NXP Semiconductors PCA8550PW,118

Overview

PCA8550PW,118 from NXP Semiconductors is a 4-bit 2-to-1 I²C multiplexer with integrated 5-bit non-volatile EEPROM and 1-bit latched output, designed for jumperless configuration in Pentium Pro/Pentium II motherboard systems. It provides 2.5 V multiplexed outputs (MUX_OUT A–D), a 3.3 V latched NON_MUXED_OUT, 5 V-tolerant inputs, and active-low OVERRIDE_N forcing all outputs to logic 0.

For engineers reviewing the PCA8550PW,118 datasheet, PCA8550PW,118 pinout, PCA8550PW,118 application, or PCA8550PW,118 equivalent, key selection criteria include I²C-addressable register write protection (WP), MUX_SELECT-controlled input/register routing, propagation delays ≤25 ns, and TSSOP16 packaging for high-density PC board layouts.

Technical Context

The PCA8550PW,118 implements a dual-path digital selection architecture: when MUX_SELECT = 0, MUX_OUT pins drive data from the internal 5-bit non-volatile EEPROM; when MUX_SELECT = 1, they route external 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 (1001110) with R/W bit, supporting read/write of the EEPROM's low 4 bits (multiplexed data) and bit 4 (non-multiplexed output). Write protection is controlled 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

TSSOP16 package: plastic thin shrink small outline, 16 leads, body width 4.4 mm (SOT403-1), optimized for high-density PCB layouts and reflow soldering.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA8550PW,118, PCA9554PW,118 offers greater I/O count but loses configuration persistence and multiplexer functionality, while PCA8574PW,118 provides basic I/O expansion without any non-volatile or multiplexing capability-making PCA8550PW,118 uniquely suited for jumperless legacy x86 platform configuration.

Availability

PCA8550PW,118 is available at Aetrix Electronics and suitable for PC motherboard design, CPU interface control, and industrial control I/O mapping requiring stable component supply and long-term lifecycle support.

Supply support for PCA8550PW,118 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 delivers I²C-addressable non-volatile configuration devices targeting legacy x86 platform modernization, enabling jumperless motherboard design and field-updatable system topology.

FAQ

What is the I²C address of the PCA8550PW,118 and how is it configured?

The PCA8550PW,118 uses a fixed 7-bit I²C address of 0x4E (binary 1001110), with the R/W bit appended externally. This address is hardwired and not configurable via pins or registers. Communication follows standard I²C protocol: after START, the master sends the 7-bit address plus R/W bit, then waits for ACK before transmitting or receiving the 8-bit data byte containing the 5-bit EEPROM value. The PCA8550PW,118 does not support address offsetting or multiple slave addressing.

How does the OVERRIDE_N pin affect PCA8550PW,118 outputs during different MUX_SELECT states?

The OVERRIDE_N pin forces all outputs (MUX_OUT A–D and NON_MUXED_OUT) to logic 0 only when OVERRIDE_N = 0 AND MUX_SELECT = 0. When OVERRIDE_N = 0 and MUX_SELECT = 1, outputs reflect MUX_IN signals (for MUX_OUT) and latched EEPROM bit 4 (for NON_MUXED_OUT). When OVERRIDE_N = 1, normal multiplexer operation resumes regardless of MUX_SELECT state. This behavior is explicitly defined in the Function Table (Table 4) of the PCA8550PW,118 datasheet.

What voltage levels are supported on PCA8550PW,118 inputs and outputs?

The PCA8550PW,118 accepts 5 V-tolerant inputs on MUX_IN A–D, OVERRIDE_N, WP, and MUX_SELECT (VIH ≥ 2.0 V, VIL ≤ 0.8 V), while operating from a 3.0–3.6 V VCC supply. Its MUX_OUT A–D outputs drive 2.5 V logic levels (VOH ≥ 2.0 V at IOH = −1 mA), and NON_MUXED_OUT delivers 3.3 V TTL-compatible levels (VOH ≥ 2.4 V at IOH = −2 mA). This mixed-voltage design enables interoperability across legacy 5 V, 3.3 V, and 2.5 V subsystems without external level shifters.

Can the PCA8550PW,118 be used in new designs outside Pentium Pro/Pentium II systems?

Yes-the PCA8550PW,118 remains viable for any application requiring I²C-programmable, non-volatile, multiplexed digital configuration with override and write protection. Its 2.5 V/3.3 V outputs, 5 V-tolerant inputs, and 100,000-cycle EEPROM make it suitable for industrial control I/O mapping, embedded bootloader setup, and FPGA configuration storage. While originally designed for Pentium Pro/Pentium II, its electrical and functional specifications are technology-agnostic and fully documented in the NXP PCA8550PW,118 datasheet.

What happens to PCA8550PW,118 outputs during an I²C write cycle?

During an I²C write cycle to the EEPROM, the MUX_OUT A–D outputs are disabled (high-impedance) after the address acknowledge bit is received. They remain disabled until the internal EEPROM write completes (~15 ms typical) if WP = 0, or until the next START condition if WP = 1. NON_MUXED_OUT remains latched and unaffected. This behavior prevents bus contention and ensures output stability during configuration updates-explicitly detailed in Figures 7 and 8 of the PCA8550PW,118 datasheet.