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SN74LS74AN

Dual D flip-flop, edge-triggered, PRE/CLR, Q+Q̅, 25MHz, PDIP-14

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Manufacturer Part：

SN74LS74AN

Package：

PDIP-14 (19.3 x 6.35 x 4.57mm, 2.54mm pitch, through-hole)

Brand：

Product Categories：

Integrated Circuits ICs, Interface ICs

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Description

Product Overview

The SN74LS74AN from Texas Instruments is a dual D-type positive-edge-triggered flip-flop with preset and clear inputs, complementary outputs, and 25MHz maximum clock frequency in a 14-pin PDIP package.

Key Specifications

Number of Flip-Flops	2 (dual D-type)
Logic Family	LS (Low-power Schottky)
Supply Voltage	4.75V to 5.25V (5V nominal)
Trigger Type	Positive-edge triggered
Outputs	True (Q) and complementary (Q̅) per flip-flop
Preset (PRE)	Active-low, asynchronous (sets Q=HIGH)
Clear (CLR)	Active-low, asynchronous (sets Q=LOW)
Maximum Clock Frequency	25MHz typical
Propagation Delay (CLK to Q)	25ns typical
Setup Time	15ns minimum before clock edge
Hold Time	0ns minimum after clock edge
Operating Temperature	0°C to +70°C
Package	PDIP-14 (19.3 x 6.35mm)

Features

Dual D-type positive-edge-triggered flip-flops
Independent preset and clear per flip-flop
Complementary outputs (Q and Q̅)
Asynchronous preset (sets Q=HIGH)
Asynchronous clear (sets Q=LOW)
25MHz maximum clock frequency

Applications

Frequency division (÷2)
Data synchronization
One-shot pulse generation
Switch debouncing
Digital delay and pipelining

Product Introduction:SN74LS74AN Product Introduction

The SN74LS74AN from Texas Instruments contains two independent D-type positive-edge-triggered flip-flops, each with asynchronous preset (PRE) and clear (CLR) inputs and complementary Q/Q̅ outputs. The 74LS74 is the most widely-used D flip-flop in TTL design. On the rising edge of the clock (CLK), the D input is transferred to the Q output. The asynchronous PRE input, when LOW, immediately sets Q=HIGH regardless of CLK or D. The asynchronous CLR input, when LOW, immediately sets Q=LOW. Both PRE and CLR override the clock. The complementary Q̅ output provides the inverted Q value without additional logic. For frequency division, connecting Q̅ to D creates a toggle flip-flop that divides the clock frequency by 2. The A suffix denotes the improved LS version. The N suffix denotes the PDIP-14 through-hole package.

Working Principle:SN74LS74AN Working Principle

Each D-type flip-flop in the SN74LS74AN captures the logic level at its D input on the rising edge of CLK. The captured value appears at Q, and the inverted value at Q̅. Between clock edges, the outputs hold their values. The asynchronous PRE (preset) input, when LOW, forces Q=HIGH and Q̅=LOW regardless of CLK or D. The asynchronous CLR (clear) input, when LOW, forces Q=LOW and Q̅=HIGH. Both PRE and CLR are active-low and override the synchronous (clocked) operation. If both PRE and CLR are simultaneously LOW, both Q and Q̅ go HIGH (invalid state); the state that results when both return HIGH is indeterminate, so this condition should be avoided. For a toggle (÷2) configuration, Q̅ connects to D. Each rising clock edge captures the opposite of the current Q value, causing Q to toggle: 0→1→0→1… The output frequency is half the clock frequency. For a one-shot (monostable) pulse, D is held HIGH, and a brief LOW pulse on CLR clears Q; when CLR returns HIGH, the next clock edge captures D=HIGH, setting Q=HIGH for one clock period.

Pin Description:SN74LS74AN Pin Definition and Functions

Pin	Name	Type	Description
1	1CLR	Input	Flip-flop 1 clear (active LOW, async)
2	1D	Input	Flip-flop 1 data input
3	1CLK	Input	Flip-flop 1 clock (rising edge triggered)
4	1PRE	Input	Flip-flop 1 preset (active LOW, async)
5	1Q	Output	Flip-flop 1 true output
6	1Q̅	Output	Flip-flop 1 complementary output
7	GND	Power	Ground
8	2Q̅	Output	Flip-flop 2 complementary output
9	2Q	Output	Flip-flop 2 true output
10	2PRE	Input	Flip-flop 2 preset (active LOW, async)
11	2CLK	Input	Flip-flop 2 clock (rising edge triggered)
12	2D	Input	Flip-flop 2 data input
13	2CLR	Input	Flip-flop 2 clear (active LOW, async)
14	VCC	Power	Supply (4.75V to 5.25V)

Application Scenarios:In which products and applications isSN74LS74AN used

÷2 Divider: Q̅ to D; CLK input; Q output = half frequency; cascade for ÷4, ÷8, etc.
Data Sync: Asynchronous input → D; system clock → CLK; Q output synchronized to clock edge
One-Shot: D=HIGH; trigger on CLR; Q goes HIGH on next clock for exactly one clock period
Debounce: Switch through RC filter → D; clock at 100Hz; samples clean state after bounce settles
Shift Register: Chain of 74LS74 flip-flops; D of each from Q of previous; shifts data one bit per clock

Alternative Models:What chips are recommended as replacements for SN74LS74AN

Model	Manufacturer	Key Difference	Package	Supply
74LS74N	TI/Nexperia	Original TTL version with 5V-only supply, typical propagation delay 10-15ns	DIP-14	5V TTL
74LS74D	TI/Nexperia	Surface-mount SOIC version of LS with identical logic function	SOIC-14	5V TTL
74HC74D	TI/Nexperia	CMOS version with wide 2-6V supply range, lower power consumption and higher noise immunity	SOIC-14	2-6V CMOS
74HC74N	TI/Nexperia	Through-hole DIP version of HC family for prototyping and repair	DIP-14	2-6V CMOS
74HCT74D	TI/Nexperia	CMOS with TTL-compatible input levels, ideal for mixing with LS devices at 5V	SOIC-14	4.5-5.5V TTL-in
74HCT74N	TI/Nexperia	Through-hole DIP version of HCT family for prototyping and repair	DIP-14	4.5-5.5V TTL-in
74AC74D	TI/Nexperia	Advanced CMOS with 2-6V supply and higher output drive current (24mA vs 6mA for HC)	SOIC-14	2-6V CMOS
74AC74N	TI/Nexperia	Through-hole DIP version of AC family for prototyping and repair	DIP-14	2-6V CMOS
74LVC74D	TI/Nexperia	Low-voltage CMOS for 1.65-3.6V modern logic with 24mA output drive and bus-hold inputs	SOIC-14	1.65-3.6V CMOS
74LVC74N	TI/Nexperia	Through-hole DIP version of LVC family for prototyping and repair	DIP-14	1.65-3.6V CMOS

The 7474 is a Dual D-Type Positive-Edge-Triggered Flip-Flop. Family variants span from the original LS TTL (5V only) to modern LVC/AUP (down to 0.8V). HC and HCT versions offer 2-6V CMOS operation with HCT providing TTL-compatible input thresholds for mixed 5V systems. CD4000-series equivalents offer the widest 3-18V supply range at the cost of lower switching speed. DIP packages (N suffix) are through-hole; SOIC (D suffix) and TSSOP are surface-mount.