Texas Instruments BQ3285ESS-N

Overview

BQ3285ESS-N from Texas Instruments is a low-power, battery-backed real-time clock (RTC) IC providing time-of-day and 100-year calendar functions with alarm, wake-up, and 242-byte nonvolatile SRAM storage. It operates from 2.7–3.6V (bq3285L variant), supports Intel/Motorola bus timing, delivers <0.5µA battery current, and integrates 32.768kHz crystal oscillator circuitry for embedded PC and industrial control applications.

For engineers reviewing the BQ3285ESS-N datasheet, BQ3285ESS-N pinout, BQ3285ESS-N application, or BQ3285ESS-N equivalent, key selection considerations include its dual-voltage compatibility (3V/5V variants), battery-backup interrupt capability, BCD/binary data format flexibility, programmable square-wave output (122µs–500ms periodic rates), and direct IBM AT-compatible replacement functionality.

Technical Context

The BQ3285ESS-N implements a fully autonomous RTC core with a 32.768kHz crystal oscillator, 1Hz update cycle, and integrated power-fail detection that switches to backup cell (BC) when VCC drops below VPFD (2.53V typical for L-version). Its register-mapped interface uses multiplexed AD0–AD7 with AS/DS/R/W/CS control signals and supports both Motorola and Intel bus timing via MOT pin configuration.

Three maskable interrupt sources-periodic (122µs–500ms), alarm (second-to-day granularity, active in battery mode), and update-ended-are managed through dedicated bits in registers B and C. The device includes 14 bytes of RTC/control registers and 242 bytes of general-purpose nonvolatile RAM, write-protected during power failure to preserve data integrity.

Key Specifications

Pinout & Package

Package: 24-pin SSOP (Small Outline Shrink Plastic Package), RoHS-compliant, body width 0.209 inch (5.30 mm).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock applications.

Compared with DS1285 and PCF8583, the BQ3285ESS-N uniquely combines 3V operation, sub-0.5µA battery current, hardware alarm wake-up during backup, and programmable 32.768kHz output - making it optimal for new 3V embedded designs requiring autonomous timekeeping and power-aware scheduling.

Availability

BQ3285ESS-N is available at Aetrix Electronics and suitable for industrial PLCs, legacy PC BIOS upgrades, smart energy meters, portable medical devices, and automotive infotainment systems requiring stable component supply and long-term lifecycle support.

Supply support for BQ3285ESS-N 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and power management technologies, with decades of expertise in precision timing solutions.

The BQ3285ESS-N belongs to TI's real-time clock product line, designed specifically for battery-backed timekeeping in industrial, computing, and medical applications where accuracy, low power, and long-term reliability are critical.

FAQ

What voltage range does the BQ3285ESS-N support?

The BQ3285ESS-N operates from 2.7V to 3.6V, making it compatible with modern 3V microcontroller systems. It includes internal power-fail detection that automatically switches to the backup cell (BC) when VCC drops below 2.53V (typical), ensuring uninterrupted RTC and SRAM operation. This 3V-specific variant replaces the 5V-only bq3285E version in low-power designs.

Does the BQ3285ESS-N support both BCD and binary time formats?

Yes, the BQ3285ESS-N supports both BCD and binary representations for time, alarm, and calendar data. The Data Format (DF) bit in register B selects the mode globally. When DF = 0, all values are stored in BCD (e.g., 0x23 for 23 seconds); when DF = 1, they are stored in pure binary (e.g., 0x17). This flexibility reduces firmware complexity in systems requiring either format.

How does the alarm wake-up feature work in battery-backup mode?

The BQ3285ESS-N asserts its open-drain INT pin low during battery backup when an alarm condition occurs - even with VCC removed. To use this, INT must be pulled up to a separate always-on supply (e.g., backup rail or coin-cell regulator). The alarm comparison runs autonomously in hardware, matching hours/minutes/seconds registers against alarm registers once per second, enabling true zero-power wake-up scheduling.

Can the BQ3285ESS-N generate a 32.768kHz output?

Yes, the BQ3285ESS-N can output a clean 32.768kHz signal on the SQW pin. This requires setting OSC2–OSC0 = 011 in register A, SQWE = 1 in register B, and 32KE = 1 in register C. Unlike lower-frequency square-wave outputs, this 32.768kHz mode is explicitly enabled by the 32KE bit and provides a stable timing reference for external power-management ICs or ADC sampling clocks.

What is the purpose of the EXTRAM pin on the BQ3285ESS-N?

The EXTRAM pin on the BQ3285ESS-N controls access mode: when low, the device maps to its 14-byte RTC/control register space (addresses 0–13); when high, it enables access to the full 242-byte nonvolatile SRAM block (including 128 bytes of extended RAM). This dual-mode addressing allows efficient use of the same parallel bus for both timekeeping and user data storage without external logic.