Datasheet
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
17
Maxim Integrated
Mismatch in the components can cause discrepancies
between the nominal transfer function and actual perfor-
mance. Also, the mismatch of the input resistors (R15,
R17, R19, and R21 in Figure 6) of the summing amplifier
and lowpass filter will cause some high-frequency sound
to be sent to the subwoofer.
The circuit in Figure 6 drives a pair of MAX9708 devices
similar to the circuit in Figure 5. The inputs to the
MAX9708 still require AC-coupling to prevent compro-
mising the click-and-pop performance of the MAX9708.
The left and right drivers should be at an 8Ω to 12Ω
impedance, whereas the subwoofer can be 4Ω to 12Ω
depending on the desired output power, the available
power-supply voltage, and the sensitivity of the individ-
ual speakers in the system. The four gain settings of
the MAX9708 allow gain adjustments to match the sen-
sitivity of the speakers.
Figure 5. Multiple Amplifiers Implement a 2.1 Audio System
MAX9708
MAX9708
HIGHPASS
FILTER
8Ω
FULL-
RANGE
SPEAKER
8Ω
FULL-
RANGE
SPEAKER
4Ω OR 8Ω
WOOFER
RIGHT
AUDIO
LEFT
AUDIO
HIGHPASS
FILTER
LOWPASS
FILTER
Σ
V
DIGITAL
OUTR+
OUTR-
OUTL+
OUTL-
OUTR+
OUTR-
OUTL+
OUTL-
INR+
INR-
MONO
INL+
INL-
INR+
SYNCIN
SYNCOUT
INR-
MONO
INL+
INL-