max9706etxt Maxim Integrated Products, Inc., max9706etxt Datasheet - Page 20

• Manufacturer Part Number: max9706etxt
• Description: 3-channel, 2.3w, Filterless Class D Amplifiers With Active Crossover
• Manufacturer: Maxim Integrated Products, Inc.

3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
The MAX9706/MAX9707 have different supplies for
each portion of the devices, allowing for the optimum
combination of headroom power dissipation and noise
immunity. The speaker amplifiers are powered from
PV
connected to the same potential as V
phone amplifiers are powered from HPV
HPV
fiers and can range from 3V to 5.5V. V
supply of the headphone amplifiers. Connect V
CPV
Connect CPV
charge pump inverts the voltage at CPV
resulting voltage appears at CPV
the device is powered by V
An input capacitor, C
impedance of the MAX9706/MAX9707 forms a high-
pass filter that removes the DC bias from an incoming
signal. The AC-coupling capacitor allows the amplifier
to automatically bias the signal to an optimum DC level.
Assuming zero-source impedance, the -3dB point of
the highpass filter is given by:
Choose C
interest. Use capacitors whose dielectrics have low-volt-
age coefficients, such as tantalum or aluminum electrolyt-
ic. Capacitors with high-voltage coefficients, such as
ceramics, may result in increased distortion at low fre-
quencies.
Select the crossover filter to suit the chosen speaker.
Many small diameter speakers (as used in notebooks
and smaller displays) are self resonant (f
1000Hz. Often these speakers have a slight peaking at
resonance, so choosing a crossover frequency at 2 x f
can be effective. Ensure the mono channel speaker has
its f
20
DD
O
DD
______________________________________________________________________________________
SS
. PV
much lower than crossover frequency (f
. The charge pump is powered by CPV
is the positive supply of the headphone ampli-
DD
IN
so f
can range from 4.5V to 5.5V and must be
f
−
DD
3
-3dB
dB
to V
is well below the lowest frequency of
=
IN
DD
2 π
, in conjunction with the input
for normal operation. The
DD
×
Component Selection
Crossover Selection
.
R
IN
1
SS
×
Power Supplies
. The remainder of
C
SS
IN
DD
O
is the negative
DD
) at 800Hz to
DD
. The head-
Input Filter
C
, and the
).
and V
SS
DD
SS
to
O
.
.
Proper layout and grounding are essential for optimum
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance. Large traces also aid in mov-
ing heat away from the package. Proper grounding
improves audio performance, minimizes crosstalk
between channels, and prevents any switching noise
from coupling into the audio signal. Connect PGND and
GND together at a single point on the PC board (star
configuration). Route all traces that carry switching
transients away from GND and the traces/components
in the audio signal path.
Connect the power-supply inputs V
together and connect CPV
Bypass HPV
allel with a 0.1µF capacitor to PGND. Bypass V
P
capacitors as close to the device as possible. Place a
bulk capacitor between PV
Use large, low-resistance output traces. Current drawn
from the outputs increase as load impedance decreas-
es. High-output trace resistance decreases the power
delivered to the load. Large output, supply, and GND
traces allow more heat to move from the device to the
air, decreasing the thermal impedance of the circuit if
possible or connect to V
The MAX9706/MAX9707 thin QFN-EP package fea-
tures an exposed thermal pad on its underside. This
pad lowers the package’s thermal impedance by pro-
viding a direct heat conduction path from the die to
the PC board. The exposed thermal pad is not inter-
nally connected. Connect the exposed pad to GND.
BIAS is the output of the internally generated DC bias
voltage. The BIAS bypass capacitor, C
PSRR and THD+N by reducing power supply and other
noise sources at the common-mode bias node, and
also generates the clickless/popless, startup/shutdown
DC bias waveforms for the speaker amplifiers. Bypass
BIAS with a 1µF capacitor to GND.
VDD
Supply Bypassing, Layout, and Grounding
with a 1µF capacitor to GND. Place the bypass
DD
and CPV
SS
DD
.
DD
with a 1µF capacitor in par-
DD
and PGND if needed.
and HPV
BIAS Capacitor
DD
BIAS
DD
and PV
together.
improves
DD
and
DD