CAUTION

The maximum junction temperature, TJ(max) listed in the Section 6.1, is an additional limitation to

prevent damage to the device. Do not violate any values listed in the Section 6.1. These limits are

provided to prevent damage to the device.

9.2.1.2 Input Considerations

Unused inputs must be terminated to either VCC or ground. These can be directly terminated if the input is

completely unused, or they can be connected with a pull-up or pull-down resistor if the input is to be used

sometimes, but not always. A pull-up resistor is used for a default state of HIGH, and a pull-down resistor is used

for a default state of LOW. The resistor size is limited by drive current of the controller, leakage current into the

SN74HC74, as specified in the Section 6.5, and the desired input transition rate. A 10-kΩ resistor value is often

used due to these factors.

The SN74HC74 has standard CMOS inputs, so input signal edge rates cannot be slow. Slow input edge rates

can cause oscillations and damaging shoot-through current. The recommended rates are defined in the Section

6.3.

Refer to the Section 8.3 for additional information regarding the inputs for this device.

9.2.1.3 Output Considerations

The positive supply voltage is used to produce the output HIGH voltage. Drawing current from the output will

decrease the output voltage as specified by the VOH specification in the Section 6.5. Similarly, the ground voltage

is used to produce the output LOW voltage. Sinking current into the output will increase the output voltage as

specified by the VOL specification in the Section 6.5.

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

Refer to Section 8.3 for additional information regarding the outputs for this device.

9.2.1.4 Timing Considerations

The SN74HC74 is a clocked device. As such, it requires special timing considerations to ensure normal

operation.

Primary timing factors to consider:

• Maximum clock frequency: the maximum operating clock frequency defined in Section 6.7 is the maximum

frequency at which the device is guaranteed to function. This value refers specifically to the triggering

waveform, measuring from one trigger level to the next.

• Pulse duration: ensure that the triggering event duration is larger than the minimum pulse duration, as

defined in the Section 6.7.

• Setup time: ensure that the data has changed at least one setup time prior to the triggering event, as defined

in the Section 6.7.

• Hold time: ensure that the data remains in the desired state at least one hold time after the triggering event,

as defined in the Section 6.7.

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 Section 11.

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 SN74HC74

to the receiving device.

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 Section 6.1 is not violated. Most CMOS inputs have a resistive load measured in

megaohms; much larger than the minimum calculated above.

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SN74HC74, SN54HC74

SCLS094F – DECEMBER 1982 – REVISED JUNE 2021

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Product Folder Links: SN74HC74 SN54HC74