Datasheet

WORST
BETTER
BEST
1W min.
W
2W
SN54HC164 , SN74HC164
www.ti.com SCLS115G –DECEMBER 1982–REVISED SEPTEMBER 2015
11 Power Supply Recommendations
The power supply can be any voltage between the minimum and maximum supply voltage rating located in the
Recommended Operating Conditions table.
Each V
CC
pin must have a good bypass capacitor in order to prevent power disturbance. For devices with a
single supply, a 0.1-μF capacitor is recommended and if there are multiple V
CC
pins then a 0.01-μF or 0.022-μF
capacitor is recommended for each power pin. It is ok to parallel multiple bypass caps to reject different
frequencies of noise. 0.1-μF and 1-μF capacitors are commonly used in parallel. The bypass capacitor should be
installed as close to the power pin as possible for best results.
12 Layout
12.1 Layout Guidelines
Reflections and matching are closely related to loop antenna theory, but different enough to warrant their own
discussion. When a PCB trace turns a corner at a 90° angle, a reflection can occur. This is primarily due to the
change of width of the trace. At the apex of the turn, the trace width is increased to 1.414 times its width. This
upsets the transmission line characteristics, especially the distributed capacitance and self– inductance of the
trace — resulting in the reflection. It is a given that not all PCB traces can be straight, and so they will have to
turn corners. Figure 6 shows progressively better techniques of rounding corners. Only the last example
maintains constant trace width and minimizes reflections.
12.2 Layout Example
Figure 6. Trace Example
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