M41ST85WMX6TR

Real Time Clock Overview

The M41ST85WMX6TR is a combination serial real-time clock, microprocessor supervisor, and NVRAM supervisor manufactured by STMicroelectronics. It integrates a low-power CMOS SRAM process with a 64-byte memory space, comprising 44 bytes of NVRAM and 20 memory-mapped RTC registers configured in binary coded decimal (BCD). The device operates on a supply voltage range of 2.7V to 3.6V with a maximum current consumption of 0.5mA. It features an ultralow battery supply current of 500nA (max) and supports a 400 kHz I²C serial interface. The component is housed in a 28-SOIC package with embedded crystal and functions within an industrial temperature range of -40°C to +85°C.

Real Time Clock Feature Summary

• Integrated Real-Time Clock with 44 bytes of general-purpose NVRAM and programmable alarm with repeat modes
• Microprocessor Supervisor featuring a programmable watchdog timer (62.5 ms to 128 s time-out) and early power-fail warning circuit
• Automatic battery switchover and write protect mechanisms for internal serial RTC and external low power SRAM
• Clock calibration register allows compensation for crystal variations over temperature

Real Time Clock Applications

• Smart Grid Distribution and Smart Meters
• Industrial systems requiring microprocessor supervision and timekeeping
• Battery-operated equipment needing low-power RTC and NVRAM functionality

Real Time Clock Procurement Notes

Verify the specific ordering suffix MX6TR corresponds to the Tape and Reel packaging configuration as indicated in distributor listings. Confirm that the RoHS compliance status aligns with Ecopack1 specifications. Ensure the industrial grade (-40°C to +85°C) meets the operational requirements of the target application environment before procurement.

Real Time Clock Selection Notes

Select this component when a combined RTC, NVRAM, and supervisor solution is required in a single 28-SOIC package. The M41ST85W series is suitable for designs operating at 3.0V or 3.3V. Consider the M41ST87W variant if tamper detection and larger NVRAM capacity are needed. Verify that the 400 kHz I²C interface speed is compatible with the system bus constraints.

Real Time Clock Part Context

The M41ST85WMX6TR belongs to the M41ST85W family of serial real-time clocks. It shares core functionalities with variants like the M41ST85YMX6, which differs primarily in supply voltage ranges (4.5V to 5.5V). The 'W' suffix typically denotes the wide temperature industrial grade, while 'MX6TR' specifies the surface-mount SOIC package and reel packaging format.

Real Time Clock Replacement Considerations

The M41ST85YMX6 serves as a functional substitute but requires a 4.5V to 5.5V supply voltage instead of 2.7V to 3.6V. Designers must verify voltage level compatibility and ensure the pinout remains identical between the W and Y variants before swapping.