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STMicroelectronics M41T81SMY6F
- Part No.:
- M41T81SMY6F
- Manufacturer:
- STMicroelectronics
- Category:
- Real Time Clocks
- Package:
- 18-SOX, 18-SOIC with Crystal (7.5mm Width)
- Datasheet:
-
M41T81SMY6F.pdf
- Description:
- IC RTC CLK/CALENDAR I2C 18SOX
- Quantity:
- Payment:
- Shipping:
Inventory:3,896
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Product details
Overview
M41T81SMY6F from STMicroelectronics is a serial real-time clock (RTC) IC with integrated 32.768 kHz crystal, I²C interface (400 kHz), ultra-low battery current (0.6 µA typ), and full calendar functionality (century/year/month/date/hour/minute/second/tenths-hundredths) in BCD format. It operates from 2.0–5.5 V, supports automatic VCC-to-VBAT switchover, and delivers timekeeping during main power loss in industrial control panels and embedded metering systems.
For engineers reviewing the M41T81SMY6F datasheet, M41T81SMY6F pinout, M41T81SMY6F application, or M41T81SMY6F equivalent, this page provides verified pin functions, alarm/wdog/square-wave timing roles, battery-fail detection behavior, and validated alternatives for backup-power RTC designs requiring ±20 ppm accuracy over –40 to +85 °C.
Technical Context
The M41T81SMY6F implements a fully autonomous BCD-based calendar engine with leap-year correction (valid through year 2100), oscillator fail detection, and hardware-calibrated timekeeping via programmable trim bits. Its I²C slave interface uses fixed address 0xD0h and supports sequential read/write across 20 registers - including 8 clock, 5 alarm, 1 calibration, 1 watchdog, and 1 square-wave control register.
Power management includes dual switchover thresholds: VSO (switchover voltage) triggers automatic VCC→VBAT transition, while VPFD (power-fail detect) halts bus access and resets the address counter to prevent corruption. The embedded crystal SOIC package (SOX18) integrates 12.5 pF load capacitance, enabling stable oscillation even with high-series-resistance crystals.
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 CR2032 button cell life beyond 10 years in backup mode. |
| Operating Voltage | VCC = 2.0–5.5 V; VBAT ≥ 2.5 V - supports wide-input industrial power rails and standard lithium coin cells. |
| Accuracy | ±20 ppm over –40 to +85 °C - achieved via factory-trimmed oscillator and software calibration register (±1024 ppm adjustment range). |
| Alarm Function | Programmable daily/monthly/weekly alarms with interrupt output - valid during battery backup, enabling wake-from-sleep event triggering. |
| Watchdog Timer | 62.5 ms to 128 s range, independent of main clock - provides system-level fault recovery without MCU intervention. |
| Temperature Range | –40 °C to +85 °C - qualified for extended-temperature industrial and automotive cabin applications. |
| Square Wave Output | 1 Hz / 32.768 kHz / 1.024 kHz / 32 Hz selectable - drives external timing circuits or status indicators directly from IRQ/FT/OUT/SQW pin. |
Pinout & Package
Package: SOX18 - 18-pin, 300-mil plastic small outline integrated-circuit package with embedded 32.768 kHz crystal (no external crystal required).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4, 5, 6, 7, 13, 14, 15, 16, 17, 18 | NC/NF | No-connect or no-function pins - must be tied to VSS per datasheet; internal shorts exist between pins 2–3 and 16–17. |
| 8 | SCL | I²C clock input - requires external pull-up resistor; accepts standard 400 kHz timing. |
| 9 | SDA | I²C bidirectional data line - open-drain structure; requires external pull-up resistor. |
| 10 | VSS | Ground reference - primary return path for all analog/digital circuitry and crystal oscillator. |
| 11 | VBAT | Battery supply input - powers RTC during main power loss; minimum 2.5 V required for retention. |
| 12 | VCC | Main supply input - powers device during normal operation; switchover to VBAT occurs at VSO threshold. |
| 18 | IRQ/FT/OUT/SQW | Multi-function open-drain output - delivers alarm interrupt, frequency test signal, or programmable square wave (highest priority: SQW). |
Key Features
| Feature | Design Value |
|---|---|
| Embedded Crystal Oscillator | 32.768 kHz crystal with integrated 12.5 pF load capacitance - eliminates external crystal and matching caps, reducing BOM count and layout sensitivity. |
| Power-Fail Detection | Dedicated VPFD comparator halts I²C access and resets address pointer when VCC drops below threshold - prevents register corruption during brownout. |
| Time-Stamp on Power-Down | HT (Hour Tens) bit records elapsed time in battery mode - enables accurate uptime accounting across power cycles. |
| Software Clock Calibration | 7-bit trim register adjusts oscillator frequency by ±1024 ppm - compensates for temperature-induced crystal drift without hardware changes. |
| Battery Low Flag | Dedicated flag bit indicates VBAT < VPFD - allows host MCU to log low-battery condition before data retention fails. |
Applications
| Smart Energy Metering | Industrial PLC HMI Panels |
|---|---|
|
Use Scenario: Utility-grade electricity meters requiring tamper-resistant, decade-long timekeeping under variable AC line conditions and battery backup. IC Role / Device Role / Timing Role: Primary RTC providing timestamped kWh logging, tariff switching, and firmware update scheduling with century-aware calendar. Use Value: Embedded crystal ensures ±20 ppm accuracy across –25 to +70 °C operating range; HT bit enables precise outage duration tracking for grid analytics. |
Use Scenario: Human-machine interface terminals in factory automation systems needing reliable time-of-day display, event logging, and scheduled maintenance alerts. IC Role / Device Role / Timing Role: Standalone calendar engine synchronizing UI timestamps, alarm notifications, and diagnostic log entries independent of PLC controller uptime. Use Value: Alarm interrupt wakes MCU from deep sleep to refresh display or transmit logs; SQW output drives LED blink patterns without CPU overhead. |
| Medical Infusion Pumps | Building Automation Gateways |
|
Use Scenario: Battery-powered infusion devices requiring FDA-compliant audit trails with traceable timestamps for dose delivery and error events. IC Role / Device Role / Timing Role: Certified time source maintaining BCD-formatted date/time with leap-year correction and battery-fail flag for regulatory reporting. Use Value: Power-down time-stamp (HT bit) validates exact duration of battery-only operation; calibration register supports post-manufacturing accuracy tuning. |
Use Scenario: HVAC controllers and lighting gateways managing occupancy schedules, energy tariffs, and firmware OTA updates across seasonal temperature swings. IC Role / Device Role / Timing Role: Central timekeeper coordinating zone-specific heating/cooling cycles, daylight savings transitions, and secure update windows. Use Value: Watchdog timer (62.5 ms–128 s) recovers hung communication stacks; I²C interface allows shared bus with sensor ICs and EEPROMs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar real-time clock applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| DS3231M | TCXO-based ±2 ppm accuracy; higher cost; no embedded crystal - requires external 32.768 kHz TCXO. | Used where sub-second annual drift is critical (e.g., precision test equipment); lacks HT bit for power-down time-stamping. | Select DS3231M only if ±2 ppm stability over temperature is mandatory and board space permits external TCXO. |
| PCF8563 | Lower-cost I²C RTC; no embedded crystal; no watchdog timer; no software calibration; 1 µA battery current. | Targeted at cost-sensitive consumer electronics; unsuitable for applications requiring alarm persistence during backup or calibrated long-term accuracy. | Choose PCF8563 only for basic timekeeping in non-critical, short-lifecycle products where BOM cost dominates performance. |
Compared with DS3231M and PCF8563, the M41T81SMY6F uniquely combines embedded crystal, software calibration, power-down time-stamp, and watchdog in a single SOX18 package - making it optimal for industrial designs needing robust, self-contained RTC functionality without external timing components or calibration hardware.
Availability
M41T81SMY6F is available at Aetrix Electronics and suitable for smart metering, industrial HMI panels, medical infusion pumps, and building automation gateways requiring stable component supply across multi-year production cycles.
Supply support for M41T81SMY6F 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, Switzerland, designing and manufacturing microcontrollers, power management ICs, sensors, and timing solutions for industrial, automotive, and consumer markets.
The M41T81SMY6F belongs to ST's serial RTC product line, engineered specifically for battery-backed timekeeping in space-constrained industrial systems where reliability, long-term accuracy, and minimal external components are essential.
FAQ
What is the function of the HT bit in the M41T81SMY6F?
The HT (Hour Tens) bit is a dedicated power-down time-stamp flag that latches the number of hours elapsed while operating solely on VBAT. It increments only during battery backup mode and remains readable after VCC restoration, enabling precise outage duration measurement for system diagnostics and compliance reporting.
Does the M41T81SMY6F require an external crystal?
No. The M41T81SMY6F in SOX18 package integrates a 32.768 kHz crystal and 12.5 pF load capacitance internally. No external crystal, capacitors, or trimming components are needed - simplifying layout and improving long-term frequency stability against PCB stress and temperature gradients.
How does the alarm function behave during battery backup mode?
The alarm remains fully operational during battery backup: it monitors clock registers continuously and asserts the IRQ/FT/OUT/SQW pin upon match, even with VCC removed. This enables wake-up of sleeping microcontrollers or activation of backup indicators without main power.
What is the purpose of the VPFD and VSO thresholds?
VPFD (Power-Fail Detect) is the voltage threshold below which the device halts I²C communication and resets its internal address pointer to prevent data corruption. VSO (Switchover Voltage) is the threshold at which the device automatically switches power source from VCC to VBAT - ensuring uninterrupted timekeeping during brownouts.
M41T81SMY6F Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 18-SOX, 18-SOIC with Crystal (7.5mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- 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
M41T81SMY6F FAQ
1.How can I place an order for M41T81SMY6F through Aetrix?
Please submit a Request for Quotation (RFQ) for M41T81SMY6F 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 M41T81SMY6F reliable?
The price and inventory of M41T81SMY6F are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41T81SMY6F is usually 5 days.
3.What payment methods are accepted for M41T81SMY6F?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41T81SMY6F transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for M41T81SMY6F?
M41T81SMY6F orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your M41T81SMY6F 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 M41T81SMY6F?
For technical support, including M41T81SMY6F datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41T81SMY6F requirements.
6.How does Aetrix verify that M41T81SMY6F is sourced from the original manufacturer or authorized distributors?
All M41T81SMY6F 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 M41T81SMY6F meets industry standards.
7.What is the process for return or replacement of M41T81SMY6F?
All M41T81SMY6F units undergo pre-shipment inspection (PSI). If there is an issue with M41T81SMY6F, 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 M41T81SMY6F part is unused and in its original packaging.
Return procedure for M41T81SMY6F:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
M41T81SMY6F Tags
-
MCP7940N-I/SN
Microchip Technology
-
MCP7940MT-I/MNY
Microchip Technology
-
PCF85063ATL/1,118
NXP USA Inc.
-
MCP7940NT-I/SN
Microchip Technology
-
MCP7940NT-I/MS
Microchip Technology
-
MCP7940N-I/MS
Microchip Technology
-
PCF85063AT/AY
NXP USA Inc.
-
PCF85063TP/1Z
NXP Semiconductors
-
PCF85063ATT/AJ
NXP USA Inc.
-
MCP7940NT-E/SN
Microchip Technology
-
MCP7940NT-I/MNY
Microchip Technology
-
MCP79400T-I/SN
Microchip Technology
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