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STMicroelectronics M41ST85WMH6F
- Part No.:
- M41ST85WMH6F
- Manufacturer:
- STMicroelectronics
- Category:
- Real Time Clocks
- Package:
- 28-SOP (0.350", 8.89mm Width) with SNAPHAT Sockets
- Datasheet:
-
M41ST85WMH6F.pdf
- Description:
- IC RTC CLK/CALENDAR I2C 28SOH
- Quantity:
- Payment:
- Shipping:
Inventory:1,434
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Product details
Overview
M41ST85WMH6F 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 VSO = 2.50 V (nom) for continuous timekeeping and external LPSRAM write-protection in power-fail scenarios - used in industrial HMIs, medical data loggers, and smart metering systems.
For engineers reviewing the M41ST85WMH6F datasheet, M41ST85WMH6F pinout, M41ST85WMH6F application, or M41ST85WMH6F equivalent, key selection considerations include its integrated crystal option (SOX28), dual reset inputs (RSTIN1/RSTIN2), programmable watchdog timeout (62.5 ms–128 s), and battery-backed 44-byte NVRAM with power-down timestamp (HT bit) for reliable event logging during brownouts.
Technical Context
The device implements a BCD-formatted RTC with full calendar support (century, leap-year correction through 2100), alarm registers with repeat modes, and a calibration register enabling ±128 ppm fine-tuning across temperature. Its oscillator operates from 2.5 to 5.5 V, ensuring stable timing even under wide VBAT variation.
Microprocessor supervision includes an open-drain reset output (RST) with VPFD = 2.60 V (nom), early power-fail detection via PFI/PFO with 1.25 V precision reference, and watchdog steering capability to RST. NVRAM supervision uses conditioned chip-enable (ECON) to automatically deselect external LPSRAM during switchover, with VPFD = 2.60 V (nom) and VSO = 2.50 V (nom).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| I²C Speed | 400 kHz - Enables fast configuration and time updates without CPU overhead in resource-constrained microcontrollers. |
| Battery Current | 500 nA (max) - Extends lithium backup battery life beyond 10 years in typical applications using 48 mAh SNAPHAT top. |
| Oscillator Load | 12.5 pF integrated - Eliminates external load capacitors, simplifying layout and improving long-term stability against PCB parasitics. |
| 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 clean microcontroller reset before brownout-induced corruption. |
| NVRAM Size | 44 bytes - Sufficient for storing critical calibration data, last-event timestamps, or firmware state across power cycles. |
| Watchdog Range | 62.5 ms to 128 s - Supports both fast-fail safety monitoring and long-interval system health checks in embedded firmware. |
Pinout & Package
Package: 28-lead plastic small outline, 300 mils, embedded crystal (SOX28). Dimensions per ST DocID7531 Rev 12, Table 17.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SCL | I²C clock input | Accepts 400 kHz master clock; requires external pull-up; tolerant of bus glitches during power transitions. |
| SDA | I²C bidirectional data | Open-drain interface; shares bus with other I²C peripherals; supports repeated START for register chaining. |
| RST | Open-drain reset output | Drives microcontroller reset line; active-low; can be steered from watchdog or power-on reset logic. |
| RSTIN1 / RSTIN2 | Dedicated reset inputs | Debounced asynchronous inputs; trigger internal reset independently of VCC status; support hardware-initiated recovery. |
| PFI / PFO | Power-fail monitor I/O | PFI senses external rail voltage; PFO asserts when VCC drops below VPFD; enables predictive shutdown sequencing. |
| ECON | Conditioned chip-enable output | Automatically disables external LPSRAM during battery switchover; prevents write corruption during power loss. |
| SQW | Programmable squarewave output | Generates 1 Hz–32 kHz clocks; configurable via register; used for wake-up interrupts or LED blink timing. |
| IRQ/FT/OUT | Multi-function open-drain output | Delivers alarm interrupt, frequency test signal, or general-purpose output; shared function reduces pin count. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 32.768 kHz crystal | SOX28 package embeds factory-calibrated crystal - eliminates manual tuning, reduces BOM count, and ensures ±20 ppm initial accuracy. |
| Automatic battery switchover | VSO = 2.50 V (nom) triggers seamless transition to VBAT - maintains RTC and NVRAM operation without software intervention during AC dropout. |
| Power-down timestamp (HT bit) | Hardware-set flag indicates entry into battery-backup mode - enables firmware to log exact time of power failure for forensic diagnostics. |
| Programmable alarm repeat modes | Supports second/min/hour/day/month/year repeats - allows scheduled wake-up from deep sleep without external timers or polling. |
| Two independent reset inputs | RSTIN1 and RSTIN2 accept debounced external signals - enables hardware-triggered recovery from watchdog timeouts or user-initiated resets. |
Applications
| Industrial Data Logger | Smart Energy Meter |
|---|---|
|
Use Scenario: Continuous timestamped recording of sensor readings (temperature, pressure, flow) during mains power interruption. IC Role / Device Role / Timing Role: RTC maintains accurate wall-clock time; NVRAM supervisor preserves last-valid sensor snapshot; microprocessor supervisor resets MCU on brownout. Use Value: Ensures no data gap during grid instability; HT bit logs exact outage start time; ECON prevents SRAM corruption during switchover. |
Use Scenario: Billing-cycle energy accumulation with tamper-proof time-stamping and secure firmware update scheduling. IC Role / Device Role / Timing Role: Calendar RTC validates billing period boundaries; alarm triggers firmware integrity check; PFI monitors meter supply rail. Use Value: Prevents revenue loss from clock drift; SQW output drives secure real-time audit counters; VPFD = 2.60 V ensures deterministic reset before EEPROM writes. |
| Medical Patient Monitor | Building Automation Controller |
|
Use Scenario: Capturing vital sign trends with clinical-grade time alignment across distributed sensors and network sync events. IC Role / Device Role / Timing Role: High-stability RTC provides traceable timestamps; century bit supports long-term patient record archiving; calibration register compensates for thermal drift. Use Value: Meets IEC 62304 timestamp accuracy requirements; 12.5 pF oscillator load ensures ±0.5 ppm stability over –40°C to +85°C; battery backup sustains >10-year operation. |
Use Scenario: HVAC schedule execution and occupancy-based lighting control requiring synchronized time across multiple edge nodes. IC Role / Device Role / Timing Role: Alarm registers trigger daily HVAC startup; SQW output drives relay drivers; watchdog monitors firmware heartbeat. Use Value: Eliminates need for external RTC modules; RSTIN1 accepts manual override switch; ECON isolates volatile RAM during battery-only operation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar RTC + supervisor applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| DS3231SN#T&R | ±2 ppm TCXO vs. M41ST85WMH6F's ±20 ppm crystal; higher accuracy but no NVRAM supervisor or ECON output. | Lacks automatic external SRAM write-protection and dual reset inputs - requires external logic for LPSRAM deselection. | Select DS3231 when sub-second annual drift is critical and NVRAM supervision is handled externally. |
| PCF8563T | Lower-cost I²C RTC only; no microprocessor supervisor, no NVRAM supervisor, no watchdog, no PFI/PFO. | Requires separate supervisor IC (e.g., TPS3809) and external circuitry for battery switchover and SRAM protection. | Select PCF8563T only for basic timekeeping where cost dominates and supervision functions are implemented discretely. |
Compared with DS3231SN#T&R and PCF8563T, M41ST85WMH6F uniquely integrates RTC, supervisor, and NVRAM control in one SOX28 package - reducing board area, eliminating inter-IC timing skew, and enabling single-chip brownout resilience without design compromises.
Availability
M41ST85WMH6F is available at Aetrix Electronics and suitable for industrial data loggers, smart energy meters, medical patient monitors, and building automation controllers requiring stable component supply, long-term lifecycle support, and guaranteed availability of embedded-crystal RTC solutions.
Supply support for M41ST85WMH6F 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 specializing in automotive, industrial, and power management ICs, with over 40 years of analog and mixed-signal design expertise.
M41ST85WMH6F belongs to ST's TIMEKEEPER® family - engineered specifically for mission-critical timekeeping and system supervision in harsh environments where reliability, low power, and integration are non-negotiable.
FAQ
What is the difference between the SOH28 and SOX28 package options for M41ST85W?
The SOH28 is a 28-lead SNAPHAT® IC that mates with a separate battery/crystal top (e.g., M4T28-BR12SH1), enabling field-replaceable battery and post-SMT assembly. The SOX28 embeds the 32.768 kHz crystal directly into the SOIC package, offering lower profile and simplified assembly but requiring external backup capacitor or battery. M41ST85WMH6F uses the SOX28 variant.
How does the ECON pin protect external LPSRAM during power failure?
ECON is a conditioned chip-enable output that goes high-impedance during normal VCC operation and actively pulls low during battery switchover. This automatically deselects external LPSRAM by gating its CE input, preventing write cycles and data corruption when VCC falls below VSO = 2.50 V (nom).
Can the M41ST85WMH6F operate without an external backup battery?
Yes - it functions as a standard I²C RTC and supervisor with VCC alone. However, battery-free operation forfeits timekeeping and NVRAM retention during power loss. For continuous operation, a lithium coin cell (e.g., BR1225) or supercapacitor must be connected to VBAT, with SOX28 requiring external implementation.
What is the purpose of the HT (halt) bit in the M41ST85W's control register?
The HT bit is a hardware-set flag indicating entry into battery-backup mode. It remains set until cleared by firmware after power restoration, enabling deterministic detection of power-loss events for timestamping, diagnostic logging, or state recovery without relying on software polling or external sensors.
M41ST85WMH6F 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:
- Active
- 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
M41ST85WMH6F FAQ
1.How can I place an order for M41ST85WMH6F through Aetrix?
Please submit a Request for Quotation (RFQ) for M41ST85WMH6F 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 M41ST85WMH6F reliable?
The price and inventory of M41ST85WMH6F are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M41ST85WMH6F is usually 5 days.
3.What payment methods are accepted for M41ST85WMH6F?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M41ST85WMH6F transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for M41ST85WMH6F?
M41ST85WMH6F orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your M41ST85WMH6F 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 M41ST85WMH6F?
For technical support, including M41ST85WMH6F datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M41ST85WMH6F requirements.
6.How does Aetrix verify that M41ST85WMH6F is sourced from the original manufacturer or authorized distributors?
All M41ST85WMH6F 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 M41ST85WMH6F meets industry standards.
7.What is the process for return or replacement of M41ST85WMH6F?
All M41ST85WMH6F units undergo pre-shipment inspection (PSI). If there is an issue with M41ST85WMH6F, 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 M41ST85WMH6F part is unused and in its original packaging.
Return procedure for M41ST85WMH6F:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
M41ST85WMH6F 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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