Analog Devices Inc./Maxim Integrated DS1321E+T&R

Overview

DS1321E+T&R from Maxim Integrated is a flexible nonvolatile SRAM controller with integrated lithium battery monitoring and power-fail detection. It converts up to four CMOS SRAMs into nonvolatile memory, provides automatic battery switchover (VBAT ≥ 2.0V), write-protection during VCCI out-of-tolerance (4.25–4.75V trip range), and open-drain RST/BW outputs. Used in industrial data loggers requiring persistent memory retention during AC loss.

For engineers reviewing the DS1321E+T&R datasheet, DS1321E+T&R pinout, DS1321E+T&R application, or DS1321E+T&R equivalent, this page delivers verified functional architecture, mode-selectable memory bank configuration (1/2/4 banks), battery voltage trip point (2.50–2.70V), and TSSOP-20 package-specific timing (tRPU = 150–350ms, tREC = 125ms).

Technical Context

The DS1321E+T&R implements a precision dual-threshold VCCI comparator (selectable 5% or 10% tolerance via TOL pin) that triggers both CEO inhibition and RST assertion within 15µs of power failure. Its internal 1MΩ battery test load enables loaded-voltage measurement every 24 hours to detect end-of-life lithium cells before data loss occurs.

It supports three memory configurations latched at power-up via MODE pin state (GND/VCCO/floating), drives VCCO ≤ VCCI − 0.2V during main supply operation, and sustains VCCO ≥ VBAT − 0.2V in backup mode with <0.2V switch drop. CEO outputs are actively held high for tREC (125ms) after VCCI recovery to prevent premature SRAM access.

Key Specifications

Pinout & Package

DS1321E+T&R is housed in a RoHS-compliant 20-pin TSSOP (U20+1) package with 0.65mm pitch, 6.5mm × 4.4mm body size, and thermal resistance θJA = 73.8°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1321E+T&R, DS1230Y-100+ offers simpler reset timing but no battery health awareness, while MAX6900AESA+ adds RTC capability at the cost of fixed memory topology and I²C dependency-neither matches DS1321E+T&R's hardware-configurable bank architecture and autonomous 24-hour battery testing.

Availability

DS1321E+T&R is available at Aetrix Electronics and suitable for industrial data loggers, medical device memory backup, and programmable logic controllers requiring stable component supply with guaranteed long-term lifecycle support.

Supply support for DS1321E+T&R 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, automotive, and communications systems.

The DS1321E+T&R belongs to Maxim's nonvolatile memory controller product line, engineered specifically to eliminate external discrete components in SRAM battery-backup systems while delivering autonomous battery health monitoring and configurable memory topology.

FAQ

What is the function of the MODE pin on the DS1321E+T&R?

The MODE pin on the DS1321E+T&R determines SRAM bank organization at power-up: grounded for four independent banks (1 SRAM each), tied to VCCO for two banks (2 SRAMs each), or floating for one bank (4 SRAMs). Its state is latched when VCCI crosses VCCTP, enabling hardware-defined memory mapping without firmware intervention. This behavior is confirmed in the DS1321E+T&R functional description and Figure 1 of the datasheet.

How does the DS1321E+T&R perform battery voltage monitoring without draining the lithium cell?

The DS1321E+T&R performs battery voltage monitoring by connecting VBAT to an internal 1MΩ test resistor for exactly one second every 24 hours (tBTCN), measuring loaded voltage against a 2.50–2.70V trip point. This infrequent, short-duration test minimizes cumulative current draw-typical battery current in backup mode is just 100nA-ensuring multi-year cell life. The DS1321E+T&R datasheet explicitly states this method prevents excessive drain while enabling reliable end-of-life prediction.

What is the maximum SRAM load current the DS1321E+T&R can drive in normal operation?

The DS1321E+T&R can supply up to 185mA to attached SRAMs when VCCO ≥ VCCI − 0.2V, and up to 260mA when VCCO ≥ VCCI − 0.3V. These values are specified in the DC Electrical Characteristics table under ICCO1 and ICCO2 parameters. Exceeding these limits risks VCCO droop and memory corruption; design margin should be maintained per DS1321E+T&R recommended operating conditions.

Can the DS1321E+T&R operate with a 3.3V main supply?

No-the DS1321E+T&R is specified only for 5V operation: VCCI min is 4.5V (TOL=VCCO) or 4.75V (TOL=GND), with absolute max 5.5V. It lacks 3.3V-compatible input thresholds or VCCO regulation for lower voltages. Attempting 3.3V operation violates the DS1321E+T&R recommended operating conditions and will cause unreliable power-fail detection, incorrect CEO timing, and potential latch-up per Absolute Maximum Ratings.

What happens to the CEO outputs during a power failure event on the DS1321E+T&R?

During a VCCI power failure, the DS1321E+T&R inhibits CEO1–CEO4 by holding them within 0.2V of VCCO to enforce SRAM write-protection. If any CEI input is active (low) when failure occurs, the corresponding CEO remains low until that CEI goes high-or is forced high after 1.5µs if CEI stays low. This ensures ongoing memory accesses complete before protection engages, as defined in the DS1321E+T&R memory backup section and AC timing specifications.