M41ST85W:3.0/3.3 V I²C combination real-time clock, NVRAM supervisor and microprocessor supervisor

The M41ST85W is a combination serial real-time clock, microprocessor supervisor, and NVRAM supervisor. It is built in a low-power CMOS SRAM process and has a 64-byte memory space with 44 bytes of NVRAM and 20 memory-mapped RTC registers. The RTC registers are configured in binary coded decimal (BCD) format.

The M41ST85W combines a 400 kHz I2C serial RTC with an automatic backup battery switchover circuit for powering an external LPSRAM as well as the internal RTC. When power begins to fail, the switchover automatically connects to the backup battery to keep the RTC and external LPSRAM alive in the absence of system power. Access to the LPSRAM is also cut off via a chip-enable gate function, thereby write-protecting the memory. A programmable watchdog and power-on reset/low voltage detect function are the key elements in the microprocessor supervisor section.

The real-time clock includes a built-in 32.768 kHz oscillator (crystal-controlled), which provides the time base for the timekeeping and calendar functions. Eight of the 20 clock registers provide the basic clock/calendar functions while the other 12 bytes provide status/control for the alarm, watchdog, and squarewave functions.

RTC addresses and data are transferred serially via the two-line, bidirectional I2C interface. The built-in address register is incremented automatically after each WRITE or READ data byte.

The M41ST85W has a built-in power sense circuit which detects power failures and automatically switches to the backup battery when a power failure occurs. During an outage, the power to sustain the SRAM and clock operations is typically supplied by a small lithium button-cell battery as is the case when using the SNAPHAT®package option.

Functions available to the user include a non-volatile, time-of-day clock/calendar, alarm interrupts, watchdog timer, and programmable squarewave generator. Other features include a power-on reset as well as two additional debounce reset inputs (RSTIN1and RSTIN2) which can also generate an output reset (RST).

The eight registers for basic clock/calendar functions 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 - valid until year 2100), 30 and 31 day months are made automatically.

The M41ST85W is offered in two 28-lead SOIC packages. The 300 mil SOH28 SNAPHAT®IC package mates with ST’s SNAPHAT battery/crystal top (ordered separately). SNAPHAT battery options include 48 mAh and 120 mAh. ST’s 300 mil SOX28 embedded crystal IC includes the 32 KHz crystal and is perfect for applications where a low profile is a must.

The SOH28 SNAPHAT SOIC includes sockets with gold plated contacts at both ends for direct connection to the SNAPHAT top. The SNAPHAT battery/crystal top is inserted atop the IC package after the completion of the surface mount assembly process which avoids potential battery and crystal damage due to the high temperatures required for device surface-mounting. The unique design allows the battery to be replaced, thus extending the life of the RTC and NVRAM indefinitely.

The SNAPHAT top is keyed to prevent reverse insertion. The SNAPHAT IC and SNAPHAT tops are shipped separately. The ICs are available in plastic anti-static tubes or in tape & reel form. The SNAPHAT tops are shipped in plastic anti-static tubes. The part numbers are M4T28-BR12SH1 (48 mAh) and M4T32-BR12SH1 (120 mAh). For the extended temperature requirement, the 120 mAh M4T32-BR12SH6 is available.

Key Features

  • Automatic battery switchover and WRITE protect for:
    • Internal serial RTC and
    • External low power SRAM (LPSRAM)
  • 400 kHz I2 C serial interface
  • 3.0/3.3 V operating voltage
    • VCC = 2.7 to 3.6 V
  • Ultralow battery supply current of 500 nA (max)
  • RoHS compliant
    • Lead-free second level interconnect
  • Serial RTC features
    • Functions in battery back-up mode
    • Century
    • Counters for:
      • Seconds, minutes, hours, day, date, month, and year
      • Century
      • Tenths/hundredths of seconds
      • Clock calibration register allows compensation for crystal variations over temperature
    • Programmable alarm with repeat modes
      • Functions in battery back-up mode
      • Century
      • Counters for:
        • Seconds, minutes, hours, day, date, month, and year
        • Century
        • Tenths/hundredths of seconds
        • Clock calibration register allows compensation for crystal variations over temperature
      • Clock calibration register allows compensation for crystal variations over temperature
    • Power-down timestamp (HT bit)
    • 2.5 to 5.5 V oscillator operating voltage
  • Microprocessor supervisor features
    • Open drain reset output
    • Reset voltage, VPFD= 2.60 V (nom)
    • Power-on reset/low voltage detect
      • Open drain reset output
      • Reset voltage, VPFD= 2.60 V (nom)
      • Two reset input pins
      • Watchdog can be steered to reset output
    • Watchdog can be steered to reset output
  • NVRAM supervisor features
    • Non-volatizes external LPSRAM
      • Automatically switches to back-up battery and deselects (write-protects) external LPSRAM via chip-enable gate
      • Power-fail deselect (write protect) voltage, VPFD= 2.60 V (nom)
      • Switchover, VSO= 2.50 V (nom)
    • Battery monitor (battery low flag)
    • Switchover, VSO= 2.50 V (nom)
  • Other features
    • 28-lead SNAPHAT®IC (SOH28) SNAPHAT battery/crystal top to be ordered separately
    • 28-lead embedded crystal SOIC (SOX28)
    • Package options:
      • 28-lead SNAPHAT®IC (SOH28) SNAPHAT battery/crystal top to be ordered separately
      • 28-lead embedded crystal SOIC (SOX28)
Product Specifications
DescriptionVersionSize
DS2151: 3.0/3.3 V I2C combination serial RTC, NVRAM supervisor and microprocessor supervisor11.2445 KB
Application Notes
DescriptionVersionSize
AN3060: Applications guide for serial real-time clocks (RTCs)3.0878 KB
AN1011: Battery technology used in NVRAM and real-time clock (RTC) products from ST4.0248 KB
AN934: How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products4.1123 KB
AN1216: Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs)2.0192 KB
AN4641: Integrating TIMEKEEPER® and real-time clock supervisor functions1.0479 KB
AN923: Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs4.0142 KB
AN1572: Power-down time-stamp function in serial real-time clocks (RTCs)2.0171 KB
AN1336: Power-fail comparator for NVRAM supervisory devices2.0127 KB
AN1012: Predicting the battery life and data retention period of NVRAMs and serial RTCs4.1439 KB
HW Model & CAD Libraries
DescriptionVersionSize
Ibis model1.026 KB
Brochures
DescriptionVersionSize
Serial real-time clock ICs1.0827 KB
Clocks and Timers Software
Part NumberManufacturerDescription
STSW-SRTC001STI2C code for Serial RTC
STSW-SRTC002STSPI code -Serial RTC
Sample & Buy
Part NumberPackagePacking TypeOperating Temperature (°C) (min)Operating Temperature (°C) (max)Unit Price (US$) *QuantityNVRAM size (B)ECCN (EU)ECCN (US)Country of Origin
M41ST85WMH6FSO-28Tape And Reel-40854.256100044NECEAR99MALAYSIA
M41ST85WMX6TRSO28 WITH EMBEDDED CRYSTALTape And Reel-40853.223100044NECEAR99MALAYSIA
Quality & Reliability
Part NumberPackageGradeRoHS Compliance GradeMaterial Declaration**
M41ST85WMH6FSO-28IndustrialEcopack1md_rj_1632-wspc-snaphat_w1rj-wspc-br12sh8.pdf
md_ab-wspc-so-wspc-28-wspc-battery_hzmhb6aa85w-wspc-(m41st85wmh6f).xml
M41ST85WMX6TRSO28 WITH EMBEDDED CRYSTALIndustrialEcopack1md_l8-wspc-so28-wspc-.30-wspc-with-wspc-embedded-wspc-crystal_asl8-wspc-b6aa85w_signed.pdf
md_l8-wspc-so28-wspc-.xml
3.0/3.3 V I2C combination serial RTC, NVRAM supervisor and microprocessor supervisor M41ST85W
circuit_diagram_7531_thumbnail.png M41ST85W
串行实时时钟(RTC)应用指南 M41T60
ST NVRAM 和实时时钟(RTC)产品中使用的电池技术 M4Z28-BR00SH
How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products M41T60
Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs) M41T94
集成TIMEKEEPER® 与实时时钟监控器功能 M41T60
Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs M41T60
串行实时时钟(RTC)的掉电时间戳功能 M41T60
Power-fail comparator for NVRAM supervisory devices M41T60
预测NVRAM 和串行RTC 的电池寿命和数据保存期限 M4Z28-BR00SH
Predicting the battery life and data retention period of NVRAMs and serial RTCs M41ST85W
Predicting the battery life and data retention period of NVRAMs and serial RTCs M4T28-BR12SH
md_rj_1632-wspc-snaphat_w1rj-wspc-br12sh8.pdf M41ST85W
md_ab-wspc-so-wspc-28-wspc-battery_hzmhb6aa85w-wspc-(m41st85wmh6f).xml M41ST85W
md_l8-wspc-so28-wspc-.30-wspc-with-wspc-embedded-wspc-crystal_asl8-wspc-b6aa85w_signed.pdf M41ST85W
md_l8-wspc-so28-wspc-.xml M41ST85W