MAX9715 Maxim Integrated Products, MAX9715 Datasheet - Page 7

• Manufacturer Part Number: MAX9715
• Description: Filterless Class D Audio Amplifier
• Manufacturer: Maxim Integrated Products

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The MAX9715 2.8W, Class D speaker amplifier with
gain control offers Class AB performance with Class D
efficiency while occupying minimal board space. A
unique modulation scheme and spread-spectrum
switching allow filterless operation to create a compact,
flexible, low-noise, efficient audio power amplifier. The
MAX9715 features high 71dB at 1kHz PSRR, low 0.06%
THD+N, industry-leading click-and-pop performance
and a low-power shutdown mode.
The MAX9715 features an undervoltage lockout that pre-
vents operation from an insufficient power supply and
click-and-pop suppression that eliminates audible tran-
sients at startup and shutdown. The speaker amplifier
includes thermal-overload and short-circuit protection.
The MAX9715 features unique, spread-spectrum opera-
tion that reduces the amplitude of spectral components at
high frequencies, reducing EMI emissions that might oth-
erwise be radiated by the speaker and cables. The
switching frequency varies randomly by ±120kHz around
the center frequency (1.22MHz). The modulation scheme
is consistent with Maxim’s Class D amplifiers but the peri-
od of the triangle waveform changes from cycle to cycle.
Audio reproduction is not affected by the spread-spec-
trum switching scheme. Instead of a large amount of
spectral energy present at multiples of the switching fre-
quency that energy is now spread over a range of fre-
quencies. The spreading is increased with frequency so
that above a few megahertz, the wideband spectrum
looks like white noise for EMI purposes (Figure 1).
Figure 1. MAX9715 Radiated Emissions with 75mm of Speaker Cable
2.8W, Low-EMI, Stereo, Filterless Class D
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Detailed Description
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FREQUENCY (MHz)
160
The spread-spectrum modulation scheme eliminates the
LC filter required by traditional Class D amplifiers, improv-
ing efficiency, reducing component count, conserving
board space and system cost. Conventional Class D
amplifiers output a 50% duty cycle square wave when no
signal is present. With no filter, the output square wave
appears across the load, resulting in finite load current,
which increases power consumption. When no signal is
present at the input, the MAX9715 outputs switch as
shown in Figure 2. The two outputs cancel each other
because the MAX9715 drives the speaker differently,
minimizing power consumption as there is no net idle-
mode voltage across the speaker.
Figure 2. MAX9715 Output without Input Signal Applied
180
V OUT+ - V OUT- = 0V
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V IN = 0V
220
OUT+
OUT-
Filterless Modulation/Common-Mode Idle
240
Audio Amplifier
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