MAX9709 Maxim Integrated Products, MAX9709 Datasheet - Page 17

• Manufacturer Part Number: MAX9709
• Description: 25W/50W Filterless Spread-Spectrum Stereo/Mono Class D Amplifier
• Manufacturer: Maxim Integrated Products

The circuit in Figure 6 uses inverting amplifiers for their
ease in biasing. Note the phase labeling at the outputs
has been reversed. The resistors should be 1% or better
in tolerance and the capacitors 5% tolerance or better.
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 causes some high-frequency sound to
be sent to the subwoofer.
Figure 5. Multiple Amplifiers Implement a 2.1 Audio System
AUDIO
RIGHT
AUDIO
LEFT
______________________________________________________________________________________
Σ
25W/50W, Filterless, Spread-Spectrum,
HIGHPASS
HIGHPASS
LOWPASS
FILTER
FILTER
FILTER
Stereo/Mono, Class D Amplifier
V
DIGITAL
The circuit in Figure 6 drives a pair of MAX9709 devices
similar to the circuit in Figure 5. The inputs to the
MAX9709 still require AC-coupling to prevent compro-
mising the click-and-pop performance of the MAX9709.
The left and right drivers should be at an 8Ω to 12Ω
impedance, whereas the subwoofer can be 4Ω to 8Ω
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 MAX9709 allow gain adjustments to match the sen-
sitivity of the speakers.
INR+
INR-
MONO
SYNCIN
INL+
INL-
SYNCOUT
INR+
INR-
MONO
INL+
INL-
MAX9709
MAX9709
OUTR+
OUTR-
OUTL+
OUTR+
OUTL-
OUTR-
OUTL+
OUTL-
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8Ω
FULL-
RANGE
SPEAKER
4Ω OR 8Ω
WOOFER
8Ω
FULL-
RANGE
SPEAKER
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