WORST

BETTER

BEST

1W min.

W

Supply Voltage VCC (V)

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

D001

VIH MIN

VIL MAX

13

SN54LVC138A, SN74LVC138A

www.ti.com

SCAS291W – MARCH 1993 – REVISED OCTOBER 2016

Product Folder Links: SN54LVC138A SN74LVC138A

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Copyright © 1993–2016, Texas Instruments Incorporated

Typical Application (continued)

9.2.3 Application Curve

Figure 4. Input High and Input Low Thresholds vs Supply Voltage

10 Power Supply Recommendations

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

Recommended Operating Conditions.

Each VCC terminal must have a good bypass capacitor to prevent power disturbance. A 0.1-µF bypass capacitor

is recommended to be placed close to the VCC terminal. It is acceptable to parallel multiple bypass capacitors to

reject different frequencies of noise; 0.1-µF and 1-µF capacitors 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 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 have to turn

corners. Figure 5 shows progressively better techniques of rounding corners. Only the last example maintains

constant trace width and minimizes reflections.

11.2 Layout Example

Figure 5. Trace Example