8 Detailed Description

8.1 Overview

Logic Diagram (Positive Logic) for one channel of SN74HCS74 describes the SN74HCS74. As the SN74HCS74

is a dual D-Type positive-edge-triggered flip-flop with clear and preset, the diagram below describes one of the

two device flip-flops.

8.2 Functional Block Diagram

One of Two Channels

CLK

C

C

PRE

D

CLR

C

C

C

C

C

C

C

C

Q

Q

Figure 8-1. Logic Diagram (Positive Logic) for one channel of SN74HCS74

8.3 Feature Description

8.3.1 Balanced CMOS Push-Pull Outputs

This device includes balanced CMOS push-pull outputs. The term "balanced" indicates that the device can sink

and source similar currents. The drive capability of this device may create fast edges into light loads so routing

and load conditions should be considered to prevent ringing. Additionally, the outputs of this device are capable

of driving larger currents than the device can sustain without being damaged. It is important for the output power

of the device to be limited to avoid damage due to overcurrent. The electrical and thermal limits defined in the

Absolute Maximum Ratings must be followed at all times.

Unused push-pull CMOS outputs should be left disconnected.

8.3.2 CMOS Schmitt-Trigger Inputs

This device includes inputs with the Schmitt-trigger architecture. These inputs are high impedance and are

typically modeled as a resistor in parallel with the input capacitance given in the Electrical Characteristics table

from the input to ground. The worst case resistance is calculated with the maximum input voltage, given in the

Absolute Maximum Ratings table, and the maximum input leakage current, given in the Electrical Characteristics

table, using Ohm's law (R = V ÷ I).

table, which makes this device extremely tolerant to slow or noisy inputs. While the inputs can be driven much

slower than standard CMOS inputs, it is still recommended to properly terminate unused inputs. Driving the

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SN74HCS74

SCLS782B – NOVEMBER 2019 – REVISED NOVEMBER 2020

Copyright © 2020 Texas Instruments Incorporated

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Product Folder Links: SN74HCS74