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MCP7940N-I/MS

MCHPMCP7940N-I/MS

Microchip Technology
Real Time Clock (RTC) IC Clock/Calendar 64B I2C, 2-Wire Serial 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
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Overview

The MCP7940N-I/MS is a low-power Real-Time Clock/Calendar (RTCC) from Microchip Technology that uses the I2C interface. It provides timekeeping in both 12-hour and 24-hour formats with leap year compensation and includes 64 bytes of user-available SRAM. The device operates across a wide voltage range of 1.8V to 5.5V and features a programmable square wave output for system clocking needs.

Why Choose This Part

The MCP7940N-I/MS is highly efficient, drawing only 1.2uA of typical current, which is ideal for long-term battery operation. Its support for a wide supply voltage up to 5.5V ensures compatibility with both 3.3V and 5V logic systems without level shifting. The inclusion of on-chip digital trimming allows for fine-tuning the clock accuracy to compensate for crystal tolerances.

Applications

Battery-Backed Timekeeping
Providing accurate time and date stamps for data logging applications where main power may be interrupted.
Embedded System Scheduling
Utilizing the dual programmable alarms to wake up a host microcontroller from deep sleep modes at specific intervals.
General Purpose SRAM Storage
Using the 64 bytes of internal SRAM to store small amounts of volatile configuration data or state variables.
System Clock Generation
Outputting a programmable square wave frequency to act as a reference clock for other peripherals.

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, 8-MSOP (0.118", 3.00mm Width)
Voltage - Supply 1.8V ~ 5.5V
Operating Temperature -40degC ~ 85degC
Supplier Device Package 8-MSOP
Voltage - Supply, Battery 1.3V ~ 5.5V
Current - Timekeeping (Max) 1.2uA @ 3.3V

Getting Started

To evaluate this RTC, engineers often use the MCP79410 RTCC PICtail Plus Daughter Board or connect the MSOP-8 package to an I2C bus using a standard breadboard adapter. Firmware development involves writing to the I2C registers at address 0xDE for the RTCC and 0xAF for the EEPROM/SRAM sections (depending on specific variant features). Ensure a 32.768 kHz crystal with the correct load capacitance is placed as close to the X1 and X2 pins as possible.

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/MS (this part) Alarm, Leap Year, .. TSSOP-8 -40degC ~ 85degC 1.2uA 1,310
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
MCP7940M-I/MS Alarm, Leap Year, .. TSSOP-8 -40degC ~ 85degC 1uA 1,604
MCP7940N-I/ST Alarm, Leap Year, .. TSSOP-8 -40degC ~ 85degC 1.2uA 729
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 very common 5V I2C RTC with 56 bytes of NV RAM, though it lacks the lower voltage 1.8V support of the MCP7940N.
DS3231 Analog Devices / Maxim Integrated - A high-precision RTC with an integrated temperature-compensated crystal oscillator (TCXO) for applications requiring superior time stability.