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PDF MAX9746 Data sheet ( Hoja de datos )
| Número de pieza | MAX9746 | |
| Descripción | Class D Audio Amplifier | |
| Fabricantes | Maxim Integrated | |
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19-0515; Rev 0; 5/06
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
General Description
The MAX9746 mono Class D audio power amplifier pro-
vides Class AB amplifier performance with Class D effi-
ciency, conserving board space and extending battery
life. The MAX9746 is designed specifically for systems
using 1.8V logic interface. Using a Class D architecture,
the MAX9746 delivers 1.2W into an 8Ω load while offer-
ing efficiencies near 90%. A low-EMI modulation
scheme renders the traditional Class D output filter
unnecessary.
The MAX9746 offers two modulation schemes: a fixed-
frequency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions due to the
modulation frequency. Furthermore, the MAX9746 oscil-
lator can be synchronized to an external clock through
the SYNC input, allowing the switching frequency to be
user defined. The SYNC input also allows multiple
MAX9746s to be cascaded and frequency locked, mini-
mizing interference due to clock intermodulation. The
device utilizes a fully differential architecture, a full-
bridged output, and comprehensive click-and-pop sup-
pression. The gain of the MAX9746 is set internally
further reducing external component count.
The MAX9746 features high 72dB PSRR, a low 0.1%
THD+N, and SNR in excess of 90dB. Short-circuit and
thermal-overload protection prevent the device from
damage during a fault condition. The MAX9746 is avail-
able in a 12-bump UCSP™ (1.5mm ✕ 2mm ✕ 0.6mm)
package. The MAX9746 is specified over the extended
-40°C to +85°C temperature range.
Applications
Cellular Phones
PDAs
MP3 Players
Portable Audio
Block Diagram
VDD
DIFFERENTIAL
AUDIO INPUT
SYNC
INPUT
MODULATOR
AND H-BRIDGE
OSCILLATOR
MAX9746
Features
♦ Filterless Amplifier Passes FCC Radiated
Emissions Standards with 100mm of Cable
♦ Unique Spread-Spectrum Mode Offers 5dB
Emissions Improvement Over Conventional
Methods
♦ Optional External SYNC Input
♦ Simple Master-Slave Setup for Stereo Operation
♦ 88% Efficiency
♦ 1.2W into 8Ω
♦ Low 0.1% THD+N
♦ High PSRR (72dB at 217Hz)
♦ Integrated Click-and-Pop Suppression
♦ 1.8V Logic-Compatible
♦ Low Quiescent Current (4mA)
♦ Low-Power Shutdown Mode (0.1µA)
♦ Short-Circuit and Thermal-Overload Protection
♦ Available in Thermally Efficient, Space-Saving
12-Bump UCSP Package (1.5mm x 2mm x 0.6mm)
Ordering Information
PART
MAX9746BEBC+T
TEMP RANGE
-40oC to +85oC
+Denotes lead-free package.
PIN-PACKAGE
12 UCSP-12
Pin Configuration
TOP VIEW
(BUMP SIDE DOWN)
1
MAX9746
23
4
VDD
A
SYNC OUT+
IN+ SHDN PGND PVDD
B
IN- GND
C
OUT-
UCSP is a trademark of Maxim Integrated Products, Inc.
UCSP
________________________________________________________________ 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.
Free Datasheet http://www.datasheet4u.com/
1 page  
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = VDD (SSM), TA = +25°C, unless otherwise noted.)
100
90
80
70
60
50
40
30
20
10
0
0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
2.5
EFFICIENCY
vs. OUTPUT POWER
VDD = 5.0V
fIN = 1kHz
RL = 8Ω
0.2 0.4 0.6 0.8
OUTPUT POWER (W)
1.0
OUTPUT POWER
vs. SUPPLY VOLTAGE
100
90
80
70
60
50
40
30
20
10
0
3.0
2.5
THD+N = 10%
2.0
1.5
THD+N = 1%
1.0
fIN = 1kHz
RL = 8Ω
3.0 3.5 4.0 4.5 5.0
SUPPLY VOLTAGE (V)
5.5
0.5
0
1
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
0
-10 OUTPUT REFERRED
INPUTS AC GROUNDED
-20 VDD = 3.3V
-30
-40
-50
-60
-70
-80
-90
-100
10
100 1k 10k
FREQUENCY (Hz)
100k
EFFICIENCY
vs. SUPPLY VOLTAGE
fIN = 1kHz
THD+N = 1%
RL = 8Ω
3.5 4.0 4.5
5.0
SUPPLY VOLTAGE (V)
5.5
OUTPUT POWER
vs. LOAD RESISTANCE
fIN = 1kHz
ZLOAD = 3.3µH IN
SERIES WITH RL
THD+N = 1%
5.0V
3.3V
10 100
LOAD RESISTANCE (Ω)
1000
EFFICIENCY
vs. SYNC FREQUENCY
90
80
70
60
50
40
30
20
10
0
800
VDD = 3.3V
fIN = 1kHz
THD+N = 1%
RL = 8Ω
1000 1200 1400 1600 1800 2000
SYNC FREQUENCY (kHz)
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
0
-10 INPUT REFERRED
VIN = 200mVP-P
-20
-30
-40
-50
-60
-70
-80
-90
-100
10
100 1k 10k
FREQUENCY (Hz)
100k
GSM POWER-SUPPLY REJECTION
MAX9746 toc16
VDD 500mV/div
MAX9746
OUTPUT
100µV/div
f = 217Hz
2ms/div
DUTY CYCLE = 88%
INPUT LOW = 3V
RL = 8Ω
INPUT HIGH = 3.5V
_______________________________________________________________________________________ 5
Free Datasheet http://www.datasheet4u.com/
5 Page 
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
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. Any power loss associated with the Class D out-
put stage is mostly due to the I ✕ R loss of the MOSFET
on-resistance, and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%; however, that efficiency is only exhibited at peak
output powers. Under normal operating levels (typical
music reproduction levels), efficiency falls below 30%,
whereas the MAX9746 still exhibits near 90% efficien-
cies under the same conditions (Figure 4).
Shutdown
The MAX9746 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9746 in a low-power (0.1µA) shutdown
mode. Connect SHDN to VDD for normal operation.
Click-and-Pop Suppression
The MAX9746 features comprehensive click-and-pop
suppression that eliminates audible transients on start-
up 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, pre-
venting clicks and pops when the H-bridge is subse-
quently enabled. For 35ms following startup, a soft-start
function gradually unmutes the input amplifiers.
100
90
80
70
60
50
40
30
20
10
0
0
EFFICIENCY vs. OUTPUT POWER
MAX9746
CLASS AB
VDD = 3.3V
f = 1kHz
RL = 8Ω
0.2 0.4
OUTPUT POWER (W)
0.6
Figure 4. MAX9746 Efficiency vs. Class AB Efficiency
Applications Information
Filterless Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s output. The
filters add cost, increase the solution size of the amplifi-
er, and can decrease efficiency. The traditional PWM
scheme uses large differential output swings (2 x VDD
peak-to-peak) and causes large ripple currents. Any
parasitic resistance in the filter components results in a
loss of power, lowering the efficiency.
The MAX9746 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 MAX9746 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 exhibit series
inductances in the 20µH to 100µH range.
Power-Conversion Efficiency
Unlike a Class AB amplifier, the output offset voltage of
a Class D amplifier 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 exam-
ple, 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 addi-
tional power drain of 8µW. Due to the high efficiency of
the Class D amplifier, this represents an additional quies-
cent-current draw of 8µW/(VDD/100η), which is in the
order of a few microamps.
Input Amplifier
Differential Input
The MAX9746 features a differential input structure,
making it compatible with many CODECs, and offering
improved noise immunity over a single-ended input
amplifier. In devices such as cellular phones, high-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.
______________________________________________________________________________________ 11
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet MAX9746.PDF ] | |
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