NXP Semiconductors PCA9557PW,112

Overview

PCA9557PW,112 from NXP Semiconductors is an 8-bit I²C-bus and SMBus I/O port expander with active LOW reset input, configurable input/output direction per pin, and polarity inversion capability. It operates from 2.3 V to 5.5 V, supports up to 400 kHz clock frequency, and features high-impedance open-drain IO0 for flexible interface design in embedded control subsystems.

For engineers reviewing the PCA9557PW,112 datasheet, PCA9557PW,112 pinout, PCA9557PW,112 application, or PCA9557PW,112 equivalent, this device serves as a low-power, pin-configurable parallel I/O extension solution for microcontroller-based systems requiring scalable digital signal routing, LED control, and interrupt-driven peripheral management without additional GPIO resources.

Technical Context

The PCA9557PW,112 implements a register-mapped I²C slave interface with four dedicated internal registers: Input Port (read-only), Output Port (read/write), Polarity Inversion (read/write), and Configuration (read/write). Each of its eight I/O pins (IO0–IO7) can be independently set as input or output via the Configuration register, and input polarity can be inverted per-pin using the Polarity Inversion register.

It integrates noise filtering on SCL/SDA inputs, internal power-on reset (VPOR = 1.65–2.1 V), and an external active LOW RESET pin that synchronously initializes all registers and the I²C state machine. The device supports up to eight addressable instances on a shared bus via A0–A2 hardware-selectable address pins (0011 A2A1A0 R/W format).

Key Specifications

Pinout & Package

TSSOP16 package (SOT403-1): 4.4 mm body width, 16-lead thin shrink small outline; requires standard reflow soldering profile; exposed pad not present (unlike HVQFN variant).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar I/O expander applications.

Compared with PCA9555PW,112 and TCA6408APWR, the PCA9557PW,112 uniquely combines dedicated hardware reset, per-pin polarity inversion, and open-drain IO0 - making it optimal for safety-aware industrial controls and mixed-voltage LED interfaces where deterministic initialization and signal flexibility are essential.

Availability

PCA9557PW,112 is available at Aetrix Electronics and suitable for industrial sensor hubs, LED status panels, embedded control subsystems, and IoT edge gateway interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for PCA9557PW,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 leader specializing in secure connectivity solutions for automotive, industrial, and IoT applications, with deep expertise in I²C ecosystem components and embedded interface IP.

The PCA9557 product line delivers cost-effective, low-power I/O expansion for resource-constrained microcontrollers, targeting applications where deterministic reset behavior, pin-level configurability, and industrial-grade reliability are mandatory.

FAQ

What is the function of the RESET pin on the PCA9557PW,112?

The RESET pin on the PCA9557PW,112 is an active LOW asynchronous input that forces all internal registers-including Input Port, Output Port, Polarity Inversion, and Configuration-to their default states and resets the I²C-bus state machine. It does not require power cycling and must be pulled HIGH via an external resistor when unused. This feature enables reliable recovery from firmware lockups in safety-critical systems using the PCA9557PW,112.

How does the PCA9557PW,112 handle I/O direction configuration?

The PCA9557PW,112 uses a dedicated Configuration register (Register 3) where each bit controls the direction of one I/O pin: a logic 1 configures the corresponding pin as a high-impedance input, and a logic 0 configures it as an output. This per-pin control is fully software-definable over I²C and persists until rewritten. Power-on defaults all bits to 1, ensuring safe high-Z startup - a key behavior of the PCA9557PW,112.

Can the PCA9557PW,112 drive LEDs directly?

Yes, the PCA9557PW,112 can drive LEDs directly using IO1–IO7 as current-sinking outputs (10 mA typical per pin at VOL = 0.4 V), while IO0's open-drain structure supports shared-anode or level-translated LED configurations. For lowest IDD in battery applications, maintain I/O voltages ≥ VDD when LEDs are off - a design consideration explicitly documented for the PCA9557PW,112 in its application notes.

What is the significance of the polarity inversion register in the PCA9557PW,112?

The polarity inversion register (Register 2) in the PCA9557PW,112 allows software to flip the logical interpretation of input signals on IO0–IO7 without changing external circuitry. When a bit is set to 1, the corresponding input reads inverted (e.g., active-low switch appears active-high in firmware). This eliminates conditional logic branches and simplifies driver development - a verified capability of the PCA9557PW,112 confirmed in its functional description.

Is the PCA9557PW,112 compatible with fast-mode I²C (400 kHz)?

Yes, the PCA9557PW,112 fully supports fast-mode I²C operation up to 400 kHz, as specified in its dynamic characteristics table. Its SCL/SDA timing parameters - including tLOW (1.3 µs min), tHIGH (0.6 µs min), and tf/tr limits - comply with I²C-bus Fast-mode specifications. This ensures interoperability with modern microcontrollers and SoCs using high-speed I²C, confirming the PCA9557PW,112's suitability for responsive peripheral control.