Analog Devices Inc./Maxim Integrated DS1211S+

Overview

DS1211S+ from Analog Devices (acquired Maxim Integrated, formerly Dallas Semiconductor) is a nonvolatile controller IC that converts up to eight CMOS RAMs into battery-backed nonvolatile memory systems. It features 3-to-8 address decoding, automatic VCC out-of-tolerance write protection, battery switchover on power-fail, PF output for processor interrupt, and dual-battery support with <100 nA battery leakage current. Used in industrial data loggers requiring persistent RAM retention during AC loss.

For engineers reviewing the DS1211S+ datasheet, DS1211S+ pinout, DS1211S+ application, or DS1211S+ equivalent, key selection criteria include its 20-pin SOIC package, TOL threshold programmability (5% or 10%), dual VBAT inputs, CE0–CE7 active-low chip enable outputs, and guaranteed operation over –40°C to +85°C industrial temperature range.

Technical Context

The DS1211S+ integrates a precision voltage monitor with user-selectable 5% or 10% VCCI tolerance detection, a 3-bit binary decoder (A/B/C inputs), and eight independent open-drain CE outputs (CE0–CE7). Its internal switchover logic disconnects VCCI and connects VBAT1 or VBAT2 to VCCO when VCCI falls outside tolerance, ensuring uninterrupted RAM supply.

It includes battery health test circuitry that verifies VBAT1/VTBAT2 at power-up, supports redundant battery configurations via OR-ing diodes, and asserts the active-low PF signal within 10 µs of VCCI dropout - enabling deterministic processor interrupt response for save-and-halt sequences.

Key Specifications

Pinout & Package

DS1211S+ is housed in a 20-pin SOIC (300-mil) package with 0.050" lead pitch and JEDEC MS-013AC outline. Pin 1 is marked by a beveled corner or dot; pin numbering follows standard counter-clockwise convention from pin 1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1211S+, DS1212S+ scales output count but retains identical timing, battery management, and industrial temp rating, while MAX6900AESA+ reduces integration at the cost of losing multi-RAM control and deterministic PF signaling - making DS1211S+ optimal for compact, multi-RAM nonvolatile designs.

Availability

DS1211S+ is available at Aetrix Electronics and suitable for industrial data loggers, medical patient monitors, telecom base station controllers, and energy meter firmware storage requiring stable component supply across extended product lifecycles.

Supply support for DS1211S+ 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

Analog Devices (via acquisition of Maxim Integrated and Dallas Semiconductor) designs high-reliability analog, mixed-signal, and power management ICs for industrial, automotive, and communications infrastructure.

The DS1211S+ belongs to the nonvolatile memory controller product line, engineered specifically to eliminate external discrete power-fail logic and enable robust, long-life battery-backed RAM subsystems in mission-critical embedded systems.

FAQ

What is the function of the TOL pin on the DS1211S+?

The TOL pin on the DS1211S+ selects the VCCI supply tolerance threshold: tied to VCCI it enables 5% detection (±250 mV), and tied to GND it enables 10% detection (±500 mV). This setting determines the voltage window within which the DS1211S+ considers VCCI valid and remains in normal operation - critical for matching system regulator specifications without redesigning the power architecture.

How does the DS1211S+ handle dual battery inputs VBAT1 and VBAT2?

The DS1211S+ implements internal OR-ing logic between VBAT1 and VBAT2, automatically selecting the higher-voltage source to power VCCO during VCCI dropout. It does not parallel the batteries; instead, it isolates them to prevent reverse current and enables true redundancy - if VBAT1 depletes, VBAT2 takes over seamlessly, extending total backup runtime beyond single-cell limits.

Can the DS1211S+ drive CMOS RAMs directly without external level-shifting?

Yes, the DS1211S+ drives CMOS RAMs directly: its VCCO output supplies the RAM core voltage, and its open-drain CE0–CE7 outputs interface cleanly with standard 5V-tolerant CMOS RAM CE inputs when pulled up to VCCO. No level shifters are needed, as all logic thresholds and drive strengths are designed for direct connection to industry-standard 5V SRAMs like the HM62256 or IS61LV256AL.

What is the purpose of the PF output on the DS1211S+?

The PF (Power-Fail) output on the DS1211S+ is an active-low, open-drain signal that asserts within 10 µs of VCCI falling outside its programmed tolerance window. It is intended to connect directly to a microcontroller's NMI or interrupt pin, triggering immediate execution of RAM save routines - ensuring deterministic response before VCCI collapses below RAM operating voltage.

Does the DS1211S+ perform battery voltage testing, and when does it occur?

Yes, the DS1211S+ performs automatic battery voltage testing at power-up: it measures both VBAT1 and VBAT2 and disables switchover to either battery if either voltage falls below 2.5V. This prevents unreliable backup activation and ensures only healthy cells are engaged - a feature confirmed in the official DS1211 datasheet and critical for field-deployed systems where battery replacement is infrequent.