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 good 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 the

following layout example.

11 Layout

11.1 Layout Guidelines

When using multiple-input and multiple-channel logic devices, inputs must never 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 or only 3 of the 4 buffer gates 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

20

19

18

17

16

15

14

GND

VCC

0.1

F

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 input

tied to GND

8

13

9

12

10

11

CLR

1Q

1D

2D

2Q

3Q

3D

4D

4Q

VCC

8Q

8D

7D

7Q

6Q

6D

5D

5Q

CLK

Unused output

left floating

GND

Figure 11-1. Example Layout for the SN74HCS273

PW Package

F

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 input

tied to GND

VCC

CLK

Unused output

left floating

GND

1Q

1D

2D

2Q

3Q

3D

4D

4Q

CLR

8Q

8D

7D

7Q

6Q

6D

5D

5Q

1

20

10

11

2

3

4

5

6

7

8

9

12

13

14

15

16

17

18

19

GND

V

CC

GND

Figure 11-2. Example Layout for the SN74HCS273

RKS Package

SN74HCS273

SCLS851D – MARCH 2021 – REVISED JANUARY 2023

www.ti.com

14

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