PCAL6524HEAZ I/O Expander: Features, Pinout, Application, and Datasheet

Published:April 01, 2024

Prof. David Reynolds stands as a luminary in the field of electrical engineering, renowned for his expertise in integrated circuits. Holding a distinguished position as a Professor of Electrical Engineering, Prof. Reynolds earned his acclaim through decades of research, teaching, and industry collaboration.

I/O expanders are integrated circuits that allow for additional input/output (I/O) pins to be added to a microcontroller or other similar devices. They serve as an interface between the microcontroller and external devices, extending the I/O capabilities of the system. In embedded systems, I/O expanders are essential for connecting a wide range of sensors, actuators, and other peripherals, enabling complex functionalities in compact designs. The PCAL6524HEAZ is a versatile I/O expander with high flexibility and reliability and is a popular choice for such applications. It offers 24 GPIO (General Purpose Input/Output) pins, which can be individually configured as inputs or outputs. This flexibility makes it suitable for a wide range of applications, from simple LED control to complex sensor interfacing. In this article, we provide an overview of the PCAL6524HEAZ, exploring its features, pinout, applications, datasheet, and more details.



PCAL6524HEAZ Description

The PCAL6524HEAZ is a 24-bit general-purpose I/O expander that enables remote I/O expansion for most microcontroller families through the Fast-mode Plus (Fm+) I2C-bus interface. Its ultra-low-voltage interface allows for direct connection to a microcontroller operating down to 0.8 V.

This device has two supply voltages: VDD(I2C-bus) and VDD(P). VDD(I2C-bus) supplies the voltage for the interface at the master side (e.g., a microcontroller), while VDD(P) supplies the voltage for core circuits and Port P. The bidirectional voltage level translation in the PCAL6524HEAZ is managed through VDD(I2C-bus), which should be connected to the VDD of the external SCL/SDA lines. This indicates the VDD level of the I2C-bus to the PCAL6524HEAZ, while the voltage level on Port P of the PCAL6524HEAZ is determined by VDD(P).

The PCAL6524HEAZ fully complies with the Fm+ I2C-bus specification at speeds up to 1 MHz. It includes Agile I/O features, such as programmable output drive strength, latchable inputs, programmable pull-up/pull-down resistors, maskable interrupt, interrupt status register, and programmable open-drain or push-pull outputs.

The PCAL6524HEAZ's open-drain interrupt (INT) output is activated when any input state differs from its corresponding Input Port register state. Additionally, the INT output can be set to activate on input pin edges. Various interrupt mask functions are available for flexibility.

The INT can be connected to a microcontroller's interrupt input, allowing the remote I/O to inform the microcontroller of incoming data on its ports without communication via the I2C Bus. This enables the PCAL6524HEAZ to remain a simple slave device. The input latch feature holds or latches the input pin state and retains the logic values that triggered the interrupt until the master can service the interrupt. This minimizes the host's interrupt service response time for fast-moving inputs.

The Port P outputs of the device have 25 mA sink capabilities, making them suitable for directly driving LEDs while consuming low device currents.

A hardware pin (ADDR) can be used to program and vary the fixed I2C-bus address, allowing up to four devices to share the same I2C-bus or SMBus.

The device comes in various package options, including QFN and TSSOP, making it easy to integrate into different PCB designs. It communicates with the host microcontroller using the I2C (Inter-Integrated Circuit) interface, which allows for easy connectivity and control.

With its high-speed I2C interface, low power consumption, and robust design, the PCAL6524HEAZ is ideal for use in consumer electronics, industrial automation, IoT devices, and more. Its versatility and reliability make it a popular choice among designers looking to expand their systems' I/O capabilities.


PCAL6524HEAZ Features

  • I2C-bus to parallel port expander: Enables communication between I2C-bus devices and parallel ports.
  • 1 MHz Fast-mode Plus I2C-bus: Supports high-speed data transfer.
  • Operating power supply voltage range: Wide voltage range for flexibility in power supply (0.8 V to 3.6 V on the I2C-bus side).
  • Allows bidirectional voltage-level translation and GPIO expansion: Supports various voltage levels for compatibility (between 0.8 V to 3.6 V SCL/SDA and 1.8 V, 2.5 V, 3.3 V, 5.5 V Port P).
  • Low standby current consumption: Consumes minimal power during standby (2.0 µA typical at 3.3 V VDD(P)).
  • Schmitt trigger action: Improves noise tolerance and signal integrity, allowing slow input transition and better-switching noise immunity at the SCL and SDA inputs.
  • 5.5 V tolerant I/O ports and 3.6 V tolerant I2C-bus pins: Ensures compatibility with different voltage levels.
  • Active LOW reset input (RESET): Allows for resetting the device.
  • Open-drain active LOW interrupt output (INT): Provides interrupt signaling.
  • Internal power-on reset: Ensures proper initialization.
  • Noise filter on SCL/SDA inputs: Filters out noise for reliable communication.
  • Latched outputs with 25 mA drive maximum capability for directly driving LEDs: Can directly drive LEDs without additional components.
  • Built-in Level Shifting: The PCAL6524HEAZ is equipped with built-in level shifting capabilities, allowing it to interface with devices that operate at different voltage levels without the need for external components.
  • Latch-up performance exceeds 100 mA per JESD 78, Class II: Ensures robust performance under high-current conditions.
  • ESD protection exceeds JESD 22: Protects against electrostatic discharge.
  • Packages offered: Available in different package options for design flexibility (HUQFN32, VFBGA36).


PCAL6524HEAZ Specifications


Type Parameter
Interface I2C
Number of I/Os 24 I/O
Voltage - Supply
 1.65V ~ 5.5V
Clock Frequency 1 MHz
Operating Supply Voltage 800 mV to 3.6 V
Operating Supply Current 1.7 mA
Output Current 25 mA
Maximum Sink Current per Bit 50 mA
Operating Temperature
 -40°C ~ 85°C
Package / Case


PCAL6524HEAZ Pinout


PCAL6524HEAZ Pin Diagram


PCAL6524HEAZ Pin Configuration



PCAL6524HEAZ Block Diagram



Benefits of Using the PCAL6524HEAZ

  1. Increased I/O capabilities: The PCAL6524HEAZ expands the number of available GPIO pins, allowing for more devices or sensors to be connected to a single microcontroller. This is particularly useful in applications requiring a large number of I/O pins.
  2. Simplified circuit design: By offloading I/O tasks to the PCAL6524HEAZ, designers can simplify their circuit designs and reduce the complexity of their PCB layouts. This can lead to cost savings and faster time to market for products.
  3. Compatibility with different microcontrollers: The PCAL6524HEAZ is compatible with a wide range of microcontrollers, making it easy to integrate into existing designs or use with new microcontroller platforms. This flexibility allows designers to choose the best microcontroller for their applications without worrying about I/O compatibility issues.


PCAL6524HEAZ Applications

Smart Home Products

The PCAL6524HEAZ expands the number of available I/O pins and enhances device functionality in smart home devices such as lighting, thermostats, and security systems.


Remote Controls

The PCAL6524HEAZ provides additional I/O functionality for controlling various functions in remote controls for TVs, set-top boxes, and other home entertainment devices.


Audio Equipment

The PCAL6524HEAZ is used in audio equipment such as amplifiers, mixers, and audio interfaces to expand the number of I/O pins available for controlling volume, tone, and other audio settings.


Industrial Automation Applications

The PCAL6524HEAZ provides additional I/O capabilities for controlling machinery and equipment in industrial automation applications such as PLCs (Programmable Logic Controllers), robotics, and industrial control systems.


IoT Devices and Projects

The PCAL6524HEAZ is used in IoT (Internet of Things) devices and projects to expand the number of available I/O pins for connecting sensors, actuators, and other components in IoT applications.


PCAL6524HEAZ Typical Application Circuit



PCAL6524HEAZ Manufacture

NXP Semiconductors is a leading manufacturer in the electronics industry, known for its wide range of semiconductor products. One of its notable products is the PCAL6524HEAZ I2C-bus I/O expander, which offers versatile I/O expansion capabilities for various applications. NXP is recognized for its innovative technology and reliable products, making it a preferred choice for many electronic applications. The PCAL6524HEAZ is widely used in smart home products, remote controls, audio equipment, industrial automation applications, and IoT devices and projects, highlighting its versatility and performance in different applications.


PCAL6524HEAZ Package


  • PCAL6524HEAZ HUQFN32  Package

  • PCAL6524HEAZ VFBGA36 Package

PCAL6524HEAZ Datasheet

Download PCAL6524HEAZ Datasheet PDF.


How to Use the PCAL6524HEAZ Safely

  1. Circuit design tips: Proper PCB layout and routing can minimize signal integrity issues and electromagnetic interference, ensuring the reliable operation of the PCAL6524HEAZ. It's also important to follow the manufacturer's guidelines for decoupling capacitors and other passive components.
  2. Debugging common issues: When encountering issues with the PCAL6524HEAZ, start by checking the connections and power supply. Use debugging tools such as oscilloscopes or logic analyzers to trace signal paths and identify potential issues. Refer to the datasheet and application notes for troubleshooting guidance.
  3. Maximizing performance and reliability: Ensure that the PCAL6524HEAZ is operated within its specified operating conditions to prevent damage and ensure reliable operation. Consider implementing error-checking mechanisms in software to detect and recover from communication errors or other issues.



In summary, the PCAL6524HEAZ I/O expander offers a range of features and benefits that make it a valuable component in modern electronics. Its ability to expand I/O capabilities, simplify circuit design, and work with different microcontrollers makes it versatile and adaptable to various applications.


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  • What is the maximum voltage for the PCAL6524HEAZ?


  • What is the difference between I2C and SPI?

    I2C uses half-duplex communication, while SPI uses full-duplex communication.

  • What is an I/O expander?

    An I/O expander is a device that allows a designer to add extra inputs and outputs (I/O) to a microprocessor (MPU) or microcontroller (MCU) system. These devices feature an efficient data bus interface, which helps reduce the I/O demands on the MPU or MCU.

  • What is the function of expander IC?

    An I/O expander effortlessly enhances existing systems by expanding functions like GPIOs, keypads, LED controls, and timers.

  • What is the difference between a shift register and a multiplexer?

    A multiplexer switches between inputs and is typically used to sample multiple inputs in an arbitrary sequence. In contrast, a shift register takes a parallel word and shifts it out as a sequence of bits. The multiplexer is more versatile than the shift register and is, therefore, usually more expensive.

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