LM3241
SNOSB38B –JANUARY 2009–REVISED APRIL 2013
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Capacitor Selection
The LM3241 is designed for use with ceramic capacitors for its input and output filters. Use a 10 µF ceramic
capacitor for input and a 4.7 µF ceramic capacitor for output. They should maintain at least 50% capacitance at
DC bias and temperature conditions. Ceramic capacitors type such as X5R, X7R, and B are recommended for
both filters. They provide an optimal balance between small size, cost, reliability and performance for cell phones
and similar applications. Table 2 lists some suggested part numbers and suppliers. DC bias characteristics of the
capacitors must be considered when selecting the voltage rating and case size of the capacitor. For CIN, use of
an 0805 (2012) size may also be considered if there is room on the system board.
Table 2. Suggested Capacitors
Capacitance, Voltage Rating, Case Size
4.7 µF, 6.3V, 0603
Model
Vendor
TDK
C1608X5R0J475M
C1005X5R0J475M
CL05A475MQ5NRNC
C1608X5R0J106M
CL05A106MQ5NUNC
4.7 µF, 6.3V, 0402
TDK
4.7 µF, 6.3V, 0402
Samsung
TDK
10 µF, 6.3V, 0603
10 µF, 6.3V, 0402
Samsung
The input filter capacitor supplies AC current drawn by the PFET switch of the LM3241 in the first part of each
cycle and reduces the voltage ripple imposed on the input power source. The output filter capacitor absorbs the
AC inductor current, helps maintain a steady output voltage during transient load changes, and reduces output
voltage ripple. These capacitors must be selected with sufficient capacitance and sufficiently low ESR
(Equivalent Series Resistance) to perform these functions. The ESR of the filter capacitors is generally a major
factor in voltage ripple.
DSBGA Package Assembly and Use
Use of the DSBGA package requires specialized board layout, precision mounting and careful re-flow
techniques, as detailed in Texas Instruments Application Note 1112. Refer to the section Surface Mount
Technology (SMD) Assembly Considerations. For best results in assembly, alignment ordinals on the PC board
should be used to facilitate placement of the device. The pad style used with DSBGA package must be the
NSMD (non-solder mask defined) type. This means that the solder-mask opening is larger than the pad size.
This prevents a lip that otherwise forms if the solder-mask and pad overlap when holding the device off the
surface of the board causing interference with mounting. See Application Note 1112 for specific instructions how
to do this.
The 6-bump package used for LM3241 has 300 micron solder balls and requires 10.82 mil pads for mounting on
the circuit board. The trace to each pad should enter the pad with a 90° angle to prevent debris from being
caught in deep corners. Initially, the trace to each pad should be 7 mil wide, for a section approximately 7 mil
long, as a thermal relief. Then each trace should neck up or down to its optimal width. The important criterion is
symmetry. This ensures the solder bumps on the LM3241 re-flow evenly and that the device solders level to the
board. In particular, special attention must be paid to the pads for bumps A2 and C2. Because VIN and GND are
typically connected to large copper planes, inadequate thermal relief can result in late or inadequate re-flow of
these bumps.
The DSBGA package is optimized for the smallest possible size in applications with red or infrared opaque
cases. Because the DSBGA package lacks the plastic encapsulation characteristic of larger devices, it is
vulnerable to light. Backside metallization and/or epoxy coating, along with front-side shading by the printed
circuit board, reduce this sensitivity. However, the package has exposed die edges. In particular, DSBGA
devices are sensitive to light in the red and infrared range shining on the package’s exposed die edges.
It is recommended that a 10 nF capacitor be added between VCON and ground for non-standard ESD events or
environments and manufacturing processes. It prevents unexpected output voltage drift.
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