General Description

The MCP7940N Real-Time Clock/Calendar (RTCC)

tracks time using internal counters for hours, minutes,

seconds, days, months, years, and day of week.

Alarms can be configured on all counters up to and

including months. For usage and configuration, the

MCP7940N supports I2C communications up to

400 kHz.

The open-drain, multi-functional output can be

configured to assert on an alarm match, to output a

selectable frequency square wave, or as a general

purpose output.

The MCP7940N is designed to operate using a

32.768 kHz tuning fork crystal with external crystal

load capacitors. On-chip digital trimming can be used

to adjust for frequency variance caused by crystal

tolerance and temperature.

SRAM and timekeeping circuitry are powered from the

back-up supply when main power is lost, allowing the

device to maintain accurate time and the SRAM

contents. The times when the device switches over to

the back-up supply and when primary power returns

are both logged by the power-fail time-stamp.

Timekeeping Features

• Real-Time Clock/Calendar (RTCC):

- Hours, Minutes, Seconds, Day of Week, Day,

Month, Year

- Leap year compensated to 2399

- 12/24 hour modes

• Oscillator for 32.768 kHz Crystals:

- Optimized for 6-9 pF crystals

• On-Chip Digital Trimming/Calibration:

- ±1 PPM resolution

- ±129 PPM range

• Dual Programmable Alarms

• Versatile Output Pin:

- Clock output with selectable frequency

- Alarm output

- General purpose output

• Power-Fail Time-Stamp:

- Time logged on switchover to and from Battery mode

Low-Power Features

• Wide Voltage Range:

- Operating voltage range of 1.8V to 5.5V

- Backup voltage range of 1.3V to 5.5V

• Low Typical Timekeeping Current:

- Operating from VCC: 1.2 μA at 3.3V

- Operating from battery backup: 925 nA at 3.0V

• Automatic Switchover to Battery Backup