MAX9750/MAX9751/MAX9755
2.6W Stereo Audio Power Amplifiers and
DirectDrive Headphone Amplifiers
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reduces both ripple and output resistance. Lower
capacitance values can be used in systems with low
maximum output power levels. See the Output Power
vs. Charge-Pump Capacitance and Load Resistance
graph in the
Typical Operating Characteristics
.
CPV
DD
Bypass Capacitor (C3)
The CPV
DD
bypass capacitor (C3) lowers the output
impedance of the power supply and reduces the
impact of the MAX9750/MAX9751/MAX9755’s charge-
pump switching transients. Bypass CPV
DD
with C3, the
same value as C1, and place it physically close to
CPV
DD
and PGND (refer to the MAX9750 Evaluation Kit
for a suggested layout).
Powering Other Circuits from a
Negative Supply
An additional benefit of the MAX9750/MAX9751/
MAX9755 is the internally generated negative supply volt-
age (CPV
SS
). CPV
SS
is used by the MAX9750/
MAX9751/MAX9755 to provide the negative supply for
the headphone amplifiers. It can also be used to power
other devices within a design. Current draw from CPV
SS
should be limited to 5mA, exceeding this affects the oper-
ation of the headphone amplifier. A typical application is
a negative supply to adjust the contrast of LCD modules.
When considering the use of CPV
SS
in this manner,
note that the charge-pump voltage of CPV
SS
is roughly
proportional to CPV
DD
and is not a regulated voltage.
The charge-pump output impedance plot appears in
the
Typical Operating Characteristics
.
Layout and Grounding
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, as well as route head away
from the device. Good grounding improves audio per-
formance, minimizes crosstalk between channels, and
prevents any switching noise from coupling into the
audio signal. Connect CPGND, PGND and GND
together at a single point on the PC board. Route
CPGND and all traces that carry switching transients
away from GND, PGND, and the traces and compo-
nents in the audio signal path.
Connect all components associated with the charge
pump (C2 and C3) to the CPGND plane. Connect V
SS
and CPV
SS
together at the device. Place the charge-
pump capacitors (C1, C2, and C3) as close to the
device as possible. Bypass HPV
DD
and PV
DD
with a
0.1µF capacitor to GND. Place the bypass capacitors
as close to the device as possible.
Use large, low-resistance output traces. As load imped-
ance decreases, the current drawn from the device out-
puts increase. At higher current, the resistance of the
output traces decrease the power delivered to the load.
For example, when compared to a 0Ω trace, a 100mΩ
trace reduces the power delivered to a 4Ω load from
2.1W to 2W. Large output, supply, and GND traces also
improve the power dissipation of the device.
The MAX9750/MAX9751/MAX9755 thin QFN package
features an exposed thermal pad on its underside. This
pad lowers the package’s thermal resistance by provid-
ing a direct heat conduction path from the die to the
printed circuit board. Connect the exposed thermal
pad to GND by using a large pad and multiple vias to a
GND plane on the bottom of the PCB.
