Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

Home > Products > Integrated Circuits (ICs) > Clock/Timing > Real Time Clocks

STMicroelectronics M41T81SMY6E

Name: M41T81SMY6E
Brand: STMicroelectronics
SKU: M41T81SMY6E
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

Compare

Part No.:: M41T81SMY6E

Manufacturer:: STMicroelectronics

Category:: Real Time Clocks

Package:: 18-SOX, 18-SOIC with Crystal (7.5mm Width)

Datasheet:: M41T81SMY6E.pdf

Description:: IC RTC CLK/CALENDAR I2C 18SOX

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:1,391

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

M41T81SMY6E from STMicroelectronics is a serial real-time clock (RTC) IC with integrated 32.768 kHz crystal oscillator, I²C interface (400 kHz), ultra-low battery current (0.6 µA typ), and full calendar functionality (century, year, month, date, day, hour, minute, second, tenths/hundredths of second in BCD). It operates across 2.0–5.5 V and supports alarm, watchdog timer (62.5 ms–128 s), power-down time-stamp, and oscillator fail detection - deployed in industrial control panels requiring long-term timestamping under intermittent power.

For engineers reviewing the M41T81SMY6E datasheet, M41T81SMY6E pinout, M41T81SMY6E application, or M41T81SMY6E equivalent, key selection criteria include embedded crystal SOIC-18 packaging, battery-backed data retention, I²C slave address 0xD0h, programmable square wave output, and automatic VCC-to-VBAT switchover at VSO (2.5–2.7 V).

Technical Context

The M41T81SMY6E implements a fully autonomous RTC core with hardware-based calendar logic that auto-corrects for 28–31-day months and leap years through 2100. Its oscillator includes integrated 12.5 pF load capacitance and stop-detection circuitry to flag timing failures.

It functions as an I²C slave device (7-bit address 0xD0h) with automatic address pointer incrementation during sequential reads/writes across 20 registers. The IRQ/FT/OUT/SQW pin supports four multiplexed functions - interrupt generation, frequency test, open-drain output driver, and programmable square wave - prioritized with square wave highest.

Key Specifications

Parameter	Value and Actual Design Meaning
Interface	I²C bus, 400 kHz max clock rate - enables direct connection to microcontroller I²C peripherals without level-shifting or protocol translation.
Battery Current	0.6 µA typical - extends lithium coin-cell life beyond 10 years in backup mode, critical for unattended remote sensors.
Operating Voltage	2.0–5.5 V on VCC; 2.5–2.7 V switchover threshold (VPFD) - ensures seamless transition to battery during brownout in 3.3 V industrial systems.
Timekeeping Accuracy	Crystal oscillator with integrated 12.5 pF load capacitance - eliminates external capacitors and improves stability over temperature and aging.
Alarm & Watchdog	Programmable alarm interrupt (active in battery mode); watchdog timer adjustable from 62.5 ms to 128 s - provides fail-safe system recovery without host CPU involvement.
Temperature Range	–40 °C to +85 °C - qualified for deployment in outdoor metering, factory automation, and transportation electronics.
Calendar Format	BCD-encoded registers (00h–07h) with century bit support - simplifies firmware parsing and avoids binary-to-BCD conversion overhead in resource-constrained MCUs.

Pinout & Package

Package: SOX18 - 18-pin plastic small outline (300 mil width), with embedded 32.768 kHz crystal. Pin 1 = NF (no function, tie to VSS); Pins 2 & 3 internally shorted; Pins 16 & 17 internally shorted.

Pin/Terminal	Circuit Role	Design Meaning
1, 9–15, 18	NC / NF	No-connect or no-function pins - must be tied to VSS per datasheet to ensure stable operation and avoid floating inputs.
2, 3	VSS	Dual ground terminals - reduce ground impedance and improve noise immunity in battery-backed timing circuits.
4	SCL	I²C clock input - requires external pull-up resistor; compatible with standard 400 kHz I²C timing budgets.
5	SDA	I²C bidirectional data line - open-drain structure mandates external pull-up; supports multi-master arbitration.
6	VCC	Main supply input - powers internal logic and oscillator; triggers automatic switchover to VBAT when falling below VPFD.
7	VBAT	Battery backup supply - maintains RTC and SRAM during main power loss; accepts 2.0–5.5 V lithium or supercapacitor sources.
8	IRQ/FT/OUT/SQW	Multi-function open-drain output - delivers alarm interrupt, frequency test signal, general-purpose output, or programmable square wave (priority order applies).
16, 17	VSS	Additional ground connections - enhance thermal dissipation and high-frequency decoupling for embedded crystal stability.

Key Features

Feature	Design Value
Embedded Crystal Oscillator	32.768 kHz crystal integrated into SOX18 package with 12.5 pF load capacitance - eliminates layout sensitivity, reduces BOM count, and improves long-term frequency stability.
Power-Down Time-Stamp (HT bit)	Hardware-tracked elapsed time during battery-only operation - enables precise uptime accounting and predictive maintenance in edge devices.
Software Clock Calibration	Adjustable calibration register (±127 ppm range) - compensates for crystal drift due to temperature without external compensation circuitry or firmware lookup tables.
Oscillator Fail Detection	Dedicated hardware monitor with fail flag and interrupt - alerts host MCU of crystal stoppage before timekeeping corruption occurs, enabling early diagnostics.
Battery Low Flag	Internal voltage comparator flags low VBAT condition - allows graceful shutdown or alert before RTC data loss, improving system reliability.

Applications

Smart Energy Metering

Industrial PLC HMI

Use Scenario: Utility-grade electricity meters logging kWh consumption with tamper-proof timestamps across power outages.

IC Role / Device Role / Timing Role: Primary time-of-day source and calendar engine; maintains accurate billing intervals using battery-backed registers and century-aware leap-year logic.

Use Value: Ensures regulatory-compliant timestamping integrity during grid instability, with embedded crystal eliminating timing variance from PCB layout or capacitor tolerance.

Use Scenario: Human-machine interface modules in programmable logic controllers logging operator actions, fault events, and maintenance cycles.

IC Role / Device Role / Timing Role: Standalone RTC subsystem providing ISO 8601-compliant timestamps independent of PLC scan cycle or firmware execution state.

Use Value: Guarantees deterministic event sequencing even during CPU reset or firmware update, enabled by automatic VCC-to-VBAT switchover and HT-bit time-stamp.

Medical Infusion Pump Logging

Transportation Telematics Unit

Use Scenario: Battery-powered infusion pumps recording drug delivery start/stop times, dosage history, and alarm events for FDA audit trails.

IC Role / Device Role / Timing Role: Certified time source with battery-fail detection and power-down time-stamp - meets IEC 62304 traceability requirements for Class C software.

Use Value: Provides verifiable, non-volatile time metadata for every therapeutic action, with oscillator fail interrupt preventing undetected clock stoppage.

Use Scenario: In-vehicle telematics units capturing GPS position, CAN bus diagnostics, and crash-event timestamps across ignition cycles.

IC Role / Device Role / Timing Role: Synchronized time base for correlating sensor data streams; generates precise 1 Hz square wave for GPS PPS alignment.

Use Value: Enables sub-second temporal correlation between GNSS, IMU, and vehicle network data - critical for accident reconstruction and fleet analytics.

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
DS3231SN#T&R	TCXO-based ±2 ppm accuracy vs. M41T81SMY6E's crystal oscillator ±20 ppm; higher cost; no embedded crystal - requires external 32.768 kHz source.	Preferred where absolute time accuracy >1 ppm/year is required (e.g., precision instrumentation); lacks power-down time-stamp (HT bit).	Select DS3231 when long-term drift compensation outweighs BOM simplicity and cost; verify external crystal layout compliance.
PCF8563T/5,118	Lower power (0.25 µA battery current) but no embedded crystal, no watchdog timer, no software calibration, and no century bit support.	Suitable for basic timekeeping in consumer wearables; cannot replace M41T81SMY6E in century-aware industrial logging or watchdog-reliant safety systems.	Choose PCF8563 only for cost-sensitive, non-critical applications lacking alarm repeat modes, century handling, or fail-safe watchdog requirements.

Compared with DS3231SN#T&R and PCF8563T/5,118, the M41T81SMY6E uniquely combines embedded crystal packaging, century-aware calendar, hardware time-stamp on power loss, and integrated watchdog - making it optimal for industrial field devices needing robust, self-contained timekeeping without external timing components or firmware calibration overhead.

Availability

M41T81SMY6E is available at Aetrix Electronics and suitable for smart energy metering, industrial PLC HMIs, medical infusion pump logging, and transportation telematics units requiring stable component supply across extended product lifecycles.

Supply support for M41T81SMY6E includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in microcontrollers, analog ICs, power management, and timing solutions for industrial, automotive, and IoT markets.

The M41T81SMY6E belongs to ST's serial RTC product line, engineered for high-reliability, battery-backed timekeeping in harsh environments - emphasizing integration (embedded crystal), autonomy (watchdog/alarm), and longevity (10+ year coin-cell operation).

FAQ

What is the I²C slave address for the M41T81SMY6E?

The fixed 7-bit I²C slave address is 0xD0 (1101000b), with R/W bit appended during transmission. This address is hardwired and not configurable. Communication follows standard I²C protocol with START/STOP conditions, ACK/NACK handshaking, and automatic address pointer incrementation across all 20 registers.

Does the M41T81SMY6E require external load capacitors for the crystal?

No. The M41T81SMY6E integrates 12.5 pF load capacitance internally for its embedded 32.768 kHz crystal. No external capacitors are needed - this eliminates layout-dependent frequency drift and reduces bill-of-materials count, directly improving production yield and long-term timing stability.

How does the power switchover mechanism work between VCC and VBAT?

The device monitors VCC against VPFD (2.5–2.7 V). When VCC falls below VPFD, it terminates ongoing I²C access, resets the address counter, and switches to VBAT within microseconds. If VBAT > VPFD, switchover occurs at VPFD; if VBAT < VPFD, switchover occurs when VCC drops below VBAT - ensuring uninterrupted timekeeping during brownouts.

Can the M41T81SMY6E generate a 1 Hz square wave output?

Yes. The IRQ/FT/OUT/SQW pin supports programmable square wave output at frequencies including 1 Hz, 32.768 kHz, 1024 Hz, and 32 Hz (per Table 4 in datasheet). Configuration is done via the SQWEN bit and frequency select bits in register 19h - enabling direct drive of LEDs, microcontroller wake-up signals, or GPS PPS synchronization.

M41T81SMY6E Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 18-SOX, 18-SOIC with Crystal (7.5mm Width)

Packaging:: Tube

Product Status:: Obsolete

Programmable:: Not Verified

Type:: Clock/Calendar

Features:: Alarm, Leap Year, Square Wave Output, Watchdog Timer

Memory Size:: -

Time Format:: HH:MM:SS:hh (24 hr)

Date Format:: YY-MM-DD-dd

Interface:: I2C, 2-Wire Serial

Voltage - Supply:: 2.7V ~ 5.5V

Voltage - Supply, Battery:: 2V ~ 3.5V

Current - Timekeeping (Max):: 100µA @ 2.7V ~ 5.5V

Operating Temperature:: -40°C ~ 85°C

Mounting Type:: Surface Mount

Grade:: -

Qualification:: -

Supplier Device Package:: 18-SOX

M41T81SMY6E FAQ

1.How can I place an order for M41T81SMY6E through Aetrix?

Please submit a Request for Quotation (RFQ) for M41T81SMY6E on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for M41T81SMY6E reliable?

The price and inventory of M41T81SMY6E are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41T81SMY6E is usually 5 days.

3.What payment methods are accepted for M41T81SMY6E?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41T81SMY6E transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for M41T81SMY6E?

M41T81SMY6E orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your M41T81SMY6E order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for M41T81SMY6E?

For technical support, including M41T81SMY6E datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41T81SMY6E requirements.

6.How does Aetrix verify that M41T81SMY6E is sourced from the original manufacturer or authorized distributors?

All M41T81SMY6E products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that M41T81SMY6E meets industry standards.

7.What is the process for return or replacement of M41T81SMY6E?

All M41T81SMY6E units undergo pre-shipment inspection (PSI). If there is an issue with M41T81SMY6E, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The M41T81SMY6E part is unused and in its original packaging.

Return procedure for M41T81SMY6E:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

Tech Hub

2026-09-03 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…

2026-09-01 74HC595 Pinout, Timing, Output Current, and Applications

The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…

2026-08-18 Operational Amplifier (Op Amp): Basics, Configurations, Feedback and Applications

Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…

2026-08-14 Jumper Cables: How to Use, Connect and Choose Them Safely

Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…