Datasheet

MAX9768

10W Mono Class D Speaker

Amplifier with Volume Control

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Applications Information

Filterless Class D Operation

The MAX9768 can be operated without a filter and

meet common EMC radiation limits when the speaker

leads are less than approximately 10cm. Lengths

beyond 10cm are possible but should be verified

against the appropriate EMC standard. Select the filter-

less modulation mode with spread-spectrum modula-

tion mode for best performance.

For longer speaker wire lengths, a simple ferrite bead

and capacitor-based filter can be used to meet EMC

limits. See Figure 7 for the correct connections of these

components. Select a ferrite bead with 100Ω to 600Ω

impedance, and rated for at least 1.5A. The capacitor

value will vary based on the ferrite bead chosen and

the actual speaker lead length. Select the capacitor

value based on EMC performance.

When doing bench evaluation without a filter or a ferrite

bead filter, include a series inductor (68µH for 8Ω load)

to model the actual loudspeaker’s behavior. If this

inductance is omitted, the MAX9768 will have reduced

efficiency and output power, as well as worse THD+N

performance.

Table 7. Setting Class D Output Modulation Scheme

D7 (MSB) D6 D5 D4 D3 D2 D1 D0 (LSB) FUNCTION

1 1 0 1 0 1 0 1 Classic PWM

1 1 0 1 0 1 1 0 FILTERLESS MODULATION*

BOOT_+

0.1μF

330pF

C10

330pF

OUT_+

BOOT_-

0.1μF

OUT_-

MAX9768

Figure 7. Ferrite Bead Filter

Power-on default.