Datasheet

PCB Layout
2-2
2.1 PCB Layout
The DAC7654 EVM is designed to demonstrate the performance quality of the
installed DAC device under test, as specified in the data sheet. Careful
analysis of the EVM’s physical restrictions and factors that contributes to the
EVM’s performance degradation is the key to a successful design
implementation. The attributes that contributes to the poor performance of the
EVM can be avoided during the schematic design phase by properly selecting
the correct components and correctly designing the circuit. The circuit should
include adequate bypassing, identifying and managing the analog and digital
signals, and knowing or understanding the components mechanical attributes.
The obscure part of the design lies particularly in the layout process. The main
concern is primarily with the placement of components and the proper routing
of signals. The bypass capacitors must be placed as close as possible to the
pins, and the analog and digital signals should be properly separated from
each other. The power and ground plane is important and should be carefully
considered in the layout process. A solid plane is ideally preferred but
sometimes impractical; so, when solid planes are not possible, a split plane
does the job. When considering a split plane design, analyze the component
placement and carefully split the board into its analog and digital sections
starting from the device under test. The ground plane plays an important role
in controlling the noise and other effects that otherwise contributes to the error
of the DAC output. To ensure that the return currents are handled properly,
route the appropriate signals only in their respective sections, meaning the
analog traces should only lay directly above or below the analog section and
the digital traces in the digital section. Minimize the length of the traces but use
the largest trace width possible in the design. These design practices
discussed are seen in the following figures.
The DAC7654 EVM board is constructed on a four-layer printed-circuit board
using a copper-clad FR−4 laminate material. The printed-circuit board has a
dimension of 43,1800 mm (1.7000 inch) X 82,5500 mm (3.2000 inch), and the
board thickness is 1,5748 mm (0.0620 inch). Figure 2−1 through Figure 2−7
show the individual artwork layers.