R2051 Series
2-wire (I2C Bus) Serial Interface Real Time Clock (RTC) with Battery Backup Switch-over Function

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  • Description

    The R2051 is a CMOS real-time clock IC connected to the CPU by two signal lines, SCL and SDA, and configured to perform serial transmission of time and calendar data to the CPU. Further, battery backup switchover circuit and a voltage detector are incorporated. The periodic interrupt circuit is configured to generate interrupt signals with six selectable interrupts ranging from 0.5 seconds to 1 month. The 2 alarm interrupt circuits generate interrupt signals at preset times. As the oscillation circuit is driven under constant voltage, fluctuation of the oscillator frequency due to supply voltage is small, and the time keeping current is small (TYP. 0.4 µA at 3V). The oscillation halt sensing circuit can be used to judge the validity of internal data in such events as power-on; The supply voltage monitoring circuit is configured to record a drop in supply voltage below two selectable supply voltage monitoring threshold settings.

    The 32.768 kHz clock output function (CMOS output) is intended to output sub-clock pulses for the external microcomputer. The oscillation adjustment circuit is intended to adjust time counts with high precision by correcting deviations in the oscillation frequency of the quartz crystal unit. Battery backup switchover function is the automatic switchover circuit between a main power supply and a backup battery of primary or secondary battery. Switchover is executed by monitoring the voltage of a main power supply, therefore the voltage of a backup battery voltage is not relevant. Since the package for these ICs is SSOP16, QFN023023-16 or TSSOP10G, high density mounting of ICs on boards is possible.

  • Spec
    Timekeeping Supply Voltage Range 1.0 V to 5.5 V
    Minimum Timekeeping Supply Voltage Typ. 0.75 V
    Supply Current 0.4 µA (VDD = 3 V)
    Connection to CPU Two signal Lines (SCL, SDA), I2C-bus Serial Interface, Maximum Clock Frequency: 400 kHz
    Clock Output 32.768 kHz (CMOS Output with Level Shifter)
    Package QFN023023-16, SSOP16, TSSOP10G
    Backup Switchover Voltage 2.4 V, 2.8 V, 4.0 V

    Protections / Functions

    ECO Clock Adjust OSC Halt Sensing Supply Voltage Monitoring Circuit Automatic Identification of Leap Years Selectable 12-hour and 24-hour Backup Switch
  • Technical
  • Quality &
    • Refer to the datasheets for the details on the product.
    • The package file or the datasheet includes package dimensions, taping specifications, taping reels dimensions, power dissipations, and recommended land pattern.

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Functional Description

ECO ECO Function
Clock Adjust Clock Adjust Function
OSC Halt Sensing OSC Halt Sensing Function
Supply Voltage Monitoring Circuit Supply Voltage Monitoring Function
Automatic Identification of Leap Years Automatic Identification of Leap Years
Selectable 12-hour and 24-hour Selectable 12-hour and 24-hour
Built-in VD with Delay Time Built-in VD with Delay Time

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Category:Real Time Clock

Features +VD
Interface 2-wire
Time Keeping
Current (µA)
Time Keeping
Voltage min (V)
Time Keeping
Voltage max (V)