Analog Devices Inc./Maxim Integrated DS1211+

Overview

DS1211+ from Maxim Integrated (now Analog Devices) is a nonvolatile controller IC that converts up to eight CMOS RAMs into battery-backed nonvolatile memory systems. It provides automatic battery switchover, unconditional write protection during VCC out-of-tolerance, power-fail interrupt signaling, 3-to-8 address decoding, and consumes <100 nA battery current. Used in industrial data loggers requiring persistent RAM retention during AC loss.

For engineers reviewing the DS1211+ datasheet, DS1211+ pinout, DS1211+ application, or DS1211+ equivalent, key selection criteria include VCC tolerance threshold (5% or 10%), dual-battery support, PF signal timing, CE output drive capability, and compatibility with 5V CMOS RAMs operating at VCCO.

Technical Context

The DS1211+ integrates a precision voltage monitor with programmable 5% or 10% VCC tolerance detection, a low-leakage CMOS 3-to-8 decoder, and dual-battery selector logic. Its PF output asserts before VCC dropout to trigger processor save routines, while CE0–CE7 outputs drive RAM chip enables with active-low polarity.

It operates exclusively from a +5V supply (VCCI), powers RAMs via separate VCCO, and supports redundant backup using VBAT1 and VBAT2. Battery test occurs automatically on power-up, and NC pin (Pin 11) is unconnected - no internal function.

Key Specifications

Pinout & Package

DS1211+ is available in 20-pin DIP (300-mil) and 20-pin SOIC (300-mil) packages. Both share identical pinout and thermal characteristics.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1212+ and MAX6900, the DS1211+ uniquely balances 8-RAM scalability, deterministic PF timing, and ultra-low battery drain-making it optimal for industrial loggers needing precise, low-cost, multi-chip nonvolatility without RTC overhead.

Availability

DS1211+ is available at Aetrix Electronics and suitable for industrial data loggers, medical patient monitors, avionics black box recorders, and energy meter firmware storage requiring stable component supply and long-term lifecycle support.

Supply support for DS1211+ 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) designs precision analog, mixed-signal, and power management ICs for industrial, automotive, and communications systems.

The DS1211+ belongs to Maxim's legacy nonvolatile memory controller product line, engineered specifically to eliminate external discrete components in battery-backed RAM subsystems for mission-critical data retention.

FAQ

What is the function of the TOL pin on the DS1211+?

The TOL pin on the DS1211+ selects the VCCI power-supply tolerance threshold: logic low configures 5% detection (±250 mV), and logic high configures 10% (±500 mV). This setting determines the voltage deviation at which the DS1211+ asserts PF and disables CE outputs. The DS1211+ uses this pin to calibrate early warning timing for system-level power-fail response without requiring external resistors or configuration registers.

Can DS1211+ support both VBAT1 and VBAT2 simultaneously?

Yes, the DS1211+ supports simultaneous connection of VBAT1 and VBAT2 through internal diode-OR logic. It automatically selects the higher-voltage battery source and isolates the lower one, enabling true redundancy and hot-swappable battery maintenance. The DS1211+ validates both inputs during power-up and only enables VCCO if at least one battery exceeds 2.0V - a feature confirmed in the original Maxim datasheet and used in field-deployed energy meters.

Is DS1211+ pin-compatible with DS1212+?

No, the DS1211+ is not pin-compatible with DS1212+. The DS1211+ uses a 20-pin package with CE0–CE7, A/B/C, and dual VBAT pins, while DS1212+ uses a 28-pin SOIC package to accommodate 16 CE outputs and additional control lines. Board redesign is required to substitute DS1212+ for DS1211+, though both share identical functional architecture and registerless operation.

What is the maximum capacitive load the DS1211+ CE outputs can drive?

The DS1211+ CE0–CE7 outputs are open-drain and rated to sink ≥2 mA per pin at VCCO = 5V, supporting standard CMOS RAM /CE inputs with up to 100 pF total load capacitance. This specification ensures reliable timing across worst-case trace lengths in 6-layer industrial PCBs. The DS1211+ datasheet confirms these drive capabilities apply across the full -40°C to +85°C temperature range without derating.

Does DS1211+ require external pull-up resistors on CE outputs?

Yes, external pull-up resistors are required on all DS1211+ CE0–CE7 outputs because they are open-drain. Typical values range from 4.7 kΩ to 10 kΩ to VCCO, selected to meet RAM /CE rise-time requirements (<100 ns) while minimizing static current. The DS1211+ itself does not integrate pull-ups; omission causes undefined RAM enable states and potential data corruption during power transitions.