Microchip Technology MCP795W21T-I/ST

Overview

MCP795W21T-I/ST from Microchip Technology is a battery-backed SPI Real-Time Clock/Calendar (RTCC) IC with integrated 2 Kbit EEPROM, EUI-48™ MAC address, programmable watchdog timer, dual event detect modules, and digital trimming. It maintains time to hundredth-of-second resolution across -40°C to +85°C, logs power-fail/power-up timestamps, and operates from 1.8V–3.6V main supply or 1.3V–3.6V backup. Used in industrial metering, medical devices, and networked edge sensors requiring traceable time-stamping.

For engineers reviewing the MCP795W21T-I/ST datasheet, MCP795W21T-I/ST pinout, MCP795W21T-I/ST application, or MCP795W21T-I/ST equivalent, key selection criteria include ±1 ppm digital trim resolution, 1.0 µA VBAT timekeeping current, dual alarm assignment to IRQ/WDO pins, 128-bit protected EEPROM for secure ID storage, and compatibility with 6–9 pF 32.768 kHz crystals.

Technical Context

The MCP795W21T-I/ST implements a fully autonomous RTCC using an internal 32.768 kHz oscillator circuit optimized for external crystals with 6–9 pF load capacitance. Its on-chip digital trimming provides ±259 ppm adjustment range at ±1 ppm resolution, enabling precise long-term accuracy without external components.

It features two independent interrupt-capable peripherals: a high-speed event detect module supporting programmable pulse counting, and a low-speed module with configurable debounce timing for mechanical switch inputs. Both feed into dedicated open-drain outputs (IRQ and WDO), which also serve alarm and watchdog functions under software configuration.

Key Specifications

Pinout & Package

14-pin SOIC (3.9 mm × 8.7 mm) and TSSOP packages; RoHS-compliant, lead-free, industrial temperature grade (-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 MCP795W21T-I/ST, MCP795W20T-I/ST omits EUI-48™ for lower BOM cost, while DS3231M+ trades SPI flexibility and dual-event detection for superior oscillator accuracy via built-in TCXO - making each suitable for distinct system-level trade-offs in connectivity, security, and timing precision.

Availability

MCP795W21T-I/ST is available at Aetrix Electronics and suitable for smart metering, industrial PLCs, medical diagnostics, and networked edge sensors requiring stable component supply, long-term lifecycle support, and guaranteed traceability.

Supply support for MCP795W21T-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 devices, and timing solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The MCP795Wxx family is designed for embedded systems requiring autonomous, battery-backed timekeeping with integrated memory, event handling, and secure identity - targeting industrial, medical, and infrastructure applications where reliability and data integrity are non-negotiable.

FAQ

What is the primary function of the MCP795W21T-I/ST?

The MCP795W21T-I/ST is a SPI-interfaced Real-Time Clock/Calendar IC with integrated 2 Kbit EEPROM, EUI-48™ MAC address, programmable watchdog timer, and dual event detect modules. Its core function is to maintain highly accurate, battery-backed time and date information - including hundredth-of-second resolution and leap-year compensation through 2399 - while providing auxiliary functions like timestamped power-fail logging and secure device identification. The MCP795W21T-I/ST operates autonomously from host processors, ensuring continuous timekeeping during MCU sleep or failure.

Does the MCP795W21T-I/ST require external load capacitors for its crystal oscillator?

Yes, the MCP795W21T-I/ST requires external load capacitors on X1 and X2 pins when using a 32.768 kHz tuning fork crystal. It is optimized for crystals with 6–9 pF specified load capacitance. The effective load capacitance (CL) depends on CX1, CX2, on-die oscillator pin capacitance (3 pF), and PCB stray capacitance. Capacitor values must be selected per Equation 5-1 in the datasheet to match the crystal's CL specification - mismatch causes frequency inaccuracy. The MCP795W21T-I/ST does not include internal load caps, so external components are mandatory for crystal operation.

How does the power-fail timestamp feature work in the MCP795W21T-I/ST?

The MCP795W21T-I/ST automatically logs the exact time of both power-fail (VCC dropout) and power-up (VCC restoration) events into dedicated registers (0x18–0x1F). When VCC drops below the switchover threshold (1.3–1.7V), the device transitions to VBAT and records the current RTCC value into the Power-Down Timestamp registers. Upon VCC return, it captures the time again in the Power-Up Timestamp registers. These timestamps are preserved across backup power cycles and accessible via SPI READ commands - enabling post-mortem analysis of power integrity issues without host MCU intervention. The MCP795W21T-I/ST performs this logging autonomously.

Can the MCP795W21T-I/ST operate with an external 32.768 kHz clock instead of a crystal?

Yes, the MCP795W21T-I/ST supports external clock input mode. By setting the EXTOSC bit in the CONTROL register (address 0x08), the device disables its internal oscillator and accepts a buffered 32.768 kHz square wave applied to the X1 pin. In this configuration, X2 must be left floating. This mode eliminates crystal-related layout sensitivity and component count, useful in noise-sensitive environments or when a system-level clock is already available. All timing, alarm, and timestamp functions remain fully operational - only the oscillator source changes. The MCP795W21T-I/ST retains full digital trimming capability even in external clock mode for fine frequency alignment.

What is the purpose of the 128-bit protected EEPROM in the MCP795W21T-I/ST?

The 128-bit protected EEPROM in the MCP795W21T-I/ST stores factory-programmed EUI-48™ MAC address and supports secure custom data storage. Access requires a multi-step hardware-enforced unlock sequence (UNLOCK instruction followed by specific timing and address conditions), preventing accidental or malicious overwrite. This area is physically isolated from main EEPROM and survives 1 million erase/write cycles. Its primary purpose is to provide a tamper-resistant, globally unique hardware identity for networked devices - essential for IoT authentication, regulatory compliance (e.g., FCC ID binding), and secure boot chain anchoring. The MCP795W21T-I/ST guarantees this ID remains intact across power cycles and firmware updates.