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Home > Products > Integrated Circuits (ICs) > Clock/Timing > Real Time Clocks

STMicroelectronics M41ST87WSS6F

Name: M41ST87WSS6F
Brand: STMicroelectronics
SKU: M41ST87WSS6F
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: M41ST87WSS6F

Manufacturer:: STMicroelectronics

Category:: Real Time Clocks

Package:: 20-SSOP (0.209", 5.30mm Width)

Datasheet:: M41ST87WSS6F.pdf

Description:: IC RTC CLK/CALENDAR I2C 20SSOP

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Product details

Overview

M41ST87WSS6F from STMicroelectronics is a secure serial real-time clock (RTC) and non-volatile RAM (NVRAM) supervisor IC with tamper detection, 128 bytes of clearable user NVRAM, dual independent power-fail comparators (VPFD ≈ 2.9 V / 2.63 V), and embedded 32.768 kHz crystal in SOX28 package. It provides timekeeping (century/year/month/date/hour/minute/second/tenths-hundredths), programmable alarm/interrupt, watchdog timer, battery-low flag, and microprocessor power-on reset - deployed in industrial security modules requiring authenticated time-stamping and memory wipe on intrusion.

For engineers reviewing the M41ST87WSS6F datasheet, M41ST87WSS6F pinout, M41ST87WSS6F application, or M41ST87WSS6F equivalent, key selection criteria include I²C-compatible 400 kHz interface timing, ultra-low 500 nA battery supply current, tamper event timestamping with RAM-clear capability, and SSOP20 vs. SOX28 package-dependent features (e.g., TPCLR, EX, WDI).

Technical Context

The M41ST87W operates as a self-contained RTC/NVRAM supervisor with two independent tamper inputs (TP1IN/TP2IN), each configurable for normally open/closed detection, sampling control, polarity, and RAM-clear triggering (CLR1/CLR2). Its internal 32.768 kHz oscillator is crystal-embedded in SOX28 and external in SSOP20 variants - oscillator stop detection (OF bit) ensures clock integrity monitoring.

It integrates dual 1.25 V reference-based power-fail comparators (PFI1/PFI2) with selectable VPFD thresholds (THS = 0/1), generating PFO1/PFO2 outputs to initiate backup switchover. The I²C interface supports automatic address increment during sequential READ/WRITE, and all registers - including TIMEKEEPER® BCD calendar, alarm, watchdog, and tamper status - are accessible via 7-bit slave address 0x68 (default).

Key Specifications

Parameter	Value and Actual Design Meaning
Supply voltage	3.0–3.6 V (VCC); supports stable RTC/NVRAM operation across industrial 3.3 V rail tolerances.
I²C bus speed	400 kHz (fast-mode); enables high-throughput register access without timing margin violations.
Battery supply current	500 nA (typ); extends lithium coin-cell life beyond 10 years in backup mode.
Tamper inputs	2 independent pins (TP1IN/TP2IN); support timestamped event logging and selective RAM clearing (internal 128B or external LPSRAM).
Power-fail threshold	VPFD ≈ 2.9 V (THS=1) or 2.63 V (THS=0); precise switchover point avoids false triggers near brown-out.
Output drivers	IRQ/OUT, RST, PFO1/PFO2, SQW/FT, F32k - all open-drain (default); configurable to full-CMOS where supported.
Crystal integration	Embedded 32.768 kHz crystal in SOX28 package only; eliminates external crystal layout sensitivity and tampering risk.

Pinout & Package

Package: SSOP20 (300 mil width), RoHS-compliant, surface-mount. Pin count: 20. No internal crystal - requires external 32.768 kHz crystal connected between XI and XO pins.

Pin/Terminal	Circuit Role	Design Meaning
VCC	Main supply input	3.0–3.6 V primary power; powers RTC, NVRAM, and logic; auto-switches to VBAT on PFI assertion.
VBAT	Battery backup input	Connects to lithium coin cell; sustains timekeeping and SRAM retention when VCC drops below VPFD.
SCL	I²C clock input	Controls serial data transfer timing; 400 kHz max frequency; requires external pull-up to VCC or VBAT.
SDA	I²C bidirectional data	Open-drain I/O; shares bus with other I²C devices; supports ACK/NACK handshake per protocol.
IRQ/OUT	Interrupt/output pin	Open-drain output; asserts on alarm, watchdog timeout, or tamper event; defaults active-low.
SQW/FT	Square wave/frequency test	Programmable output (open-drain or CMOS); delivers 1 Hz, 32.768 kHz, or custom square waves.
F32k	32 kHz square wave output	Dedicated open-drain 32.768 kHz output; usable for system clock synchronization or calibration reference.
PFI1 / PFI2	Power-fail input 1/2	Analog comparator inputs; compare against internal 1.25 V reference to detect VCC droop.
PFO1 / PFO2	Power-fail output 1/2	Open-drain outputs; indicate comparator trip; drive external hold or enable circuits during switchover.
RSTIN1 / RSTIN2	External reset inputs	Debounced asynchronous inputs; trigger RST output pulse (active-low, open-drain) on edge or level.
RST	Reset output	Open-drain microprocessor reset signal; asserted low during power-on or external reset assertion.
TP1IN / TP2IN	Tamper detection inputs	Independent digital inputs; sampled at configurable rate; trigger timestamped event and optional RAM clear.
XI / XO	Crystal oscillator interface	Connect external 32.768 kHz tuning-fork crystal; XO drives internal oscillator circuitry.
VSS	Ground reference	System ground return; all analog/digital references tied to this node.
NC	No connect	Unbonded pin; must be tied to VSS per datasheet to prevent floating noise coupling.

Key Features

Feature	Design Value
Secure tamper response	Timestamped event logging + hardware-triggered RAM clear (128B NVRAM or external LPSRAM) upon TP1IN/TP2IN assertion.
Auto-switchover supervision	Dual independent PFI comparators with selectable VPFD (2.63 V / 2.9 V) ensure reliable battery backup activation before system crash.
Full-time 32 kHz output	F32k pin delivers continuous 32.768 kHz square wave - usable for precision timing in adjacent circuits without software overhead.
Programmable watchdog	WDI input accepts strobe pulses; timeout period set via register; IRQ/OUT asserts on expiration to force system recovery.
Electronic serial number	Unique 8-byte factory-programmed ID stored in ROM; enables device authentication and firmware binding in secure boot flows.
Power-on reset generation	Internal POR circuit asserts RST for ≥200 ms at power-up; eliminates need for external RC reset generator.

Applications

Industrial Security Module

Energy Metering System

Use Scenario: Tamper-proof time-stamped event logging in utility-grade electricity meters exposed to physical intrusion attempts.

IC Role / Device Role / Timing Role: RTC/NVRAM supervisor providing authenticated timestamping, memory wipe on cover removal, and backup power management during grid outage.

Use Value: Prevents post-event data manipulation by clearing NVRAM and recording exact tamper time (down to hundredths of second) before power loss.

Use Scenario: Accurate billing interval tracking and firmware update validation in smart meters operating across wide temperature ranges.

IC Role / Device Role / Timing Role: Primary timebase and calendar engine; maintains BCD-encoded date/time with leap-year correction and century bit handling.

Use Value: Eliminates software-based time drift compensation; guarantees ±2 ppm accuracy over –40°C to +85°C using embedded crystal (SOX28) or calibrated external crystal (SSOP20).

Medical Data Logger

POS Terminal with Audit Trail

Use Scenario: Long-term patient vital sign recording in portable diagnostic devices requiring FDA-compliant audit trails.

IC Role / Device Role / Timing Role: Secure timekeeper with battery-backed NVRAM storing timestamps and sensor metadata; tamper detection disables logging on enclosure breach.

Use Value: Meets 21 CFR Part 11 requirements via hardware-enforced timestamp integrity and write-once event logging with irreversible RAM clear.

Use Scenario: Transaction timestamping and receipt generation in payment terminals subject to PCI PTS physical security mandates.

IC Role / Device Role / Timing Role: Trusted time source and NVRAM supervisor; stores encrypted transaction logs with tamper-evident time stamps.

Use Value: Enables cryptographic signing of time-stamped logs using unique 8-byte electronic serial number - critical for forensic auditability.

Equivalent & Alternatives

The following parts are listed as comparable options for similar RTC/NVRAM supervisor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
DS3231SN#T&R	Higher accuracy (±2 ppm, integrated TCXO); no tamper detection; 236 bytes NVRAM; I²C only; no watchdog or PFI comparators.	Lacks tamper response, power-fail supervision, and RAM-clear functionality - unsuitable for security-critical or industrial backup switchover use cases.	Select DS3231 when highest RTC accuracy is primary requirement and security features are handled externally.
PCF2129A	Lower power (200 nA battery current); no tamper inputs; no PFI comparators; no watchdog; 128 bytes NVRAM; I²C only.	Missing all security and supervision functions - limited to basic timekeeping in cost-sensitive consumer applications.	Choose PCF2129A only for ultra-low-power, non-secure RTC needs where tamper detection and backup control are unnecessary.

Compared with DS3231SN and PCF2129A, the M41ST87WSS6F uniquely combines tamper timestamping with hardware RAM clear, dual PFI comparators for seamless backup switchover, and watchdog supervision - making it the sole option among these three for certified industrial security loggers.

Availability

M41ST87WSS6F is available at Aetrix Electronics and suitable for industrial security modules, smart energy meters, medical data loggers, and PCI PTS-certified POS terminals requiring stable component supply, long-lifecycle availability, and traceable sourcing for safety-critical deployments.

Supply support for M41ST87WSS6F 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, analog ICs, MEMS, and power management solutions for automotive, industrial, and consumer markets.

The M41ST87W belongs to ST's TIMEKEEPER® secure RTC product line, engineered specifically for applications demanding authenticated time-stamping, tamper-resilient memory, and autonomous power-fail response in harsh or regulated environments.

FAQ

What is the function of the TPCLR pin on M41ST87WSS6F?

The TPCLR pin is available only in the SOX28 package (not SSOP20) and serves as a hardware-controlled RAM clear trigger. When asserted, it initiates immediate clearing of the 128-byte user NVRAM and optionally external LPSRAM, independent of software control - enabling fail-safe data erasure during physical tampering events.

Does M41ST87WSS6F support both 3.3 V and 5.0 V operation?

No - the M41ST87W variant is specified exclusively for 3.0–3.6 V operation. The 5.0 V version is the M41ST87Y (discontinued for new designs). Attempting 5.0 V operation on M41ST87WSS6F exceeds absolute maximum ratings and risks permanent damage to the I²C interface and internal logic.

How does the M41ST87W handle leap year correction?

The M41ST87W implements automatic leap year correction in hardware: its BCD-encoded calendar registers (century/year/month/date) adjust February day count to 29 days in years divisible by 4, except century years not divisible by 400 - matching Gregorian calendar rules without firmware intervention.

Can the SQW/FT pin generate a 1 Hz output for real-time clock display?

Yes - the SQW/FT pin is programmable to output 1 Hz, 32.768 kHz, or custom frequencies (e.g., 1024 Hz, 4096 Hz) via register configuration. In 1 Hz mode, it drives LED or LCD segment drivers directly for wall-clock display, with open-drain output supporting standard pull-up resistor interfacing.

M41ST87WSS6F Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 20-SSOP (0.209", 5.30mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Active

Programmable:: Not Verified

Type:: Clock/Calendar

Features:: Alarm, Leap Year, NVSRAM, Square Wave Output, Supervisor, Watchdog Timer

Memory Size:: 128B

Time Format:: HH:MM:SS:hh (24 hr)

Date Format:: YY-MM-DD-dd

Interface:: I2C, 2-Wire Serial

Voltage - Supply:: 2.7V ~ 3.6V

Voltage - Supply, Battery:: 2.5V ~ 3.6V

Current - Timekeeping (Max):: 0.5mA @ 2.7V ~ 3.6V

Operating Temperature:: -40°C ~ 85°C

Mounting Type:: Surface Mount

Grade:: -

Qualification:: -

Supplier Device Package:: 20-SSOP

M41ST87WSS6F FAQ

1.How can I place an order for M41ST87WSS6F through Aetrix?

Please submit a Request for Quotation (RFQ) for M41ST87WSS6F on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for M41ST87WSS6F reliable?

The price and inventory of M41ST87WSS6F are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41ST87WSS6F is usually 5 days.

3.What payment methods are accepted for M41ST87WSS6F?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41ST87WSS6F transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for M41ST87WSS6F?

M41ST87WSS6F orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your M41ST87WSS6F order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for M41ST87WSS6F?

For technical support, including M41ST87WSS6F datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41ST87WSS6F requirements.

6.How does Aetrix verify that M41ST87WSS6F is sourced from the original manufacturer or authorized distributors?

All M41ST87WSS6F products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that M41ST87WSS6F meets industry standards.

7.What is the process for return or replacement of M41ST87WSS6F?

All M41ST87WSS6F units undergo pre-shipment inspection (PSI). If there is an issue with M41ST87WSS6F, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The M41ST87WSS6F part is unused and in its original packaging.

Return procedure for M41ST87WSS6F:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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