MAX9704 Maxim Integrated Products, MAX9704 Datasheet - Page 10

• Manufacturer Part Number: MAX9704
• Description: 10W Stereo/15W Mono Filterless Spread-Spectrum Class D Amplifiers
• Manufacturer: Maxim Integrated Products

The MAX9703/MAX9704 have a shutdown mode that
reduces power consumption and extends battery life.
Driving SHDN low places the device in low-power
(0.2µA) shutdown mode. Connect SHDN to a logic high
for normal operation.
The MAX9703/MAX9704 feature comprehensive click-
and-pop suppression that eliminates audible transients
on startup and shutdown. While in shutdown, the H-
bridge is pulled to GND through 330kΩ. During startup,
or power-up, the input amplifiers are muted and an inter-
nal loop sets the modulator bias voltages 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, C
be at least 0.18µF with a voltage rating of at least 7V.
The MAX9703/MA9704 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 MAX9703/MAX9704, drive SS to GND by
using a MOSFET pulldown (Figure 3). Driving SS to
GND during the power-up/down or shutdown/turn-on
cycle optimizes click-and-pop suppression.
10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Amplifiers
10
Figure 2. MAX9704 Efficiency vs. Class AB Efficiency
______________________________________________________________________________________
100
90
80
70
60
50
40
30
20
10
0
0
EFFICIENCY vs. OUTPUT POWER
MAX9704
2
Click-and-Pop Suppression
4
6
OUTPUT POWER (W)
8
10 12 14 16 18
CLASS AB
Mute Function
V
f = 1kHz
R
DD
L
= 8Ω
= 15V
Shutdown
20
SS
should
Traditional class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM out-
put. The filters add cost, increase the solution size of
the amplifier, and can decrease efficiency. The tradi-
tional PWM scheme uses large differential output
swings (2
currents. Any parasitic resistance in the filter compo-
nents results in a loss of power, lowering the efficiency.
The MAX9703/MAX9704 do not require an output filter.
The devices rely on the inherent inductance of the
speaker coil and the natural filtering of both the speak-
er 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 MAX9703/MAX9704 out-
put 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 speak-
er not designed to handle the additional power can be
damaged. For optimum results, use a speaker with a
series inductance > 30µH. Typical 8Ω speakers exhibit
series inductances in the range of 30µH to 100µH.
Optimum efficiency is achieved with speaker induc-
tances > 60µH.
The MAX9703/MAX9704 feature an internal, 6V regula-
tor output (V
pin simplifies system design and reduces system cost
by providing a logic voltage high for the MAX9703/
MAX9704 logic pins (G_, FS_). V
logic voltage high in shutdown mode. Do not apply V
as a 6V potential to surrounding system components.
Bypass REG with a 6.3V, 0.01µF capacitor to GND.
Figure 3. MAX9703/MAX9704 Mute Circuit
MUTE SIGNAL
✕
V
REG
Internal Regulator Output (V
DD
GPIO
Applications Information
). The MAX9703/MAX9704 REG output
peak-to-peak) and causes large ripple
0.18µF
Filterless Operation
REG
SS
www.DataSheet4U.com
is not available as a
MAX9703/
MAX9704
REG
REG
)