MCP795W22-I/ST

Real Time Clock Overview

The MCP795W22-I/ST is a battery-backed SPI Real-Time Clock/Calendar (RTCC) from Microchip Technology, housed in a 14-lead TSSOP package. It operates within an industrial temperature range of -40°C to +85°C and supports a primary supply voltage of 1.8V to 3.6V with backup operation down to 1.3V. The device features a 32.768 kHz oscillator optimized for 6-9 pF crystals, on-chip digital trimming with ±1 ppm resolution, and dual programmable alarms. Memory includes 64 bytes of battery-backed SRAM, 2 Kbits of EEPROM, and a 128-bit protected area preprogrammed with an EUI-64 MAC address.

Real Time Clock Feature Summary

• Real-Time Clock/Calendar tracking hundredths of seconds through the year, with leap year compensation to 2399.
• Integrated 2 Kbit EEPROM and 64-byte SRAM, plus a 128-bit protected block containing a factory-programmed EUI-64 address.
• Dual Event Detect Modules: High-Speed for pulse counting and Low-Speed for switch debouncing.
• Programmable Watchdog Timer with dedicated output pin and automatic switchover timestamp logging.

Real Time Clock Applications

• Industrial controllers requiring robust timekeeping and system watchdog functionality.
• Smart meters and utility devices utilizing the EUI-64 address for unique identification.
• Medical equipment needing precise calendar tracking and power-fail event logging.
• Automotive infotainment systems operating across wide industrial temperature ranges.

Real Time Clock Procurement Notes

Verify that the specific suffix 'I/ST' corresponds to the Industrial temperature grade (-40°C to +85°C) and the 14-lead TSSOP package. Confirm the presence of the EUI-64 protected memory block, as this distinguishes the W22 variant from other models in the MCP795WXX family. Ensure ordering documentation matches the manufacturer's part number exactly to avoid confusion with similar RTC components.

Real Time Clock Selection Notes

Select the MCP795W22-I/ST when an application requires a 2 Kbit EEPROM size and a unique EUI-64 identifier. This model is appropriate for designs needing high-speed event detection or switch debouncing capabilities integrated directly into the clock module. Consider the 1.8V minimum operating voltage if the design utilizes low-power microcontrollers. Verify that the external crystal load capacitance requirements align with the device's optimization for 6-9 pF crystals.

Real Time Clock Part Context

This component belongs to the MCP795WXX series of battery-backed RTCCs. Unlike the MCP795BXX series which may feature different boot-up characteristics, the WXX series relies on standard external crystals. The '22' designation specifically indicates the 2 Kbit EEPROM capacity and the inclusion of the EUI-64 protected memory area, distinguishing it from the 1 Kbit variants.

Real Time Clock Replacement Considerations

Direct substitutes within the same family include the MCP795W22-I/SL (SOIC package) or the MCP795W21-I/ST (EUI-48 address). For applications not requiring the EUI-64 block, the MCP795W20-I/ST offers identical electrical performance with blank protected memory. Cross-family replacements like the MCP7940N require interface changes from SPI to I2C.

Real Time Clock FAQ

How does the MCP795W22 handle power loss events?

The device automatically switches to the VBAT supply when VCC drops below the trip voltage. It logs the exact time of power failure and power restoration in dedicated timestamp registers (PWRDN and PWRUP).

What is the purpose of the protected EEPROM area?

The 128-bit protected EEPROM area is designed for storing critical data such as the factory-programmed EUI-64 MAC address. It requires a specific software unlock sequence to write, preventing accidental modification.

Can the device operate without a battery?

Yes, if the VBAT pin is connected to VSS (Ground), the device will operate solely on VCC. However, timekeeping and SRAM contents will be lost if primary power is removed.