SN74HCS20 datasheet(12/23 Pages) TI1

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SN74HCS20

SCLS791A – MARCH 2020 – REVISED JUNE 2020

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Typical Application (continued)

9.2.2 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.

2. Ensure the capacitive load at the output is

≤ 70 pF. This is not a hard limit, however it will ensure optimal

performance. This can be accomplished by providing short, appropriately sized traces from the SN74HCS20

to the receiving device.

3. Ensure the resistive load at the output is larger than (VCC / 25 mA) Ω. This will ensure that the maximum

output current from the Absolute Maximum Ratings is not violated. Most CMOS inputs have a resistive load

measured in megaohms; much larger than the minimum calculated above.

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

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

Calculation

9.2.3 Application Curves

Figure 10. Application timing diagram

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