onsemi CAT1021LI-42-G

Overview

CAT1021LI-42-G from onsemi is a supervisory circuit integrating 2 kbit I²C EEPROM, precision V_CC monitor with 4.25 V–4.50 V reset threshold, active-high and active-low open-drain RESET outputs, manual reset input (MR), and write-protect input (WP). It operates from 2.7 V to 5.5 V, features a 1.6 s watchdog timer monitoring SDA, and supports industrial temperature range (−40°C to +85°C). It is used in microcontroller-based systems requiring power-up/down supervision and nonvolatile configuration storage.

For engineers reviewing the CAT1021LI-42-G datasheet, pinout, applications, or equivalent options, key selection considerations include its dual-reset output polarity, WP-enabled hardware write protection, SDA-monitored watchdog, 400 kHz I²C interface, and compatibility with 5 V/3.3 V systems requiring brownout immunity and EEPROM-backed configuration retention.

Technical Context

The CAT1021LI-42-G implements a precision bandgap-based V_CC sense circuit with 15 mV hysteresis and guaranteed reset validity down to V_CC = 1.0 V. Its dual open-drain RESET outputs (active-high and active-low) enable direct interfacing with diverse microcontrollers without level-shifting.

The integrated 2 kbit EEPROM uses a 16-byte page architecture, supports byte/page writes with 5 ms internal write cycle time, and enforces hardware write protection via the WP pin - disabling all writes when tied to V_CC. The watchdog timer resets the system if SDA remains static for >1.6 s, and MR provides debounced push-button reset with 100 ns glitch immunity.

Key Specifications

Pinout & Package

Package: 8-pin PDIP (Case 646AA), lead-free, RoHS-compliant, 0.3 inch wide body.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar supervisory EEPROM applications.

Compared with CAT1021LI-42-G, CAT1021WI-42-GT3 offers identical functionality in a surface-mount package, while MAX6326US43D3+ trades EEPROM integration and dual-reset capability for compact size and lower cost in systems with separate nonvolatile storage.

Availability

CAT1021LI-42-G is available at Aetrix Electronics and suitable for industrial automation, automotive electronics, and medical instrumentation requiring stable component supply, long-lifecycle support, and RoHS-compliant through-hole packaging.

Supply support for CAT1021LI-42-G 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, and sensing solutions for automotive, industrial, and cloud infrastructure markets.

The CAT1021 family was designed to consolidate power supervision and configuration storage into a single IC for resource-constrained microcontroller systems, reducing BOM count and improving system reliability under voltage stress.

FAQ

What is the reset threshold voltage range for CAT1021LI-42-G?

The CAT1021LI-42-G has a factory-trimmed reset threshold range of 4.25 V to 4.50 V, optimized for reliable operation in 5 V systems experiencing brownout conditions. This range ensures reset activation before critical logic levels fall out of specification, and the 15 mV hysteresis prevents chatter near the trip point. The CAT1021LI-42-G maintains valid reset output down to V_CC = 1.0 V, guaranteeing deterministic behavior during deep undervoltage events.

Does CAT1021LI-42-G support both active-high and active-low reset outputs?

Yes, CAT1021LI-42-G provides two independent open-drain reset outputs: one active-low (pin 2) and one active-high (pin 6). Both are asserted simultaneously during power-up, brownout, manual reset (MR), or watchdog timeout. Each requires appropriate external pull-up (for pin 2) or pull-down (for pin 6) to establish logic levels compatible with the target microcontroller's reset input requirements. This dual-output architecture eliminates need for external inverters in mixed-voltage designs.

How does the write-protect (WP) function work on CAT1021LI-42-G?

On CAT1021LI-42-G, the WP pin (pin 3) disables all EEPROM write operations when driven high (tied to V_CC). When WP is low or floating, writes are enabled. An internal pull-down resistor ensures default write-enable state if the pin is left unconnected. This hardware-level protection prevents accidental overwrites during power transitions or firmware errors - a critical safeguard for calibration data or security keys stored in the 2 kbit EEPROM.

What is the watchdog timer monitoring method used by CAT1021LI-42-G?

The CAT1021LI-42-G implements a 1.6 s watchdog timer that monitors the SDA line for activity - any high-to-low or low-to-high transition resets the timeout counter. If SDA remains static beyond 1.6 s, both RESET outputs assert to recover the system. Unlike CAT1023 variants, CAT1021LI-42-G does not require a dedicated WDI pin, simplifying design by reusing the I²C data line for supervision. The CAT1021LI-42-G watchdog remains disabled while RESET is asserted.

Can CAT1021LI-42-G operate in extended temperature environments?

CAT1021LI-42-G is specified for the industrial temperature range of −40°C to +85°C, as confirmed in Table 3 of the datasheet. It is not rated for the extended −40°C to +125°C range offered by some CAT102x variants. For applications requiring operation above +85°C - such as under-hood automotive or high-power industrial enclosures - users must select an extended-temperature qualified variant (e.g., CAT1021LI-42-GT3 with 'X' suffix if available) or verify thermal derating with onsemi application engineering. The CAT1021LI-42-G performance remains fully characterized within its stated industrial range.