Renesas ISL1221IUZ

Overview

ISL1221IUZ from Renesas (formerly Intersil) is a low-power real-time clock IC with integrated event detection, time stamping, 2-byte battery-backed SRAM, and 15-frequency selectable FOUT output. It operates from 2.7V to 5.5V, consumes only 400nA on battery, and maintains calendar accuracy through 2099 with leap-year correction. It serves as a secure timing and tamper-monitoring core in utility meters and network infrastructure.

For engineers reviewing the ISL1221IUZ datasheet, ISL1221IUZ pinout, ISL1221IUZ application, or ISL1221IUZ equivalent, this page delivers verified technical context, I²C timing compliance (400kHz), VBAT switchover thresholds (2.2V ±35mV), event sampling rates (1/4–2Hz), and crystal compensation range (−94ppm to +140ppm) - all confirmed for the exact ISL1221IUZ MSOP-10 package.

Technical Context

The ISL1221IUZ implements a crystal-based RTC with dual-mode operation: full functionality under VDD (2.7–5.5V) and reduced-mode operation under VBAT (1.8–5.5V), where only RTC, event detection, time stamping, and SRAM remain active while I²C is disabled. Its oscillator uses an external 32.768kHz crystal with on-chip analog and digital trimming registers enabling ±94ppm to +140ppm frequency compensation.

Event monitoring supports configurable sampling (1/4Hz, 1Hz, 2Hz), glitch filtering (0/3.9ms/15.625ms/31.25ms), and tamper-triggered register freeze. The IRQ/EVDET pin provides open-drain interrupt signaling for alarm or event detection, while FOUT delivers 15 programmable frequencies up to 32.768kHz - both functional in battery mode.

Key Specifications

Pinout & Package

ISL1221IUZ is housed in a Pb-free, RoHS-compliant 10-lead MSOP package (3.0mm × 4.9mm, 0.5mm pitch). Thermal resistance θ_JA = 120°C/W enables operation in compact, sealed enclosures without forced airflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS3231M and M41T81S, the ISL1221IUZ uniquely combines sub-500nA battery operation, programmable event sampling, hardware timestamping with RTC freeze, and on-chip crystal compensation - making it optimal for security-critical, battery-constrained infrastructure endpoints.

Availability

ISL1221IUZ is available at Aetrix Electronics and suitable for utility metering, network infrastructure equipment, and POS terminal designs requiring stable component supply, long-life battery operation, and tamper-evident time logging.

Supply support for ISL1221IUZ 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 support for legacy Intersil timing products. Renesas is a global semiconductor leader focused on embedded processing, analog, power, and connectivity solutions.

The ISL1221IUZ belongs to Renesas' secure real-time clock product line, designed specifically for infrastructure applications demanding tamper detection, battery-backed time integrity, and field-calibratable accuracy across industrial temperature ranges.

FAQ

What is the minimum VBAT voltage required to retain RTC and SRAM functionality in the ISL1221IUZ?

The ISL1221IUZ maintains full RTC and 2-byte SRAM operation down to VBAT = 1.8V. Below this threshold, timekeeping halts and SRAM contents may be lost. This 1.8V specification enables compatibility with widely available 3V lithium coin cells across their full discharge curve, supporting >10-year backup life in typical utility meter deployments.

Does the ISL1221IUZ support I²C communication while operating from VBAT only?

No - the I²C interface (SCL and SDA) is automatically disabled during VBAT-only operation to minimize leakage current. However, all RTC, event detection, time stamping, and SRAM functions remain fully active. Configuration and data read/write must occur during VDD-powered operation; timestamped event data stored in SRAM is preserved and readable after VDD restoration.

How does the ISL1221IUZ implement tamper detection with time stamping?

The ISL1221IUZ monitors the EVIN pin for logic-high transitions. Upon detection, it sets the EVT bit in the status register, writes the current RTC value (seconds, minutes, hours, date, month, year) into dedicated time-stamp registers, and can optionally freeze RTC advancement. This entire sequence occurs autonomously in both VDD and VBAT modes without host MCU intervention.

What crystal specifications are recommended for use with the ISL1221IUZ?

The ISL1221IUZ requires a standard 32.768kHz fundamental-mode quartz crystal with load capacitance of 12.5pF. Recommended parameters include series resistance ≤50kΩ, shunt capacitance ≤7pF, and drive level ≤1µW. The device's on-chip analog trimming register (ATR) allows fine-tuning of effective load capacitance from 9pF to 40.5pF to compensate for board parasitics and temperature drift.

Can the ISL1221IUZ generate a 1Hz square wave output on the FOUT pin?

Yes - the ISL1221IUZ supports 15 selectable FOUT frequencies, including exactly 1Hz. This is configured via the FO[3:0] bits in the control register and is active in both VDD and VBAT operating modes. The FOUT pin is open-drain, requiring an external pull-up resistor; output low voltage is guaranteed ≤0.4V at 3mA sink current.