MAX9752 datasheet(13/29 Pages) MAXIM

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Filterless Modulation/Common-Mode Idle

The MAX9752/MAX9753/MAX9754 use Maxim’s unique

modulation scheme that eliminates the LC filter required

by traditional Class D amplifiers, improving efficiency,

reducing component count, and conserving board

space and system cost (Figure 4). With no input signal,

the outputs are two low-duty-cycle pulses that are in-

phase. This lowers the high-frequency energy and spec-

tral content. In comparison, conventional Class D

amplifiers output a 50% duty cycle when no input signal

is present. For most applications with short speaker

cables, no filtering is required.

Efficiency

Efficiency of a Class D amplifier is attributed to the

region of operation of the output stage transistors. In a

Class D amplifier, the output transistors act as switches

and consume negligible power. Any power loss associ-

ated with the Class D output stage is mostly due to the

I2R loss of the MOSFET on-resistance, and quiescent

current overhead.

The theoretical best efficiency of a linear amplifier is 78%,

however, that efficiency is only exhibited at peak output

powers. Under normal operating levels (typical music

reproduction levels), efficiency falls below 30%, whereas

the MAX9752/MAX9753/MAX9754 still exhibit > 80%

efficiencies under the same conditions (Figure 5).

2.2W, Low-EMI, Stereo, Class D Power Amplifiers

with DirectDrive Headphone Amplifiers

______________________________________________________________________________________

FREQUENCY (MHz)

280

260

240

200

220

100

120

140

160

180

300

Figure 3. MAX9752/MAX9753/MAX9754 Radiated Emissions with 76mm of Speaker Cable

VIN_ = 0V

OUT_-

OUT_+

VOUT_+ - VOUT_- = 0V

Figure 4. Second-Generation Class D Output Waveform with

No Signal

100

0.5

1.5

1.0

2.0

EFFICIENCY vs. OUTPUT POWER

OUTPUT POWER (W)

MAX9752

MAX9753

MAX9754

CLASS AB

RL = 8

Figure 5. MAX9752/MAX9753/MAX9754 Class D Efficiency vs.

MAX9750/MAX9751/MAX9755 Class AB Efficiency

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