MAX9715 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX9715

2.8W, Low-EMI, Stereo, Filterless Class D Audio Amplifier

Maxim Integrated 

2.8W, Low-EMI, Stereo, Filterless Class D

Audio Amplifier

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FREQUENCY (MHz)

Figure 1. MAX9715 Radiated Emissions with 75mm of Speaker Cable

Detailed Description

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).

VIN = 0V

OUT-

OUT+

VOUT+ - VOUT- = 0V

Figure 2. MAX9715 Output without Input Signal Applied

Filterless Modulation/Common-Mode Idle

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.

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