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MCP7940N-I/ST

MCHPMCP7940N-I/ST

Microchip Technology
Real Time Clock (RTC) IC Clock/Calendar 64B I2C, 2-Wire Serial 8-TSSOP (0.173", 4.40mm Width)
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Overview

The MCP7940N-I/ST is a feature-rich Real-Time Clock and Calendar (RTCC) IC with integrated 64-byte SRAM and automatic battery switchover. It operates over a wide voltage range of 1.8V to 5.5V and features an ultra-low timekeeping current of 1.2uA at 3.3V, making it ideal for battery-backed applications. This AEC-Q100 qualified device includes digital trimming for high-accuracy calibration and a power-fail time-stamp to log the exact moment power was lost.

Why Choose This Part

The MCP7940N offers extreme versatility with dual programmable alarms and a square wave output that can be used as a system clock. Its integrated power-fail monitoring circuit automatically switches to the battery input, ensuring time is never lost during main supply drops. The inclusion of 64 bytes of user-accessible SRAM provides a convenient place to store critical system state or calibration data without wearing out EEPROM.

Applications

Power-Fail Event Logging
Utilizes the on-chip power-fail time-stamp to record the duration and time of power outages in industrial control systems.
Automotive Telematics
Provides reliable timekeeping for vehicle tracking and diagnostics, meeting AEC-Q100 standards for harsh environments.
Battery-Powered Wearables
Acts as the primary timekeeper in low-power devices, consuming only 1.2uA while the main MCU is in deep sleep.
Smart Metering
Enables accurate time-of-use billing and event logging with digital trimming for long-term precision.

Key Specifications

Type Clock/Calendar
Features Alarm, Leap Year, Square Wave Output, SRAM
Interface I2C, 2-Wire Serial
Date Format YY-MM-DD-dd
Memory Size 64B
Time Format HH:MM:SS (12/24 hr)
Mounting Type Surface Mount
Package / Case 8-TSSOP (0.173", 4.40mm Width)
Voltage - Supply 1.8V ~ 5.5V
Operating Temperature -40degC ~ 85degC
Supplier Device Package 8-TSSOP
Voltage - Supply, Battery 1.3V ~ 5.5V
Current - Timekeeping (Max) 1.2uA @ 3.3V

Getting Started

To interface with the MCP7940N, connect the I2C bus pins (SDA and SCL) to your microcontroller with appropriate pull-up resistors and attach a 32.768 kHz crystal to the X1/X2 pins. Microchip provides the MCP7940N RTCC PICtail Plus Daughter Board (AC164140) for evaluation using their Explorer development platforms. Engineers should use the digital trimming register to compensate for crystal frequency drift across temperature to maintain high accuracy.

MCP7940 Family

Comparing specs that differ across variants. The current part is highlighted.

Part Number Features Package Temp Range Current - Timekeeping (Max) Stock
MCP7940N-I/ST (this part) Alarm, Leap Year, .. TSSOP-8 -40degC ~ 85degC 1.2uA 729
MCP7940NT-I/MS Alarm, Leap Year, .. TSSOP-8 -40degC ~ 85degC 1.2uA 22,374
MCP7940NT-I/SN Alarm, Leap Year, .. SOIC-8 -40degC ~ 85degC 1.2uA 32,168
MCP7940M-I/SN Alarm, Leap Year, .. SOIC-8 -40degC ~ 85degC 1uA 1,594
MCP7940N-I/MS Alarm, Leap Year, .. TSSOP-8 -40degC ~ 85degC 1.2uA 1,310
MCP7940M-I/MS Alarm, Leap Year, .. TSSOP-8 -40degC ~ 85degC 1uA 1,604
MCP7940MT-I/MNY Alarm, Leap Year, .. WFDFN-8 -40degC ~ 85degC 1uA 10,857
MCP7940MT-I/SN Alarm, Leap Year, .. SOIC-8 -40degC ~ 85degC 1uA 2,696
MCP79400T-I/SN Alarm, Leap Year, .. SOIC-8 -40degC ~ 85degC 1.2uA 3,428
MCP7940NT-E/MS Alarm, Leap Year, .. TSSOP-8 -40degC ~ 125degC 1.2uA 7,080
MCP7940N-I/P Alarm, Leap Year, .. DIP-8 -40degC ~ 85degC 1.2uA 1,254
MCP7940N-I/SN Alarm, Leap Year, .. SOIC-8 -40degC ~ 85degC 1.2uA 8,482
Also available as: MCP7940N

Also Consider

DS1307 Analog Devices / Maxim Integrated - A widely used alternative for 5V systems that also includes 56 bytes of NV SRAM, though it lacks the lower voltage 1.8V support.
MCP79410 MCHPMicrochip Technology - A similar RTCC that adds 1Kbit of EEPROM and a unique pre-programmed EUI-48 or EUI-64 MAC address for networked applications.