8.4 Detailed Design Procedure

1. Add a decoupling capacitor from VCC to GND. The capacitor needs to be placed physically close to the

device and electrically close to both the VCC and GND pins. An example layout is shown in the Layout

section.

2. Ensure the capacitive load at the output is ≤ 50pF. This is not a hard limit; by design, however, it will

optimize performance. This can be accomplished by providing short, appropriately sized traces from the

SN74ACT08-Q1 to one or more of the receiving devices.

3. Ensure the resistive load at the output is larger than (VCC / IO(max))Ω. Doing this will prevent the maximum

output current from the Absolute Maximum Ratings from being violated. Most CMOS inputs have a resistive

load measured in MΩ; much larger than the minimum calculated previously.

4. Thermal issues are rarely a concern for logic gates; the power consumption and thermal increase, however,

can be calculated using the steps provided in the application report, CMOS Power Consumption and Cpd

Calculation.

8.5 Application Curves

OC

PG

ON/OFF

OT

RESET

Figure 8-2. Typical application timing diagram

8.6 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 0.1μF capacitor is recommended for this device. It is acceptable to parallel multiple bypass

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

The bypass capacitor should be installed as close to the power terminal as possible for best results.

8.7 Layout

8.7.1 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.

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SN74ACT08-Q1

SCAS993B – MARCH 2024 – REVISED FEBRUARY 2025

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