DS1321E

Controllers Overview

The DS1321E is a flexible nonvolatile memory controller with an integrated lithium battery monitor, designed to convert CMOS SRAMs into nonvolatile memory. It operates within an industrial temperature range of -40°C to +85°C and supports supply voltages from 4.75V to 5.5V (TOL=GND) or 4.5V to 5.5V (TOL=VCCO). The device manages up to four SRAMs via three configurable modes: Mode 0 (4 banks x 1 SRAM), Mode 1 (2 banks x 2 SRAMs), and Mode 2 (1 bank x 4 SRAMs). It features automatic power-fail detection, write protection, processor reset generation, and periodic battery health monitoring.

Controllers Feature Summary

• Converts standard CMOS SRAMs into nonvolatile memory by automatically switching to battery backup during power failures.
• Monitors lithium battery voltage under load to provide advanced warning of impending end-of-life conditions.
• Unconditionally write-protects attached SRAMs when the main supply voltage falls out of tolerance.
• Generates a system reset signal to hold the processor in reset during power failure and power-up transients.

Controllers Applications

• Battery-backed nonvolatile memory systems for data retention
• Processor-based systems requiring power-fail detection and reset generation
• Industrial control applications requiring extended temperature operation

Controllers Procurement Notes

Verify the specific package variant required, as the base model DS1321 is available in 16-pin PDIP, 16-pin SO, and 20-pin TSSOP configurations. Confirm RoHS compliance status, indicated by the '+' suffix in ordering part numbers. Ensure the design accounts for the open-drain nature of the Battery Warning and Reset outputs, which require external pull-up resistors for proper logic level signaling.

Controllers Selection Notes

Select the appropriate MODE pin configuration based on the number of SRAMs and desired bank organization. Choose between 5% or 10% power-fail detection sensitivity by connecting the TOL pin to GND or VCCO respectively. Consider the thermal resistance characteristics of the chosen package if operating near maximum temperature limits. Verify that the lithium battery voltage meets the minimum requirements for the internal test load circuitry.

Controllers Part Context

The DS1321E belongs to the DS1321 family of flexible nonvolatile controllers manufactured by Analog Devices Inc./Maxim Integrated. This series addresses the need for reliable data storage in CMOS SRAMs by integrating power management and battery monitoring functions into a single CMOS circuit. The E suffix specifically denotes the 20-pin TSSOP package version within this product line.

Controllers Replacement Considerations

DS1321E+

Controllers FAQ

How does the DS1321E detect battery end-of-life?

It periodically connects the battery to an internal resistive load for one second every 24 hours. If the loaded battery voltage falls below a factory-programmed trip point, the Battery Warning output is activated.

What happens to the Chip Enable outputs during a power failure?

When VCCI falls out of tolerance, the DS1321 inhibits the four Chip Enable outputs (CEO1-CEO4) to write-protect the SRAMs, holding them high until VCCI returns to nominal levels.

Can the DS1321E monitor the battery continuously?

No, continuous monitoring would drastically reduce battery life. It only tests the battery for one second every 24 hours while VCCI is nominal.