20W Stereo Class D Speaker Amplifier

with Volume Control

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13

Pin Description (continued)

PIN

NAME

FUNCTION

26

SYNCOUT

SYNC Signal Output

31, 32

OUTR+

Right-Channel Positive Speaker Output

33

BOOTR+

Right-Channel Positive Speaker Output Boost Flying-Capacitor Connection. Connect a 0.1µF

ceramic capacitor between BOOTR+ and OUTR+.

34, 35, 39,

43, 44

PGND

Power Ground

36, 37

OUTR-

Right-Channel Negative Speaker Output

38

BOOTR-

Right-Channel Negative Speaker Output Boost Flying-Capacitor Connection. Connect a 0.1µF

ceramic capacitor between BOOTR- and OUTR-.

40

BOOTL-

Left-Channel Negative Speaker Output Boost Flying-Capacitor Connection. Connect a 0.1µF

ceramic capacitor between BOOTL- and OUTL-.

41, 42

OUTL-

Left-Channel Negative Speaker Output

—EP

Exposed Pad. The external pad lowers the package’s thermal impedance by providing a direct

heat conduction path from the die to the PCB. Connect the exposed thermal pad to PGND.

Detailed Description

The MAX9744 20W filterless, stereo Class D audio

power amplifier offers Class AB performance with Class

D efficiency with a minimal board space solution. The

MAX9744 features a spread-spectrum modulation

scheme offering significant improvements to switch-

mode amplifier technology. This device features analog

or digitally adjustable volume control, externally set

input gain, shutdown mode, SYNC input and output,

mute, and industry-leading click-and-pop suppression.

The MAX9744 features extensive click-and-pop sup-

pression circuitry that eliminates audible clicks-and-

pops at startup and shutdown.

The MAX9744 features a 64-step, dual-mode (analog

ume control mode, the voltage applied to SDA/VOL

sets the volume level. Two address inputs (ADDR1,

ADDR2) set the volume control function between ana-

mode, there are three selectable slave addresses

allowing for multiple devices on a single bus.

The MAX9744 offers spread-spectrum and fixed-fre-

quency modes of operation with classic PWM or filter-

less modulation output schemes. The filterless

modulation scheme uses minimum pulse outputs when

the audio inputs are at the zero crossing. As the input

voltage increases or decreases, the duration of the

pulse at one output increases while the other output

pulse duration remains the same. This causes the net

The minimum-width pulse topology reduces EMI and

increases efficiency.

Operating Modes

Fixed-Frequency Modulation Mode

The MAX9744 features two fixed-frequency modes:

300kHz and 360kHz. Connect SYNC to GND to select

300kHz switching frequency; leave SYNC unconnected

to select the 360kHz switching frequency. The

MAX9744 frequency spectrum consists of the fundamen-

tal switching frequency and its associated harmonics

(see the Wideband Output Spectrum graphs in the

Typical

Operating Characteristics). For applications where exact

spectrum placement of the switching fundamental is

important, program the switching frequency so that the

harmonics do not fall within a sensitive frequency band

(Table 1). Audio reproduction is not affected by chang-

ing the switching frequency.