or power-up, the input amplifiers are muted and an

internal loop sets the modulator bias voltages to the

correct levels, preventing clicks and pops when the H-

bridge is subsequently enabled. Following startup, a

soft-start function gradually un-mutes the input ampli-

fiers. The value of the soft-start capacitor has an impact

should be at least 180nF.

Mute Function

The MAX9713/MAX9714 feature a clickless/popless

mute mode. When the device is muted, the outputs

stop switching, muting the speaker. Mute only affects

the output state, and does not shut down the device. To

mute the MAX9713/MAX9714, drive SS to GND by

using a MOSFET pulldown (Figure 4). Driving SS to

GND during the power-up/down or shutdown/turn-on

cycle optimizes click-and-pop suppression.

Applications Information

Filterless Operation

Traditional class D amplifiers require an output filter to

recover the audio signal from the amplifier’s PWM out-

put. The filters add cost, increase the solution size of

the amplifier, and can decrease efficiency. The tradi-

tional PWM scheme uses large differential output

currents. Any parasitic resistance in the filter compo-

nents results in a loss of power, lowering the efficiency.

The MAX9713/MAX9714 do not require an output filter.

The devices rely on the inherent inductance of the

speaker coil and the natural filtering of both the speak-

er and the human ear to recover the audio component

of the square-wave output. Eliminating the output filter

results in a smaller, less costly, more efficient solution.

Because the frequency of the MAX9713/MAX9714 out-

put is well beyond the bandwidth of most speakers,

voice coil movement due to the square-wave frequency

6W, Filterless, Spread-Spectrum

Mono/Stereo Class D Amplifiers

_______________________________________________________________________________________

9

Figure 3. MAX9714 Efficiency vs. Class AB Efficiency

0

30

20

10

40

50

60

70

80

90

100

02

4

6

EFFICIENCY vs. OUTPUT POWER

OUTPUT POWER (W)

MAX9714

f = 1kHz

CLASS AB

Figure 2. SSM Radiated Emissions

MAX9713/

MAX9714

SS

0.18µF

GPIO

MUTE SIGNAL

Figure 4. MAX9713/MAX9714 Mute Circuit