Datasheet

MAX9759
3.2W, High Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
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Spread-Spectrum Modulation (SSM) Mode
The MAX9759 features a unique spread-spectrum mode
that reduces peak component energy in the wideband
spectrum, improving EMI emissions that may be radiat-
ed by the speaker and cables by 5dB. Proprietary tech-
niques ensure that the cycle-to-cycle variation of the
switching period does not degrade audio reproduction
or efficiency (see the Typical Operating Characteristics).
Select SSM mode by setting SYNC = V
DD
. In SSM
mode, the switching frequency varies by ±70kHz around
the center frequency (1.2MHz). The modulation scheme
remains the same, but the period of the sawtooth wave-
form 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 (Figure 3).
OUT+
OUT-
V
IN-
V
IN+
V
OUT+
- V
OUT-
t
ON(MIN)
t
SW
Figure 1. MAX9759 Outputs with an Input Signal Applied
SYNC INPUT MODE
GND FFM with f
S
= 1100kHz
FLOAT FFM with f
S
= 1500kHz
V
DD
SSM with f
S
= 1200kHz ±70kHz
Clocked FFM with f
S
= external clock frequency
Table 1. Operating Modes