NXP Semiconductors PCF8574AT/3,518

Overview

PCF8574AT/3,518 from NXP Semiconductors is an 8-bit quasi-bidirectional I²C-bus I/O expander with active-low open-drain interrupt output, operating from 2.5 V to 6 V, supporting up to 100 kHz I²C communication, and featuring 8 latched I/O ports that default to inputs with 100 µA internal pull-up at power-on - used in LED signage, keypad interfaces, and industrial control systems.

For engineers reviewing the PCF8574AT/3,518 datasheet, PCF8574AT/3,518 pinout, PCF8574AT/3,518 application, or PCF8574AT/3,518 equivalent, this device delivers low-standby-current (2.5 µA typical) remote GPIO expansion with hardware address selection (A0–A2), interrupt-driven input change detection, and direct LED drive capability without external drivers.

Technical Context

The PCF8574AT/3,518 implements a single-register quasi-bidirectional I/O architecture where each of P0–P7 functions as input or output without direction register overhead; port states are read/written via one 8-bit data byte over I²C, and internal Power-On Reset initializes all ports as high-impedance inputs with 100 µA weak pull-up to VDD.

Its interrupt logic asserts INT (active LOW) on any input state transition relative to the last-read register value, enabling event-driven microcontroller wake-up; the open-drain INT output supports wired-OR connection across multiple expanders on the same bus, and slave addressing uses fixed 7-bit prefix (0x38–0x3F for PCF8574A family) plus A2/A1/A0 hardware pins.

Key Specifications

Pinout & Package

PCF8574AT/3,518 is housed in a plastic small outline package (SO16) with 16 leads, 7.5 mm body width, and standard surface-mount footprint (SOT162-1). Pin numbering follows JEDEC MS-012AC.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCF8574AT/3,518, PCA8574AT/3,518 offers 4× faster I²C speed and broader voltage tolerance while retaining pin compatibility, whereas PCA9674APW,118 provides 8× more address options and doubled sink current but requires PCB layout revision due to TSSOP20 footprint.

Availability

PCF8574AT/3,518 is available at Aetrix Electronics and suitable for industrial control, LED signage, and keypad interface applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for PCF8574AT/3,518 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 focused on secure connectivity solutions for automotive, industrial, and IoT applications, with broad analog, digital, and mixed-signal product portfolios.

The PCF8574AT/3,518 belongs to NXP's legacy I²C I/O expander family, designed specifically for cost-sensitive, low-power embedded systems needing simple, reliable GPIO expansion without complex configuration registers.

FAQ

What is the I²C slave address range for PCF8574AT/3,518?

The PCF8574AT/3,518 uses the PCF8574A address prefix (0x38–0x3F in 7-bit format), determined by A2/A1/A0 pin states. For example, A2=A1=A0=LOW yields 0x38 (write) / 0x39 (read). This differs from PCF8574 (0x40–0x47), allowing both families to coexist on the same I²C bus.

How does the quasi-bidirectional I/O architecture of PCF8574AT/3,518 differ from standard push-pull GPIO?

The PCF8574AT/3,518 uses quasi-bidirectional ports with no direction register: writing '1' configures the pin as input (100 µA pull-up), writing '0' activates strong sink for output LOW. Output HIGH relies on weak pull-up unless accelerated during ACK cycle - simplifying firmware but requiring external pull-ups for robust HIGH-level logic.

Can PCF8574AT/3,518 drive LEDs directly without external transistors?

Yes - PCF8574AT/3,518 can directly drive LEDs in sink configuration: each port pin guarantees ≥10 mA sink current at 5 V, and total package sink is rated at 80 mA. Use series current-limiting resistors; avoid simultaneous HIGH-to-LOW transitions on multiple pins to prevent exceeding thermal limits.

What happens to PCF8574AT/3,518 I/O states during power-on reset?

At power-on, the internal POR circuit initializes all P0–P7 ports as inputs with 100 µA weak pull-up to VDD, setting them to logic HIGH. The INT output is released (HIGH) after reset completes. No external reset pin is required - behavior is fully automatic and deterministic.

Is PCF8574AT/3,518 pin-compatible with PCF8574T/3,518?

No - PCF8574AT/3,518 and PCF8574T/3,518 share the same SO16 package and pinout, but differ in I²C slave address prefix (0x38–0x3F vs. 0x40–0x47). They are electrically and mechanically compatible, but firmware must use correct address mapping to avoid bus conflicts when both types are present.