DS1340U-18+

Real Time Clock Overview

The DS1340U-18+ is a low-power real-time clock and calendar manufactured by Analog Devices Inc./Maxim Integrated. It operates within a supply voltage range of 1.71V to 5.5V and supports an I2C bidirectional serial interface with a maximum clock frequency of 400kHz. The device provides timekeeping for seconds, minutes, hours, day, date, month, and year, including automatic leap-year correction. It features a built-in power-fail detect circuit that automatically switches to a backup supply on the VBACKUP pin (1.3V to 3.7V) when VCC drops below the power-fail threshold. The component is housed in an 8-pin µSOP package and functions over an operating temperature range of -40°C to +85°C.

Real Time Clock Feature Summary

• I2C Serial Interface: Supports standard mode (100kHz) and fast mode (400kHz) communication protocols.
• Trickle-Charger Capability: Includes internal current-limiting resistors and diode selection for charging backup batteries or super capacitors via the VBACKUP pin.
• Automatic Power-Fail Switching: Detects power failures and seamlessly transitions to backup power while maintaining timekeeping data.
• Oscillator Stop Flag (OSF): Indicates if the oscillator has stopped due to power loss or insufficient voltage, ensuring data validity checks.

Real Time Clock Applications

• Portable Instruments
• Point-of-Sale Equipment
• Medical Equipment
• Telecommunications

Real Time Clock Procurement Notes

Verify the specific suffix 'U-18+' corresponds to the 8-pin µSOP package and 1.8V nominal supply voltage range. Confirm RoHS compliance status as indicated by the '+' suffix. Check manufacturer discontinuation notices, as older Maxim Integrated RTC variants may have reached end-of-life status.

Real Time Clock Selection Notes

Select this variant for systems requiring a 1.8V nominal supply voltage with a wide operating range down to 1.71V. Ensure the design accommodates an external 32.768kHz crystal on pins X1 and X2, as the integrated crystal option is only available in the DS1340C series. Verify that the I2C bus pull-up voltages are compatible with the open-drain SDA and SCL outputs.

Real Time Clock Part Context

This component belongs to the DS1340 family of real-time clocks, which are functionally equivalent to the ST M41T00. The 'U' designation identifies the surface-mount µSOP package, while '18' specifies the 1.8V operating voltage range. Other family members include the SO package versions (Z suffix) and the integrated crystal version (C suffix).

Real Time Clock Replacement Considerations

The DS1340U-18+ is pin-compatible and functionally equivalent to the ST M41T00. Direct replacements within the same manufacturer's portfolio include other DS1340 variants such as DS1340Z-18+ (SO package) or DS1340U-3+ (3V supply), provided the voltage requirements match the system design.