STMicroelectronics M41T82RM6F

Overview

M41T82RM6F from STMicroelectronics is an I²C real-time clock (RTC) IC in 8-lead SOIC package, providing timekeeping with BCD-encoded calendar registers (century, year, month, date, day, hour, minute, second, tenths/hundredths), automatic leap-year correction, and battery switchover at VCC < 2.93 V. It delivers ±5 ppm factory-calibrated accuracy after two reflows, ultra-low 365 nA battery current, and operates from 2.0 V to 5.5 V. Used in industrial control panels for timestamped event logging under intermittent power.

For engineers reviewing the M41T82RM6F datasheet, M41T82RM6F pinout, M41T82RM6F application, or M41T82RM6F equivalent, key selection criteria include battery-backed SRAM retention, I²C alarm interrupt reliability during backup mode, oscillator fail detection, and compatibility with 32.768 kHz external crystal layout constraints.

Technical Context

The M41T82RM6F implements a dedicated 32.768 kHz crystal oscillator with internal load capacitance tuning (analog calibration) and periodic counter correction (digital calibration), enabling post-reflow accuracy optimization. Its power-sense circuit triggers automatic switchover to VBAT when VCC drops below 2.93 V, with built-in reset generation on power-up (trec = 250 ms).

It uses a fixed-reference switchover architecture (VSO = VRST), supports I²C 400 kHz protocol with open-drain SDA/SCL, and includes a programmable alarm with interrupt output routed to the FT/RST pin - the sole multifunction terminal enabling both frequency test and reset assertion.

Key Specifications

Pinout & Package

Package: 8-lead SOIC (4.90 mm × 3.90 mm), RoHS-compliant, surface-mount.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1307+ and PCF8563, the M41T82RM6F provides superior long-term stability through dual-stage calibration, mandatory century-bit support for Y2100 readiness, and integrated oscillator health monitoring - critical for unattended industrial logging systems.

Availability

M41T82RM6F is available at Aetrix Electronics and suitable for industrial data loggers, smart energy meters, medical infusion pumps, and building HVAC controllers requiring stable component supply across multi-year production cycles.

Supply support for M41T82RM6F 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 designing and manufacturing microcontrollers, power management ICs, sensors, and timing solutions for industrial, automotive, and consumer markets.

The M41T82 belongs to ST's serial RTC product line, engineered specifically for high-reliability, battery-backed timekeeping in space-constrained industrial equipment where accuracy, longevity, and diagnostic capability are non-negotiable.

FAQ

What crystal specifications are required for M41T82RM6F?

The M41T82RM6F requires a standard 32.768 kHz tuning-fork crystal with load capacitance of 12.5 pF, series resistance ≤50 kΩ, and drive level ≤1 µW. ST recommends ECS-.327-12.5-34Q or equivalent; PCB layout must minimize trace length between XI/XO pins and crystal terminals to avoid start-up failure.

Does M41T82RM6F support I²C clock stretching?

No, the M41T82RM6F does not support I²C clock stretching. It operates strictly as a standard I²C slave with fixed timing parameters: tLOW ≥ 1.3 µs, tHIGH ≥ 0.6 µs, and tSU;STA ≥ 4.7 µs. Host MCU must adhere to these limits; violating them may cause ACK failures or register access corruption.

How is the century bit implemented in the M41T82RM6F calendar?

The M41T82RM6F encodes the century in bits 7–6 of the hour register (address 0x03), using binary values: 00 = 20xx, 01 = 21xx, 10 = 22xx, 11 = 23xx. This explicit two-bit field ensures unambiguous Y2100 handling and eliminates software-based century inference errors common in legacy RTCs.

Can the FT/RST pin be used simultaneously for reset generation and alarm signaling?

No - the FT/RST pin operates in mutually exclusive modes: it asserts a reset pulse during power-up (trec = 250 ms) or outputs alarm interrupt during normal operation, but never both concurrently. The alarm function is active only when VCC ≥ 2.93 V and the alarm enable bit is set; reset is automatic and unconditional on power application.