Unused Input

Input

Output

Input

Unused Input

Output

Output

Input

SN54AHCT245, SN74AHCT245

SCLS233P – OCTOBER 1995 – REVISED JULY 2014

www.ti.com

Typical Application (continued)

10.2.3 Application Curves

Figure 5. Typical Application Curve

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 6 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 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 6. Layout Diagram

10

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