MAX9779 Maxim Integrated Products, MAX9779 Datasheet - Page 15

• Manufacturer Part Number: MAX9779
• Description: 2.6W Stereo Audio Power Amplifier and DirectDrive Headphone Amplifier
• Manufacturer: Maxim Integrated Products

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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.
Use capacitors with an ESR less than 100mΩ for opti-
mum performance. Low-ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For
best performance over the extended temperature
range, select capacitors with an X7R dielectric. Table 4
lists suggested manufacturers.
The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump. A
C1 value that is too small degrades the device’s ability
to provide sufficient current drive, which leads to a loss
of output voltage. Increasing the value of C1 improves
load regulation and reduces the charge-pump output
resistance to an extent. See the Output Power vs.
Charge-Pump Capacitance and Load Resistance
graph in the Typical Operating Characteristics. Above
2.2µF, the on-resistance of the switches and the ESR of
C1 and C2 dominate.
The output capacitor value and ESR directly affect the
ripple at CPV
output ripple. Likewise, decreasing the ESR of C2
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.
The CPV
impedance of the power supply and reduces the
impact of the MAX9779’s charge-pump switching
Table 2. Suggested Capacitor Manufacturers
Taiyo Yuden
TDK
SUPPLIER
DD
bypass capacitor (C3) lowers the output
SS
. Increasing the value of C2 reduces
______________________________________________________________________________________
Charge-Pump Capacitor Selection
2.6W Stereo Audio Power Amplifier and
800-348-2496
807-803-6100
CPV
PHONE
Output Capacitor (C2)
Flying Capacitor (C1)
DD
DirectDrive Headphone Amplifier
Bypass Capacitor
BIAS Capacitor
BIAS
, improves
847-925-0899
847-390-4405
FAX
transients. Bypass CPV
and place it physically close to CPV
to the MAX9779 Evaluation Kit for a suggested layout).
An additional benefit of the MAX9779 is the internally gen-
erated negative supply voltage (CPV
by the MAX9779 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
be limited to 5mA; exceeding this affects the operation of
the headphone amplifier. A typical application is a nega-
tive supply to adjust the contrast of LCD modules.
When considering the use of CPV
note that the charge-pump voltage of CPV
proportional to CPV
The charge-pump output impedance plot appears in
the Typical Operating Characteristics.
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 components in the audio signal path.
Connect all components associated with the charge
pump (C2 and C3) to the CPGND plane. Connect V
and CPV
pump capacitors (C1, C2, and C3) as close to the
device as possible. Bypass HPV
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.
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SS
together at the device. Place the charge-
Powering Other Circuits from a
DD
DD
and is not a regulated voltage.
with C3, the same value as C1,
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Layout and Grounding
DD
Negative Supply
DD
SS
SS
and PV
). CPV
and PGND (refer
in this manner,
SS
SS
DD
is roughly
SS
is used
should
with a
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