Datasheet

EN
BP
VOUT
7 20 µs
VIN
8 30 µs
VCON
LM3243
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SNVS782B OCTOBER 2010REVISED FEBRUARY 2013
Figure 24. Startup Sequence and Conditions
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 AN-1112. Please refer to the section Surface
Mount Assembly Considerations. For best results in assembly, local alignment fiducials 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 would otherwise form if the solder-
mask and pad overlap, which would hold the device off the surface of the board and interfere with mounting. See
Application Note AN-1112 for specific instructions how to do this.
The 16-bump package used for LM3243 has 265 micron solder balls and requires 0.225 mm pads for mounting
the circuit board. The trace to each pad should enter the pad with a 90°entry angle to prevent debris from being
caught in deep corners. Initially, the trace to each pad should be 5.6 mil wide, for a section approximately 5 mil
long, as a thermal relief. Then each trace should neck up or down to its optimal width. An important criterion is
symmetry to insure the solder bumps on the LM3243 re-flow evenly and that the device solders level to the
board. In particular, special attention must be paid to the pads for bumps A1, A3, B1, and B3 since PGND and
PVIN are typically connected to large copper planes, inadequate thermal reliefs can result in inadequate re-flow
of these bumps.
The DSBGA package is optimized for the smallest possible size in applications with red-opaque 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 that are sensitive to light in
the read and infrared range shining on the package’s exposed die edges.
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