M41T81SM6F - Serial RTC 2.7-5.5V I2C 8-SOIC | STMicroelectronics
Teilenummer: M41T81SM6F ✓ Aktiv| Menge | Stückpreis | Gesamt |
|---|---|---|
| 1 | $2.85 | $2,85 |
| 10 | $2.55 | $25,50 |
| 100 | $2.18 | $218,00 |
| 500 | $1.86 | $930,00 |
| 1.000 | $1.55 | $1.550,00 |
M41T81SM6F Übersicht
A Real-Time Clock (RTC) is a dedicated integrated circuit that keeps track of wall-clock time even when the main system is powered down. RTCs sit at the bottom of the timekeeping hierarchy: RTC -> clock/calendar IC -> clock and timing -> semiconductor. They are essential wherever a system must maintain accurate time/date stamping across power cycles, such as data loggers, metering equipment, and industrial controllers. The M41T81S is one of the few RTCs that integrates both the 32.768 kHz crystal interface and the compensation circuitry in a single 8-pin package, reducing BOM and board area.
Key features include 2.7 V to 5.5 V single-supply operation, low typical current consumption for battery-backed operation, programmable alarm and watchdog functions, automatic leap-year compensation through year 2099, and a software clock calibration function that can compensate crystal aging in 5 ppm steps. The I2C slave address is fixed at 0x68 with the A0 pin grounded.
Internally, the M41T81S combines an external 32.768 kHz crystal oscillator circuit with a binary-coded decimal (BCD) counter chain. Eight bytes of on-chip SRAM back the clock/calendar registers and are accessed via the standard I2C protocol. The device supports both 100 kHz Standard-mode and 400 kHz Fast-mode I2C, making it compatible with most microcontroller families. The byte-wide register map follows the ST M41Txx family convention for drop-in software portability.
Typical applications include industrial automation controllers, point-of-sale terminals, metering (electricity/water/gas), data loggers, medical devices requiring timestamped events, automotive telematics and infotainment subsystems, security and access-control panels, and any battery-backed embedded system needing persistent wall-clock time.
When designing with the M41T81SM6F, place the 32.768 kHz crystal within 5 mm of the OSCIN/OSCOUT pins and guard those traces with a ground ring to minimize stray capacitance. Provide a backup battery (typically a 3 V coin cell) on VCC with a series Schottky or Schottky-plus-resistor OR-ing network so the RTC domain remains powered during main-rail outages. Use 100 nF decoupling close to VCC and observe the I2C pull-up sizing rules for the chosen bus speed.
This page consolidates distributor pricing, parametric drop-in alternatives, and practical layout notes that complement the manufacturer datasheet, giving engineers a single reference for sourcing and designing in the M41T81SM6F.
Drop-in-Alternativen für M41T81SM6F – gleiches Gehäuse, Pin-kompatibel. Bauteile mit anderem Gehäuse, die eine PCB-Überarbeitung erfordern, sind ausgeschlossen.
Schnellvergleichstool – Wählen Sie Alternativbauteile für den Direktvergleich:
M41T81SM6
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
M41T80M6F
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
M41T82RM6F
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
M41T81S-SMD
✅ Drop-In ⚠️ Spezifikationen ungeprüft📋 Referenzalternative (nicht im Katalog)
DS1338Z-33+
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
PCF8563T/5
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
M41T81SM6F Technische Daten
| Manufacturer | STMicroelectronics |
| Product Type | Serial Real-Time Clock (RTC) |
| Funktion | Clock/Calendar with Alarms |
| Serial Interface | I2C (2-Wire), 400 kHz Fast-mode |
| Supply Voltage (VCC) | 2.7 V to 5.5 V |
| Timekeeping Format | BCD (binary-coded decimal) |
| Timekeeper Registers | Tenths of seconds, seconds, minutes, hours, day, date, month, year, century |
| Internal SRAM | 64 bytes (64x8) |
| Internal Oscillator Frequency | 32.768 kHz (external crystal controlled) |
| Betriebstemperaturbereich | -40 C to +85 C |
| Gehäuse / Bauform | 8-SOIC (0.154 inch / 3.90 mm width) |
| Montageart | Surface Mount |
| Programmable Alarms | Yes (date/day/time alarm) |
| Watchdog / SQW Output | Yes |
| Leap Year Compensation | Automatic through 2099 |
| RoHS-Status | Compliant |
| MSL-Level | 1 (unlimited) |
M41T81SM6F Pin-Konfiguration
| Pin 1 | OSCI — 32.768 kHz oscillator input (crystal connection) |
| Pin 2 | OSCO — 32.768 kHz oscillator output (crystal connection) |
| Pin 3 | INTOUT — Interrupt/active-low reset output (open-drain) |
| Pin 4 | VCC — Supply voltage (2.7 V to 5.5 V); connect to backup battery via trickle charger |
| Pin 5 | SDA — I2C serial data (open-drain; external pull-up required) |
| Pin 6 | SCL — I2C serial clock (open-drain; external pull-up required) |
| Pin 7 | FT/OUT — Frequency test / square-wave output (32.768 kHz, 32 kHz, or 1 Hz) |
| Pin 8 | GND — Ground |
Typische Anwendungen
M41T81SM6F ist geeignet für 7 Anwendungs: Industrial Automation Controllers, Data Loggers and Measurement Equipment, Point-of-Sale (POS) Terminals, Utility Meters (Electricity / Water / Gas), Medical Devices with Time-Stamped Events, Automotive Infotainment and Telematics, Security and Access Control Panels.
Industrial Automation Controllers
The M41T81SM6F fits industrial PLCs, HMI panels, and motor-control boards where persistent wall-clock time is required for event logging and shift scheduling. Its 2.7-5.5 V supply matches 24 V->5 V or 24 V->3.3 V industrial rails, and the integrated trickle charger supports direct backup-battery connection. The 64 bytes of SRAM double as non-volatile parameter storage during power events, while BCD-coded registers simplify time arithmetic in legacy firmware. Compared to software RTC emulation, the dedicated hardware oscillator delivers +/-2 minute/year accuracy and immune-to-system-load timing.
Empfohlen
Data Loggers and Measurement Equipment
For data loggers, the M41T81SM6F provides a hardware-secure timestamp that survives power cycling, ensuring accurate sample-time tagging even when the main MCU resets. Its 400 kHz Fast-mode I2C allows high-speed time reads without burdening the host processor, and the on-chip alarm can wake the logger at preset intervals for low-duty-cycle sampling. The 32.768 kHz external crystal interface permits precision time base calibration, important when correlating multi-instrument data. Industrial temperature grade (-40 to +85 C) supports outdoor and factory-floor deployment.
Empfohlen
Point-of-Sale (POS) Terminals
The M41T81SM6F is well suited to POS terminals where each transaction must be timestamped for auditing and tax-compliance reasons. The integrated watchdog function detects host-MCU lockups and forces a reset, while the alarm interrupt can wake the terminal for end-of-day batch close. The 8-SOIC footprint keeps the analog/digital mixed-signal layout simple, and the I2C bus can be shared with the secure element and EEPROM. Low current draw preserves coin-cell backup across power outages, keeping legal-time accuracy through retail trading hours.
Empfohlen
Utility Meters (Electricity / Water / Gas)
In electricity, water, and gas metering, the M41T81SM6F delivers tamper-resistant wall-clock time and supports time-of-use (TOU) billing tariffs by generating interrupts at programmable tariff boundaries. The wide 2.7-5.5 V supply range accommodates battery-powered meters that step up from a 3.6 V lithium thionyl-chloride cell. With its 64 bytes of SRAM and on-chip trickle charger, the part can keep time for 10+ years on a single primary cell - critical for non-replaceable meter deployments - while the industrial -40 to +85 C range covers outdoor cabinet temperatures.
Empfohlen
Medical Devices with Time-Stamped Events
Patient monitors, infusion pumps, and laboratory analyzers benefit from the M41T81SM6F's hardware-backed timekeeping for regulatory traceability (FDA 21 CFR Part 11 / EU Annex 11). The BCD register format outputs human-readable time directly, simplifying log files for clinical review. The integrated watchdog ensures the host MCU cannot leave the time without supervision, and the -40 to +85 C industrial range covers most clinical-environment thermal envelopes. Low quiescent current is essential in battery-powered portable diagnostic devices.
Empfohlen
Automotive Infotainment and Telematics
Although the M41T81SM6F is not AEC-Q100 qualified, it is widely used in non-safety automotive subsystems such as infotainment head units, telematics control units (TCUs), and event-data recorders where wall-clock time must persist through battery disconnects. The 32.768 kHz crystal reference delivers tighter timekeeping than the vehicle's CAN time-master, and the 8-SOIC footprint suits space-constrained behind-dash PCBAs. Combined with a GNSS receiver, the M41T81S provides backup time during satellite outages and tunnels, while the alarm function wakes the TCU for periodic data uploads.
Empfohlen
Security and Access Control Panels
The M41T81SM6F's alarm and watchdog features make it a fit for intrusion-detection panels, where each door event must be timestamped and the host MCU must be supervised. The 8-SOIC pinout allows retrofit into existing panel designs that already use ST M41Txx RTCs. Wide supply tolerance supports battery-backup during AC mains failure, and BCD time format simplifies printout on text LCDs. The integrated trickle charger can recharge the NiMH backup cell without external components, reducing BOM cost in volume security installations.
Empfohlen
Zusammenfassung der empfohlenen Produkte
Technische Referenzdaten für M41T81SM6F – Vergleich, Designhinweise und Compliance-Informationen.
Auswahlhilfe
Vergleich mit Alternativen
| Parameter | Dieses Produkt | M41T81SM6 | M41T80M6F | M41T82RM6F | DS1338Z-33+ | PCF8563T/5 |
|---|---|---|---|---|---|---|
| Brand | STMicroelectronics | STMicroelectronics | STMicroelectronics | STMicroelectronics | Analog Devices | NXP Semiconductors |
| Package | 8-SOIC | 8-SOIC - same | 8-SOIC - same | 8-SOIC - same | 8-SOIC - same | 8-SOIC - same |
| Supply Voltage | 2.7 V to 5.5 V | 2.7 V to 5.5 V | 2.7 V to 5.5 V | 2.7 V to 5.5 V | 3.0 V to 5.5 V | 1.0 V to 5.5 V |
| I2C Address | 0x68 | 0x68 | 0x68 | 0x68 | 0x68 | 0x51 |
| Max I2C Speed | 400 kHz Fast-mode | 400 kHz | 100 kHz Standard-mode | 400 kHz | 400 kHz | 400 kHz |
| Crystal Type | External 32.768 kHz | External | External | Internal resonator | External | External |
| User SRAM / NV RAM | 64 bytes | 64 bytes | 64 bytes | 236 bytes | 56 bytes NV | None |
| Watchdog / Alarm | Yes / Yes | Yes / Yes | No / Yes | Yes / Yes | No / No | No / Yes |
| Operating Temperature | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C |
Wichtigste Unterscheidungsmerkmale
- Industry-standard M41T81 register map with wide third-party firmware support (vs. PCF8563T/5)
- Integrated trickle charger and watchdog timer in 8-SOIC (vs. DS1338Z-33+)
- External crystal architecture gives highest timing accuracy and calibration headroom (vs. M41T82RM6F)
Designhinweise
Place the 32.768 kHz crystal within 5 mm of the OSCI and OSCO pins (pins 1 and 2 of the 8-SOIC). Keep the crystal traces short, symmetric, and surrounded by a grounded guard ring to minimize stray capacitance. Avoid routing noisy digital signals (SDA/SCL transitions, MCU GPIOs) directly beneath or beside the crystal traces, as capacitive coupling will detune the oscillator and pull the time base off-frequency. Load capacitors (typically 12.5 pF each) must be sized to match the crystal's load capacitance rating - mis-sizing is the most common cause of +/-10 minute/day timekeeping error.
The M41T81SM6F has an integrated trickle charger on VCC that can recharge a backup NiMH or super-capacitor cell. Configure the trickle-charge resistor (typically 2 kohm to 30 kohm, software-selectable in the register map) based on the chemistry and capacity of the backup source. For lithium primary cells (CR2032), disable the trickle charger by clearing the TCS bit, as recharging a primary lithium cell is unsafe. Use a Schottky diode OR-ing network from main 5 V and backup battery to VCC to prevent reverse current into the main rail.
I2C SDA (pin 5) and SCL (pin 6) are open-drain outputs requiring external pull-ups. For 400 kHz Fast-mode operation on a 3.3 V bus, use 1 kohm to 4.7 kohm pull-ups sized for the total bus capacitance; for 5 V systems with multiple slaves, 4.7 kohm is a typical starting point. Estimate: rise time must be <300 ns for Fast-mode. Place pull-ups close to the M41T81SM6F if it is the slowest edge device, or close to the bus midpoint for multi-drop buses. Decouple VCC (pin 4) with a 100 nF ceramic placed within 3 mm of the package.
Three common pitfalls: (1) reading time before the oscillator has stabilized - allow 1-2 seconds after VCC > 2.7 V before reading the ST (seconds) register, otherwise the part returns all-ones; (2) forgetting to clear the OF (oscillator fail) flag after initial power-up - this flag is sticky and will set the FT/OUT pin to 32.768 kHz test mode; (3) writing to the HT (halt update) bit during the I2C transaction can corrupt time registers - read the HT bit, wait until it is clear, perform your multi-byte read, then set HT again if desired.
Compliance-Informationen
RoHS and REACH compliant per ST product page. The M41T81SM6F is not AEC-Q100 qualified; for AEC-Q100 automotive RTC applications, evaluate the M41T83SQ or similar parts explicitly listed as automotive-grade.
