Accurate I²C RTC with Integrated TCXO/Crystal/FRAM

Nonvolatile Memory Has No Backup Supply and No Write Cycle Limits

Please check latest availability status for a specific part variant.


The DS32B35/DS32C35 accurate real-time clocks (RTC) are clock/calendars that include an integrated temperature-compensated crystal oscillator (TCXO), crystal, and a bank of nonvolatile memory (FRAM) in a single package. The nonvolatile memory is available in two densities: 2048 x 8 and 8192 x 8 bits. The integration of the crystal resonator enhances the long-term accuracy of the devices as well as reduces the piece part count in a manufacturing line. The devices operate as a slave device on an I²C serial interface, and are available in both commercial and industrial temperature ranges in a 300-mil, 20-pin SO package.

The clock/date provides seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year.

The DS32B35/DS32C35 include a bank of nonvolatile memory that does not require a backup energy source to maintain memory contents. In addition, there are no read or write cycle limitations. The memory array can be accessed at maximum cycle rates for the life of the product with no wear-out mechanisms.

Other device features include two time-of-day alarms, a selectable output that provides either an interrupt or programmable square wave, and a calibrated 32.768kHz square-wave output. A reset input/output pin provides a power-on reset for other devices. Additionally, the reset pin is monitored as a pushbutton input for generating a reset externally.

A precision temperature-compensated voltage reference and comparator circuit monitor the status of VCC to detect power failures, to provide a reset output, and to automatically switch to the backup supply for the RTC/TCXO when necessary. Additionally, the active-low RST pin is monitored as a pushbutton input for generating a reset externally.
DS32B35, DS32C35: Typical Operating Circuit DS32B35, DS32C35: Typical Operating Circuit Enlarge+

Key Features

  • Integrated 32.768kHz Crystal
  • Fast (400kHz) I²C Interface
  • RTC Counts Seconds, Minutes, Hours, Day, Date, Month, and Year with Leap Year Compensation Valid Up to 2100
  • RTC Accuracy ±2ppm from 0°C to +40°C
  • RTC Accuracy ±3.5ppm from -40°C to 0°C and +40°C to +85°C
  • Nonvolatile Memory with 10 Years of Guaranteed Backup Time and Write Protection
  • Two Available Densities of Nonvolatile Memory
    • 2048 Bytes (DS32B35)
    • 8192 Bytes (DS32C35)
  • No Cycle Limitations on Memory
  • Power-Switching Circuit Selects Between Main Power and Battery Backup for the RTC
  • Programmable Square Wave with Frequency of 32.768kHz, 8.192kHz, 4.096kHz, or 1Hz
  • Two Time-of-Day Alarms
  • Reset Output/Pushbutton Reset (Debounced) Input
  • Programmable Output Provides Interrupt or Square Wave
  • Calibrated 32.768kHz Open-Drain Output
  • Temp Sensor with ±3°C Accuracy
  • 3.3V Operating Voltage
  • Commercial and Industrial Temperature Ranges
  • 300-mil, 20-Pin SO Package


  • GPS
  • Industrial Controls
  • Instrumentation
  • Servers
  • Telematics
  • Utility Power Meters

Technical Documents

App Note 5143 Feature Comparison of the DS323x Real-Time Clocks
Product Reliability Reports: DS32B35.pdf 
Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C   Material Composition  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

Quality Management System >
Environmental Management System >


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