WORST

BETTER

BEST

1W min.

W

14

SN74LVC1G80

SCES221S – APRIL 1999 – REVISED NOVEMBER 2016

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Copyright © 1999–2016, Texas Instruments Incorporated

10 Power Supply Recommendations

The power supply can be any voltage between the minimum and maximum supply voltage rating listed in

Absolute Maximum Ratings . Each VCC terminal must have a good bypass capacitor to prevent power

disturbance. For devices with a single supply, a 0.1-µF bypass capacitor is recommended. If multiple pins are

labeled VCC, then a 0.01-µF or 0.022-µF capacitor is recommended for each VCC because the VCC pins are

tied together internally. For devices with dual-supply pins operating at different voltages, for example VCC and

VDD, a 0.1-µF bypass capacitor is recommended for each supply pin. To reject different frequencies of noise,

use multiple bypass capacitors in parallel. Capacitors with values of 0.1 µF and 1 µF are commonly used in

parallel. The bypass capacitor must be installed as close to the power terminal as possible for best results.

11 Layout

11.1 Layout Guidelines

Reflections and matching are closely related to the loop antenna theory but are different enough to be discussed

separately from the theory. When a PCB trace turns a corner at a 90° angle, a reflection can occur. A reflection

occurs primarily because of the change of width of the trace. At the apex of the turn, the trace width increases to

1.414 times the width. This increase upsets the transmission-line characteristics, especially the distributed

capacitance and self–inductance of the trace which results in the reflection. Not all PCB traces can be straight

and therefore some traces must turn corners. Figure 7 shows progressively better techniques of rounding

corners. Only the last example (BEST) maintains constant trace width and minimizes reflections.

11.2 Layout Example

Figure 7. Trace Example