Microchip Technology MCP79402-I/ST

Overview

MCP79402-I/ST from Microchip Technology is a battery-backed I²C Real-Time Clock/Calendar (RTCC) with integrated 64-byte SRAM, 8-byte protected EEPROM (preprogrammed with EUI-64™), dual programmable alarms, and digital trimming. It operates from 1.8V–5.5V, consumes 1.2 µA at 3.3V V_CC, and maintains time during power loss via automatic switchover to backup supply (VBAT = 1.3V–5.5V). Used in industrial metering, smart sensors, and embedded control systems requiring precise timestamping and nonvolatile memory.

For engineers reviewing the MCP79402-I/ST datasheet, MCP79402-I/ST pinout, MCP79402-I/ST application, or MCP79402-I/ST equivalent, this page delivers verified specifications, package mapping, I²C timing compliance (up to 400 kHz), oscillator calibration resolution (±1 ppm), power-fail timestamp logging, and functional alternatives for design-in validation.

Technical Context

The MCP79402-I/ST implements a fully autonomous RTCC core synchronized to an external 32.768 kHz crystal or clock source, with on-chip digital trimming (±129 ppm range, ±1 ppm resolution) to compensate for crystal tolerance and temperature drift. Its oscillator failure detection (OSCRUN flag) and timeout period (T_OSF = 1 ms) ensure runtime integrity monitoring.

All timekeeping registers (seconds through year), alarm comparators (two independent modules), power-fail timestamp (switchover and restore events), and configuration logic are accessible via I²C using two distinct slave addresses: 0xD8/D9 (RTCC/SRAM) and 0xA8/A9 (EEPROM). The MFP pin supports configurable square-wave output (1 Hz to 32.768 kHz), alarm assertion, or general-purpose open-drain output.

Key Specifications

Pinout & Package

Package: 8-lead SOIC (Small Outline Integrated Circuit), lead pitch 1.27 mm, body width 3.9 mm, RoHS-compliant, rated for industrial temperature range (−40°C to +85°C).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock/calendar applications.

Compared with DS3231M+, the MCP79402-I/ST trades integrated temperature compensation for lower BOM cost, programmable trimming, and built-in EUI-64™ identity; versus MCP79401-I/ST, it provides extended MAC addressing essential for IPv6 and modern IoT stack compatibility.

Availability

MCP79402-I/ST is available at Aetrix Electronics and suitable for smart metering, industrial data loggers, and medical device timekeeping requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for MCP79402-I/ST includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Microchip Technology Inc. is a leading provider of microcontrollers, analog components, and timing solutions, headquartered in Chandler, Arizona, with global manufacturing and support infrastructure.

The MCP7940X family was designed specifically for embedded systems requiring robust, low-power, battery-backed timekeeping with integrated memory and secure identity - targeting industrial, medical, and energy applications.

FAQ

What is the primary function of the MCP79402-I/ST in a system?

The MCP79402-I/ST serves as a standalone Real-Time Clock/Calendar (RTCC) that maintains accurate time and date across power cycles using a 32.768 kHz crystal, battery backup, and internal counters. It also provides 64-byte SRAM, 8-byte EUI-64™ EEPROM, dual alarms, and power-fail timestamping - making MCP79402-I/ST ideal for systems needing reliable timekeeping without host MCU intervention.

Does the MCP79402-I/ST support both 12-hour and 24-hour time formats?

Yes, the MCP79402-I/ST supports both 12-hour and 24-hour time formats. The format is selected via the 12/24 bit in the RTCHOUR register (address 0x02), and the setting applies consistently across all timekeeping and alarm registers. The MCP79402-I/ST automatically handles AM/PM toggling and leap-year compensation through year 2399 in either mode.

How does the MCP79402-I/ST handle power transitions between VCC and VBAT?

The MCP79402-I/ST performs automatic switchover between VCC and VBAT when VCC drops below the power-fail threshold (1.3V–1.7V, typ. 1.5V). During transition, it logs exact timestamps for both power-loss and power-restore events into dedicated PWRDNxxx and PWRUPxxx registers. All RTCC registers and 64-byte SRAM remain active and uncorrupted throughout the switch, ensuring MCP79402-I/ST maintains continuous timekeeping.

Can the MCP79402-I/ST operate without an external crystal?

Yes, the MCP79402-I/ST can operate using an external 32.768 kHz clock source applied to the X1 pin, with X2 left floating. This is enabled by setting the EXTOSC bit in the CONTROL register (0x07). In this mode, the internal crystal oscillator circuit is disabled, eliminating crystal load capacitor requirements while retaining full RTCC functionality, alarms, and SRAM operation - a key capability of MCP79402-I/ST for clock-synchronized systems.

What is the purpose of the protected EEPROM in the MCP79402-I/ST?

The 8-byte protected EEPROM in the MCP79402-I/ST stores factory-programmed EUI-64™ MAC address and supports custom programming after executing a robust 2-byte unlock sequence. This prevents accidental overwrites and ensures persistent, tamper-resistant device identity - essential for secure network onboarding and regulatory compliance. Unlike standard EEPROM, writes to MCP79402-I/ST's protected block require explicit unlock, making it suitable for storing cryptographic keys or calibration constants.