Analog Devices Inc./Maxim Integrated DS17485-5

Overview

The DS17485-5 from Maxim Integrated is a battery-backed real-time clock/calendar IC with 4096 bytes of NV SRAM, 114 bytes of general-purpose RAM, time-of-day alarm, six maskable interrupts, and programmable square-wave output. It operates at +3.0V or +5.0V, supports 12-/24-hour format with leap-year compensation through 2099, and integrates power-on control via PWR and KS pins for embedded system wake-up.

For engineers reviewing the DS17485-5 datasheet, DS17485-5 pinout, DS17485-5 application, or DS17485-5 equivalent, this page delivers verified timing accuracy (±1 min/month for EDIP variants), VCC/VBAT/VBAUX power-fail switching behavior, multiplexed AD0–AD7 bus interface timing, IRQ/SQW/PWR terminal functions, and industrial temperature support (–40°C to +85°C).

Technical Context

The DS17485-5 implements a fully autonomous RTC core with double-buffered time/calendar registers, automatic month-end and leap-year correction, and a 15-stage divider chain feeding a 13-tap programmable square-wave generator. Its power-control circuitry uses a precision temperature-compensated voltage reference to monitor VCC against VPF (4.25–4.5V @ 5V mode) and seamlessly switch to VBAT or VBAUX upon primary supply failure.

It features a multiplexed 8-bit address/data bus (AD0–AD7) with ALE-latched addressing, active-low RD/WR/CS controls, and open-drain IRQ/PWR outputs requiring external pullups. The device supports both crystal (X1/X2, 32.768kHz, 6pF or 12.5pF load) and external oscillator inputs, and includes a 64-bit silicon serial number and SMI recovery stack.

Key Specifications

Pinout & Package

DS17485-5 is available in 28-pin PDIP, SO, or TSOP packages. Pin count and function mapping match the DS17x85 family; no integrated crystal or battery (unlike DS17487 EDIP).

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS3231M and PCF8583, the DS17485-5 uniquely combines parallel bus compatibility, hardware-assisted system power control (PWR/KS), 4kB NV SRAM, and industrial temperature rating - making it irreplaceable in legacy-replacement and energy-gated embedded designs.

Availability

DS17485-5 is available at Aetrix Electronics and suitable for smart utility metering, industrial security panels, network infrastructure clocking, and medical timestamping requiring stable component supply across long product lifecycles.

Supply support for DS17485-5 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 high-performance analog and mixed-signal semiconductors for industrial, communications, and computing applications.

The DS17485-5 belongs to the DS17x85 RTC family, engineered to replace the DS12887 in systems needing enhanced SRAM, hardware wake-up, and robust power-fail management - targeting metering, security, and infrastructure equipment.

FAQ

What voltage options does the DS17485-5 support?

The DS17485-5 supports two operating voltage ranges: +2.7V to +3.7V and +4.5V to +5.5V. This dual-voltage capability allows direct integration into both modern 3V systems and legacy 5V designs without level-shifting. The DS17485-5 automatically detects the applied VCC range and configures internal regulators and thresholds accordingly - for example, VPF shifts from 2.5–2.7V in 3V mode to 4.25–4.5V in 5V mode. Both modes maintain full functionality including RTC, SRAM, and interrupt generation.

How does the DS17485-5 handle power failure and battery switchover?

The DS17485-5 uses a precision temperature-compensated comparator to continuously monitor VCC against the power-fail threshold (VPF). When VCC drops below VPF, the device immediately disables read/write access and switches power to the higher of VBAT or VBAUX - preserving RTC operation and SRAM contents. The DS17485-5 guarantees seamless transition with no time loss or register corruption. Recovery occurs after tREC (20–150ms) once VCC rises above VPF, ensuring stable initialization before host access resumes.

What is the role of the PWR and KS pins on the DS17485-5?

The PWR pin is an open-drain output used to control external power supplies; it activates automatically on wake-up alarm or KS input assertion, and remains software-controllable after boot. The KS (Kickstart) pin is an active-low input that triggers PWR assertion when VCC is absent - enabling hardware-initiated power-on from switches or sensors. For the DS17485-5, KS requires VBAUX and the auxiliary-battery-enable bit (ABE) set to 1. These pins together form a complete hardware power-gating solution, eliminating the need for external supervisors or discrete logic in battery-backed systems.

Does the DS17485-5 include an integrated crystal or battery?

No, the DS17485-5 does not integrate a crystal or battery. It is a bare-die RTC IC in PDIP/SO/TSOP packages requiring an external 32.768kHz crystal connected to X1/X2 (with 6pF or 12.5pF load capacitance) and a separate lithium coin cell on VBAT. This contrasts with the DS17487, which packages crystal and battery in a 24-pin EDIP module. The DS17485-5's discrete design allows board-level optimization of crystal layout, thermal management, and battery selection - critical for high-reliability metering and industrial applications.

What memory resources does the DS17485-5 provide?

The DS17485-5 provides three distinct memory regions: 114 bytes of general-purpose battery-backed RAM accessible via the AD0–AD7 bus; 4096 bytes of extended battery-backed NV SRAM (unique to DS17485/DS17487 variants); and 18 bytes of dedicated RTC/calendar/alarm registers. All memory retains data during VCC loss using VBAT or VBAUX. The extended SRAM is ideal for firmware parameter storage, event logs, or calibration tables - avoiding wear-prone EEPROM and enabling byte-level writes without erase cycles. The DS17485-5's RAM clear function (RCLR pin) allows secure erasure of user RAM without affecting RTC registers.