Vcc

Unused Input

Input

Output

Input

Unused Input

Output

17

SN74LVC1404

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SCES469F – AUGUST 2003 – REVISED MARCH 2020

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11 Power Supply Recommendations

The power supply can be any voltage between the MIN and MAX supply voltage rating located in the

Recommended Operating Conditions table.

Each VCC pin should have a good bypass capacitor to prevent power disturbance. For devices with a single

supply, 0.1 μf is recommended; if there are multiple VCC pins, then 0.01 μf or 0.022 μf is recommended for each

power pin. It is acceptable to parallel multiple bypass caps to reject different frequencies of noise. A 0.1 μf and a

1 μf 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

When using multiple-bit logic devices, inputs should 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 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 9 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 will be 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 will disable the output section of the

part when asserted. This will not disable the input section of the I/Os, so they cannot float when disabled.

12.2 Layout Example

Figure 9. Layout Diagram