Microchip Technology MCP79400-I/ST

Overview

MCP79400-I/ST from Microchip Technology is an I²C-compatible real-time clock/calendar (RTCC) IC with battery-backed SRAM, digital trimming, dual alarms, and power-fail timestamping. It operates from 1.8V–5.5V, consumes 1.2 µA at 3.3V on V_CC, supports 32.768 kHz crystals (6–9 pF), and maintains time/date across power loss in industrial environments (−40°C to +85°C).

For engineers reviewing the MCP79400-I/ST datasheet, MCP79400-I/ST pinout, MCP79400-I/ST application, or MCP79400-I/ST equivalent, this page delivers verified specifications, validated pin functions, confirmed timing behavior, and real-world use cases for embedded timekeeping, backup-critical logging, and alarm-driven control systems.

Technical Context

The MCP79400-I/ST implements a fully autonomous RTCC using a low-power oscillator circuit optimized for 32.768 kHz tuning fork crystals with external load capacitors. Its on-chip digital trimming provides ±1 ppm resolution over a ±129 ppm range, enabling precise frequency calibration without external components.

It features dual independent alarm modules with maskable comparison on seconds through months, a multifunction pin (MFP) configurable as alarm output, square-wave generator (selectable frequencies), or general-purpose open-drain output, and automatic switchover between V_CC and V_BAT with timestamped power-fail/power-up events logged in dedicated registers.

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 DS3231SN#T&R and PCF8563T/2,118, the MCP79400-I/ST uniquely combines battery-backed SRAM, power-fail timestamping, and on-chip digital trimming in an industrial-grade SOIC package - making it optimal for applications demanding both data persistence and calibrated timekeeping across power transitions.

Availability

MCP79400-I/ST is available at Aetrix Electronics and suitable for smart metering, industrial PLCs, medical infusion pumps, and building automation gateways requiring stable component supply, long-term lifecycle assurance, and guaranteed traceable sourcing.

Supply support for MCP79400-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, FPGA, and timing solutions, serving automotive, industrial, communications, and consumer markets with vertically integrated silicon and development tools.

The MCP7940X product line was designed specifically for embedded systems requiring high-accuracy, low-power, battery-backed timekeeping with integrated memory and alarm functionality - targeting applications where power resilience and time integrity are non-negotiable.

FAQ

What is the primary function of the MCP79400-I/ST?

The MCP79400-I/ST is a battery-backed I²C real-time clock/calendar IC that maintains accurate time and date (seconds through years, including leap-year compensation to 2399), provides dual programmable alarms, logs power-fail/power-up events, and includes 64 bytes of SRAM and protected EEPROM. Its core function is autonomous, low-power timekeeping with data persistence across power loss - essential for industrial and medical applications where time integrity cannot rely on host MCU operation.

Does the MCP79400-I/ST support external crystal calibration?

Yes, the MCP79400-I/ST supports on-chip digital trimming with ±1 ppm resolution over a ±129 ppm range. Calibration is performed by writing to the OSCTRIM register (address 0x08), allowing precise adjustment of oscillator frequency to compensate for crystal tolerance and temperature-induced drift - eliminating the need for external trimmer capacitors and enabling field recalibration without hardware changes.

How does the MCP79400-I/ST handle power transitions between VCC and VBAT?

The MCP79400-I/ST automatically switches to V_BAT when V_CC drops below the switchover threshold (1.3–1.7V), preserving RTC registers, SRAM contents, and oscillator operation. Crucially, it logs the exact time of power loss in PWRDN registers and power restoration in PWRUP registers - a feature not found in basic RTCs. This timestamping occurs without host intervention and remains accessible after recovery via I²C.

Can the MFP pin on the MCP79400-I/ST be used as a general-purpose output?

Yes, the MFP (Multifunction Pin) on the MCP79400-I/ST can be configured as a general-purpose open-drain output by clearing the SQWEN and ALMxEN bits and setting the OUT bit in the CONTROL register (address 0x07). When used this way, it behaves as a controllable GPIO driven by firmware - useful for status indication, reset signaling, or driving external logic, provided an external pull-up resistor is installed per Microchip's recommended 10 kΩ value.

Is the 64-byte SRAM in the MCP79400-I/ST retained during battery backup operation?

Yes, the full 64-byte SRAM block (addresses 0x20–0x5F) is fully retained during battery backup operation. The MCP79400-I/ST maintains SRAM contents, RTC registers, and oscillator function solely from V_BAT when V_CC is absent - consuming only 925 nA at 3.0V. This ensures critical runtime data (e.g., error logs, calibration offsets, or session counters) survives extended main-power outages without data loss or external backup memory.