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, with a nominal rating of 1.8V. The device features an I2C bidirectional serial bus interface supporting standard (100kHz) and fast (400kHz) modes. It provides seconds, minutes, hours, day, date, month, and year information in BCD format, including automatic leap-year correction. Key electrical parameters include an active supply current of up to 150µA at 1.89V and a standby current of up to 100µA. It includes a trickle charger, oscillator stop flag, and software calibration capabilities.

Real Time Clock Feature Summary

• I2C Serial Interface: Supports standard mode (100kHz) and fast mode (400kHz) communication via SDA and SCL pins.
• Trickle Charger: Built-in capability on the VBACKUP pin for charging backup batteries or super capacitors using selectable resistors.
• Automatic Power-Fail Detection: Detects power failures and switches to backup supply without stopping timekeeping; inhibits register access during switch.
• Software Clock Calibration: Allows compensation for crystal and temperature variations via digital calibration bits in the control register.

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 operating voltage range. Confirm RoHS compliance status as indicated by the '+' designation. Check for end-of-life or limited availability status through authorized distributors, as older Maxim Integrated parts may have restricted supply chains.

Real Time Clock Selection Notes

Select the DS1340U-18+ when a low-voltage (1.8V) I2C RTC with integrated trickle charging is required. Ensure the application supports the 8-pin µSOP surface-mount package. Verify that the external crystal matches the specified load capacitance of 12.5pF for accurate timing. Consider the DS1340C variant if an integrated crystal solution is preferred to save board space.

Real Time Clock Part Context

The DS1340U-18+ belongs to the DS1340 family of real-time clocks. It is functionally equivalent and pin-compatible with the ST M41T00. The 'U' suffix denotes the µSOP package, while '18' indicates the 1.8V operating voltage range. This part serves as an enhanced second source for legacy designs requiring low-power timekeeping with battery backup management.

Real Time Clock Replacement Considerations

The DS1340U-18+ is pin-compatible with the ST M41T00. Other variants in the same family include DS1340Z-18+ (SO package) and DS1340U-3+ (3V package). For integrated crystal solutions, consider the DS1340C series. Verify register map compatibility when substituting with other I2C RTCs.