MAX9736 Maxim Integrated Products, MAX9736 Datasheet - Page 13

• Manufacturer Part Number: MAX9736
• Description: Mono/Stereo High-Power Class D Amplifier
• Manufacturer: Maxim Integrated Products

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The MAX9736A/MAX9736B filterless, stereo Class D
audio power amplifiers offer Class AB performance and
Class D efficiency with minimal board space. The
MAX9736A outputs 2x15W in stereo mode and 30W in
mono mode. The MAX9736B outputs 2x6W in stereo
mode and 12W in mono mode. These devices operate
from an 8V to 28V supply range.
The MAX9736 features a filterless, spread-spectrum
switching mode (MOD = high) or a classic PWM fixed-
frequency switching mode (MOD = low).
The MAX9736 features externally set gain and a low-
power shutdown mode that reduces supply current to
less than 1µA. Comprehensive click-and-pop circuitry
minimizes noise into and out of shutdown or mute.
The MAX9736 features two output modulation schemes,
filterless modulation (MOD = high) or classic PWM (MOD
= low). Maxim’s unique, filterless modulation scheme
eliminates the LC filter required by traditional Class D
amplifiers, reducing component count, conserving
board space, and reducing system cost. Configure for
classic PWM output when using a full LC filter.
Click-and-pop protection does not apply when the out-
put is switching between modulation schemes. To
maintain click-and-pop protection when switching
between output schemes the device must enter shut-
down mode and be configured to the new output
scheme before the startup sequence is finished.
The MAX9736 features a unique, patented spread-spec-
trum mode that flattens the wideband spectral compo-
nents, improving EMI radiated by the speaker and
cables. The switching frequency of the Class D amplifier
varies randomly by ±6kHz around the 300kHz center fre-
quency. Instead of a large amount of spectral energy
present at multiples of the switching frequency, the ener-
gy is spread over a bandwidth that increases with fre-
quency. Above a few megahertz, the wideband spectrum
looks like white noise for EMI purposes. A proprietary
amplifier topology ensures this white noise does not cor-
rupt the noise floor in the audio bandwidth. The spread-
spectrum mode is enabled only with filterless modulation.
Mono/Stereo High-Power Class D Amplifier
Filterless Modulation/PWM Modulation
______________________________________________________________________________________
Detailed Description
Spread-Spectrum Mode
Operating Modes
The high 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 switches
and consume negligible power. Power loss associated
with the Class D output stage is due to the I
the MOSFET on-resistance, various switching losses,
and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is 78%
at peak output power. Under typical music reproduction
levels, the efficiency falls below 30%, whereas the
MAX9736 exhibits > 80% efficiency under the same con-
ditions (Figure 1).
The MAX9736 features a shutdown mode that reduces
power consumption and extends battery life in portable
applications. The shutdown mode reduces supply cur-
rent to 1µA (typ). Drive SHDN high for normal opera-
tion. Drive SHDN low to place the device in low-power
shutdown mode. In shutdown mode, the outputs are
high impedance; and the common-mode voltage at the
output decays to zero. In shutdown mode, connect
REGEN low to minimize current consumption.
The MAX9736 features a clickless-and-popless mute
mode. When the device is muted, the signal is attenuat-
ed at the speaker and the outputs stop switching. To
mute the MAX9736, drive MUTE low. Hold MUTE low
during system power-up and power-down to ensure
that clicks and pops caused by circuits before the
MAX9736 are suppressed.
Figure 1. MAX9736A Efficiency vs. Class AB Efficiency
100
90
80
70
60
50
40
30
20
10
0
0
vs. TOTAL OUTPUT POWER
TOTAL OUTPUT POWER (W)
5
MAX9736A
EFFICIENCY
CLASS AB
10
15
Mute Function
Efficiency
Shutdown
20
2
R loss of
13