NXP Semiconductors PCF8574AT/3,512

Overview

PCF8574AT/3,512 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 monitoring, and industrial control systems.

For engineers reviewing the PCF8574AT/3,512 datasheet, PCF8574AT/3,512 pinout, PCF8574AT/3,512 application, or PCF8574AT/3,512 equivalent, key selection criteria include its SO16 package compatibility, interrupt-driven input change detection, quasi-bidirectional port behavior without direction register, and support for up to eight devices on one I²C bus via A0–A2 address pins.

Technical Context

The PCF8574AT/3,512 implements a single-register quasi-bidirectional I/O architecture where each of P0–P7 functions as input or output based on data written - no direction register required. Its interrupt logic asserts INT (active LOW) on any input state change relative to the port register, enabling event-driven microcontroller polling avoidance.

It uses Standard-mode I²C (100 kHz max), supports hardware slave addressing via A0–A2 (eight unique addresses per variant), and incorporates internal Power-On Reset that initializes all I/Os as inputs with 100 µA weak pull-up to VDD - eliminating external reset circuitry in most embedded designs.

Key Specifications

Pinout & Package

PCF8574AT/3,512 is supplied in SO16 (plastic small outline, 16-lead, 7.5 mm body width) per SOT162-1 package standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCF8574AT/3,512, PCA8574AT/3,518 offers doubled I²C speed and improved voltage flexibility while maintaining drop-in compatibility, whereas PCA9674APW,118 delivers significantly higher scalability and performance at the cost of package and pinout change - making it unsuitable for direct replacement but ideal for next-generation architectures.

Availability

PCF8574AT/3,512 is available at Aetrix Electronics and suitable for industrial control, LED signage, and keypad monitoring applications requiring stable component supply across extended product lifecycles.

Supply support for PCF8574AT/3,512 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.

The PCF8574AT/3,512 belongs to NXP's legacy I²C I/O expander family, designed specifically for cost-sensitive, space-constrained embedded systems needing simple, reliable remote GPIO expansion with minimal firmware overhead.

FAQ

What is the I²C address range supported by PCF8574AT/3,512?

The PCF8574AT/3,512 uses the PCF8574A slave address format: fixed prefix 0111 (7h) with three programmable bits (A2–A0), yielding seven-bit addresses 70h through 7Fh. Each combination corresponds to a unique device on the same I²C bus - eight distinct addresses total. This differs from the PCF8574 (prefix 0100, addresses 40h–4Fh), allowing coexistence of both variants.

How does the quasi-bidirectional I/O behavior of PCF8574AT/3,512 differ from standard push-pull GPIO?

Unlike push-pull I/O requiring direction registers, PCF8574AT/3,512's quasi-bidirectional ports operate with a single data register: writing '1' configures the pin as input (weak 100 µA pull-up to VDD), writing '0' forces strong LOW output. Input reads reflect actual pin voltage - enabling simultaneous input sensing and output driving without mode switching, simplifying firmware for mixed-use cases like keypad + LED control.

Can PCF8574AT/3,512 drive LEDs directly without external transistors?

Yes - PCF8574AT/3,512 can directly drive LEDs when configured as outputs. Each port sinks ≥10 mA (min @ 5 V), and the total package sink capability is 80 mA. For reliable operation, use a series current-limiting resistor per LED. Multiple pins (e.g., P0–P3) may be paralleled to drive higher-current loads like multi-segment displays, provided total sink current stays within 80 mA limit.

What happens to the I/O states of PCF8574AT/3,512 during power-on reset?

At power-on, the internal POR circuit initializes all eight I/O ports (P0–P7) as inputs with a 100 µA weak pull-up current source to VDD. This ensures predictable HIGH state on all pins before firmware intervention, preventing floating inputs and unintended activation of connected peripherals - eliminating need for external reset sequencing or pull-up resistors in most applications.

Is PCF8574AT/3,512 pin-compatible with PCF8574T/3,512?

No - PCF8574AT/3,512 and PCF8574T/3,512 share identical SO16 packaging and pinout, but differ in I²C slave address mapping: PCF8574AT/3,512 uses prefix 0111 (70h–7Fh), while PCF8574T/3,512 uses prefix 0100 (40h–4Fh). They are functionally identical otherwise and can coexist on the same bus, but are not interchangeable without firmware address reconfiguration.