STMicroelectronics M41T94MQ6E

Overview

M41T94MQ6E from STMicroelectronics is a serial real-time clock (RTC) IC with integrated 44-byte NVRAM, programmable watchdog timer (62.5 ms–128 s), battery switchover circuitry, and SPI interface (2 MHz max). It maintains time in BCD format across century/year/month/date/hour/minute/second/tenths-hundredths, supports automatic leap-year correction through 2100, and delivers ultra-low 500 nA battery current for long-term backup in power-loss scenarios - deployed in industrial HMIs, medical data loggers, and smart metering systems.

For engineers reviewing the M41T94MQ6E datasheet, M41T94MQ6E pinout, M41T94MQ6E application, or M41T94MQ6E equivalent, key selection criteria include its dual-package support (16-lead SOIC vs. 28-lead SOH28 with SNAPHAT® integration), VCC/VBAT voltage thresholds (2.55–2.70 V or 4.20–4.50 V), alarm interrupt persistence during battery backup, and SPI mode compatibility (CPOL/CPHA = '0','0' or '1','1').

Technical Context

The M41T94MQ6E implements a dedicated RTC core with 8 BCD-formatted clock registers (century to hundredths of second), plus 12 bytes of control RAM for alarm, watchdog, and square-wave configuration. Its oscillator operates at 32.768 kHz using an external crystal with built-in 12.5 pF load capacitance, enabling stable timing even with high-series-resistance crystals.

SPI communication uses chip-enable (E)–gated synchronous transfers at up to 2 MHz, supporting MSB-first read/write sequences across 64 total bytes (clock + control + 44-byte user RAM). Power-fail detection triggers automatic VCC-to-VBAT switchover below VSO (2.65 V when THS = VSS), followed by write protection until VCC exceeds VPFD + tREC (min 100 µs).

Key Specifications

Pinout & Package

Package: 16-lead SOIC (SO16, MQ suffix), 3.9 mm × 9.9 mm body, 1.27 mm pitch, RoHS-compliant lead-free finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1307+ and PCF8563, the M41T94MQ6E uniquely integrates oscillator load capacitance, dual-threshold power-fail detection, battery-mode alarm persistence, and SPI+watchdog functionality - making it optimal for industrial systems requiring autonomous, long-life, feature-rich timekeeping without external support components.

Availability

M41T94MQ6E is available at Aetrix Electronics and suitable for industrial data loggers, smart energy meters, medical diagnostic devices, and building automation controllers requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant sourcing.

Supply support for M41T94MQ6E 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 management ICs, sensors, and timing solutions for industrial, automotive, and consumer markets.

The M41T94MQ6E belongs to ST's real-time clock product line, engineered specifically for robust, battery-backed timekeeping in harsh environments - emphasizing autonomous power switchover, calendar accuracy through 2100, and minimal external component count.

FAQ

What crystal specifications are required for the M41T94MQ6E?

The M41T94MQ6E requires a standard 32.768 kHz tuning-fork crystal with series resistance ≤50 kΩ. Its integrated 12.5 pF load capacitance eliminates external capacitors, enabling direct connection between XI and XO pins. Crystal tolerance should be ≤20 ppm for ±2 ppm annual timekeeping accuracy over –40°C to +85°C.

How does the M41T94MQ6E handle leap years and month-end rollovers?

The M41T94MQ6E performs automatic calendar correction in hardware: it advances dates correctly for 28-, 29- (leap years through 2100), 30-, and 31-day months, and increments the year register on December 31. The century bit (bit 7 of the century/year register) enables unambiguous year representation across 2000–2100 transitions.

Can the SQW pin output frequencies other than 1 Hz?

Yes - the SQW pin is programmable to output 32.768 kHz, 1 kHz, 64 Hz, or 1 Hz via the square-wave control register (address 0x14). This allows use as a system clock source, ADC sampling trigger, or LED blink timing signal without requiring external dividers or firmware intervention.

What happens to the alarm function during battery-only operation?

The alarm function remains fully operational during battery backup mode: the alarm interrupt (IRQ/FT/OUT) asserts as scheduled, and the alarm flag persists in the control register. This enables time-triggered wake-up of sleeping microcontrollers - critical for low-power data logging and event-driven sensing applications.