NXP Semiconductors PCA9557D,112

Overview

The PCA9557D,112 from NXP Semiconductors is an 8-bit I²C-bus and SMBus I/O port expander with active LOW reset input, open-drain IO0, and programmable input/output configuration. It operates from 2.3 V to 5.5 V, supports up to 400 kHz clock frequency, and features polarity inversion, noise-filtered SCL/SDA inputs, and 3 address pins enabling up to 8 devices on one bus. It is used in embedded subsystem control where GPIO expansion and robust bus communication are required.

For engineers reviewing the PCA9557D,112 datasheet, PCA9557D,112 pinout, PCA9557D,112 application, or PCA9557D,112 equivalent, key selection criteria include its SO16 package compatibility, 8-bit bidirectional I/O configurability via register writes, reset-driven initialization behavior, and 5 V tolerant I/Os suitable for mixed-voltage system interfacing.

Technical Context

The PCA9557D,112 implements a register-mapped I²C slave interface with four internal registers: Input Port (read-only), Output Port (read/write), Polarity Inversion (read/write), and Configuration (read/write). Each I/O pin's direction and logic polarity is independently controlled through dedicated bits in the Configuration and Polarity Inversion registers.

Its I²C-bus logic includes noise filtering on SCL/SDA, supports Standard-Mode (100 kHz) and Fast-Mode (400 kHz) operation, and incorporates internal power-on reset with VPOR = 1.65–2.1 V. The RESET pin provides external asynchronous reset without power cycling, and all I/Os default to high-impedance inputs at power-up or reset.

Key Specifications

Pinout & Package

PCA9557D,112 is housed in a plastic small outline package (SO16) per JEDEC standard SOT109-1, with 16 leads, 3.9 mm body width, and gull-wing lead form. Pin 1 is index-marked; leads are Pb-free and RoHS compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9555D,112 and TCA6408APWR, the PCA9557D,112 uniquely combines hardware reset, polarity inversion, and sub-µA standby current in an SO16 footprint-making it optimal for fault-resilient, low-power industrial I/O expansion.

Availability

PCA9557D,112 is available at Aetrix Electronics and suitable for industrial sensor hubs, embedded control panels, power management subsystems, and IoT edge node interfaces requiring stable component supply and long-term manufacturability.

Supply support for PCA9557D,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 IoT applications.

The PCA9557D,112 belongs to NXP's I²C-bus I/O expander product line, designed specifically for reliable, low-power GPIO extension in resource-constrained embedded systems with strict ESD and reset requirements.

FAQ

What is the function of the RESET pin on the PCA9557D,112?

The RESET pin on the PCA9557D,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 reinitializes the I²C-bus state machine. This occurs without removing power from VDD, enabling deterministic recovery from bus lockups or firmware errors. The PCA9557D,112 requires a minimum pulse width of 6 ns on RESET and must be pulled up to VDD via an external resistor when not actively driven.

How does the PCA9557D,112 handle I/O direction configuration?

The PCA9557D,112 uses Register 3 (Configuration register) to define each of its 8 I/O pins as input or output: a logic 1 sets the corresponding pin as high-impedance input, while a logic 0 configures it as output. This register is read/write accessible over I²C, allowing dynamic reconfiguration during runtime. The PCA9557D,112 defaults all pins to inputs on power-up or RESET, preventing unintended output states during system initialization.

Is the PCA9557D,112 compatible with 3.3 V and 5 V systems?

Yes, the PCA9557D,112 operates from 2.3 V to 5.5 V and features 5 V tolerant inputs and outputs-including SCL, SDA, A0–A2, RESET, and all I/O pins-regardless of VDD level. This allows direct interfacing with 5 V peripherals even when powered from a 3.3 V rail, eliminating level-shifter requirements in mixed-voltage designs using the PCA9557D,112.

What is the significance of the polarity inversion register in the PCA9557D,112?

Register 2 (Polarity Inversion register) in the PCA9557D,112 enables per-pin logic inversion for inputs only: writing a 1 to a bit flips the sensed logic level on the corresponding I/O pin before it reaches the Input Port register. This eliminates software XOR operations in firmware when interfacing with active-low sensors or switches, directly simplifying driver code and reducing CPU load. The PCA9557D,112 retains original polarity for outputs and unaffected pins.

Does the PCA9557D,112 support Fast-Mode I²C operation?

Yes, the PCA9557D,112 fully supports Fast-Mode I²C operation up to 400 kHz, as confirmed by its dynamic characteristics table and compliance with SMBus timing specifications. Its SCL/SDA inputs include integrated noise filters to suppress spikes ≤50 ns, enhancing robustness in electrically noisy industrial environments. The PCA9557D,112 maintains valid setup/hold times and acknowledges within 0.9 µs at Fast-Mode speeds, ensuring reliable communication in time-critical applications.