Real-Time Clock/Calendar with Power Manager and Battery Charger

General Description

The CBC921xx combines a real-time clock (RTC) with a backup battery charger and other powermanagement features. In the event of an outage ofthe primary power source, automatic switchover tothe backup battery enables extended timekeepingand optionally provides power to external devices tomaintain their operation during the power outageThe circuit can be used in applications to providean uninterrupted continuous time clock/calendarwith time-based interrupts or alarms for wake-upfrom sleep to active mode operation with adjustableintervals to save power in the overall system.


  • Power bridging to provide uninterruptible RTC
    function during exchange of main batteries
  • Consumer appliances that have real-time
    clocks; provides switchover power from main
    supply to backup battery
  • Ultra-Low Power Timer using only 20nA
  • Wireless sensors and RFID tags and other
    powered, low duty cycle applications
  • Business and industrial systems such as:
    network routers, point-of-sale terminals, singleboard computers, test equipment, multi-function
    printers, industrial controllers, and utility meters

      • Reliable system timekeeping
      • Battery-powered devices
      • Internet of Things, portable devices
      • Daily alarms

3mm x 3mm x 0.55mm 16-pin MLPQ Package

In normal operation the RTC function is supported bya primary power source, which can be a single batterycell, multiple alkaline cells, or a regulated powersupply ranging from 2.85V to 5.5V. A backup batterythat might be used is charged with a temperaturecompensated voltage derived from the primaryvoltage source. Backup battery charging is done ona configurable schedule and temperature-dependentduty cycle, both of which are designed to increaseservice life of the backup battery while minimizingpower consumption from the main power source.

The power management has a low quiescent currentand high efficiency for backup battery charging. The RTC circuit has very low quiescent currentand accuracy to ± 1 ppm. An open drain internalpower switch is controlled by interrupts and a sleepmanager to facilitate power saving by disconnectingmain power from external devices according to userdefined schedules. Additional features include an onchip temperature sensor with 10-bit ADC and VOUTpin to power external devices while in backup mode.


  • Ultra-low power Real-Time Clock (RTC) with
    power-fail detect and battery management
  • Low power timer and power manager extend run
    time in battery-powered systems
  • Backup battery charger controls 4.1V
    rechargeable micro-batteries and 3.2V
    rechargeable coin cells and supercaps; no offchip components required for battery charger
  • Buck charge pump supply extends run time on
    backup battery:
    20nA RTC using internal RC oscillator
    50nA RTC using crystal oscillator
  • Counters for hundredths, seconds, minutes,
    hours, date, month, year, century, and weekdays
    based on a 32.768KHz crystal oscillator or
    internal RC oscillator
  • Integrated power switch reduces system power
  • Automatic leap year calculation
  • Alarm capability on all counters
  • Configurable multi-use outputs for interrupts,
    output clock, and managing external devices
  • 64 bytes of RAM
  • Internal temperature measurement with
    10-bit ADC enables oscillator temperature
  • Advanced crystal calibration to ± 1 ppm
  • Ultra-low Iq VIN POR circuit (< 25nA)
  • Fixed indicators for PGOOD, charging current on,
    and charging disabled
  • Temperature range -40°C to +85°C
  • Serial communication: I2C-bus and SPI options

CBC921 PMRTC Typical Application Schematic, Features, and Block Diagram

CBC921 PMRTC diagram
  • Ultra-low power Real-Time Clock
    • 50nA with crystal oscillator
    • 20nA with RC oscillator
  • Integrated low-side (VSS) power switch
  • On-chip temperature sensor with 10-bit ADC
  • I2C- and SPI-bus options
  • Battery charger and cutoff circuit
    • 4.1V option for EnerChips and Li-ion
    • 3.2V option for coin cells and supercaps
  • Programmable charger with auto shutoff minimizes power consumption
  • Full clock/calendar, alarm, and interrupt functions

Ordering information

CBC921 PMRTC Typical Application Schematic, Features, and Block Diagram

  • The CBC921 PMRTC will begin sampling in Q4 2018, beginning with the I2C-bus version and both 4.1V and 3.2V backup battery charge voltage options
  • Designer application development will be supported by an evaluation kit, the EVAL-14, which will also be available in Q4 2018
  • Contact Cymbet support for more information and to request samples

Full CBC921 PMRTC DataSheet is available here

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