NXP PCF8575TS/1,118: A Comprehensive Technical Overview of the 16-Bit I2C I/O Expander

In the realm of embedded systems and IoT design, efficiently managing a multitude of digital inputs and outputs (I/Os) with a limited number of microcontroller GPIO pins is a common challenge. The NXP PCF8575TS/1,118 stands as a pivotal solution, a 16-bit remote I/O expander that communicates via the ubiquitous I2C-bus (Inter-Integrated Circuit). This device provides a simple, cost-effective method for extending the digital capabilities of a host controller, making it indispensable in applications ranging from industrial control to consumer electronics.

Architecture and Functional Description

The PCF8575TS/1,118 is housed in a space-saving SSOP24 package and is designed to operate as a slave device on the I2C-bus. Its core functionality is to provide 16 quasi-bidirectional I/O ports. Each port can be independently configured to function as either an input or an output through software control, offering immense flexibility.

The quasi-bidirectional architecture is a key feature. Unlike standard bidirectional ports, these I/Os have a built-in current source on the output high, eliminating the need for external pull-up resistors when driving signals high. This simplifies board design and reduces component count. The device features three hardware address pins (A0, A1, A2), allowing up to eight identical devices to be connected on the same I2C-bus, thereby expanding a single microcontroller's I2C port to control up to 128 I/O bits.

Key Features and Performance

I2C-Bus Interface: Operates at standard (100 kHz) and fast (400 kHz) modes, ensuring compatibility with a vast array of microcontrollers.

Wide Voltage Range: Supports an operating supply voltage from 2.5 V to 5.5 V, facilitating seamless integration into both 3.3 V and 5 V systems.

High Current Drive Capability: Each output can sink up to 25 mA, allowing it to directly drive LEDs or other low-power peripherals without additional buffer circuits.

Interrupt Output: A dedicated open-drain interrupt (INT) pin is a critical feature. It is activated when any input state changes, signaling the master controller that an input requires attention. This eliminates the need for continuous polling, significantly improving system efficiency and reducing software overhead.

Low Power Consumption: The device is designed for power-sensitive applications, featuring extremely low standby current.

Application Scenarios

The versatility of the PCF8575TS/1,118 makes it suitable for a broad spectrum of applications. It is commonly used for:

Sensor Hub Aggregation: Reading a large number of digital sensors (e.g., switches, buttons, presence detectors).

LED Matrix Control: Driving arrays of indicators and LEDs in front panels or display boards.

Industrial Control Systems: Monitoring status signals and controlling actuators in PLCs and factory automation.

System Configuration: Reading DIP switches or driving relays to configure system parameters.

ICGOODFIND Summary

The NXP PCF8575TS/1,118 is an exceptionally versatile and robust I/O expansion solution. Its simple I2C interface, high drive capability, and hardware interrupt function make it an ideal choice for designers looking to overcome GPIO limitations. It effectively reduces system cost and complexity while providing reliable performance across a wide voltage range, solidifying its status as a go-to component in modern electronic design.

Keywords:

I2C-bus

Quasi-bidirectional

I/O Expander

Interrupt Output

GPIO Extension