Rainbow Electronics MAX9792 - Manual (Page 22)

MAX9791/MAX9792
Windows Vista-Compliant Class D Speaker
Amplifiers with DirectDrive Headphone Amplifiers
22 ______________________________________________________________________________________
Click-and-Pop Suppression
The MAX9791/MAX9792 feature a common-mode bias
voltage of 0V. A 0V BIAS allows the MAX9791/MAX9792
to quickly turn on/off with no resulting clicks and pops.
With the HDA CODEC outputs biased and the
MAX9791/MAX9792 inputs sitting as 0V in shutdown
and normal operation, the R
IN
x C
IN
time constant is
eliminated.
Speaker Amplifier
The MAX9791/MAX9792 speaker amplifiers feature
Maxim’s comprehensive, industry leading click-and-
pop suppression. During startup and shutdown, the
click-and-pop suppression circuitry eliminates any
audible transient sources internal to the device.
Headphone Amplifier
In conventional single-supply headphone amplifiers,
the output-coupling capacitor is a major contributor of
audible clicks and pops. Upon startup, the amplifier
charges the coupling capacitor to its bias voltage, typi-
cally V
DD /2. During shutdown, the capacitor is dis-
charged to GND; a DC shift across the capacitor
results, which in turn appears as an audible transient at
the speaker. Because the MAX9791/MAX9792 do not
require output-coupling capacitors, no audible transient
occurs.
The MAX9791/MAX9792 headphone amplifiers feature
extensive click-and-pop suppression that eliminates
any audible transient sources internal to the device.
Applications Information
Filterless Class D Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s output. The
filters add cost and size and can decrease efficiency
and THD+N performance. The traditional PWM scheme
uses large differential output swings (2 x PVDD peak-
to-peak) causing large ripple currents. Any parasitic
resistance in the filter components results in a loss of
power, lowering the efficiency.
The MAX9791/MAX9792 do not require an output filter.
The devices rely on the inherent inductance of the speak-
er coil and the natural filtering of both the speaker and
the human ear to recover the audio component of the
square-wave output. Eliminating the output filter results in
a smaller, less costly, and more efficient solution.
Because the frequency of the MAX9791/MAX9792 out-
put is well beyond the bandwidth of most speakers,
voice coil movement due to the square-wave frequency
is very small. For optimum results, use a speaker with a
series inductance > 10µH. Typical 8
Ω speakers exhibit
series inductances in the 20µH to 100µH range.
MAX9791A/B
MAX9792A
SPKR_EN
SINGLE
CONTROL
HP_EN
Figure 8. Enabling Either the Speaker or Headphone Amplifier
with a Single Control Pin
MAX9791
SPKR_IN_
R IN1
OUT_+
OUT_-
MONO
CLASS D
AMPLIFIER
R FB
20k Ω
C IN1
Figure 9. Setting Speaker Amplifier Gain