Renesas X4285S8-2.7

Overview

X4285S8-2.7 from Xicor (now part of Renesas) is a CPU supervisor IC integrating power-on reset control, watchdog timer, supply voltage supervision, and 128 Kbit serial EEPROM with Block Lock™ protection. It operates from 2.7V to 5.5V, features four standard V_CC reset thresholds (including factory-set 2.7V), delivers <1 µA standby current with watchdog disabled, and supports 400 kHz 2-wire (I²C-compatible) interface - used in embedded microcontroller systems for reliable boot sequencing and data retention.

For engineers reviewing the X4285S8-2.7 datasheet, X4285S8-2.7 pinout, X4285S8-2.7 application, or X4285S8-2.7 equivalent, key selection considerations include its programmable V_TRIP threshold (adjustable via VP on WP pin), 64-byte page write capability with 5 ms typical write cycle, open-drain active-HIGH RESET output, and hardware/software-configurable Block Lock protection covering 64–16K byte segments.

Technical Context

The X4285S8-2.7 implements a dual-function reset architecture: power-on reset asserts RESET for ≥250 ms after V_CC stabilization, while low-V_CC detection holds RESET active until V_CC exceeds the selected trip point (e.g., 2.7V) for 200 ms and remains valid down to 1V. Its watchdog timer monitors SDA transitions during SCL HIGH and offers three timeout options (200 ms, 600 ms, 1.4 s) controlled by nonvolatile WD1/WD0 bits.

The integrated 128 Kbit EEPROM is organized as 16K × 8, supports byte and 64-byte page writes, uses self-timed internal write cycles, and enforces write protection via three mechanisms: power-up/down circuitry, volatile WEL/RWEL latches, and nonvolatile BP2–BP0 block lock bits - all accessible via I²C at address FFFFh.

Key Specifications

Pinout & Package

Package: 8-lead SOIC (JEDEC MS-012) - surface-mount compatible with standard reflow profiles and PCB assembly processes.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6361KA27+T and STM8T142M2U6, the X4285S8-2.7 uniquely combines field-adjustable V_TRIP, 400 kHz I²C, and 128 Kbit Block Lock™ EEPROM in a single 8-pin SOIC - reducing component count, eliminating external memory, and enabling post-deployment voltage tuning without hardware revision.

Availability

X4285S8-2.7 is available at Aetrix Electronics and suitable for industrial PLC controllers, medical infusion pumps, smart energy meters, automotive body control modules, and embedded telemetry gateways requiring stable component supply, long-term EEPROM data retention, and robust brownout resilience.

Supply support for X4285S8-2.7 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. Its legacy products emphasize reliability, low-power design, and integration density.

The X4285 series targets embedded systems needing consolidated power supervision and persistent storage - designed to replace discrete reset ICs + EEPROMs while improving system-level robustness and reducing PCB footprint.

FAQ

What is the factory-default reset threshold voltage for the X4285S8-2.7?

The X4285S8-2.7 ships with a factory-default V_TRIP of 2.7V, matching its suffix designation. This threshold is laser-trimmed and stable over temperature and time. It can be reprogrammed to custom values (e.g., 3.0V or 3.3V) using the VP pulse sequence on the WP pin, as documented in the datasheet's "V_CC Threshold Reset Procedure" section. The X4285S8-2.7 retains this setting across power cycles due to nonvolatile storage.

Does the X4285S8-2.7 support I²C standard-mode or fast-mode timing?

The X4285S8-2.7 supports fast-mode I²C operation at up to 400 kHz, as explicitly specified in its "Features" list and electrical characteristics table. It complies with I²C bus protocol conventions including start/stop conditions, acknowledge polling, and 7-bit slave addressing with S0/S1 device select inputs. The X4285S8-2.7 does not support high-speed mode (3.4 MHz) or SMBus-specific timeouts.

How does the watchdog timer in the X4285S8-2.7 get reset during normal operation?

The X4285S8-2.7 watchdog timer resets on a HIGH-to-LOW transition of the SDA line while SCL is held HIGH - corresponding to an I²C start condition. This allows the host microcontroller to service the watchdog using standard bus activity without dedicated GPIO toggling. The X4285S8-2.7 does not require periodic register writes; bus-level protocol events suffice. Timeout intervals (200/600/1400 ms) are set nonvolatily via WD1/WD0 bits.

Can the EEPROM in the X4285S8-2.7 be partially protected while leaving other sections writable?

Yes - the X4285S8-2.7 implements granular Block Lock™ protection using BP2/BP1/BP0 bits to secure eight distinct memory zones: none, 64/128/256/512 bytes, upper 1/4, upper 1/2, or full 16K-byte array. Protection is enforced at the hardware level and persists through power cycles. The X4285S8-2.7 allows mixing protected and unprotected regions, enabling bootloader code to remain locked while application data remains modifiable.

What happens to the RESET output of the X4285S8-2.7 during a brownout event?

During a brownout, the X4285S8-2.7 asserts its active-HIGH RESET output when V_CC falls below the programmed V_TRIP (e.g., 2.7V) and holds it active until V_CC rises above that threshold for ≥200 ms. Crucially, RESET remains asserted even if V_CC drops as low as 1V - ensuring the connected microcontroller stays held in reset under severe undervoltage conditions where many supervisors release prematurely. The X4285S8-2.7 guarantees this behavior across its full industrial temperature range.