Overview
The M41ST85WMH6TR, produced by STMicroelectronics, is a versatile electronic component that combines the functions of a serial real-time clock (RTC), microprocessor supervisor, and NVRAM supervisor. Built using a low-power CMOS SRAM process, this device is designed to provide reliable timekeeping, memory management, and system supervision. It features a 64-byte memory space, including 44 bytes of NVRAM and 20 memory-mapped RTC registers, all configured in binary coded decimal (BCD) format. The device is particularly useful in applications requiring precise timekeeping, automatic backup battery switchover, and robust system supervision.
Key Specifications
| Parameter | Specification |
|---|---|
| Operating Voltage | 3.0/3.3 V (VCC = 2.7 to 3.6 V) |
| I²C Serial Interface | 400 kHz |
| NVRAM Size | 44 bytes |
| RTC Registers | 20 memory-mapped registers in BCD format |
| Crystal Oscillator | 32.768 kHz, crystal-controlled |
| Temperature Range | –40°C to +85°C |
| Package Options | 28-lead SNAPHAT® IC (SOH28), 28-lead embedded crystal SOIC (SOX28) |
| Battery Supply Current | Ultralow, 500 nA (max) |
| RoHS Compliance | Yes, lead-free second level interconnect |
| Watchdog Timer | Programmable, 62.5 ms to 128 s time-out period |
| Alarm Functions | Programmable alarm with repeat modes |
| Power-on Reset/Low Voltage Detect | Yes, with open drain reset output |
Key Features
- Automatic battery switchover and WRITE protect for internal serial RTC and external low power SRAM (LPSRAM)
- Programmable watchdog timer with 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 with open drain reset output
- Programmable squarewave generator (1 Hz to 32 kHz)
- Non-volatile time-of-day clock/calendar with automatic corrections for month and year variations
- Alarm interrupts and programmable alarm repeat modes
- Battery monitor (battery low flag)
- SNAPHAT® package option for easy battery and crystal replacement
Applications
The M41ST85WMH6TR is suitable for a wide range of applications that require precise timekeeping, reliable system supervision, and non-volatile memory. These include:
- Industrial control systems
- Medical devices
- Aerospace and defense systems
- Automotive systems
- Consumer electronics requiring real-time clock functions
- Embedded systems needing robust power management and supervision
Q & A
- What is the primary function of the M41ST85WMH6TR?
The primary function is to serve as a combination serial real-time clock, microprocessor supervisor, and NVRAM supervisor. - What is the operating voltage range of the M41ST85WMH6TR?
The operating voltage range is 2.7 to 3.6 V. - What type of interface does the M41ST85WMH6TR use for serial communication?
The device uses a 400 kHz I²C serial interface. - How much NVRAM does the M41ST85WMH6TR have?
The device has 44 bytes of general-purpose NVRAM. - What is the temperature range for the M41ST85WMH6TR?
The operating temperature range is –40°C to +85°C. - Does the M41ST85WMH6TR support automatic battery switchover?
Yes, it supports automatic battery switchover and WRITE protect for both internal serial RTC and external LPSRAM. - What is the purpose of the watchdog timer in the M41ST85WMH6TR?
The watchdog timer is programmable and can be set between 62.5 ms to 128 s to monitor system activity and reset the system if necessary. - Can the alarm functions be programmed in the M41ST85WMH6TR?
Yes, the alarm functions are programmable with repeat modes. - How does the M41ST85WMH6TR handle power failures?
The device has an early power-fail warning circuit and automatically switches to a backup battery during power failures. - What package options are available for the M41ST85WMH6TR?
The device is available in 28-lead SNAPHAT® IC (SOH28) and 28-lead embedded crystal SOIC (SOX28) packages.
