STMicroelectronics M41T94MH6F

Overview

M41T94MH6F from STMicroelectronics is a serial real-time clock IC with integrated 32.768 kHz oscillator, 44 bytes of NVRAM, programmable alarm, watchdog timer (62.5 ms–128 s), and RESET output. It operates from 2.7–5.5 V, draws ≤500 nA in battery backup mode, and supports SPI up to 2 MHz. Used in industrial control panels for time-stamped event logging during mains failure.

For engineers reviewing the M41T94MH6F datasheet, M41T94MH6F pinout, M41T94MH6F application, or M41T94MH6F equivalent, key selection criteria include battery-switchover voltage thresholds (VPFD = 4.20–4.50 V when THS = VCC), BCD calendar register layout, SNAPHAT®-compatible 28-pin SOIC packaging, and SPI timing compliance with (CPOL, CPHA) = ('0','0') or ('1','1').

Technical Context

The M41T94MH6F implements a full BCD calendar engine with automatic leap-year correction through year 2100, century bit handling, and power-down timestamping. Its oscillator integrates 12.5 pF load capacitance and supports high-series-resistance crystals for robustness.

It features dual reset inputs (RSTIN1/RSTIN2) with debouncing, open-drain IRQ/FT/OUT for alarm/frequency test/square wave output, and a dedicated WDI input for external watchdog triggering. The device uses automatic address incrementing over 64-byte memory map including 8 clock registers, 12 alarm/watchdog control bytes, and 44 user RAM bytes.

Key Specifications

Pinout & Package

Package: SOH28 - 28-lead plastic small outline, 330 mil width, RoHS-compliant, lead-free second-level interconnect. Designed for direct mating with SH-series SNAPHAT® housings containing integrated 32.768 kHz crystal and lithium battery (e.g., M4TXX-BR12SH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS3231M+ and PCF8563T, the M41T94MH6F uniquely combines SPI interface, integrated oscillator with 12.5 pF load, SNAPHAT®-ready SOH28 packaging, and dual reset inputs-making it optimal for industrial systems requiring robust, self-contained timekeeping with hardware-level fault response.

Availability

M41T94MH6F is available at Aetrix Electronics and suitable for industrial HMI logging, medical device timestamping, and smart energy metering requiring stable component supply across extended product lifecycles.

Supply support for M41T94MH6F 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, analog ICs, MEMS, and power devices for industrial, automotive, and consumer markets.

The M41T94MH6F belongs to ST's real-time clock portfolio targeting embedded systems needing autonomous, battery-backed timekeeping with minimal external components and high reliability under voltage transients.

FAQ

What is the function of the THS pin on the M41T94MH6F?

The THS (Threshold Select) pin configures the power-fail deselect voltage (VPFD) range: when tied to VSS, VPFD is 2.55–2.70 V; when tied to VCC, VPFD is 4.20–4.50 V. This allows system designers to match the RTC's switchover point to their specific power-supply brown-out threshold without external circuitry.

Can the M41T94MH6F operate without an external crystal?

No-the M41T94MH6F requires an external 32.768 kHz tuning-fork crystal connected between XI and XO pins. Its internal oscillator circuit includes 12.5 pF load capacitance but does not contain a resonator; the crystal must be mounted either externally (SO16 package) or within the SNAPHAT® top (SOH28 package).

How does the M41T94MH6F handle leap-year calculation?

The M41T94MH6F performs fully autonomous leap-year correction in hardware using the century bit and BCD calendar registers. It correctly advances from Feb 28 to Mar 1 in non-leap years, Feb 29 in leap years (including year 2000), and accounts for all 28/29/30/31-day months-no firmware intervention is needed through year 2100.

Is the 44-byte NVRAM accessible during battery backup mode?

Yes-the full 44-byte NVRAM remains readable and writable during battery backup mode. The device retains clock/calendar registers, alarm settings, and user RAM contents while drawing ≤500 nA from VBAT, enabling persistent data storage across extended mains outages.