M41ST85WMH6F Real-Time Clock (RTC) ICs by STMicroelectronics

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

Status: Active
Series: M41ST85W
RoHS: Compliant
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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 I 2 C 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 I 2 C 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 ( RSTIN1 and 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.

Prices starting from US$4.70


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Logo for Future Electronics Future Electronics US$6.48
936
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Logo for Newark Electronics Newark Electronics US$4.70
831
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Logo for element14 element14 US$8.49
831
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Logo for Avnet America Avnet America US$5.80
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Features

Automatic battery switchover and WRITE protect for: Internal serial RTC and External low power SRAM (LPSRAM)
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
VCC= 2.7 to 3.6 V
Ultralow battery supply current of 500 nA (max)
RoHS compliant Lead-free second level interconnect
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 yearCenturyTenths/hundredths of secondsClock calibration register allows compensation for crystal variations over temperature Programmable alarm with repeat modesFunctions in battery back-up mode Power-down timestamp (HT bit) 2.5 to 5.5 V oscillator operating voltage
400 kHz I2C
44 bytes of general purpose NVRAM
Counters for:Seconds, minutes, hours, day, date, month, and yearCenturyTenths/hundredths of secondsClock calibration register allows compensation for crystal variations over temperature
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 modesFunctions in battery back-up mode
Functions in battery back-up mode
Power-down timestamp (HT bit)
2.5 to 5.5 V oscillator operating voltage
Microprocessor supervisor features Programmable watchdog62.5 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 detectOpen drain reset outputReset voltage, VPFD= 2.60 V (nom)Two reset input pinsWatchdog can be steered to reset output
Programmable watchdog62.5 ms to 128 s time-out period
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 detectOpen drain reset outputReset voltage, VPFD= 2.60 V (nom)Two reset input pinsWatchdog can be steered to reset output
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 LPSRAMAutomatically switches to back-up battery and deselects (write-protects) external LPSRAM via chip-enable gatePower-fail deselect (write protect) voltage, VPFD= 2.60 V (nom)Switchover, VSO= 2.50 V (nom) Battery monitor (battery low flag)
Non-volatizes external LPSRAMAutomatically switches to back-up battery and deselects (write-protects) external LPSRAM via chip-enable gatePower-fail deselect (write protect) voltage, VPFD= 2.60 V (nom)Switchover, VSO= 2.50 V (nom)
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 separately28-lead embedded crystal SOIC (SOX28)
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 separately28-lead embedded crystal SOIC (SOX28)
28-lead SNAPHAT®IC (SOH28) SNAPHAT battery/crystal top to be ordered separately
28-lead embedded crystal SOIC (SOX28)

Resources




Alternative Descriptions

M41ST Series 3.3 V I2C Serial RTC NVRAM / Microprocessor Superviser - SOH-28 | Future Electronics
Soh28/I°/512Bit Battery/Rtc + Supervisor | Newark Electronics
SOH28/I°/512BIT BATTERY/RTC + SUPERVISOR | element14
Real Time Clock Serial 64Byte 28-Pin SOH T/R | Avnet America


Frequently Asked Questions

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What category does M41ST85WMH6F fall under?

The M41ST85WMH6F is listed under Clocks and Timers > Real-Time Clock (RTC) ICs > RTC - Serial Interface.

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Is the M41ST85WMH6F RoHS compliant?

Yes. This part has been flagged as RoHS Compliant by STMicroelectronics.

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