SN74CBTU4411_16 Datasheet, PDF (15/21 Pages) Texas Instruments – Multiplexer/Demultiplexer

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11 Layout
SN74CBTU4411
SCDS192A – APRIL 2005 – REVISED FEBRUARY 2016
11.1 Layout Guidelines
When using multiple bit logic devices, inputs should not float. In many cases, functions or parts of functions of
digital logic devices are unused. Some examples are 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 should not be left unconnected because the
undefined voltages at the outside connections result in undefined operational states.
Figure 7 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 should be
applied to any particular unused input depends on the function of the device. Generally they are tied to GND or
V_CC, whichever makes more sense or is more convenient. It is acceptable to float outputs unless the part is a
transceiver. If the transceiver has an output enable pin, it disables the outputs section of the part when asserted.
This does not disable the input section of the I/Os, so they also cannot float when disabled.
11.2 Layout Example
V_cc
Input
Unused Input
Output
Unused Input
Output
Input
Figure 7. Layout Diagram
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