SN74HCS259 datasheet(14/19 Pages) TI

14 / 19 page

Two channels within the same device with the same input signals can be connected in parallel for additional

output drive strength.

Unused outputs can be left floating. Do not connect outputs directly to VCC or ground.

Refer to Feature Description section for additional information regarding the outputs for this device.

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

section.

2. Ensure the capacitive load at the output is ≤ 50 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 SN74HCS259

to the receiving device(s).

3. Ensure the resistive load at the output is larger than (VCC / IO(max)) 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 Curve

CLR

D routed to Q6

D routed to Q0

S[2:0] = 0b110

S[2:0] = 0b000

Figure 9-2. Application timing diagram

SN74HCS259

SCLS836 – SEPTEMBER 2020

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SN74HCS259 датащи(PDF) 14 Page - Texas Instruments