reduce efficiency. If the audio performance of the ferrite
bead filters does not meet the system requirements, then
a full inductor/capacitor (LC) filter should be considered.
Gain Selection
Table 4 shows the suggested gain settings to attain a
maximum output power from a given peak input voltage
and given load.
Inductor/Capacitor Output Filters
Using a full inductor and capacitor (LC) output filter
provides significant attenuation of the fundamental
switching energy.
Output Offset
Unlike a Class AB amplifier, the output offset voltage of
Class D amplifiers does not noticeably increase quies-
cent current draw when a load is applied. This is due to
the power conversion of the Class D amplifier. For
example, an 8mVDC 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
Select inductors rated for the expected RMS current
load. For example, if using a Class D amplifier up to
10W into 8Ω, the inductor should be rated for 1.25A
RMS or more. Furthermore, the inductor should maintain
a constant inductance value across the expected cur-
rent range. Inductors which change in value as a func-
tion of current will cause harmonic distortion.
additional quiescent current draw of: 8µW / (V
/ 100 ✕
DD
η), which is in the order of a few microamps.
The output capacitors can also affect audio perfor-
mance. Ceramic capacitors are often selected for their
size and cost advantage, but they cause distortion. If
the application constraints dictate ceramic capacitors,
selecting higher voltage rating and larger package size
mitigates some of the shortcomings. Best performance
is obtained with plastic film capacitors, but these are
larger and more expensive.
Input Amplifier
Differential Input
The MAX9741 features a differential input structure, mak-
ing them compatible with many CODECs, and offering
improved noise immunity over a single-ended input ampli-
fier. In devices such as PCs, noisy digital signals can be
picked up by the amplifier’s input traces. The signals
appear at the amplifiers’ inputs as common-mode noise. A
differential input amplifier amplifies the difference of the
two inputs, any signal common to both inputs is canceled.
Filterless Operation
In some cases, a Class D amplifier can be used without
an output filter. The intrinsic inductance of the loud-
speaker stores energy from the high-speed PWM pulses,
Table 4. Gain Settings
Table 3. Filter Component Suppliers
G1
0
G2
0
GAIN (dB)
29.6
SUPPLIER
PRODUCT
WEBSITE
Ferrite beads,
capacitors
Murata
www.murata.com
0
1
19.1
1
0
13
Ferrite beads,
capacitors
Taiyo Yuden
TDK
www.t-yuden.com
1
1
16
Ferrite beads,
capacitors
www.tdk.co.jp/tetop01
Fairrite
Ferrite beads
Inductors
www.fair-rite.com
www.coilcraft.com
www.sumida.com
Coilcraft
Sumida
Inductors
www.panasonic.com/indu
strial/components
Panasonic
Inductors
10 ______________________________________________________________________________________
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Single-Ended Input
The MAX9741 can be configured as single-ended input
amplifiers by capacitively coupling either input to GND
and driving the other input (Figure 4).
0.47µF
SINGLE-ENDED
AUDIO INPUT
IN+
IN-
Component Selection
MAX9741
Input Filter
0.47µF
An input capacitor, C , in conjunction with the input
IN
impedance of the MAX9741, forms a highpass filter that
removes the DC bias from an incoming signal. The AC-
coupling capacitor allows the amplifier to bias the sig-
nal to an optimum DC level. Assuming zero-source
impedance, the -3dB point of the highpass filter is
given by:
Figure 4. Single-Ended Input
When sharing inputs, it is common to mute the unused
device, rather than completely shutting it down, prevent-
ing the unused device inputs from distorting the input
signal. Mute the MAX9741 by driving SS low through an
open-drain output or MOSFET. Driving SS low turns off
the Class D output stage, but does not affect the input
bias levels of the MAX9741. Be aware that during normal
operation, the voltage at SS can be up to 7V, depending
on the MAX9741 supply.
1
f
=
-
3dB
2π R
C
IN IN
Choose C so f
is well below the lowest frequency
-3dB
IN
of interest. Setting f
too high affects the low-fre-
-3dB
quency response of the amplifier. Use capacitors with
dielectrics that 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.
Supply Bypassing/Layout
Proper power-supply bypassing ensures low-distortion
operation. For optimum performance, bypass V
to
DD
PGND with a 0.1µF or greater capacitor as close to each
pin as possible. In some applications, a 0.1µF
V
DD
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩ for opti-
mum performance. Low-ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For
best performance over the extended temperature
range, select capacitors with an X7R dielectric.
capacitor in parallel with a larger value, low-ESR ceramic
or aluminum electrolytic capacitor provides good results.
A low-impedance, high-current power-supply connection
to V
is assumed. Additional bulk capacitance should
DD
be added as required depending on the application and
power-supply characteristics. AGND and PGND should
be star connected to system ground. Refer to the
MAX9741 Evaluation Kit for layout guidance.
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump. A
C1 value that is too small degrades the device’s ability
to provide sufficient current drive. Increasing the value
of C1 improves load regulation and reduces the
charge-pump output resistance to an extent. Above
1µF, the on-resistance of the switches and the ESR of
C1 and C2 dominate.
Class D Amplifier Thermal Considerations
Class D amplifiers provide much better efficiency and
thermal performance than a comparable Class AB
amplifier. However, the system’s thermal performance
must be considered with realistic expectations and
consideration of many parameters. This application
note examines Class D amplifiers using general exam-
ples to illustrate good design practices.
Hold Capacitor (C2)
The output capacitor value and ESR directly affect the rip-
ple at CHOLD. Increasing C2 reduces output ripple.
Likewise, decreasing the ESR of C2 reduces both ripple
and output resistance. Lower capacitance values can be
used in systems with low maximum output power levels.
Continuous Sine Wave vs. Music
When a Class D amplifier is evaluated in the lab, often
a continuous sine wave is used as the signal source.
While this is convenient for measurement purposes, it
represents a worst-case scenario for thermal loading
on the amplifier. It is not uncommon for a Class D
amplifier to enter thermal shutdown if driven near maxi-
mum output power with a continuous sine wave.
Sharing Input Sources
In certain systems, a single audio source can be shared
by multiple devices (speaker and headphone amplifiers).
______________________________________________________________________________________ 11
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Audio content, both music and voice, has a much lower
RMS value relative to its peak output power. Figure 5
shows a sine wave and an audio signal in the time
domain. Both are measured for RMS value by the oscil-
loscope. Although the audio signal has a slightly higher
peak value than the sine wave, its RMS value is almost
half that of the sine wave. Therefore, while an audio sig-
nal may reach similar peaks as a continuous sine wave,
the actual thermal impact on the Class D amplifier is
highly reduced. If the thermal performance of a system
is being evaluated, it is important to use actual audio
signals instead of sine waves for testing. If sine waves
must be used, the thermal performance will be less
than the system’s actual capability.
20ms/div
Figure 5. RMS Comparison of Sine Wave vs. Audio Signal
PC Board Thermal Considerations
The exposed pad is the primary route of heat away
from the IC. With a bottom-side exposed pad, the PC
board and its copper becomes the primary heatsink for
the Class D amplifier. Solder the exposed pad to a
large copper polygon. Add as much copper as possi-
ble from this polygon to any adjacent pin on the Class
D amplifier as well as to any adjacent components, pro-
vided these connections are at the same potential.
These copper paths must be as wide as possible. Each
of these paths contributes to the overall thermal capa-
bilities of the system.
First, the Class D amplifier’s power dissipation must be
calculated.
P
10W
OUT
η
P
=
− P =
OUT
78% −10W = 2.82W
DISS
Then the power dissipation is used to calculate the die
temperature, T , as follows:
C
T
= T +P
×θ = 40°C+2.82W×21°C/W = 99.2°C
JA
C
A
DISS
The copper polygon to which the exposed pad is
attached should have multiple vias to the opposite side
of the PC board, where they connect to another copper
polygon. Make this polygon as large as possible within
the system’s constraints for signal routing.
Load Impedance
The on-resistance of the MOSFET output stage in Class
D amplifiers affects both the efficiency and the peak-
current capability. Reducing the peak current into the
2
load reduces the I R losses in the MOSFETs, increas-
Additional improvements are possible if all the traces
from the device are made as wide as possible.
Although the IC pins are not the primary thermal path
out of the package, they do provide a small amount.
The total improvement would not exceed approximately
10%, but it could make the difference between accept-
able performance and thermal problems.
ing efficiency. To keep the peak currents lower, choose
the highest impedance speaker which can still deliver
the desired output power within the voltage swing limits
of the Class D amplifier and its supply voltage.
Optimize MAX9741 Efficiency with
Load Impedance and Supply Voltage
To optimize efficiency, load the output stage with 12Ω
to 16Ω speakers. The MAX9741 exhibits highest effi-
ciency performance when driving higher load imped-
ance (see the Typical Operating Characteristics). If a
12Ω to 16Ω load is not available, select a lower supply
voltage when driving 4Ω to 10Ω loads.
With a bottomside exposed pad, the lowest resistance
thermal path is on the bottom of the PC board. The topside
of the IC is not a significant thermal path for the device.
Thermal Calculations
The die temperature of a Class D amplifier can be esti-
mated with some basic calculations. For example, the
die temperature is calculated for the below conditions:
For best performance, choose a speaker impedance to
complement the required output power and the available
supply voltage. For example, if operating from a 24V sup-
ply and a peak output of 10W per channel is desired, using
12Ω speakers provides the best audio performance and
power efficiency. The amplifier outputs are short-circuit
protected at approximately 2A. Selecting a higher imped-
ance driver helps prevent exceeding the current limit.
• T = +40°C
A
• P
= 10W (5W + 5W)
OUT
• Efficiency (η) = 78%
• θ = 21°C/W
JA
12 ______________________________________________________________________________________
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Application Circuit
10V TO 25V
33µF
25V
2.2µF
25V*
2.2µF
25V*
2
3
5
6
37 38
40 41
PGND
PGND
V
V
DD
DD
0.47µF
0.47µF
17 INL+
OUTL+ 54
OUTL+
53
OUTL- 52
51
MODULATOR
H-BRIDGE
16
INL-
OUTL-
31
32
FS1
FS2
V
V
REG
REG
OSCILLATOR
MODULATOR
0.47µF
0.47µF
INR+
INR-
OUTR+ 48
OUTR+
27
26
47
OUTR- 46
H-BRIDGE
45
OUTR-
18
SHDN
V
IH
29 G1
30 G2
20 SS
V
V
MAX9741
GAIN
CONTROL
REG
REG
9
8
C1P
C1N
C1
0.1µF
25V
SHUTDOWN
CONTROL
CHARGE PUMP
V
REG
REG
24
0.47µF
0.01µF
10V
22 AGND
CHOLD
10
C2
1µF
25V
V
DD
LOGIC INPUTS SHOWN FOR A = 16dB (SSM).
V
V
IN
= LOGIC-HIGH > 2.5V.
*CAPACITOR VOLTAGE RATINGS MAY BE REDUCED WHEN
OPERATING WITH REDUCED SUPPLY VOLTAGES.
______________________________________________________________________________________ 13
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Pin Configuration
TOP VIEW
42 41 40 39 38 37 36 35 34 33 32 31 30 29
28
27
26
25
24
23
22
21
20
19
18
N.C.
N.C.
N.C.
INR+
INR-
N.C.
REG
N.C.
AGND
N.C.
SS
43
44
45
46
OUTR-
OUTR-
OUTR+ 47
OUTR+ 48
N.C. 49
MAX9741
N.C. 50
OUTL- 51
OUTL- 52
N.C.
SHDN
OUTL+
53
OUTL+ 54
N.C. 55
N.C. 56
17 INL+
16 INL-
15 N.C.
+
1
2
3
4
5
6
7
8
9
10 11 12 13 14
THIN QFN
8mm x 8mm
Chip Information
TRANSISTOR COUNT: 4630
PROCESS: BiCMOS
14 ______________________________________________________________________________________
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D 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
56L THIN QFN, 8x8x0.8mm
1
E
21-0135
2
______________________________________________________________________________________ 15
12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D 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
56L THIN QFN, 8x8x0.8mm
2
E
21-0135
2
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2006 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
Quijano
相关型号：
MAX9741ETN+T
Audio Amplifier, 12W, 2 Channel(s), 1 Func, BICMOS, 8 X 8 MM, 0.80 MM HEIGHT, ROHS COMPLIANT, MO-220WLLD-5, TQFN-56
MAXIM
MAX9742ETX+T
Audio Amplifier, 21W, 2 Channel(s), 1 Func, Bipolar, 6 X 6 MM, 0.80 MM HEIGHT, LEAD FREE, MO-220WJJD-1, TQFN-36
MAXIM
MAX9744ETH+
Volume Control Circuit, 2 Channel(s), BICMOS, 7 X 7 MM, 0.80 MM HEIGHT, ROHS COMPLIANT, MO-220, TQFN-44
MAXIM
©2020 ICPDF网 联系我们和版权申明