Overview
The M41ST85WMX6, 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 features a 64-byte memory space, including 44 bytes of NVRAM and 20 memory-mapped RTC registers. The RTC registers are configured in binary coded decimal (BCD) format and include counters for seconds, minutes, hours, day, date, month, year, and century, along with tenths/hundredths of seconds.
The device includes an automatic backup battery switchover circuit, which ensures the RTC and external low power SRAM (LPSRAM) remain operational during power failures. It also features a 400 kHz I²C serial interface, a programmable watchdog, power-on reset/low voltage detect, and a programmable squarewave generator. The M41ST85WMX6 is available in 28-lead SOIC packages, including the SNAPHAT® IC package and the embedded crystal SOIC package, making it suitable for a variety of applications requiring precise timekeeping and supervisory functions.
Key Specifications
| Parameter | Value |
|---|---|
| Supply Voltage (VCC) | 2.7 V to 3.6 V |
| Operating Temperature | -40°C to +85°C |
| NVRAM Size | 44 bytes |
| I²C Interface Frequency | 400 kHz |
| Battery Supply Current | 500 nA (max) |
| Oscillator Frequency | 32.768 kHz (crystal-controlled) |
| Watchdog Time-out Period | 62.5 ms to 128 s |
| Reset Voltage (VPFD) | 2.60 V (nom) |
| Package Options | 28-lead SNAPHAT® IC (SOH28), 28-lead embedded crystal SOIC (SOX28) |
Key Features
- Automatic battery switchover and WRITE protect for internal serial RTC and external LPSRAM
- 400 kHz I²C serial interface
- 3.0/3.3 V operating voltage with VCC = 2.7 to 3.6 V
- Ultralow battery supply current of 500 nA (max)
- RoHS compliant and lead-free second level interconnect
- Programmable alarm with repeat modes and power-down timestamp (HT bit)
- Programmable watchdog 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 external LPSRAM with automatic switchover to backup battery and write protection via chip-enable gate
Applications
The M41ST85WMX6 is suitable for a wide range of applications that require precise timekeeping, microprocessor supervision, and NVRAM management. These include:
- Industrial control systems
- Medical devices
- Aerospace and defense systems
- Automotive systems
- Consumer electronics requiring real-time clock functions
- Embedded systems needing supervisory and NVRAM capabilities
Q & A
- What is the primary function of the M41ST85WMX6?
The M41ST85WMX6 is a combination serial real-time clock, microprocessor supervisor, and NVRAM supervisor.
- What is the operating voltage range of the M41ST85WMX6?
The operating voltage range is 2.7 V to 3.6 V.
- What is the frequency of the I²C interface?
The I²C interface operates at 400 kHz.
- How much NVRAM does the M41ST85WMX6 have?
The device has 44 bytes of NVRAM.
- What is the purpose of the automatic battery switchover feature?
The automatic battery switchover feature ensures that the internal serial RTC and external LPSRAM remain operational during power failures by switching to a backup battery.
- What are the package options for the M41ST85WMX6?
The device is available in 28-lead SNAPHAT® IC (SOH28) and 28-lead embedded crystal SOIC (SOX28) packages.
- What is the range of the programmable watchdog time-out period?
The programmable watchdog time-out period ranges from 62.5 ms to 128 s.
- Does the M41ST85WMX6 support power-on reset and low voltage detection?
Yes, it includes power-on reset/low voltage detect with an open drain reset output.
- What is the frequency range of the programmable squarewave generator?
The programmable squarewave generator operates from 1 Hz to 32 kHz.
- Is the M41ST85WMX6 RoHS compliant?
Yes, the device is RoHS compliant and features lead-free second level interconnect.
