MAX9776 Maxim Integrated Products, MAX9776 Datasheet - Page 20

• Manufacturer Part Number: MAX9776
• Description: (MAX9775 / MAX9776) Stereo Class D Audio Subsystem
• Manufacturer: Maxim Integrated Products

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The MAX9775/MAX9776 feature a fixed-frequency
modulation mode with a 1.1MHz switching frequency,
set through the I
cy modulation mode, the frequency spectrum of the
Class D output consists of the fundamental switching
frequency and its associated harmonics (see the
Wideband Output Spectrum Fixed-Frequency Mode
graph in the Typical Operating Characteristics ).
The MAX9775/MAX9776 feature a unique, patented
spread-spectrum modulation that flattens the wideband
spectral components. Proprietary techniques ensure that
2 x 1.5W, Stereo Class D Audio Subsystem
with DirectDrive Headphone Amplifier
Figure 2. Output with an Input Signal Applied (Spread-Spectrum Modulation Mode)
20
______________________________________________________________________________________
V
V
V
OUT+
IN+
IN-
- V
OUT-
OUT+
OUT-
2
C interface (Table 2). In fixed-frequen-
t
ON(MIN)
Spread-Spectrum Modulation
Fixed-Frequency Modulation
Operating Modes
t
SW
t
SW
the cycle-to-cycle variation of the switching period does
not degrade audio reproduction or efficiency (see the
Typical Operating Characteristics ). Select spread-spec-
trum modulation mode through the I
2). In spread-spectrum modulation mode, the switching
frequency varies randomly by ±30kHz around the center
frequency (1.16MHz). The modulation scheme remains
the same, but the period of the sawtooth waveform
changes from cycle to cycle (Figure 2). Instead of a
large amount of spectral energy present at multiples of
the switching frequency, the energy is now spread over
a bandwidth that increases with frequency. Above a few
megahertz, the wideband spectrum looks like white
noise for EMI purposes (see Figure 3).
t
SW
t
SW
2
C interface (Table