Clock/Timing - Real Time Clocks

Part Number	Description / PDF	Quantity
ISL1219IUZ Intersil (Renesas Electronics America)	IC RTC EVENT REC I2C 10-MSOP	0
DS1685-5 Analog Devices, Inc.	DS1685 5V REAL-TIME CLOCK	0
ISL12022IBZ-T Intersil (Renesas Electronics America)	IC RTC CLK/CALENDAR I2C 8-SOIC	0
RX-8035SA:B PURE SN R Epson	IC RTC RECORDER I2C SER 14SOP	0
MCP79412T-I/ST Roving Networks / Microchip Technology	IC RTC CLK/CALENDAR I2C 8-TSSOP	0
DS1743P-85+ Analog Devices, Inc.	REAL TIME CLOCK, NON-VOLATILE, 0	470
ISL12026AIVZ-T Intersil (Renesas Electronics America)	IC RTC CLK/CALENDAR I2C 8-TSSOP	0
DS12C887A+ Maxim Integrated	IC RTC CLK/CALENDAR PAR 24-EDIP	60
DS12885SN+T&R Maxim Integrated	IC RTC CLK/CALENDAR PAR 24-SOIC	0
PT7C4302AUEX Zetex Semiconductors (Diodes Inc.)	REAL TIME CLOCK MSOP-8	0
MCP7940M-I/P Roving Networks / Microchip Technology	IC RTC CLK/CALENDAR I2C 8DIP	71
RTC-72421A: PURE SN Epson	IC REAL TIME CLOCK/CALENDAR	0
ISL12020CBZ Intersil (Renesas Electronics America)	REAL TIME CLOCK, NON-VOLATILE	481
DS1302Z+T&R Maxim Integrated	IC RTC CLK/CALENDAR SER 8-SOIC	24951
MCP79522T-I/MN Roving Networks / Microchip Technology	IC RTC CLK/CALENDAR SPI 10-TDFN	0
RTC-72421B: ROHS Epson	IC RTC CLK/CALENDAR PAR 18-DIP	1610
DS17885S-5/T&R+ Maxim Integrated	IC RTC CLK/CALENDAR PAR 24-SOIC	0
PCF8523T/1,118 NXP Semiconductors	IC RTC CLK/CALENDAR I2C 8-SOIC	3571
BQ4285EP Texas Instruments	RTC, VOLATILE	6270
BQ3285S-SB2 Texas Instruments	IC RTC CLK/CALENDAR PAR 24-SOP	284

Clock/Timing - Real Time Clocks

1. Overview

Real-Time Clocks (RTCs) are integrated circuits designed to maintain accurate timekeeping in electronic systems, even during power interruptions. They provide critical time-of-day, date, and alarm functions through battery-backed or capacitor-powered circuits. RTCs are essential for applications requiring precise temporal synchronization in embedded systems, consumer electronics, industrial automation, and automotive systems.

2. Major Types and Functional Classification

Type	Functional Features	Application Examples
Parallel Interface RTCs	8/16-bit parallel data buses, fast access	Industrial controllers, legacy systems
I2C/SPI Interface RTCs	Serial communication, low pin count	Smartphones, IoT devices
Embedded Crystal RTCs	Integrated crystal oscillator, reduced footprint	Wearables, medical devices
Low-Power RTCs	Sub-1 A standby current, extended battery life	Energy harvesting systems, sensors

3. Structure and Components

Typical RTC architecture includes:

32.768kHz crystal oscillator circuit
Binary counter with BCD/time registers
Power supply monitoring and switching circuitry
Communication interface (I2C, SPI, etc.)
Alarm and interrupt generation modules
Temperature compensation circuitry (for high-precision variants)

Common packaging: 8-24 pin DIP/SOP/TSSOP, with optional integrated crystal in QFN packages.

4. Key Technical Specifications

Parameter	Importance	Typical Values
Timekeeping Accuracy	Determines cumulative error over time	2ppm (0 C-40 C), 20ppm industrial
Supply Current	Impacts battery life	800nA-2 A @ 3V
Operating Temperature	Defines environmental reliability	-40 C to +85 C standard
Interface Speed	Limits system communication bandwidth	400kHz I2C, 10MHz SPI
Timekeeping Voltage	Determines minimum operation threshold	1.3V-3.7V

5. Application Areas

Key industries and equipment:

Consumer Electronics: Smartphones, Set-top boxes, Digital cameras
Industrial Automation: PLCs, SCADA systems, Data loggers
Medical Devices: Patient monitors, Infusion pumps, Diagnostic equipment
Automotive: Telematics units, ADAS, In-vehicle infotainment
Smart Energy: Smart meters, Grid sensors, Energy storage systems

Case Study: DS3231 RTC in solar inverters maintains time-stamped energy production logs during grid outages.

6. Leading Manufacturers and Products

Manufacturer	Product Series	Key Features
Analog Devices	ADT74x	0.5ppm accuracy, I2C interface
Maxim Integrated	DS3231	Integrated TCXO, 2ppm
STMicroelectronics	M41T82	Auto-calibration, 256Hz output
NXP Semiconductors	PCF8523	Low-cost I2C, 1.8V operation
Texas Instruments	RV-8263-C3	3V lithium-backed, alarm functions

7. Selection Guidelines

Key considerations:

Accuracy requirements ( 2ppm vs 20ppm)
Interface compatibility (I2C vs SPI vs parallel)
Power budget (active vs standby current)
Environmental conditions (temperature, vibration)
Package size vs PCB space limitations
Battery backup vs capacitor-based solutions
Additional features (alarms, square wave outputs)

Example: For wearables: prioritize ultra-low power (M41T94 @ 600nA) with small TSSOP package.

8. Industry Trends

Emerging trends include:

Integration with MEMS oscillators replacing traditional crystals
Advancements in temperature compensation algorithms ( 0.1ppm achievable)
System-in-Package (SiP) solutions combining RTC with sensors
Increased adoption in edge computing devices for timestamped data processing
Automotive-grade RTCs for autonomous vehicle synchronization

Market drivers: Growth in IoT devices (projected 12% CAGR 2023-2030) and industrial automation systems.