MCP79402-I/ST

Real Time Clock Overview

The MCP79402-I/ST is a battery-backed I²C Real-Time Clock/Calendar (RTCC) from Microchip Technology, housed in an 8-lead TSSOP package. It operates within a voltage range of 1.8V to 5.5V and supports industrial temperatures from -40°C to +85°C. The device tracks time using internal counters for hours, minutes, seconds, day of week, date, month, and year, with leap year compensation through 2399. It features 64 bytes of battery-backed SRAM and 8 bytes of protected EEPROM preprogrammed with an EUI-64 MAC address. Timekeeping current is typically 1.2 µA at 3.3V on VCC and 925 nA at 3.0V on backup.

Real Time Clock Feature Summary

• Integrated RTCC with dual programmable alarms and power-fail timestamp logging.
• 64-byte user-accessible SRAM and 8-byte protected EEPROM containing a factory-programmed EUI-64™ MAC address.
• On-chip digital trimming allows frequency calibration with ±1 ppm resolution over a ±129 ppm range.
• Versatile multifunction pin (MFP) configurable as alarm output, selectable frequency square wave, or general purpose output.

Real Time Clock Applications

• Systems requiring precise timekeeping with automatic switchover to battery backup upon primary power loss.
• Networked devices utilizing the preprogrammed EUI-64 address for unique identification.
• Industrial equipment operating within -40°C to +85°C temperature ranges.
• Applications needing non-volatile storage for critical data via the protected EEPROM unlock sequence.

Real Time Clock Procurement Notes

Verify the specific suffix 'I/ST' corresponds to the Industrial temperature grade (-40°C to +85°C) and TSSOP-8 package. Confirm that the EUI-64™ MAC address is required, as this distinguishes the MCP79402 from the unprogrammed MCP79400 or EUI-48 MCP79401. Ensure the design includes external load capacitors matched to the selected 32.768 kHz crystal's specified load capacitance.

Real Time Clock Selection Notes

Select the MCP79402 when a unique 64-bit identifier is needed alongside timekeeping functions. The device supports I²C clock rates up to 400 kHz at voltages above 2.5V. Designers must account for the open-drain nature of SDA, SCL, and MFP pins by implementing appropriate pull-up resistors. If EUI-48 addressing is sufficient, the MCP79401 variant may be considered; otherwise, the MCP79400 offers no preprogrammed ID.

Real Time Clock Part Context

The MCP79402 belongs to the MCP7940X family, which shares identical pinouts and core functionality but differs in EEPROM content. The family includes the MCP79400 (unprogrammed), MCP79401 (EUI-48), and MCP79402 (EUI-64). All variants support the same low-power features, digital trimming, and alarm configurations, allowing for flexible inventory management based on identification requirements.

Real Time Clock Replacement Considerations

The MCP79401T-I/ST serves as a functional substitute if EUI-48 addressing is acceptable. The MCP79400T-I/ST is compatible for applications not requiring a preprogrammed MAC address. Verify that any replacement maintains the TSSOP-8 package and Industrial temperature rating.