M41ST85W

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

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  • 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 I2C 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
      • 400 kHz I2C
      • 44 bytes of general purpose NVRAM
      • 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
      • Power-down timestamp (HT bit)
      • 2.5 to 5.5 V oscillator operating voltage
    • Microprocessor supervisor features
      • Programmable watchdog
        • 62.5 ms to 128 s time-out period
      • Early power-fail warning circuit (PFI/PFO) with 1.25 V precision reference
      • 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
    • 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)
    • Other features
      • Programmable squarewave generator (1 Hz to 32 KHz)
      • –40°C to +85°C operation
      • Package options:
        • 28-lead SNAPHAT®IC (SOH28) SNAPHAT battery/crystal top to be ordered separately
        • 28-lead embedded crystal SOIC (SOX28)

Circuit Diagram

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CAD/EDA Symbols, Footprints and Models

Quality and Reliability

Part Number Marketing Status Package Grade RoHS Compliance Grade Material Declaration**
M41ST85WMH6F
Active
SO-28 Industrial Ecopack1
M41ST85WMX6TR
Active
SO28 WITH EMBEDDED CRYSTAL Industrial Ecopack1

M41ST85WMH6F

Package:

SO-28

Material Declaration**:

PDF XML

Marketing Status

Active

Package

SO-28

Grade

Industrial

RoHS Compliance Grade

Ecopack1

M41ST85WMX6TR

Package:

SO28 WITH EMBEDDED CRYSTAL

Material Declaration**:

PDF XML

Marketing Status

Active

Package

SO28 WITH EMBEDDED CRYSTAL

Grade

Industrial

RoHS Compliance Grade

Ecopack1

(**) 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.

Sample & Buy

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ECCN (US)
ECCN (EU)
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Temperature (°C) Budgetary Price (US$)*/Qty
More info
min
max
M41ST85WMH6F Available at 5 distributors

Distributor availability ofM41ST85WMH6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 907 1 Order Now
AVNET AMERICA 55 0 Order Now
Newark Element14 AMERICA 1 0 Order Now
ARROW AMERICA 1 1 Order Now
MOUSER WORLDWIDE 550 1 Order Now

Distributor reported inventory date: 2020-09-30

Distributor Name

DIGIKEY

Stock

907

Min.Order

1

Region

WORLDWIDE Order Now

AVNET

Stock

55

Min.Order

0

Region

AMERICA Order Now

Newark Element14

Stock

1

Min.Order

0

Region

AMERICA Order Now

ARROW

Stock

1

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

550

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-09-30

Sample & Buy Buy now
Active
EAR99 NEC Tape And Reel SO-28 -40 85 4.256 / 1k
MORE INFO

NVRAM size (B):

44

Country of Origin:

MALAYSIA

M41ST85WMX6TR Available at 4 distributors

Distributor availability ofM41ST85WMX6TR

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 1757 1 Order Now
RS COMPONENTS EUROPE 772 1 Order Now
AVNET AMERICA 1000 0 Order Now
MOUSER WORLDWIDE 5632 1 Order Now

Distributor reported inventory date: 2020-09-30

Distributor Name

DIGIKEY

Stock

1757

Min.Order

1

Region

WORLDWIDE Order Now

RS COMPONENTS

Stock

772

Min.Order

1

Region

EUROPE Order Now

AVNET

Stock

1000

Min.Order

0

Region

AMERICA Order Now

MOUSER

Stock

5632

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-09-30

Sample & Buy Buy now
Active
EAR99 NEC Tape And Reel SO28 WITH EMBEDDED CRYSTAL -40 85 3.223 / 1k
MORE INFO

NVRAM size (B):

44

Country of Origin:

PHILIPPINES

M41ST85WMH6F

Marketing Status

Active

ECCN (US)

EAR99

Budgetary Price (US$)*/Qty

4.256 / 1k

Distributor availability ofM41ST85WMH6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 907 1 Order Now
AVNET AMERICA 55 0 Order Now
Newark Element14 AMERICA 1 0 Order Now
ARROW AMERICA 1 1 Order Now
MOUSER WORLDWIDE 550 1 Order Now

Distributor reported inventory date: 2020-09-30

Distributor Name

DIGIKEY

Stock

907

Min.Order

1

Region

WORLDWIDE Order Now

AVNET

Stock

55

Min.Order

0

Region

AMERICA Order Now

Newark Element14

Stock

1

Min.Order

0

Region

AMERICA Order Now

ARROW

Stock

1

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

550

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-09-30

ECCN (EU)

NEC

Packing Type

Tape And Reel

Package

SO-28

Operating Temperature (°C)

(min)

-40

(max)

85

Budgetary Price (US$)* / Qty

4.256 / 1k

NVRAM size (B)

44

Country of Origin

MALAYSIA

M41ST85WMX6TR

Marketing Status

Active

ECCN (US)

EAR99

Budgetary Price (US$)*/Qty

3.223 / 1k

Distributor availability ofM41ST85WMX6TR

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 1757 1 Order Now
RS COMPONENTS EUROPE 772 1 Order Now
AVNET AMERICA 1000 0 Order Now
MOUSER WORLDWIDE 5632 1 Order Now

Distributor reported inventory date: 2020-09-30

Distributor Name

DIGIKEY

Stock

1757

Min.Order

1

Region

WORLDWIDE Order Now

RS COMPONENTS

Stock

772

Min.Order

1

Region

EUROPE Order Now

AVNET

Stock

1000

Min.Order

0

Region

AMERICA Order Now

MOUSER

Stock

5632

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-09-30

ECCN (EU)

NEC

Packing Type

Tape And Reel

Package

SO28 WITH EMBEDDED CRYSTAL

Operating Temperature (°C)

(min)

-40

(max)

85

Budgetary Price (US$)* / Qty

3.223 / 1k

NVRAM size (B)

44

Country of Origin

PHILIPPINES

(*) 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