Logic - Latches

Image	Part Number	Description / PDF	Quantity	Rfq
	74ALVCH16373DGG,51 Nexperia	IC 16BIT D TRANSP LATCH 48TSSOP	0
	74HCT573DB-Q100J Nexperia	IC TRANSP LATCH OCT D 20SSOP	0
	74HCT259DB,118 Nexperia	IC 8BIT ADDRESSABLE LATCH 16SSOP	0
	74ALVCH16843DGG,11 Nexperia	IC 18BIT BUS INTRFC D 56TSSOP	0
	74ALVT16373DGG,518 Nexperia	IC 16BIT TRANSP D LATCH 48TSSOP	0
	74HC75DB,118 Nexperia	IC LATCH QUAD BISTABLE 16SSOP	0
	74LVT16373ADGG,518 Nexperia	IC 16BIT TRANSP LATCH D 48TSSOP	0
	74LVT16373ADGG,512 Nexperia	IC 16BIT TRANSP LATCH D 48TSSOP	0
	74HC259DB,118 Nexperia	IC 8BIT ADDRESSABLE LATCH 16SSOP	0

Logic - Latches

1. Overview

Logic latches are fundamental components in digital electronics, serving as bistable multivibrators that store one bit of binary data. They operate in two stable states (0 or 1) and are controlled by input signals to maintain or change their output states. Latches are essential building blocks for memory units, registers, and sequential logic circuits. Their importance spans across modern computing, telecommunications, industrial automation, and consumer electronics, enabling temporary data storage and synchronization in digital systems.

2. Major Types and Functional Classification

Type	Functional Characteristics	Application Examples
SR Latch	Set-Reset functionality; asynchronous operation	Basic memory units, control circuits
D Latch	Data storage with single data input (D) and clock control	Shift registers, data buffers
JK Latch	Universal latch with toggling capability; eliminates invalid states	Counters, state machines
T Latch	Toggle mode operation; simplified JK variant	Frequency division circuits

3. Structure and Composition

Logic latches typically consist of transistor-based gate structures, often implemented using CMOS or TTL technology. A standard latch includes:

Input terminals (e.g., Data, Set, Reset, Clock)
Cross-coupled inverters for state retention
Control logic gates (NAND/AND-OR) for signal processing
Output terminals (Q and Q for complementary outputs)

Modern IC latches are fabricated on silicon wafers with sub-micron process nodes (e.g., 180nm, 130nm), featuring multiple latches per package (e.g., 8-bit registers) in standard footprints like SOIC, TSSOP, and QFN.

4. Key Technical Specifications

Parameter	Description	Importance
Supply Voltage (V_CC)	Operating voltage range (e.g., 1.65-5.5V)	Determines compatibility with system power rails
Propagation Delay	Time between input change and output response (ns)	Impacts maximum operating frequency
Power Consumption	Static and dynamic current draw ( A/mA)	Crucial for battery-powered devices
Operating Temperature	Temperature range (-40 C to +125 C)	Defines environmental durability
Output Drive Strength	Current delivery capability (mA)	Affects fan-out and signal integrity

5. Application Fields

Major industries utilizing latches include:

Telecommunications: Network switches, routers, optical transceivers
Computing: CPU registers, cache memory, ALU components
Industrial Automation: PLCs, sensor data buffers, motor controllers
Consumer Electronics: Smartphones, wearables, display drivers
Automotive: CAN bus controllers, ADAS data registers

6. Leading Manufacturers and Products

Manufacturer	Key Products	Features
Texas Instruments	SN74LVC1G374	Low-voltage D latch with 1.5ns delay
STMicroelectronics	CD4042B	CMOS latch with clock polarity control
NXP Semiconductors	74HC373	Octal D latch for bus interfacing
ON Semiconductor	MC74VHC1G373	Ultra-low power single latch

7. Selection Guidelines

Key selection criteria:

Functional requirements (e.g., SR vs. D latch functionality)
Speed vs. power consumption trade-offs
Package type for PCB space constraints
Environmental operating conditions
Cost optimization for mass production
Supply voltage compatibility with existing system components

Case Study: For a portable IoT device, prioritize ultra-low power latches like ON Semi's MC74VHC1G373 with <1 A quiescent current, while high-speed applications (e.g., networking ASICs) require devices with sub-ns propagation delays.

8. Industry Trends

Emerging trends shaping latch technology include:

Continued process node scaling (e.g., 28nm FD-SOI for radiation-hardened latches)
Integrated error correction features for mission-critical applications
Development of latch arrays with programmable interconnects
Advanced packaging (3D ICs, chiplets) for higher density
Low-voltage operation (<0.8V) for energy-efficient computing