Analog Devices Inc./Maxim Integrated DS17285S-3/T&R

Overview

DS17285S-3/T&R from Maxim Integrated is a 24-pin real-time clock/calendar IC with integrated power-control circuitry, 114 bytes of battery-backed NV SRAM, 2kB extended NV SRAM, and multiplexed byte-wide interface. It supports +3.0V operation, automatic VCC-to-VBAT/VBAUX switchover on power fail, and system wake-up via time-of-day alarm or external kickstart (KS) input. Used in utility meters and industrial embedded systems requiring long-term timekeeping under intermittent power.

For engineers reviewing the DS17285S-3/T&R datasheet, DS17285S-3/T&R pinout, DS17285S-3/T&R application, or DS17285S-3/T&R equivalent, key selection considerations include its 3V-only supply range, EDIP-compatible 24-pin DIP package with no X1/X2 pins, PWR output for system power-on control, IRQ interrupt with six maskable flags, and support for BCD/binary time format with leap-year compensation through 2099.

Technical Context

The DS17285S-3/T&R implements a temperature-compensated voltage monitor to detect VCC drop below 2.5V–2.7V (VPF), triggering automatic switchover to VBAT or VBAUX. Its internal oscillator is disabled in this part variant-X1 and X2 pins are NC-as confirmed by EDIP package documentation and pin description tables.

It uses a multiplexed AD0–AD7 bus with ALE-latched addressing, supporting read/write cycles at ≥360ns cycle time under 3V operation. Control registers A–D and extended bank-1 registers (e.g., 48h/49h for century/date alarm) enable configuration of alarm masking, square-wave output (SQW), and power-control logic including PWR assertion and KS-triggered wake-up.

Key Specifications

Pinout & Package

DS17285S-3/T&R is supplied in a 24-pin plastic DIP (PDIP) package, RoHS-compliant and tape-and-reel packaged (T&R). Pin layout matches standard DS12887 footprint for drop-in replacement in legacy designs. X1 and X2 pins are not connected (N.C.) - oscillator must be provided externally or omitted per application.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock applications.

Compared with DS17285S-3/T&R, DS1307 offers simpler integration but no system power control or extended memory, while PCF8583P provides more RAM but lacks UL recognition, wake-up capability, and leap-year accuracy through 2099 - making DS17285S-3/T&R the only option meeting utility meter certification and industrial power-gating requirements.

Availability

DS17285S-3/T&R is available at Aetrix Electronics and suitable for smart utility metering, industrial data loggers, access control panels, and network infrastructure equipment requiring stable component supply across multi-year production cycles.

Supply support for DS17285S-3/T&R includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and power management ICs for industrial, medical, and communications applications.

The DS17285S-3/T&R belongs to Maxim's legacy real-time clock family engineered for high-reliability embedded systems requiring battery-backed timekeeping, system-level power sequencing, and regulatory compliance (UL recognition).

FAQ

What is the operating voltage range for DS17285S-3/T&R?

The DS17285S-3/T&R operates from +2.7V to +3.7V on VCC. Operation outside this range risks functional failure or damage. VBAT and VBAUX inputs accept 2.5V–3.7V for backup power. The device includes a precision voltage monitor that triggers automatic switchover to backup power when VCC drops below 2.5V–2.7V (VPF), ensuring continuous RTC operation and data retention in DS17285S-3/T&R.

Does DS17285S-3/T&R include an integrated crystal or battery?

No, DS17285S-3/T&R is the PDIP version without integrated crystal or battery - it requires an external 32.768kHz crystal connected to X1/X2 pins. In contrast, the DS17287 variant packages crystal and lithium cell in an EDIP module. DS17285S-3/T&R's X1 and X2 pins are functional and must be used; they are not NC. This distinction is critical for board layout and BOM accuracy in DS17285S-3/T&R designs.

How does the PWR output function in DS17285S-3/T&R?

The PWR pin in DS17285S-3/T&R is an open-drain output that drives external power supplies. It activates automatically on wake-up alarm or KS pin transition when VCC is absent, and remains software-controllable via register bits after system boot. A pullup resistor to VBAUX (≤3.9V) is required. This enables DS17285S-3/T&R to serve as the central power sequencer in battery-operated infrastructure nodes - a capability absent in most competing RTCs.

Can DS17285S-3/T&R operate in both 12-hour and 24-hour time formats?

Yes, DS17285S-3/T&R supports both formats via the 24/12 bit in Register B. In 12-hour mode, the MSB of the hours byte indicates PM. The device retains all time/calendar data in double-buffered registers, enabling glitch-free reads during updates. Format selection is persistent across power cycles and requires reinitialization only if changed - a feature confirmed in DS17285S-3/T&R's control register specification and essential for global UI localization.

What is the data retention period for DS17285S-3/T&R's NV SRAM?

DS17285S-3/T&R guarantees ≥10 years of data retention in its 114-byte base NV SRAM and 2048-byte extended NV SRAM when backed by a 3.0V lithium coin cell at +25°C, per Maxim's characterization data. Retention depends on VBAT/VBAUX voltage stability and temperature; operation below 2.5V or above +85°C degrades endurance. This 10-year spec is validated for DS17285S-3/T&R under standard conditions and forms the basis for utility meter certification lifetimes.