Datasheet

Shutdown
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.
Click-and-Pop Suppression
The MAX9703/MAX9704 feature comprehensive clicka-
nd-pop suppression that eliminates audible transients on
startup and shutdown. While in shutdown, the Hbridge is
pulled to PGND through 330kΩ. 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 Hbridge is subse-
quently 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
SS
should be at least 0.18μF
with a voltage rating of at least 7V.
Mute Function
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 out-
put stage and does not shut down the device. To mute
the MAX9703/MAX9704, drive SS to PGND by using a
MOSFET pulldown (Figure 3). Driving SS to PGND during
the power-up/down or shutdown/turn-on cycle optimizes
click-and-pop suppression.
Applications Information
Filterless Operation
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 traditional
PWM scheme uses large differential output swings (2
V
DD
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 MAX9703/MAX9704 do not require an output fil-
ter. The devices rely 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 MAX9703/MAX9704 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 > 30μH. Typical 8Ω speakers exhibit series
inductances in the range of 30μH to 100μH. Optimum
efficiency is achieved with speaker inductances > 60μH.
Internal Regulator Output (V
REG
)
The MAX9703/MAX9704 feature an internal, 6V regula-
tor output (V
REG
). The MAX9703/MAX9704 REG output
pin simplifies system design and reduces system cost by
providing a logic voltage high for the MAX9703/ MAX9704
logic pins (G_, FS_). V
REG
is not available as a logic
voltage high in shutdown mode. Do not apply V
REG
as a
6V potential to surrounding system components. Bypass
REG with a 6.3V, 0.01μF capacitor to AGND.
Figure 2. MAX9704 Efficiency vs. Class AB Efficiency
Figure 3. MAX9703/MAX9704 Mute Circuit
0
30
20
10
40
50
60
70
80
90
100
0
6
8
10 12 14
16
18
2 4
20
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
V
DD
= 15V
f = 1kHz
R
L
= 8Ω
MAX9704
CLASS AB
SS
0.18µF
GPIO
MUTE SIGNAL
MAX9703/
MAX9704
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
www.maximintegrated.com
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