Vcc

Unused Input

Input

Output

Input

Unused Input

Output

13

SN74LVC1G97

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SCES416N – DECEMBER 2002 – REVISED JANUARY 2017

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11 Layout

11.1 Layout Guidelines

When using multiple-bit logic devices, inputs must never float.

In many cases, functions (or parts of functions) of digital logic devices are unused, for example, when only two

inputs of a triple-input AND gate are used or when only 3 of the 4 buffer gates are used. Such input pins must

not be left unconnected, because the undefined voltages at the outside connections result in undefined

operational states. Figure 13 specifies the rules that must be observed under all circumstances. All unused

inputs of digital logic devices must be connected to a high or low bias to prevent them from floating. The logic

level that must be applied to any particular unused input depends on the function of the device. Generally they

are tied to GND or VCC, whichever makes more sense or is more convenient. It is generally acceptable to float

outputs, unless the part is a transceiver. If the transceiver has an output enable pin, it disables the output section

of the part when asserted, which does not disable the input section of the I/Os. Therefore, the I/Os cannot float

when disabled.

11.2 Layout Example

Figure 13. Layout Diagrams