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STMicroelectronics M41ST85WMH6TR
- Part No.:
- M41ST85WMH6TR
- Manufacturer:
- STMicroelectronics
- Category:
- Real Time Clocks
- Package:
- 28-SOP (0.350", 8.89mm Width) with SNAPHAT Sockets
- Datasheet:
-
M41ST85WMH6TR.pdf
- Description:
- IC RTC CLK/CALENDAR I2C 28SOH
- Quantity:
- Payment:
- Shipping:
Inventory:3,947
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Product details
Overview
M41ST85WMH6TR from STMicroelectronics is a 3.0/3.3 V I²C combination real-time clock (RTC), microprocessor supervisor, and NVRAM supervisor in a 28-lead SOIC package with embedded crystal (SOX28). It integrates a 32.768 kHz oscillator with 12.5 pF load capacitance, supports 400 kHz I²C communication, delivers ultralow battery current of 500 nA (max), and provides automatic battery switchover at 2.50 V (VSO) for continuous RTC and external LPSRAM operation in power-fail scenarios - used in industrial PLCs requiring tamper-resistant timekeeping and non-volatile memory retention during brownouts.
For engineers reviewing the M41ST85WMH6TR datasheet, M41ST85WMH6TR pinout, M41ST85WMH6TR application, or M41ST85WMH6TR equivalent, this device serves as a single-chip solution for time-stamped logging, watchdog supervision, and battery-backed SRAM control in space-constrained embedded systems where long-term accuracy and fail-safe reset behavior are critical.
Technical Context
The M41ST85WMH6TR implements a BCD-formatted RTC with century bit support, programmable alarm (with repeat modes), and clock calibration register for temperature-induced crystal drift compensation. Its oscillator operates from 2.5 to 5.5 V and maintains stability across –40°C to +85°C using integrated 12.5 pF load capacitance.
The microprocessor supervisor includes dual reset inputs (RSTIN1/RSTIN2), open-drain reset output (RST), early power-fail warning (PFI/PFO) referenced to 1.25 V, and a programmable watchdog timer with 62.5 ms–128 s timeout range. The NVRAM supervisor automatically deselects external LPSRAM via ECON signal at VPFD = 2.60 V (nom) and asserts battery-low flag when VBAT drops below 2.5 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| I²C Speed | 400 kHz - Enables fast configuration and timestamp reads without CPU overhead in resource-limited microcontrollers. |
| Battery Current | 500 nA (max) - Ensures >10-year backup life with standard 120 mAh lithium coin cell under typical conditions. |
| Switchover Voltage | VSO = 2.50 V (nom) - Triggers seamless transition to battery before system logic fails, preserving RTC and SRAM state. |
| Reset Threshold | VPFD = 2.60 V (nom) - Provides precise low-voltage detect for reliable power-on reset and brownout recovery. |
| Oscillator Load | 12.5 pF integrated - Eliminates external capacitors, reduces board area, and improves start-up reliability across temperature. |
| Alarm Modes | Repeat daily/monthly/yearly - Supports scheduled wake-up or event-triggered interrupts without host intervention. |
| Square Wave Output | 1 Hz to 32 kHz programmable - Delivers precise timing reference for external peripherals or LED blinking without MCU timer usage. |
Pinout & Package
Package: 28-lead SOIC (SOX28), 300 mil width, with embedded 32.768 kHz crystal - no external crystal or load caps required; requires user-supplied backup battery or capacitor.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SCL | I²C clock input | Master-generated clock synchronizing all serial transfers; pulled high externally. |
| SDA | I²C bidirectional data line | Open-drain interface supporting multi-master arbitration and shared bus topology. |
| RST | Open-drain reset output | Asserts low during power-on, brownout, or watchdog timeout; drives external MCU reset directly. |
| PFI / PFO | Power-fail input/output pair | PFI monitors VCC against 1.25 V reference; PFO signals impending failure with 100 µs response. |
| ECON | Conditioned chip-enable output | Automatically disables external LPSRAM write access during VCC drop, preventing corruption. |
| IRQ/FT/OUT | Multi-function open-drain output | Delivers alarm interrupt, square wave test signal, or general-purpose output per configuration. |
| WDI | Watchdog input | Strobes watchdog timer; failure to toggle within timeout period triggers RST assertion. |
| RSTIN1 / RSTIN2 | Dual debounce reset inputs | Accept pushbutton or system-level reset signals; debounced internally to prevent chatter-induced resets. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated crystal oscillator | 32.768 kHz with 12.5 pF load - removes layout sensitivity, improves frequency stability over temperature and aging. |
| Power-down timestamp (HT bit) | Records exact time of last power loss - enables forensic analysis of system failures and uptime accounting. |
| 44-byte NVRAM + 20 RTC registers | Memory-mapped BCD registers accessible via single I²C address - simplifies firmware integration and eliminates format conversion. |
| Programmable square wave generator | 1 Hz to 32 kHz output - replaces discrete oscillator circuits for display refresh, sensor sampling, or audio tone generation. |
| Battery low monitoring | Dedicated VBL flag at 2.5 V threshold - alerts host before RTC/NVRAM data loss, enabling graceful shutdown or log preservation. |
Applications
| Industrial Data Logger | Medical Infusion Pump |
|---|---|
|
Use Scenario: Continuous timestamped recording of sensor readings and fault events during mains power interruption. IC Role / Device Role / Timing Role: RTC maintains accurate wall-clock time; NVRAM supervisor preserves buffer contents; supervisor ensures safe pump halt on voltage anomaly. Use Value: Guarantees audit-trail integrity and regulatory compliance (IEC 62304) by retaining time-stamped logs even after 72-hour battery-only operation. |
Use Scenario: Precise dosing schedule execution and therapy session logging in battery-powered portable infusion devices. IC Role / Device Role / Timing Role: Real-time clock tracks elapsed therapy time; watchdog prevents runaway motor control; PFI/PFO detects battery depletion. Use Value: Meets FDA-required dose accuracy tolerance (±1%) by eliminating time drift and ensuring deterministic reset behavior during battery swap. |
| Smart Energy Meter | Building Automation Controller |
|
Use Scenario: Tamper-proof energy consumption logging with power-loss recovery and tariff switching based on local time. IC Role / Device Role / Timing Role: RTC provides metering timebase; alarm triggers tariff change; ECON protects EEPROM writes during grid flicker. Use Value: Achieves ANSI C12.1 compliance for timekeeping accuracy (±10 ppm over –25°C to +70°C) and prevents billing errors during transient outages. |
Use Scenario: HVAC scheduling, occupancy-based lighting control, and firmware update coordination across distributed nodes. IC Role / Device Role / Timing Role: SQW output drives real-time scheduler; RSTIN1 accepts door-switch reset; IRQ/FT/OUT signals maintenance alerts. Use Value: Reduces BOM count by consolidating RTC, watchdog, and power-monitor functions into one AEC-Q200-compatible component. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar RTC + supervisor applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| DS3231M+ | Higher RTC accuracy (±2 ppm), integrated TCXO, but no NVRAM supervisor or ECON function. | Lacks automatic external SRAM write-protection and chip-enable gating - requires external logic for memory safety. | Choose for metrology-grade timekeeping where memory supervision is handled separately. |
| PCF8563T | Lower cost RTC-only IC; no microprocessor supervisor, no watchdog, no PFI/PFO, no battery switchover circuitry. | Requires companion supervisor IC (e.g., MAX809) and external battery management - increases footprint and design complexity. | Choose only when full supervision functionality is unnecessary and BOM cost is primary constraint. |
Compared with DS3231M+ and PCF8563T, the M41ST85WMH6TR uniquely integrates RTC, supervisor, and NVRAM control in one SOX28 package - reducing PCB area by 40% and eliminating inter-IC timing skew in time-critical fail-safe sequences.
Availability
M41ST85WMH6TR is available at Aetrix Electronics and suitable for industrial data loggers, medical infusion pumps, smart energy meters, and building automation controllers requiring stable component supply across extended product lifecycles.
Supply support for M41ST85WMH6TR 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 analog, MCU, power, and sensing solutions for industrial, automotive, and consumer markets.
The M41ST85W belongs to ST's TIMEKEEPER® family - engineered specifically for robust, long-life timekeeping and system supervision in harsh environments where power resilience and data integrity are non-negotiable.
FAQ
What is the maximum operating temperature range for the M41ST85WMH6TR?
The M41ST85WMH6TR is rated for continuous operation from –40°C to +85°C ambient temperature. This range is validated per STMicroelectronics' production testing and applies to both RTC accuracy and supervisor functionality, including oscillator stability and reset threshold consistency.
Does the SOX28 package include the backup battery?
No - the SOX28 package embeds the 32.768 kHz crystal but does not include the backup battery. Users must provide an external lithium coin cell or supercapacitor connected to VBAT. In contrast, the SOH28 SNAPHAT® variant mates with a separate battery/crystal top (e.g., M4T32-BR12SH1).
How does the ECON pin protect external LPSRAM during power failure?
ECON is an active-low, conditioned chip-enable output that goes high (deasserted) when VCC falls below VPFD = 2.60 V (nom), disabling external LPSRAM write access. This prevents data corruption by ensuring no partial writes occur during brownout transitions - verified in ST's AN1012 application note.
Can the M41ST85WMH6TR operate without an external crystal?
Yes - the SOX28 variant has the 32.768 kHz crystal permanently embedded in the package. No external crystal or load capacitors are required. The oscillator is factory-tuned and characterized across temperature, delivering ±20 ppm accuracy over the full operating range without user trimming.
M41ST85WMH6TR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 28-SOP (0.350", 8.89mm Width) with SNAPHAT Sockets
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Programmable:
- Not Verified
- Type:
- Clock/Calendar
- Features:
- Alarm, Leap Year, NVSRAM, Square Wave Output, Supervisor, Watchdog Timer
- Memory Size:
- 44B
- 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 ~ 3.5V
- Current - Timekeeping (Max):
- 0.5mA @ 2.7V ~ 3.6V
- Operating Temperature:
- -40°C ~ 85°C
- Mounting Type:
- Surface Mount
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 28-SOH
M41ST85WMH6TR FAQ
1.How can I place an order for M41ST85WMH6TR through Aetrix?
Please submit a Request for Quotation (RFQ) for M41ST85WMH6TR 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 M41ST85WMH6TR reliable?
The price and inventory of M41ST85WMH6TR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41ST85WMH6TR is usually 5 days.
3.What payment methods are accepted for M41ST85WMH6TR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41ST85WMH6TR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for M41ST85WMH6TR?
M41ST85WMH6TR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your M41ST85WMH6TR 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 M41ST85WMH6TR?
For technical support, including M41ST85WMH6TR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41ST85WMH6TR requirements.
6.How does Aetrix verify that M41ST85WMH6TR is sourced from the original manufacturer or authorized distributors?
All M41ST85WMH6TR 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 M41ST85WMH6TR meets industry standards.
7.What is the process for return or replacement of M41ST85WMH6TR?
All M41ST85WMH6TR units undergo pre-shipment inspection (PSI). If there is an issue with M41ST85WMH6TR, 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 M41ST85WMH6TR part is unused and in its original packaging.
Return procedure for M41ST85WMH6TR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
M41ST85WMH6TR Tags
-
MCP7940N-I/SN
Microchip Technology
-
MCP7940MT-I/MNY
Microchip Technology
-
PCF85063ATL/1,118
NXP USA Inc.
-
MCP7940NT-I/SN
Microchip Technology
-
MCP7940NT-I/MS
Microchip Technology
-
MCP7940N-I/MS
Microchip Technology
-
PCF85063AT/AY
NXP USA Inc.
-
PCF85063TP/1Z
NXP Semiconductors
-
PCF85063ATT/AJ
NXP USA Inc.
-
MCP7940NT-E/SN
Microchip Technology
-
MCP7940NT-I/MNY
Microchip Technology
-
MCP79400T-I/SN
Microchip Technology
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