NXP Semiconductors PCA8550D,112

Overview

PCA8550D,112 from NXP Semiconductors is a 4-bit 2-to-1 I²C multiplexer with integrated 5-bit non-volatile EEPROM and a latched 1-bit non-multiplexed output, designed for jumperless configuration in Pentium Pro/Pentium II motherboard systems. It features 2.5 V multiplexed outputs, a 3.3 V latched non-multiplexed output, 5 V tolerant inputs, and an active-low OVERRIDE_N input forcing all outputs to logic 0.

For engineers reviewing the PCA8550D,112 datasheet, PCA8550D,112 pinout, PCA8550D,112 application, or PCA8550D,112 equivalent, key selection criteria include I²C address compatibility (0x4C), EEPROM write-protection via WP pin, MUX_SELECT-controlled routing between register and external inputs, and SO16 package suitability for high-density PC motherboard layouts.

Technical Context

The PCA8550D,112 implements a dual-path digital selection architecture: when MUX_SELECT = 0, MUX_OUT pins drive data from the internal 5-bit non-volatile register; when MUX_SELECT = 1, they route MUX_IN_A–D signals. The NON_MUXED_OUT pin is transparent during MUX_SELECT = 0 and latched on transition to MUX_SELECT = 1.

I²C communication uses a fixed 7-bit address (0x4C) with R/W bit, supporting read/write of the 5-bit register (bits [4:0] = NON_MUXED + MUX_DATA[3:0]). Write protection is enforced by the WP pin: logic 0 enables writes; logic 1 disables them. Internal pull-ups exist on OVERRIDE_N, WP, and MUX_SELECT.

Key Specifications

Pinout & Package

PCA8550D,112 is housed in a plastic small outline package (SO16) per SOT109-1: 16-pin, 3.9 mm body width, 1.27 mm lead pitch, surface-mount compatible.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar I²C-configurable DIP switch applications.

Compared with PCA9554PW,118 and PCA8574PW,118, the PCA8550D,112 uniquely integrates non-volatile configuration storage, hardware-selectable signal routing, and dedicated override functionality - making it irreplaceable for Pentium Pro/II motherboard strap signal management where boot-time determinism and field update capability are mandatory.

Availability

PCA8550D,112 is available at Aetrix Electronics and suitable for PC motherboard design, CPU interface configuration, and industrial x86-based control systems requiring stable component supply and long-term obsolescence support.

Supply support for PCA8550D,112 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

NXP Semiconductors is a global semiconductor company headquartered in Eindhoven, Netherlands, specializing in secure connectivity solutions for automotive, industrial, and consumer applications.

The PCA8550 product line was developed specifically to replace mechanical DIP switches in high-performance x86 computing platforms, delivering programmable, persistent, and noise-immune configuration for CPU strap signals in Pentium Pro and Pentium II systems.

FAQ

What is the I²C address of the PCA8550D,112 and how is it configured?

The PCA8550D,112 uses a fixed 7-bit I²C address of 0x4C (1001100b), with no address pins or hardware configurability. This address is hardwired internally and remains constant across all operating conditions. Communication begins with this address followed by a read/write bit; the device acknowledges only when this exact address is presented on the bus. No external resistors or straps affect the address, ensuring predictable bus enumeration in multi-device systems containing the PCA8550D,112.

How does the OVERRIDE_N pin function and what happens to outputs when it is asserted?

When OVERRIDE_N is driven LOW (logic 0), the PCA8550D,112 forces all four MUX_OUT pins (A–D) and the NON_MUXED_OUT pin to logic 0, regardless of MUX_SELECT state or EEPROM contents. This override takes precedence over all other control logic and is intended for fail-safe system reset or diagnostic modes. The override remains active as long as OVERRIDE_N is held LOW; outputs return to normal operation within 25 ns after OVERRIDE_N transitions HIGH, per tOVM specification.

Can the PCA8550D,112 be used with 3.3 V-only systems, and what are the voltage domain constraints?

Yes, the PCA8550D,112 operates from a 3.0 V to 3.6 V VCC supply and delivers 2.5 V multiplexed outputs and a 3.3 V non-multiplexed output - both compatible with standard 3.3 V logic families. Its 5 V tolerant inputs (MUX_IN, OVERRIDE_N, WP, MUX_SELECT) allow connection to higher-voltage control sources without level shifters. However, the 2.5 V MUX_OUT outputs must interface only with 2.5 V–compatible loads; driving 3.3 V inputs directly may violate VIH thresholds unless verified per application conditions.

What is the role of the MUX_SELECT pin beyond selecting multiplexer input source?

In addition to selecting between EEPROM register data (MUX_SELECT = 0) and external MUX_IN signals (MUX_SELECT = 1), the MUX_SELECT pin controls latching of the NON_MUXED_OUT signal. When MUX_SELECT transitions from LOW to HIGH, the current value on NON_MUXED_OUT is captured and held until the next such transition. This ensures stable reporting of the EEPROM's bit-4 status during dynamic reconfiguration, preventing glitches that could mislead CPU strap detection logic during boot sequences involving the PCA8550D,112.

How many write cycles does the internal EEPROM support, and what is its data retention period?

The PCA8550D,112's internal 5-bit EEPROM is rated for a minimum of 100,000 write cycles and guarantees data retention for at least 10 years under normal operating conditions (Tamb = 0 °C to +70 °C). These specifications are validated per JEDEC standards and reflect actual cell endurance - not typical or average values. Field updates to the EEPROM (e.g., BIOS configuration changes) can therefore be performed routinely throughout the product lifecycle without risk of premature wear-out.