EN

BP

VOUT

7 20 µs

VIN

8 30 µs

VCON

LM3253

www.ti.com

SNVS791Q – FEBRUARY 2012 – REVISED MAY 2013

Figure 25. 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 (SNVA009). 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 (SNVA009) for specific instructions how to do this.

The 16-bump package used for LM3253 has 265 micron solder balls and requires 0.225 mml 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 LM3253 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 red and infrared range shining on the package’s exposed die edges.

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