Low-power serial real-time clock (RTC) with alarm

The M41T6x is a low-power serial real-time clock (RTC) with a built-in 32.768 kHz oscillator. Eight registers are used for the clock/calendar function and are configured in binary-coded decimal (BCD) format. An additional eight registers provide status/control of alarm, 32 KHz output, calibration, and watchdog functions. Addresses and data are transferred serially via a two-line, bidirectional I2C interface. The built-in address register is incremented automatically after each WRITE or READ data byte.

Functions available to the user include a time-of-day clock/calendar, alarm interrupts (M41T62/65), 32 KHz output (M41T62/64), programmable square wave output (M41T62/64), and watchdog output (M41T65). The eight clock address locations contain the century, year, month, date, day, hour, minute, second and tenths/hundredths of a second in 24-hour BCD format. Corrections for 28-, 29- (leap year), 30- and 31-day months are made automatically.

The M41T6x is supplied in two very small packages: a tiny, 3 x 3 mm 16-pin QFN which requires a user-supplied 32 KHz crystal, and an ultra-small 1.5 x 3.2 mm LCC with embedded crystal - no external crystal is required.

Key Features

  • Serial real-time clock (RTC) with alarm functions
    • 400 kHz I2 C serial interface
    • Memory mapped registers for seconds, minutes, hours, day, date, month, year, and century
    • Tenths/hundredths of seconds register
  • 350 nA timekeeping current at 3 V
  • Timekeeping down to 1.0 V
  • 1.3 V to 4.4 V I2 C bus operating voltage
    • 4.4 V max VCC suitable for lithium-ion battery operation
  • Low operating current of 35 μA (at 400 kHz I2 C speed)
  • 32 KHz square wave output is on at power-up. Suitable for driving a microcontroller in low-power mode. Can be disabled. (M41T62/64)
  • Programmable 1 Hz to 32 KHz square wave output (M41T62/64)
  • Programmable alarm with interrupt function (M41T62/65)
  • 32 KHz crystal oscillator integrates crystal load capacitors, works with high series resistance crystals
  • Oscillator stop detection monitors clock operation
  • Accurate programmable watchdog
    • 62.5 ms to 31 min timeout
  • Software clock calibration. Can adjust timekeeping to within ±2 parts per million (±5 seconds per month)
  • Automatic leap year compensation
  • –40 to +85 °C operation
  • Two package options:
    • Very small 3 x 3 mm, lead-free & halogen-free (ECOPACK2® ) 16-lead QFN
    • Ultra-small 1.5 x 3.2 mm, lead-free & halogen-free (ECOPACK2® ) 8-pin ceramic leadless chip carrier with embedded 32 KHz crystal - no external oscillator components required (M41T62)

Circuit Diagram

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Technical Documentation

Product Specifications
Description Version Size
DS3840 DS3840: Low-power serial real-time clocks (RTCs) with alarm 22.0 955 KB
Application Notes
Description Version Size
AN3060 AN3060: Applications guide for serial real-time clocks (RTCs) 3.0 878 KB
AN1011 AN1011: Battery technology used in NVRAM and real-time clock (RTC) products from ST 4.0 248 KB
AN934 AN934: How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products 4.1 123 KB
AN1216 AN1216: Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs) 2.0 192 KB
AN4641 AN4641: Integrating TIMEKEEPER® and real-time clock supervisor functions 1.0 479 KB
AN923 AN923: Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs 4.0 142 KB
AN1572 AN1572: Power-down time-stamp function in serial real-time clocks (RTCs) 2.0 171 KB
AN1336 AN1336: Power-fail comparator for NVRAM supervisory devices 2.0 127 KB

Publications and Collaterals

Description Version Size
Serial real-time clock ICs 1.0 827 KB
White Papers
Description Version Size
Smart watches and fitness bands benefit from the ultra-small date/time chip from STMicroelectronics 1.0 160 KB

Tools and Software

Embedded Software
Evaluation Tools
Clocks and Timers Software
Solution Evaluation Tools

Sample & Buy

Part Number Package Packing Type Operating Temperature (°C) (min) Operating Temperature (°C) (max) Marketing Status Unit Price (US$) * Quantity NVRAM size (B) ECCN (EU) ECCN (US) Country of Origin More info Order from ST Order from Distributors
M41T62LC6F LCC8 3.2x1.5 mm Tape And Reel -40 85 Active - - - NEC EAR99 - MORE INFO Get Sample Add to cart DISTRIBUTOR AVAILABILITY
M41T62Q6F VFQFPN 16 3x3x0.9 Tape And Reel -40 85 Active - - - NEC EAR99 MALAYSIA MORE INFO Get Sample Add to cart DISTRIBUTOR AVAILABILITY

(*) Suggested Resale Price per unit (USD) for BUDGETARY USE ONLY. For quotes, prices in local currency, please contact your local ST Sales Office  or our Distributors

Quality & Reliability

Part Number Marketing Status Package Grade RoHS Compliance Grade Material Declaration**
M41T62LC6F ActiveLCC8 3.2x1.5 mmIndustrialEcopack2 0 0
M41T62Q6F ActiveVFQFPN 16 3x3x0.9IndustrialEcopack2 0

(**) The Material Declaration forms available on st.com may be generic documents based on the most commonly used package within a package family. For this reason, they may not be 100% accurate for a specific device. Please contact our sales support for information on specific devices.