STMicroelectronics M41T93SMY6E

Overview

M41T93SMY6E from STMicroelectronics is a serial SPI real-time clock (RTC) IC with integrated 32.768 kHz oscillator, battery switchover circuitry, and 7-byte battery-backed SRAM. It provides BCD-formatted timekeeping (tenths/hundredths of seconds through century), programmable alarm(s), watchdog timer, 8-bit counter/timer, and 32 kHz square wave output. Designed for non-volatile timekeeping in power-constrained industrial and embedded systems.

For engineers reviewing the M41T93SMY6E datasheet, M41T93SMY6E pinout, M41T93SMY6E application, or M41T93SMY6E equivalent, key selection criteria include ultra-low 365 nA battery current, ±5 ppm factory calibration (SOX18), dual-alarm interrupt capability during backup mode, VCC-to-VBAT switchover at 2.38–3.0 V depending on variant, and SPI Mode 0 (CPOL=0, CPHA=0) interface compatibility.

Technical Context

The M41T93SMY6E implements a fully autonomous RTC subsystem with hardware-managed battery switchover at fixed VSO/VRST thresholds (2.32 V for Z-grade), automatic calendar correction for leap years and variable month lengths, and coherent register access via atomic read/write sequences. Its oscillator fail detection circuit monitors crystal activity and asserts an interrupt flag upon stoppage.

It supports two independent alarms with repeat modes (once, daily, weekly, monthly), a free-running 8-bit countdown timer with selectable clock sources (244.1 μs to 4.25 hrs), and a programmable square wave output (32 kHz default, configurable to 1 Hz, 1.024 kHz, or 4.096 kHz). All control registers-including digital/analog calibration, IRQ priority, and timer enable-are accessible over SPI without external logic.

Key Specifications

Pinout & Package

Package: SOX18 - 18-lead plastic SOIC (300 mil), 11.61 × 7.62 mm, with embedded 32.768 kHz crystal. No external crystal required.

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 M41T93SMY6E uniquely balances SPI compatibility, embedded crystal (SOX18), ultra-low 365 nA backup current, and dual-alarm interrupt capability - making it optimal for space-constrained industrial controllers needing robust, self-contained timekeeping without I²C dependency.

Availability

M41T93SMY6E is available at Aetrix Electronics and suitable for industrial data loggers, smart metering systems, medical wearables, and POS terminals requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for M41T93SMY6E 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 M41T93 belongs to ST's real-time clock product line, engineered specifically for high-reliability, low-power timekeeping in systems requiring battery-backed operation, automatic calendar handling, and seamless power-fail response without host firmware intervention.

FAQ

What is the function of the DU pin on M41T93SMY6E?

The DU (Do Not Use) pin is a reserved terminal that must be externally tied to VCC. It serves no functional purpose in normal operation and leaving it unconnected may cause undefined behavior or increased leakage current. This requirement is explicitly stated in the SOX18 mechanical drawing and pin function table of the official datasheet (DocID12615 Rev 8, page 8).

Does M41T93SMY6E support SPI Mode 3 (CPOL=1, CPHA=0)?

No. The M41T93SMY6E supports SPI Mode 0 only (CPOL=0, CPHA=0), as confirmed in Section 1.1.3 and Figure 6 of the datasheet. Attempting Mode 3 will result in incorrect data sampling because SDI latching occurs on the rising edge of SCL, which only aligns with CPOL=0. Any MCU SPI peripheral must be configured accordingly.

How does the M41T93SMY6E handle leap year calculation?

The M41T93SMY6E performs automatic leap year correction in hardware using the century bits (CB1:CB0) and year register. It correctly advances from February 28 to March 1 in leap years (divisible by 4, except century years not divisible by 400) without host software involvement, as documented in Section 1 Description (page 6) and Figure 18 (century bit logic).

Can the SQW output be disabled or reconfigured to other frequencies?

Yes. The SQW output defaults to 32 kHz on power-up but can be disabled (SQWE = 0) or set to 1 Hz, 1.024 kHz, or 4.096 kHz via the square wave register (address 0x14). Configuration is persistent across power cycles and remains active in battery backup mode, as specified in Section 3.9 and Table 10 of the datasheet.