STMicroelectronics M41T56M6F

Overview

M41T56M6F from STMicroelectronics is a serial real-time clock (RTC) IC with integrated 32.768 kHz crystal oscillator, 56-byte NVRAM, and I²C interface operating at 100 kHz. It provides full BCD-coded timekeeping (seconds to century), automatic leap-year compensation, and ultra-low battery current of 450 nA - enabling decade-long data retention on a 3 V lithium coin cell in industrial metering and backup power systems.

For engineers reviewing the M41T56M6F datasheet, M41T56M6F pinout, M41T56M6F application, or M41T56M6F equivalent, key selection considerations include battery-switchover voltage (VSO = 2.5 V), software calibration resolution (±2 ppm at 25 °C), I²C timing compliance (tLOW ≥ 4.7 µs), and SO8 package thermal performance (–40 °C to 85 °C).

Technical Context

The M41T56M6F implements a slave-mode I²C interface with fixed 7-bit address 0xD0, supporting sequential read/write access across 64 bytes (8 clock registers + 56 NVRAM). Its oscillator uses internal 12.5 pF load capacitance for stable 32.768 kHz operation even with high-series-resistance crystals.

Power management includes automatic VCC-to-VBAT switchover at 2.5 V, write-protection activation during brown-out (VPFD threshold), and 250 ms clock-update hold during register reads to prevent read-modify-write corruption. Calibration occurs at the ÷256 stage via five-bit signed offset (–15 to +16 counts) applied to the divider chain.

Key Specifications

Pinout & Package

Supplied in an 8-lead, 150-mil plastic SOIC (SO8) package compliant with RoHS and lead-free second-level interconnect requirements.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar RTC with NVRAM applications.

Compared with DS1337+T&R and PCF8563T, the M41T56M6F delivers superior long-term accuracy through factory-trimmed oscillator and software calibration, larger NVRAM for extended logging, and reduced system-level design complexity via integrated crystal drive.

Availability

M41T56M6F is available at Aetrix Electronics and suitable for smart metering, industrial HMI, medical infusion pumps, and building automation controllers requiring stable component supply across multi-year production cycles.

Supply support for M41T56M6F 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 analog, MCU, power, and sensor solutions for industrial, automotive, and consumer markets.

The M41T56 belongs to ST's real-time clock product line, engineered specifically for high-reliability, battery-backed timekeeping in industrial and medical equipment where long-term accuracy and data retention are mission-critical.

FAQ

What is the minimum VCC voltage required to maintain RTC operation before battery switchover?

The M41T56M6F sustains timekeeping down to 2.5 V on VCC. Below this threshold, it automatically switches to VBAT while preserving all clock and NVRAM contents. This 2.5 V switchover point is fixed and not user-adjustable, ensuring predictable behavior during brown-out conditions without firmware intervention.

Can the FT/OUT pin output both 1 Hz and 32.768 kHz signals?

Yes - the FT/OUT pin is configurable via the OUT bit (D7) in the control register (address 7). When OUT = 0, it outputs a 1 Hz square wave; when OUT = 1, it outputs the raw 32.768 kHz oscillator signal. Both modes use open-drain output requiring an external pull-up resistor.

How does the M41T56M6F handle leap years in its hardware calendar?

Leap-year compensation is fully automatic and implemented in hardware. The device recognizes February 29 in years divisible by 4, excluding years divisible by 100 unless also divisible by 400 - matching the Gregorian calendar rule without firmware calculation or register updates.

Is external crystal load capacitance required for the M41T56M6F?

No - the M41T56M6F integrates 12.5 pF load capacitance internally. Only a standard 32.768 kHz tuning-fork crystal is needed between OSCI and OSCO pins. Adding external capacitors will degrade frequency accuracy and is explicitly discouraged in the datasheet.