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2 wire interface Real-Time Clock ICs with Battery Backup switch-over Function


Data Sheet

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. 0.4µA 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 32.768kHz 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 (5.0x6.4x1.25: R2051Sxx), QFN023023-16(2.3×2.3×0.4:R2051Lxx), or TSSOP10G (4.0x2.9x1.0: R2051Txx), high density mounting of ICs on boards is possible.


Minimum Timekeeping supply voltage Typ. 0.75V (Max. 1.00V); VDD pin
Low power consumption 0.4µA TYP (1.0µA MAX.) at VDD=3V
Built-in Backup switchover circuit (can be used for a primary battery, a secondary battery, or an electric double layer capacitor)
Only two signal lines (SCL and SDA) required for connection to the CPU. ( I 2C-Bus Interface, 400kHz)
Time counters (counting hours, minutes, and seconds) and calendar counters (counting years, months, days, and weeks) (in BCD format)
Interrupt circuit configured to generate interrupt signals (with interrupts ranging from 0.5 seconds to 1 month) to the CPU and provided with an interrupt flag and an interrupt halt (except R2051Txx)
2 alarm interrupt circuits (Alarm_W for week, hour, and minute alarm settings and Alarm_D for hour and minute alarm settings) (except R2051Txx)
Built-in voltage detector with delay(R2051Lxx, R2051Sxx)
With Power-on flag to prove that the power supply starts from 0V
32-kHz clock output pin (CMOS output. "H" level is always equal to VCC.)
Supply voltage monitoring circuit with two supply voltage monitoring threshold settings
Automatic identification of leap years up to the year 2099
Selectable 12-hour and 24-hour mode settings
High precision oscillation adjustment circuit
Built-in oscillation stabilization capacitors (CG and CD)
CMOS process
  • SSOP16 (5.0mm x 6.4mm x 1.25mm : R2051Sxx)
  • TSSOP10G (4.0mm x 2.9mm x 1.0mm : R2051Txx)
  • FFP12 (2.0mm × 2.0mm × 1.0mm :R2051Kxx) : Discontinued
  • QFN023023-16 (2.3mm x 2.3mm x 0.4mm :R2051Lxx)


  • Communication devices (multi function phone, portable phone, PHS or pager)
  • OA devices (fax, portable fax)
  • Computer (desk-top and mobile PC, portable word-processor, PDA, electric note or video game)
  • AV components (portable audio unit, video camera,camera, digital camera or remote controller)
  • Home appliances (rice cooker, electric oven)
  • Other (car navigation system, multi-function watch)

Documents Download

Data Sheet Package Info. Mark Info. Quality Assurance Data
R2051x Series QFN023023-16 to be prepared Reliability
SSOP-16 to be prepared Reliability
TSSOP10G to be prepared Reliability

All PDF files are less than 1MB unless otherwise stated.

Note : Discontinued Products

FFP12 (R2051K) is already discontinued.

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