SPI RTC with backup battery management
The Maxim Integrated DS1390U-3+ is a serial real-time clock (RTC) that keeps time as YY-MM-DD-dd and HH:MM:SS:hh in 12/24-hour format. Communication is over SPI. An integrated trickle-charger maintains a backup battery or supercap on the Vbat rail, so the clock holds through a main-supply dropout. The alarm output and square-wave generator can drive a host interrupt or toggle a logic line without polling. Supply range is 2.7 V to 3.3 V for the main rail; the battery backup input accepts 1.3 V to 3.7 V. Timekeeping current peaks at 125 µA over the full supply range, which keeps the load on the backup source low. The part is rated for -40°C to 85°C — industrial equipment, outdoor telecom, and factory-floor controllers are the natural fit.
Package and mounting
Housed in a 10-lead TFSOP/MSOP (3.00 mm body width). The supplier device package is 10-uMAX/uSOP.
Lifecycle and compliance
The DS1390U-3+ carries an Active product status and is ROHS3 compliant. No end-of-life notification or last-time-buy window is in effect. For a production BOM that needs a qualified SPI RTC with battery-charging support, this part is a current, manufacturable choice without near-term obsolescence risk.