MCP79411-I/ST

Real Time Clock Overview

The MCP79411-I/ST is a battery-backed I2C Real-Time Clock/Calendar (RTCC) from Microchip Technology, housed in an 8-lead SOIC package. It operates within a voltage range of 1.8V to 5.5V and supports an industrial temperature range of -40°C to +85°C. The device features a 32.768 kHz oscillator with on-chip digital trimming for ±1 ppm resolution. Key specifications include 64 bytes of battery-backed SRAM, 1 Kbit of EEPROM, and a preprogrammed 64-bit EUI-48 MAC address. Timekeeping accuracy is maintained via automatic switchover to a backup supply (1.3V to 5.5V), with typical timekeeping currents of 1.2 µA at 3.3V (VCC) and 925 nA at 3.0V (VBAT).

Real Time Clock Feature Summary

• Integrated RTCC with dual programmable alarms and power-fail timestamp logging.
• 1 Kbit EEPROM with software write-protect and 64-byte battery-backed SRAM.
• Preprogrammed 64-bit EUI-48 MAC address in protected EEPROM area.
• On-chip digital trimming compensates for crystal frequency variance (±129 ppm range).
• I2C interface compatible up to 400 kHz with open-drain multifunction output pin.

Real Time Clock Applications

• Embedded systems requiring precise timekeeping and calendar functions.
• Devices needing non-volatile storage for configuration data or user memory.
• Networked equipment utilizing the integrated EUI-48 MAC address for identification.
• Battery-powered applications requiring low standby current and automatic power switchover.

Real Time Clock Procurement Notes

Verify that the ordering suffix 'I' corresponds to the Industrial temperature range (-40°C to +85°C) and '/ST' denotes the 8-lead SOIC package. Confirm the specific variant is MCP79411 to ensure the presence of the preprogrammed EUI-48 address, as opposed to the unprogrammed MCP79410 or EUI-64 MCP79412. Cross-reference the datasheet revision DS20002266J for accurate electrical characteristics.

Real Time Clock Selection Notes

Select this component when an I2C-compatible RTCC with integrated non-volatile memory and unique hardware addressing is required. Ensure the application utilizes a 32.768 kHz crystal with a load capacitance between 6 pF and 9 pF. Verify that the system voltage remains within the 1.8V to 5.5V operating range and that the I2C bus pull-up resistors are appropriately sized for the desired clock speed.

Real Time Clock Part Context

The MCP79411 belongs to the MCP7941X family, which includes the MCP79410 and MCP79412. These devices share identical functionality and pinouts but differ in their protected EEPROM content: the MCP79410 is unprogrammed, the MCP79411 contains an EUI-48 address, and the MCP79412 contains an EUI-64 address. All variants support the same SOIC, MSOP, TSSOP, and TDFN packages.

Real Time Clock Replacement Considerations

Direct functional substitutes within the same family include the MCP79410-I/ST and MCP79412-I/ST. Note that the MCP79410 lacks the preprogrammed MAC address, while the MCP79412 uses a 64-bit address format. Other packages such as MSOP or TSSOP may be used if pin compatibility is verified, provided the thermal and mechanical constraints are met.

Real Time Clock FAQ

How does the MCP79411 handle power loss?

The device automatically switches to the VBAT backup supply when VCC drops below the trip voltage (typically 1.5V). It logs the exact time of power failure and restoration using the Power-Fail Timestamp registers, maintaining time and SRAM data during the outage.

What is the purpose of the MFP pin?

The Multifunction Pin (MFP) is an open-drain output configurable as an alarm indicator, a selectable frequency square wave generator, or a general-purpose output controlled by the CONTROL register.

Can the EUI-48 address be rewritten?

No, the 64-bit protected EEPROM area containing the EUI-48 address requires a robust unlock sequence for writing. It is designed for permanent storage of unique identifiers and is not intended for frequent rewriting.