Renesas X4285S8

Overview

X4285S8 from Xicor (now part of Renesas) is a CPU supervisor IC integrating power-on reset control, watchdog timer, supply voltage supervision, and 128Kbit serial EEPROM with Block Lock™ protection. It features selectable watchdog timeout (200 ms / 600 ms / 1.4 s), four standard V_CC reset thresholds (2.63V / 2.93V / 3.08V / 4.38V), and operates from 2.7V to 5.5V. Used in microcontroller-based embedded systems for reliable boot sequencing and data retention.

For engineers reviewing the X4285S8 datasheet, X4285S8 pinout, X4285S8 application, or X4285S8 equivalent, key selection considerations include its dual active-reset output polarity (RESET active-low, RESET active-high), programmable V_TRIP threshold, 400kHz I²C-compatible 2-wire interface, 64-byte page write capability, and hardware write protection via WP pin and WPEN bit.

Technical Context

The X4285S8 implements a dedicated low-voltage detection circuit with hysteresis and 250ms reset timeout after V_CC recovery, ensuring stable processor initialization. Its watchdog timer monitors SDA transitions during SCL HIGH and supports three nonvolatile timeout settings via WD1/WD0 bits in the control register.

EEPROM functionality uses a 16K × 8-bit organization (128Kbit total), internally segmented into 64-byte pages with self-timed 5ms typical write cycles. Block Lock™ protection is controlled by BP2/BP1/BP0 bits and can lock 64–512 bytes, 4K–16K segments, or full array - independent of WP pin state when WPEN = 0.

Key Specifications

Pinout & Package

Package: 8-lead SOIC (JEDEC MS-012) - 5.0mm × 4.0mm body, 1.27mm pitch, RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar CPU supervisor with integrated EEPROM applications.

Compared with MAX6361KA29+T and STM8AF6266TCY, the X4285S8 uniquely combines dual-polarity reset, field-programmable V_TRIP, and hardware watchdog transition sensing - enabling safer, more flexible system supervision without MCU intervention or external components.

Availability

X4285S8 is available at Aetrix Electronics and suitable for industrial PLC controllers, medical infusion pumps, automotive body control modules, smart energy meters, and battery-powered IoT gateways requiring stable component supply across extended product lifecycles.

Supply support for X4285S8 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

Xicor was a fabless semiconductor company specializing in nonvolatile memory and power management ICs, acquired by Renesas Electronics in 2008. Known for innovation in EEPROM architecture and system-level supervision.

The X4285S8 belongs to Xicor's CPU Supervisor + EEPROM family, designed specifically to consolidate reset, watchdog, voltage monitoring, and secure data storage into a single 8-pin package for space-constrained embedded systems.

FAQ

What is the function of the dual RESET/RESET outputs on the X4285S8?

The X4285S8 provides two independent reset signals: RESET (open-drain, active-low) and RESET (push-pull, active-high). Both assert simultaneously during power-up, brownout, or watchdog timeout. This dual-output architecture eliminates the need for external inverters or level translators when interfacing with MCUs that require either polarity - for example, RESET drives legacy 8051 reset inputs, while RESET interfaces directly with ARM Cortex-M series.

Can the V_TRIP threshold of the X4285S8 be customized, and how is it done?

Yes, the X4285S8's V_TRIP threshold is factory-set to 4.38V but can be reprogrammed to any value between ~1.7V and 4.6V using a nonvolatile programming sequence. This requires applying the target voltage to V_CC, 12–15V to the WP pin, and issuing a specific two-byte write command (A0h followed by 00h) with WEL bit enabled. The procedure is detailed in the datasheet Figure 1 and supports precision brownout tuning for standards-compliant designs.

How does the watchdog timer on the X4285S8 detect MCU failure?

The X4285S8 watchdog timer monitors the SDA line for a falling-edge transition while SCL is HIGH - which corresponds to an I²C start condition. If no such transition occurs within the selected timeout period (200ms / 600ms / 1.4s), the device asserts RESET/RESET. This method avoids false triggers from normal data transfers and ensures the MCU is actively managing the I²C bus - not just powered on.

What EEPROM protection mechanisms does the X4285S8 provide beyond standard write enable?

The X4285S8 implements three layered EEPROM protections: (1) Power-up/down write inhibit circuitry that blocks writes until V_CC stabilizes; (2) Block Lock™ with eight programmable protection modes (64B–16KB) set via nonvolatile BP bits; and (3) Hardware write protect using WP pin + WPEN bit - when both are HIGH, all nonvolatile writes (including control register) are blocked regardless of software state.

Is the X4285S8 pin-compatible with the X4283S8, and what is the key functional difference?

Yes, the X4285S8 and X4283S8 share identical pinout, package, and electrical specifications. The sole functional difference is reset output polarity: X4285S8 provides RESET (active-low) and RESET (active-high), whereas X4283S8 provides RESET (active-low) and RESET (active-low). This makes X4285S8 suitable for systems requiring active-high reset assertion without external inversion.