Analog Devices Inc./Maxim Integrated DS1312

Overview

DS1312 from Maxim Integrated is a nonvolatile controller with integrated lithium battery monitor, designed to convert standard CMOS SRAM into nonvolatile memory by managing power switching, write-protection, and battery health monitoring. It operates over -40°C to +85°C, supports 5% or 10% VCC tolerance detection via TOL pin, and delivers <0.2V switch drop between VCCI and VCCO.

For engineers reviewing the DS1312 datasheet, DS1312 pinout, DS1312 application, or DS1312 equivalent, key selection considerations include its dual-role as SRAM backup controller and battery voltage monitor with factory-programmed 24-hour test interval, open-drain BW/RST outputs, and support for 8-pin DIP, 8-pin SOIC, 16-pin SOIC, and 20-pin TSSOP packages.

Technical Context

The DS1312 implements precision comparator-based VCC monitoring with two selectable trip points (4.50–4.75V at TOL=GND; 4.25–4.50V at TOL=VCCO), enabling configurable power-fail detection. Its internal 1.2 MΩ test load connects to VBAT for one second every 24 hours to measure loaded-battery voltage against a 2.5–2.7V trip threshold (VBTP).

During VCC failure, the device inhibits CEO within 1.5 µs while preserving in-progress memory access, holds RST active for 150–350 ms on power-up, and sustains VCCO at VBAT − 0.2V in backup mode. All outputs (BW, RST, CEO) are open-drain with 4 mA sink capability and require external pull-ups.

Key Specifications

Pinout & Package

DS1312 is available in 8-pin DIP (300 mil), 8-pin SOIC (150 mil), 16-pin SOIC (300 mil), and 20-pin TSSOP packages. Pin functions are consistent across variants except for NC placements and presence of RST (DS1312S/DS1312E only).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar nonvolatile SRAM controller applications.

Compared with DS1230Y and MAX6900, the DS1312 uniquely combines autonomous SRAM write-protection, configurable power-fail detection, lithium-loaded battery monitoring, and processor reset generation in a single chip-eliminating need for external timing or control logic in embedded memory backup designs.

Availability

DS1312 is available at Aetrix Electronics and suitable for industrial data loggers, medical device memory backup, point-of-sale terminals, and smart meter firmware storage requiring stable component supply and long-term lifecycle support.

Supply support for DS1312 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 and mixed-signal ICs for industrial, medical, and communications applications, emphasizing reliability, low power, and integration.

The DS1312 belongs to Maxim's nonvolatile memory controller product line, engineered specifically to eliminate external components in SRAM-based data retention systems while delivering predictive battery health management.

FAQ

What is the primary function of the DS1312 in an SRAM-based system?

The DS1312 converts standard CMOS SRAM into nonvolatile memory by autonomously switching power from VCCI to VBAT during supply failure, inhibiting CEO to enforce write-protection, and monitoring lithium battery health. It ensures data integrity during power loss and provides early warning of battery end-of-life through its dedicated BW output-functions fully implemented without external firmware or controllers.

How does the DS1312 perform battery voltage monitoring without draining the lithium cell?

The DS1312 performs battery monitoring by connecting VBAT to an internal 1.2 MΩ test resistor for exactly one second every 24 hours (tBTCN). This brief, periodic loaded measurement avoids continuous current draw, limiting average battery current to ≤100 nA in backup mode and enabling >10-year lithium cell life-consistent with the DS1312's design goal of maintenance-free operation.

What is the significance of the TOL pin on the DS1312?

The TOL pin configures the DS1312's VCC trip point: grounding TOL selects 5% tolerance (4.50–4.75V), while tying it to VCCO selects 10% tolerance (4.25–4.50V). This hardware-selectable threshold allows system designers to match the DS1312's power-fail response to their specific supply regulation margin and noise immunity requirements-without requiring firmware changes or external components.

Can the DS1312 be used with SRAM devices requiring more than 140mA at VCCO ≥ VCCI − 0.2V?

No-the DS1312 specifies maximum RAM supply current ICCO1 as 140mA when VCCO ≥ VCCI − 0.2V (and 200mA when VCCO ≥ VCCI − 0.3V). Exceeding these limits risks VCCO droop or thermal overload. For higher-current SRAMs, the DS1312 must be paired with an external pass transistor or replaced with a higher-capacity controller like the DS1230Y in high-current configurations.

Why does the DS1312 require external pull-up resistors on BW and RST pins?

The DS1312 implements BW and RST as open-drain outputs capable of sinking up to 4 mA but unable to source current. External pull-up resistors (typically 4.7kΩ to VCCO) are mandatory to establish valid logic-high states during inactive periods. This architecture allows wired-OR connection to shared interrupt/reset buses and ensures compatibility with diverse processor input thresholds-core to the DS1312's role in heterogeneous embedded systems.