NXP Semiconductors PCA8550PW,112

Overview

PCA8550PW,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 TTL 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,112 datasheet, PCA8550PW,112 pinout, PCA8550PW,112 application, or PCA8550PW,112 equivalent, this device serves as an I²C-configurable DIP switch replacement with write-protect control, power-on reset, and Schmitt-trigger inputs for noise immunity in legacy x86 platform configuration management.

Technical Context

The PCA8550PW,112 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 pass through 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; data byte format reserves bits [7:3] as zero, bit [2] as the latched NON_MUXED_OUT value, and bits [1:0] as the lower two MUX bits (full 4-bit MUX data is stored in EEPROM but only 2 bits appear in I²C data byte per spec). Write protection is controlled by WP pin logic level, and 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, lead pitch 0.65 mm, suitable for high-density PCB layouts with 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,112, the PCA8550D,118 offers greater thermal stability in high-power environments, while the PCA8550DB,118 provides mechanical robustness in vibration-prone industrial assemblies - both retain full functional equivalence but differ in PCB area, thermal profile, and assembly process compatibility.

Availability

PCA8550PW,112 is available at Aetrix Electronics and suitable for desktop motherboard design, Pentium Pro/II system boot control, embedded x86 platform management, and legacy industrial control backplane applications requiring stable component supply and long-term configuration integrity.

Supply support for PCA8550PW,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 x86-based computing platforms, delivering I²C-programmable configuration with non-volatile storage and hardware safety features for legacy PC architecture.

FAQ

What is the I²C address of the PCA8550PW,112?

The PCA8550PW,112 uses a fixed 7-bit I²C address of 0x4C (1001100b), followed by a read/write bit. This hardwired address eliminates address conflicts on shared buses and requires no external address pins - simplifying integration into systems with multiple PCA8550PW,112 devices only if used with distinct I²C segments or multiplexers.

How does the OVERRIDE_N pin affect PCA8550PW,112 outputs?

The OVERRIDE_N pin is an active-low signal that forces all four MUX_OUT pins (A–D) and the NON_MUXED_OUT pin to logic 0, overriding both EEPROM contents and MUX_IN inputs. This occurs only when OVERRIDE_N = 0 *and* MUX_SELECT = 0 per the function table; it provides a hardware fail-safe for known-safe system states during power-up or fault recovery.

Can the PCA8550PW,112 operate with a 5 V supply?

No - the PCA8550PW,112 requires a 3.0 V to 3.6 V DC supply on VCC. However, its MUX_IN, OVERRIDE_N, WP, and MUX_SELECT inputs are 5 V tolerant, allowing direct connection to 5 V logic without level shifters. Exceeding 3.6 V on VCC violates absolute maximum ratings and may cause permanent damage to the PCA8550PW,112.

What happens to MUX_OUT during an I²C write cycle to the PCA8550PW,112?

During an I²C write to the PCA8550PW,112, the MUX_OUT pins are disabled after the address acknowledge bit. If WP = 0, outputs remain disabled until the internal EEPROM write completes (~15 ms). If WP = 1, outputs are re-enabled upon the next I²C START condition. This prevents transient glitches on critical configuration lines while EEPROM programming occurs.

Is the NON_MUXED_OUT pin always latched in the PCA8550PW,112?

No - the NON_MUXED_OUT pin is latched only on the rising edge of MUX_SELECT. When MUX_SELECT = 0, NON_MUXED_OUT is transparent and reflects the current EEPROM value. When MUX_SELECT transitions from 0 to 1, the value present at that instant is captured and held, decoupling it from subsequent EEPROM writes or MUX_IN changes - ensuring stable interrupt or control signaling during configuration updates.