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 should have a bypass capacitor to prevent power

disturbance. A 0.1-μF capacitor is recommended for this device. It is acceptable to parallel multiple bypass caps

to reject different frequencies of noise. The 0.1-μF and 1-μF capacitors are commonly used in parallel. The

bypass capacitor should be installed as close to the power terminal as possible for best results, as shown in

Figure 11-1.

11 Layout

11.1 Layout Guidelines

When using multiple-input and multiple-channel logic devices inputs must not ever be left floating. 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. Such unused input pins must not be left unconnected because the undefined

voltages at the outside connections result in undefined operational states. All unused inputs of digital logic

devices must be connected to a logic high or logic low voltage, as defined by the input voltage specifications, 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, the inputs are tied to GND or VCC, whichever makes more sense for the logic

function or is more convenient.

11.2 Layout Example

1

2

3

4

5

6

7

14

13

12

11

10

9

8

1A

1B

2B

2C

2Y

GND

V

CC

1C

1Y

3B

3A

3Y

GND

V

CC

3C

2A

0.1

F

Unused

inputs tied to

GND

Bypass capacitor

placed close to the

device

Avoid 90°

corners for

signal lines

Recommend GND flood fill for

improved signal isolation, noise

reduction, and thermal dissipation

Unused

output left

floating

Unused input

tied to VCC

Figure 11-1. Example layout for the CD74HC27

CD74HC27, CD54HC27

SCHS132D – AUGUST 1997 – REVISED APRIL 2021

www.ti.com

12

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