NXP Semiconductors PCA8550D,118

Overview

PCA8550D,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 PCA8550D,118 datasheet, PCA8550D,118 pinout, PCA8550D,118 application, or PCA8550D,118 equivalent, this device serves as an I²C-configurable DIP switch replacement with write-protect control, power-on reset, and Schmitt-trigger inputs - critical for legacy x86 platform configuration and BIOS strap selection.

Technical Context

The PCA8550D,118 implements a dual-path selection architecture: when MUX_SELECT = 0, MUX_OUT pins drive data from the internal 5-bit EEPROM; when MUX_SELECT = 1, they route external MUX_IN A–D signals. The NON_MUXED_OUT 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; data byte format reserves top three bits as zero, bit 4 as NON_MUXED data, and bits 3–0 as multiplexed data. Write protection is controlled by WP pin: WP = 0 enables EEPROM writes, WP = 1 disables them. Internal pull-ups exist on OVERRIDE_N, WP, and MUX_SELECT.

Key Specifications

Pinout & Package

PCA8550D,118 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 PCA8550D,118, both alternatives lack integrated EEPROM, multiplexer logic, and dedicated override/latch functionality - making them unsuitable for Pentium-era strap configuration. PCA8550D,118 remains uniquely qualified for legacy x86 platform hardware configuration where firmware-controlled DIP switching is required.

Availability

PCA8550D,118 is available at Aetrix Electronics and suitable for Pentium Pro/II motherboard design, BIOS strap management, and legacy x86 platform configuration requiring stable component supply and long-term obsolescence support.

Supply support for PCA8550D,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 was specifically developed to replace mechanical DIP switches in high-reliability x86 computing platforms, delivering programmable hardware configuration via I²C with non-volatile persistence and robust input tolerance.

FAQ

What is the I²C address of the PCA8550D,118?

The PCA8550D,118 uses a fixed 7-bit I²C address of 0x4C (1001100b), followed by a read/write bit. This hardwired address eliminates address pin conflicts and simplifies bus integration in systems with multiple PCA8550D,118 devices - though only one can occupy 0x4C on a given bus segment without arbitration.

How does the OVERRIDE_N pin affect PCA8550D,118 outputs?

When OVERRIDE_N is pulled low, the PCA8550D,118 forces all four MUX_OUT pins and the NON_MUXED_OUT pin to logic 0, regardless of MUX_SELECT state or EEPROM contents. This provides a hardware-level fail-safe mechanism - essential for thermal shutdown or recovery sequences where deterministic strap clearing is required.

Can PCA8550D,118 operate with a 5 V supply?

No - the PCA8550D,118 requires a 3.0 V to 3.6 V DC supply on VCC (Pin 16). While its MUX_IN, OVERRIDE_N, MUX_SELECT, and WP inputs tolerate up to 5 V, the core logic and outputs are designed for 3.3 V operation. Applying 5 V to VCC will exceed absolute maximum ratings and may cause permanent damage to the PCA8550D,118.

What happens to MUX_OUT during an I²C write cycle to PCA8550D,118?

During an I²C write to the PCA8550D,118 EEPROM, MUX_OUT outputs are disabled after the address acknowledge bit. If WP = 0, outputs re-enable after internal EEPROM write completion (~15 ms). If WP = 1, outputs remain disabled until the next START condition - preventing spurious strap transitions during configuration updates.

Is PCA8550D,118 pin-compatible with other PCA8550 variants like PCA8550DB or PCA8550PW?

Yes - PCA8550D,118 (SO16/SOT109-1), PCA8550DB,118 (SSOP16/SOT338-1), and PCA8550PW,118 (TSSOP16/SOT403-1) share identical pin numbering, signal mapping, and electrical behavior. Only package dimensions and thermal characteristics differ; PCB layout must match the specific footprint (SO16, SSOP16, or TSSOP16) for each variant.