NXP Semiconductors PCA8550DB,118

Overview

PCA8550DB,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 PCA8550DB,118 datasheet, PCA8550DB,118 pinout, PCA8550DB,118 application, or PCA8550DB,118 equivalent, key selection criteria include I²C-addressable EEPROM register access, MUX_SELECT-controlled input/register routing, write-protect (WP) pin behavior, and SSOP16 package compatibility with legacy PC platform timing and voltage requirements.

Technical Context

The PCA8550DB,118 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 drive external MUX_IN A–D signals. The NON_MUXED_OUT pin is transparent during MUX_SELECT = 0 and latched on the rising edge of MUX_SELECT.

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 controlled by WP: low enables writes; high disables them. Internal pull-ups exist on OVERRIDE_N, WP, and MUX_SELECT.

Key Specifications

Pinout & Package

PCA8550DB,118 is housed in a plastic shrink small outline package (SSOP16) per SOT338-1: 16 leads, 5.3 mm body width, 0.65 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 PCA8550DB,118, PCA9554PW,118 offers greater I/O count but requires external state management, while PCA8574PW,118 provides basic port expansion without configuration memory or override safety-making PCA8550DB,118 uniquely suited for legacy x86 platform jumperless design.

Availability

PCA8550DB,118 is available at Aetrix Electronics and suitable for PC motherboard design, Pentium Pro/II system integration, and industrial embedded configuration requiring stable component supply and long-lifecycle support.

Supply support for PCA8550DB,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 developed specifically to replace mechanical DIP switches in x86 computing platforms, delivering I²C-programmable configuration with non-volatile storage and hardware-safe override capability.

FAQ

What is the I²C address of the PCA8550DB,118?

The PCA8550DB,118 uses a fixed 7-bit I²C address of 0x4C (1001100b), followed by a read/write bit. This address is hardwired and not configurable-ensuring predictable bus arbitration in multi-device systems. The PCA8550DB,118 responds only to this address during I²C transactions, and no external address pins are provided.

How does the OVERRIDE_N pin affect PCA8550DB,118 outputs?

When OVERRIDE_N is pulled low, the PCA8550DB,118 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 hardware override is asynchronous and prioritized over all other functions-providing fail-safe output control during system reset or fault conditions. The PCA8550DB,118 resumes normal operation immediately upon OVERRIDE_N returning high.

Can the PCA8550DB,118 operate with a 5 V supply?

No-the PCA8550DB,118 requires VCC between 3.0 V and 3.6 V only. While its digital inputs (MUX_IN, OVERRIDE_N, WP, MUX_SELECT) are 5 V tolerant, applying 5 V to VCC exceeds the absolute maximum rating of +4.6 V and risks permanent damage. The PCA8550DB,118 is designed for 3.3 V systems like Pentium Pro/II motherboards, and its 2.5 V MUX_OUT outputs are incompatible with 5 V logic families without level translation.

What happens to PCA8550DB,118 outputs during an I²C write cycle?

During an I²C write to the EEPROM register, the PCA8550DB,118 disables all MUX_OUT outputs until the internal write completes (~15 ms typical). If WP is low, outputs remain disabled until EEPROM programming finishes; if WP is high, outputs are disabled only until the next START condition. NON_MUXED_OUT remains latched and stable throughout. This behavior prevents glitches on downstream logic during register update-ensuring deterministic operation of the PCA8550DB,118.

Is the PCA8550DB,118 pin-compatible with other PCA8550 variants?

Yes-the PCA8550DB,118 (SSOP16/SOT338-1), PCA8550D,118 (SO16/SOT109-1), and PCA8550PW,118 (TSSOP16/SOT403-1) share identical pinouts and electrical specifications. Only the package dimensions and thermal characteristics differ. PCB layout must match the chosen variant's footprint (e.g., SSOP16 for PCA8550DB,118), but signal routing, decoupling, and firmware are fully interchangeable across all three packages.