DS1338U-33/T&R

Real Time Clock Overview

The DS1338U-33+T&R is a low-power serial real-time clock (RTC) and 56-byte NV SRAM in an 8-pin uSOP package. It operates on a 3.0V to 5.5V supply with a 1.3V to 3.7V backup input. The device provides full BCD clock/calendar data, automatic leap-year compensation up to 2100, and I2C interface support for standard (100kHz) and fast (400kHz) modes. Key features include programmable square-wave output, power-fail detection, and industrial temperature range (-40°C to +85°C).

Real Time Clock Feature Summary

• Integrated 56-byte battery-backed NV SRAM with unlimited writes.
• Automatic power-fail detect and switch circuitry maintains timekeeping.
• Programmable square-wave output signal at 1Hz, 4.096kHz, 8.192kHz, or 32.768kHz.
• Full binary-coded decimal (BCD) clock/calendar with leap-year compensation valid to 2100.

Real Time Clock Applications

• Handhelds (GPS, POS Terminal)
• Consumer Electronics (Set-Top Box, Digital Recording, Network Appliance)
• Office Equipment (Fax/Printer, Copier)
• Medical (Glucometer, Medicine Dispenser)
• Telecommunications (Router, Switcher, Server)

Real Time Clock Procurement Notes

Verify the 'u' suffix indicates the 8-pin uSOP package and '33' specifies the 3.0V minimum operating voltage. Confirm the '+T&R' suffix denotes lead-free/RoHS compliance and reel/cut-tape packaging format as per manufacturer standards.

Real Time Clock Selection Notes

Select this part when an 8-pin surface-mount RTC with integrated NV RAM is required. Ensure the system supports I2C communication and that the primary supply voltage remains above 3.0V during normal operation. Verify compatibility with the 32.768kHz external crystal requirements if not using the C-version variant.

Real Time Clock Part Context

This component belongs to the DS1338 family of serial RTCs. The 'U' designation distinguishes it from the SOIC ('Z') and integrated crystal ('C') variants. It shares core functionality with other DS1338 models but differs in package type and specific voltage thresholds defined by the ordering suffix.

Real Time Clock Replacement Considerations

Direct pin-compatible replacements within the same family include DS1338Z-33+ (SOIC package) and DS1338U-3+ (different voltage threshold). Cross-family substitutes require verification of I2C compatibility and package dimensions.

Real Time Clock FAQ

How does the DS1338 handle month-end date adjustments?

The end-of-month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year, valid up to the year 2100.

What is the function of the SQW/OUT pin?

The SQW/OUT pin provides a programmable square-wave output signal. When enabled, it can output frequencies of 1Hz, 4.096kHz, 8.192kHz, or 32.768kHz.

How is power failure detected and managed?

A built-in power-sense circuit detects when VCC falls below the power-fail voltage (VPF) and automatically switches the device to the VBAT backup supply to maintain timekeeping.