8 Detailed Description

8.1 Overview

The SN74HCS174 is a positive-edge-triggered hex D-type flip-flop with direct clear (CLR) input. Information at

the data (D) inputs meeting the setup time requirements is transferred to the outputs on the positive-going edge

of the clock (CLK) pulse. Clock triggering occurs at a particular voltage level and is not directly related to the

transition time of the positive-going edge of CLK. When CLK is at either the high or low level, the D input has no

effect at the output.

8.2 Functional Block Diagram

D

R

Q

xD

xQ

One of Six D-Type Flip-Flops

CLK

CLR

Shared Control Logic

Figure 8-1. Logic Diagram (Positive Logic) for SN74HCS174

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).

The Schmitt-trigger input architecture provides hysteresis as defined by ΔVT in the Electrical Characteristics

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

inputs with slow transitioning signals will increase dynamic current consumption of the device. For additional

information regarding Schmitt-trigger inputs, please see Understanding Schmitt Triggers.

8.3.3 Latching Logic

This device includes latching logic circuitry. Latching circuits commonly include D-type latches and D-type flip-

flops, but include all logic circuits that act as volatile memory.

When the device is powered on, the state of each latch is unknown. There is no default state for each latch at

start-up.

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SN74HCS174

SCLS842 – SEPTEMBER 2020

Copyright © 2020 Texas Instruments Incorporated

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Product Folder Links: SN74HCS174