2 x 1.5W, Stereo Class D Audio Subsystem
with DirectDrive Headphone Amplifier
5/MAX976
Charge-Pump Capacitor Selection
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. Most
surface-mount ceramic capacitors satisfy the ESR
requirement. For best performance over the extended
temperature range, select capacitors with an X7R dielec-
tric or better. Table 12 lists suggested manufacturers.
Connect all of the power-supply inputs (CPV , V
,
DD
DD
and PV ) together. Bypass CPV
with a 1µF capaci-
DD
DD
tor to CPGND. Bypass V
Bypass PV
with 1µF capacitor to GND.
with a 1µF capacitor in parallel with a
DD
DD
0.1µF capacitor to PGND. Place the bypass capacitors
as close to the MAX9775/MAX9776 as possible. Place
a bulk capacitor between PV
and PGND if needed.
DD
Use large, low-resistance output traces. Current drawn
from the outputs increases as load impedance
decreases. High output trace resistance decreases the
power delivered to the load. Large output, supply, and
GND traces also allow more heat to move from the
MAX9775/MAX9776 to the PCB, decreasing the thermal
impedance of the circuit.
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the 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 reduces the charge-pump out-
put resistance to an extent. Above 1µF, the on-resistance
of the switches and the ESR of C1 and C2 dominate.
TQFN Applications Information
The MAX9776 TQFN-EP package features an exposed
thermal pad on its underside. This pad lowers the
package’s thermal impedance by providing a direct
heat conduction path from the die to the PCB. The
exposed pad is internally connected to GND. Connect
the exposed thermal pad to the PCB GND plane.
Output Capacitor (C2)
The output capacitor value and ESR directly affect the
ripple at CPV . Increasing the value of C2 reduces
SS
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. Load Resistance and Charge-Pump Capacitor Size
graph in the Typical Operating Characteristics.
WLP Applications Information
For the latest application details on WLP construction,
dimensions, tape carrier information, PCB techniques,
bump-pad layout, and recommended reflow tempera-
ture profile, as well as the latest information of reliability
testing results, refer to Application Note 1±91:
Understanding the Basics of the Wafer-Level Chip-
Scale Package (WL-CSP) available on Maxim’s website
at www.maxim-ic.com/ucsp.
CPV
Bypass Capacitor (C3)
DD
The CPV
bypass capacitor (C3) lowers the output
DD
impedance of the power supply and reduces the
impact of the MAX9775/MAX9776’s charge-pump
switching transients. Bypass CPV
and place it physically close to the CPV
Use a value for C3 that is equal to C1.
with C3 to PGND
DD
and PGND.
DD
WLP Thermal Consideration
When operating at maximum output power, the WLP
thermal dissipation can become a limiting factor. The
WLP package does not dissipate as much power as a
TQFN and as a result will operate at a higher tempera-
ture. At peak output power into a 4Ω load, the
MAX9775/MAX9776 can exceed its thermal limit, trig-
gering thermal protection. As a result, do not choose
the WLP package when maximum output power into 4Ω
is required.
Supply Bypassing, 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. 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 PCB. Route all
traces that carry switching transients away from GND
and the traces/components in the audio signal path.
Table 12. Suggested Capacitor Manufacturers
SUPPLIER
Taiyo Yuden
TDK
PHONE
FAX
WEBSITE
www.t-yuden.com
www.component.tdk.com
±00-34±-2496
±07-±03-6100
±47-925-0±99
±47-390-4405
______________________________________________________________________________________ 33
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