242B NVSRAM and timekeeping at 2 mA
The DS1685E-3+ is a parallel-interface real-time clock from Analog Devices that combines a full calendar (YY-MM-DD-dd) and 12/24-hour timekeeping with 242 bytes of NVSRAM, an alarm comparator, and a programmable square-wave output — all in a 24-TSSOP package. The timekeeping current draw is 2 mA max at 3 V, so the battery-backed supply (2.5 V to 3.7 V) carries the RTC through power-loss events without draining a coin cell faster than the application's shelf-life budget.
Supply rails and temperature grade
The main supply range is 2.7 V to 3.7 V, with a separate battery-backup input accepting 2.5 V to 3.7 V — the RTC switches seamlessly to the backup rail when Vcc drops below the trip point, preserving the time and NVSRAM contents. The NVSRAM is not a separate chip — it is the 242-byte static RAM inside the RTC that retains data as long as the backup battery is present. That is enough space for system configuration bytes, calibration constants, or a small event log without adding a serial EEPROM to the BOM.
Housed in a 24-TSSOP (4.40 mm width) with a surface-mount footprint, the DS1685E-3+ shares the same 0.65 mm pitch and body size as other 24-TSSOP RTCs in the DS1685 family. The supplier device package is listed as 24-TSSOP — the same as the package/case — so the PCB land pattern is unambiguous. Supplied in tube format, which is typical for prototype and low-volume builds; reel options may be available under a different ordering suffix.