Table 1. operating modes – Rainbow Electronics MAX9712 User Manual
Page 9
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
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spread over a bandwidth that increases with frequency.
Above a few MHz, the wideband spectrum looks like
white noise for EMI purposes (Figure 3).
External Clock Mode
The SYNC input allows the MAX9712 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
MAX9712. The period of the SYNC clock can be ran-
domized, enabling the MAX9712 to be synchronized to
another MAX9712 operating in SSM mode.
Filterless Modulation/Common-Mode Idle
The MAX9712 uses Maxim’s unique, patented modula-
tion scheme that eliminates the LC filter required by
traditional class D amplifiers, improving efficiency,
reducing component count, conserving board space
and system cost. Conventional class D amplifiers out-
put a 50% duty cycle square wave when no signal is
present. With no filter, the square wave appears across
Figure 1. MAX9712 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
FLOAT
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