Datasheet

MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
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scheme remains the same, but the period of the saw-
tooth 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 (Figure 3).
External Clock Mode
The SYNC input allows the MAX9700 to be synchro-
nized to a system clock (allowing a fully synchronous
system), or allocating the spectral components of the
switching harmonics to insensitive frequency bands.
Applying an external TTL clock of 800kHz to 2MHz to
SYNC synchronizes the switching frequency of the
MAX9700. The period of the SYNC clock can be ran-
domized, enabling the MAX9700 to be synchronized to
another MAX9700 operating in SSM mode.
Filterless Modulation/Common-Mode Idle
The MAX9700 uses Maxim’s modulation scheme
that eliminates the LC filter required by traditional
class D amplifiers, improving efficiency, reducing
component count, and conserving board space
and system cost. Conventional class D amplifiers
Figure 1. MAX9700 Outputs with an Input Signal Applied
OUT+
OUT-
V
IN-
V
IN+
V
OUT+
- V
OUT-
t
ON(MIN)
t
SW
SYNC INPUT MODE
GND FFM with f
S
= 1100kHz
UNCONNECTED
FFM with f
S
= 1450kHz
V
DD
SSM with f
S
= 1220kHz ±120kHz
Clocked FFM with f
S
= external clock frequency
Table 1. Operating Modes