NXP Semiconductors PCA8574AD,518

Overview

The PCA8574AD,518 from NXP Semiconductors is an 8-bit quasi-bidirectional I²C-bus I/O expander with active-low open-drain interrupt output, operating from 2.3 V to 5.5 V, supporting up to 400 kHz Fast-mode I²C communication and delivering 25 mA sink per port for direct LED drive in embedded control systems.

For engineers reviewing the PCA8574AD,518 datasheet, PCA8574AD,518 pinout, PCA8574AD,518 application, or PCA8574AD,518 equivalent, this device enables remote GPIO expansion with hardware-addressable slave addressing (A0–A2), Power-On Reset initialization to input mode, and low 4.5 µA typical standby current - critical for battery-powered industrial and mobile interfaces.

Technical Context

The PCA8574AD,518 implements a single-register quasi-bidirectional I/O architecture where each of eight ports (P0–P7) functions as either input or output without direction register overhead; input state monitoring and output activation are controlled via one 8-bit data register accessed over I²C.

Its interrupt logic asserts INT (active LOW, open-drain) on any input state change relative to the last-read register value, enabling event-driven microcontroller wake-up; internal Power-On Reset initializes all ports as inputs with 100 µA weak pull-up to VDD, eliminating external biasing for keypad or switch sensing.

Key Specifications

Pinout & Package

PCA8574AD,518 is supplied in SO16 (SOT162-1) plastic small outline package, 16-pin, 7.5 mm body width, lead pitch 1.27 mm, RoHS-compliant, surface-mountable.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar I²C I/O expander applications.

Compared with PCF8574AT/3, PCA8574AD,518 delivers 4× faster I²C, lower voltage operation, and robust LED drive; versus PCA9674A, it maintains identical register mapping and simpler address configuration while trading off maximum bus scalability for proven field reliability in cost-sensitive industrial designs.

Availability

PCA8574AD,518 is available at Aetrix Electronics and suitable for industrial control, medical instrumentation, and mobile device design requiring stable component supply, long-lifecycle support, and RoHS-compliant SO16 packaging.

Supply support for PCA8574AD,518 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 broad portfolio spanning MCUs, interface ICs, and power management.

The PCA8574AD,518 belongs to NXP's remote I/O expander product line, designed specifically to simplify GPIO extension in resource-constrained embedded systems using standardized I²C infrastructure.

FAQ

What is the I²C bus speed supported by the PCA8574AD,518?

The PCA8574AD,518 supports Fast-mode I²C operation up to 400 kHz, doubling the throughput of legacy 100 kHz PCF8574 devices. This enables faster polling cycles and reduced latency in real-time control loops. The PCA8574AD,518 maintains full compatibility with standard I²C masters and does not require special timing adjustments beyond those specified in the NXP datasheet Rev. 3.

How does the PCA8574AD,518 handle power-on initialization?

The PCA8574AD,518 incorporates an internal Power-On Reset (POR) circuit that initializes all eight I/O ports (P0–P7) as inputs with a 100 µA weak pull-up to VDD. This eliminates the need for external pull-up resistors in keypad or switch-sensing applications. The PCA8574AD,518 remains in reset until VDD exceeds VPOR, ensuring deterministic startup behavior across its 2.3–5.5 V operating range.

Can the PCA8574AD,518 directly drive LEDs without external components?

Yes, the PCA8574AD,518 provides 25 mA sink capability per port (P0–P7), sufficient to drive standard 20 mA LEDs with only a series current-limiting resistor. Its 200 mA total package sink limit allows multiple ports to be combined for higher-current loads. The PCA8574AD,518's quasi-bidirectional architecture simplifies firmware by avoiding direction register writes during LED on/off toggling.

What is the function of the INT pin on the PCA8574AD,518?

The INT pin on the PCA8574AD,518 is an active-LOW open-drain interrupt output that asserts when any input port state (P0–P7) differs from its corresponding register value. It connects directly to a microcontroller's external interrupt input, enabling event-driven response instead of periodic I²C polling. The PCA8574AD,518 automatically deasserts INT upon reading the input register or writing new data, ensuring clean edge-triggered behavior.

How many PCA8574AD,518 devices can share one I²C bus?

Up to eight PCA8574AD,518 devices can coexist on a single I²C bus using hardware address pins A0, A1, and A2. Each combination of HIGH/LOW on these pins selects a unique 7-bit slave address (70h–7Fh). Since PCA8574AD,518 shares the same address space as PCA8574A but differs from PCA8574 (40h–4Fh), up to 16 total expanders (8 × PCA8574 + 8 × PCA8574A) may operate concurrently - supporting up to 128 I/O lines. The PCA8574AD,518 requires no software address remapping.