Renesas ISL12028IV27Z-T

Overview

ISL12028IV27Z-T from Renesas (formerly Intersil) is a low-power real-time clock/calendar IC with integrated 512×8-bit EEPROM, I²C interface, dual non-volatile alarms, CPU supervisor (POR, watchdog timer, low-voltage reset), and automatic battery backup switching. It operates from 2.7V to 5.5V main supply and retains timekeeping down to 1.8V on VBAT, uses an external 32.768kHz crystal, and delivers ±30ppm digital frequency adjustment via 64-position trim capacitor - deployed in utility meters and industrial control systems requiring long-term time accuracy and data retention.

For engineers reviewing the ISL12028IV27Z-T datasheet, ISL12028IV27Z-T pinout, ISL12028IV27Z-T application, or ISL12028IV27Z-T equivalent, this device supports I²C communication at 400kHz, provides three selectable frequency outputs (1Hz/4.096kHz/32.768kHz) on IRQ/FOUT, features 800nA battery current, 50-year EEPROM data retention, and programmable VRESET threshold (2.63V) - critical for fail-safe timekeeping in power-interrupted environments.

Technical Context

The ISL12028IV27Z-T implements a fully autonomous RTC core with leap-year-corrected calendar logic valid through 2099, separate BCD-encoded registers for seconds, minutes, hours, date, month, year, and day-of-week, and dual alarm engines supporting match-based triggering on second/minute/hour/day-of-week/date/month with repeat mode. Its oscillator compensation block integrates a digitally controlled 64-position trim capacitor and six discrete frequency adjustment settings (±30ppm), eliminating external load capacitors.

Power management includes intelligent VDD/VBAT switchover with 2.6V VTRIP threshold and 50mV hysteresis, open-drain RESET output with 250ms power-up delay and configurable trip voltage, and a watchdog timer with three timeout options (225ms/750ms/1.75s). The I²C interface remains functional during battery backup when enabled via register control, and EEPROM supports 16-byte page writes across 32 pages with BlockLock™ protection.

Key Specifications

Pinout & Package

ISL12028IV27Z-T is housed in a RoHS-compliant, 14-lead TSSOP package (M14.173), optimized for compact industrial PCB layouts and reflow-compatible assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS3231SN#T&R and PCF8563T/1,118, the ISL12028IV27Z-T uniquely combines EEPROM, dual alarms, watchdog, and oscillator trimming in one TSSOP package - making it optimal for cost-sensitive industrial designs requiring integrated data logging and fail-safe timing without external components.

Availability

ISL12028IV27Z-T is available at Aetrix Electronics and suitable for utility metering, HVAC control systems, and industrial network routers requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for ISL12028IV27Z-T 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

Renesas Electronics acquired Intersil in 2017 and maintains full technical and supply chain support for legacy Intersil timing products including the ISL12028 family.

The ISL12028 product line was designed for industrial and metering applications demanding integrated timekeeping, non-volatile event logging, and robust power-fail response - combining RTC, EEPROM, supervisor, and alarm functions in a single chip.

FAQ

What is the backup power supply range for the ISL12028IV27Z-T?

The ISL12028IV27Z-T accepts a backup supply voltage (VBAT) from 1.8V to 5.5V. When VDD fails, the device automatically switches to VBAT and continues timekeeping functionality down to 1.8V. Operation below 1.8V is not guaranteed, and battery voltage decay below this threshold may cause clock stoppage or data corruption after a VDD power-down cycle. The ISL12028IV27Z-T specifies 800nA typical battery current at 1.8V, enabling multi-year operation on standard coin cells.

Does the ISL12028IV27Z-T support I²C communication during battery backup mode?

Yes, the ISL12028IV27Z-T supports I²C communication during battery backup mode, but only when explicitly enabled via the I²C Enable During Battery Backup (IEBB) bit in the control register. By default, the I²C interface is disabled during VBAT-only operation to minimize current draw. Once enabled, SDA and SCL remain functional for reading RTC registers, checking alarm status, or accessing EEPROM - critical for diagnostics and maintenance during extended outages. The ISL12028IV27Z-T does not require external level shifters for this mode.

How does the oscillator compensation work in the ISL12028IV27Z-T?

The ISL12028IV27Z-T integrates a 64-position digitally controlled trim capacitor and six discrete frequency adjustment settings (±30ppm) to calibrate the 32.768kHz crystal oscillator. Compensation is performed by writing to the ATR (Analog Trim Register) to select one of six coarse trim values, then fine-tuning with the 6-bit digital trim capacitor. This eliminates external load capacitors and allows factory or field calibration - for example, adjusting for crystal aging or temperature-induced drift. The ISL12028IV27Z-T achieves stable timekeeping without requiring manual capacitor selection or board-level trimming.

What are the key differences between ISL12028 and ISL12028A variants?

The ISL12028IV27Z-T uses Legacy Mode Power Control (BSW = 1), while the ISL12028A uses Standard Mode (BSW = 0). Legacy Mode requires VDD < VBAT for proper battery switchover, whereas Standard Mode supports VBAT > VDD configurations. The ISL12028IV27Z-T has a fixed 2.63V VRESET threshold and is compatible with VDD-supplied pull-ups on SCL/SDA. The ISL12028A is obsolete with no recommended replacement; the ISL12028IV27Z-T remains actively supported and stocked by Renesas and authorized distributors.

Can the ISL12028IV27Z-T generate multiple frequency outputs?

Yes, the ISL12028IV27Z-T's IRQ/FOUT pin can be configured via software to output 1Hz, 4.096kHz, or 32.768kHz signals - all derived from the internal 32.768kHz crystal oscillator. These outputs are CMOS push-pull, require no external pull-up resistors, and can drive downstream logic or timing circuits directly. The selection is made by setting bits in the Frequency Output Control register; the pin defaults to interrupt mode after power-up. This eliminates the need for external dividers or buffers in systems requiring auxiliary clock sources.