Analog Devices Inc./Maxim Integrated DS1216B

Overview

DS1216B from Maxim Integrated is a 28-pin SmartWatch RAM socket integrating a real-time clock, nonvolatile RAM controller, and embedded lithium battery. It converts standard 16K×8 or 64K×8 CMOS SRAM into nonvolatile memory while maintaining time/date with ±1 minute/month accuracy at +25°C and automatic leap-year compensation through 2100. It is used in smartwatch and portable medical device memory subsystems requiring battery-backed timekeeping and data retention.

For engineers reviewing the DS1216B datasheet, DS1216B pinout, DS1216B application, or DS1216B equivalent, key selection considerations include its 28-pin DIP package, VCC/VCCB dual-switched power routing for density upgrades, pattern-based RTC register access via DQ0, write-protection activation at VTP = 4.25V–4.5V, and compatibility with 0°C to +70°C industrial temperature operation.

Technical Context

The DS1216B implements a serial 64-bit pattern-matching protocol (C5h, 3Ah, A3h, 5Ch, C5h, 3Ah, A3h, 5Ch) on DQ0 to enable RTC register access-prior to match, all cycles route to mated SRAM; after match, next 64 cycles access eight BCD-formatted 8-bit registers. Its nonvolatile controller monitors VCC continuously and switches to internal lithium backup (VBAT = 2.0–3.6V) within 2ms recovery time when VCC drops below VTP.

Power management includes a <0.2V dropout switch between VCC and VCCB/VCCD, unconditional write protection during power fail, and factory-shipped freshness seal that electrically disconnects the lithium cell until first VCC application. The RST pin features an internal pullup and supports oscillator disable/reset control via register bits.

Key Specifications

Pinout & Package

DS1216B uses a 28-pin 600-mil-wide DIP package with gold-plated gas-tight socket contacts. Pin 1 is RST (active-low reset), pins 2–11 and 13–28 provide pass-through connectivity to mated SRAM, and pins 3 (VCC), 26 (VCCB), and 28 (VCC) are switched power outputs routed to RAM VCC pins based on density configuration.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar nonvolatile RAM + RTC socket applications.

Compared with DS1216C and DS1216D, the DS1216B offers lowest-cost entry into SmartWatch RAM functionality for 16K×8 systems with optional 64K×8 upgrade path, while retaining identical RTC accuracy, battery life, and pattern-match security-but requires one-time board modification for density scaling.

Availability

DS1216B is available at Aetrix Electronics and suitable for smartwatch memory subsystems, portable medical loggers, and industrial data recorders requiring stable component supply with guaranteed 10-year data retention and ±1 minute/month RTC accuracy.

Supply support for DS1216B 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 DS1216B belongs to the SmartWatch RAM socket product line, engineered to eliminate discrete RTC + battery + power-switch designs in space-constrained portable electronics while guaranteeing synchronized time-stamped nonvolatile memory operation.

FAQ

What is the primary function of the DS1216B in a smartwatch design?

The DS1216B integrates a real-time clock, nonvolatile RAM controller, and embedded lithium battery into a 28-pin DIP socket. In a smartwatch, it converts a standard CMOS SRAM into nonvolatile memory while maintaining accurate time/date. Its transparent watch function ensures RAM operations proceed normally, while the RTC runs autonomously-enabling timestamped activity logs and sensor data retention across power cycles without host CPU involvement. The DS1216B achieves this with no additional board area beyond the SRAM footprint.

How does the DS1216B handle power failure and prevent data corruption?

The DS1216B continuously monitors VCC and triggers automatic switchover to its internal lithium battery when VCC drops below the VTP threshold (4.25V–4.5V). Within 2ms, it enables unconditional write protection to prevent unintended writes to both RTC registers and mated SRAM. Its <0.2V dropout power switch ensures minimal voltage loss during transition, and the embedded lithium source (2.0–3.6V) sustains timekeeping and data retention for up to 10 years. The DS1216B also enforces a 64-bit pattern match before RTC access, adding a hardware-level safeguard against accidental register modification.

What memory densities does the DS1216B support, and what board modifications are needed?

The DS1216B supports 16K×8 and 64K×8 CMOS SRAM densities. For 16K×8 operation, no board modification is required. To upgrade to 64K×8, the trace labeled "U" near the lower-density RAM's VCC pin must be cut, and the two square-metal pads labeled "G" must be shorted-this reroutes switched VCC to the appropriate address input pin on the higher-density SRAM. This modification is documented in Figure 2 of the DS1216B datasheet and is specific to the DS1216B; the DS1216C variant eliminates this requirement.

How is RTC register access implemented on the DS1216B, and why is it secure?

RTC register access on the DS1216B requires a precise 64-bit serial pattern (C5h, 3Ah, A3h, 5Ch, C5h, 3Ah, A3h, 5Ch) sent LSB-first on DQ0 using consecutive write cycles gated by CE and WE. Only after full match does the next 64 cycles access eight BCD-formatted 8-bit registers. This scheme prevents accidental RTC access-the false-trigger probability is less than 1 in 10¹⁹. The DS1216B also ignores pattern attempts if RST is low during matching, and aborts sequences on any intervening read cycle, ensuring robust isolation between RAM and RTC domains.

What is the significance of the "freshness seal" in the DS1216B's lithium energy source?

The DS1216B ships with its embedded lithium cell electrically disconnected from the circuitry, preserving full energy capacity until first power application. When VCC exceeds the lithium cell voltage during initial power-up, internal circuitry automatically connects the battery for backup operation. This freshness seal ensures the DS1216B delivers its rated 10-year data retention from day one-not from manufacturing date-and eliminates shelf-life degradation concerns. The DS1216B's datasheet confirms this feature prevents capacity loss during storage and guarantees optimal RTC runtime in end equipment.