STMicroelectronics M41T94MQ6F

Overview

M41T94MQ6F from STMicroelectronics is a serial real-time clock (RTC) IC with integrated 44-byte NVRAM, programmable alarm, watchdog timer, and battery-backed power-fail switchover. It features a 32.768 kHz crystal oscillator with 12.5 pF load capacitance, SPI interface up to 2 MHz, ultralow 500 nA battery supply current, and operates from 2.7–5.5 V. Used in industrial control panels for time-stamped event logging during mains failure.

For engineers reviewing the M41T94MQ6F datasheet, M41T94MQ6F pinout, M41T94MQ6F application, or M41T94MQ6F equivalent, key selection criteria include battery-switchover voltage thresholds (VPFD = 2.55–2.70 V or 4.20–4.50 V), BCD-formatted calendar registers with leap-year correction through year 2100, and SNAPHAT®-compatible 28-pin SOIC packaging with integrated crystal/battery support.

Technical Context

The M41T94MQ6F implements a full BCD calendar engine with automatic month-length and leap-year compensation (valid until 2100), using eight dedicated clock registers for century, year, month, date, day, hour, minute, second, and tenths/hundredths of a second. Its SPI slave interface supports CPOL/CPHA = ('0','0') or ('1','1') modes with strict timing: tCL/tCH ≥ 200 ns, fSCL ≤ 2 MHz, and input data latched on SCL rising edge.

Power management includes dual threshold detection (VSO = 2.65 V, VPFD = 2.55–2.70 V or 4.20–4.50 V), automatic VCC-to-battery switchover, and write protection hold time (tREC) after VCC recovery. The IRQ/FT/OUT pin serves triple function: open-drain interrupt output, frequency test point, and general-purpose output - configurable via control register bits.

Key Specifications

Pinout & Package

Package: 16-lead SOIC (SO16/MQ), RoHS-compliant, 150 mil width. Pinout validated per STMicroelectronics DocID7564 Rev 8 Figures 2 and 3, Table 1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS3231SN#T&R and PCF8563T, the M41T94MQ6F uniquely combines SPI interface, ultra-low 500 nA battery draw, dual VPFD thresholds, hardware reset inputs, and programmable watchdog - making it optimal for industrial systems requiring deterministic power-fail response and long-term autonomous operation.

Availability

M41T94MQ6F is available at Aetrix Electronics and suitable for industrial control panels, smart energy meters, medical device logging, and building automation controllers requiring stable component supply across extended product lifecycles.

Supply support for M41T94MQ6F 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 ICs, sensors, and timing solutions for industrial, automotive, and embedded markets.

The M41T94MQ6F belongs to ST's real-time clock product line, engineered specifically for industrial systems needing reliable, low-power, battery-backed timekeeping with integrated power-fail management and hardware watchdog functionality.

FAQ

What crystal specifications are required for the M41T94MQ6F?

The M41T94MQ6F requires a standard 32.768 kHz tuning-fork crystal with series resistance ≤ 70 kΩ and shunt capacitance ≤ 7 pF. Its internal 12.5 pF load capacitance eliminates external capacitors, and the oscillator operates reliably across –40°C to +85°C ambient temperatures with typical frequency stability of ±20 ppm.

How does the M41T94MQ6F handle leap years and month-end rollovers?

The M41T94MQ6F implements fully autonomous calendar logic in hardware: it automatically adjusts day count for 28-, 29- (leap year), 30-, and 31-day months using BCD-encoded registers. Leap-year calculation is valid through year 2100 and requires no firmware intervention - all corrections occur transparently during clock update cycles.

Can the M41T94MQ6F operate without an external crystal?

No. The M41T94MQ6F requires an external 32.768 kHz crystal connected between XI and XO pins. It contains no internal RC oscillator; its timing accuracy and long-term stability depend entirely on the connected crystal and its matching to the internal 12.5 pF load capacitance. Operation without crystal results in halted RTC functionality.

What is the function of the THS pin, and how should it be configured?

The THS (Threshold Select) pin configures the power-fail detection voltage range: tying THS to VSS selects VPFD = 2.55–2.70 V for 3.3 V systems; tying THS to VCC selects VPFD = 4.20–4.50 V for 5 V systems. This single-pin configuration avoids external resistor dividers and ensures correct switchover behavior during brownouts.