Analog Devices Inc./Maxim Integrated DS1321+

Overview

DS1321+ from Maxim Integrated is a flexible nonvolatile controller that converts CMOS SRAM into battery-backed nonvolatile memory, featuring automatic VCC fail detection (4.5–4.75 V trip), lithium battery voltage monitoring with 2.5–2.7 V trip point, and open-drain RST/BW outputs. It supports up to four SRAMs in three configurable banks and operates across –40°C to +85°C in 16-pin PDIP, SO, or 20-pin TSSOP packages.

For engineers reviewing the DS1321+ datasheet, DS1321+ pinout, DS1321+ application, or DS1321+ equivalent, key selection considerations include VCC tolerance select (TOL pin), mode-configurable SRAM bank mapping (MODE pin), battery warning timing (24-hour test cycle), and backup current capability (≤500 µA in battery mode).

Technical Context

The DS1321+ integrates precision voltage comparators for dual-threshold VCC monitoring (5% or 10% tolerance selectable via TOL), a low-leakage battery test circuit that applies a 1 MΩ internal load every 24 hours, and a controlled write-protection scheme that delays CEO inhibition up to 1.5 µs to complete in-progress memory accesses during power failure.

Its architecture includes an internal power switch with <0.2 V dropout between VBAT and VCCO, open-drain reset (RST) with 150–350 ms active hold on power-up, and battery warning (BW) latching behavior requiring physical battery replacement to clear - not resettable by power cycling alone.

Key Specifications

Pinout & Package

DS1321+ is available in 16-pin PDIP (300 mil), 16-pin SO (150 mil), and 20-pin TSSOP packages. All variants share identical functional pin assignments except for NC placements; pin compatibility is maintained across packages for drop-in substitution where board layout permits.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1321+, DS1230Y-100+ offers simpler implementation but sacrifices battery health awareness and memory topology flexibility, while MAX6900A+ adds RTC capability at the expense of SRAM control granularity and 5 V compatibility.

Availability

DS1321+ is available at Aetrix Electronics and suitable for industrial data loggers, medical diagnostic devices, programmable logic controllers, point-of-sale terminals, and embedded instrumentation requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for DS1321+ 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 DS1321+ belongs to Maxim's nonvolatile memory interface product line, engineered specifically to eliminate external discrete components in SRAM-based data retention systems while delivering accurate battery health assessment and robust power-fail response.

FAQ

What is the primary function of the DS1321+ in a system?

The DS1321+ serves as a flexible nonvolatile controller that converts standard CMOS SRAM into battery-backed memory. It monitors VCC for out-of-tolerance conditions, automatically switches to lithium battery backup, write-protects SRAM during power failure, and provides advanced battery health warning via the BW pin. Its core role is ensuring data integrity across power disruptions without firmware intervention.

How does the DS1321+ detect impending lithium battery failure?

The DS1321+ performs a loaded-battery voltage measurement every 24 hours by connecting VBAT to an internal 1 MΩ resistor for one second. If the resulting voltage falls below the factory-trimmed 2.5–2.7 V trip point, the open-drain BW pin is latched active. This method avoids false warnings from stable open-circuit voltage and requires physical battery replacement-not power cycling-to clear the warning.

Can the DS1321+ support different SRAM configurations, and how is this controlled?

Yes, the DS1321+ supports three SRAM memory configurations via the MODE pin: 4 banks × 1 SRAM (MODE = GND), 2 banks × 2 SRAMs (MODE = VCCO), or 1 bank × 4 SRAMs (MODE floating). The MODE state is latched at VCCI = VCCTP during power-up, enabling hardware-defined memory topology without software reconfiguration.

What is the significance of the TOL pin on the DS1321+?

The TOL pin selects the VCC trip point tolerance: tied to GND for 5% tolerance (4.50–4.75 V) or to VCCO for 10% tolerance (4.25–4.50 V). This allows system designers to match the DS1321+'s power-fail detection threshold to their specific power supply regulation and noise margin requirements without changing the IC.

Does the DS1321+ require external pull-up resistors, and why?

Yes, the DS1321+ requires external pull-up resistors on both the RST and BW pins because they are open-drain outputs. These resistors establish valid logic-high levels when the outputs are inactive. The DS1321+ can sink up to 10 mA on each pin, so pull-up values must be selected to ensure proper voltage levels and timing margins under worst-case load conditions.