on November 10th 100

How to Integrate the PCF8574 in Microcontroller Designs?

If you're looking for a way to easily expand the I/O capabilities of your microcontroller projects, the PCF8574 offers a flexible and reliable solution with its 8-bit I/O expander designed for the I2C bus. This article covers everything you need to know, from functionality and features to practical applications.

Catalog

PCF8574 Overview and Functionality

The PCF8574 is an 8-bit I/O expander designed for the I2C bus, operating between 2.5V and 6V. It adds extra I/O capacity to your design with ease, connecting directly to most microcontrollers via the SCL and SDA lines.

With eight quasi-bidirectional ports (P0 to P7), it allows each port to act as either an input or output without a separate control signal. The ports hold their state until updated and can handle higher current, which is useful for directly powering LEDs. When first powered, all ports default to high, acting as a current source.

This makes the PCF8574 a flexible option for expanding I/O in designs that need more control options.

PCF8574 Pin Layout and Configuration

Type	Parameter
Lifecycle Status	ACTIVE (Last Updated: 6 days ago)
Factory Lead Time	6 Weeks
Contact Plating	Gold
Mounting Type	Surface Mount
Package / Case	20-TSSOP (0.173, 4.40mm Width)
Surface Mount	YES
Number of Pins	20
Weight	76.997305mg
Number of I/Os	8
Operating Temperature	-40°C ~ 85°C
Packaging	Tube
JESD-609 Code	e4
Pbfree Code	Yes
Part Status	Active
Moisture Sensitivity Level (MSL)	1 (Unlimited)
Number of Terminations	20
ECCN Code	EAR99
Voltage - Supply	2.5V ~ 6V
Terminal Position	DUAL
Terminal Form	GULL WING
Peak Reflow Temperature (°C)	260
Supply Voltage	5V
Terminal Pitch	0.65mm
Base Part Number	PCF8574
Pin Count	20
Number of Outputs	8
Output Type	Push-Pull
Power Supplies	3/5V
Interface	I2C
Number of Ports	1
Number of Bits	8
Clock Frequency	100kHz
Supply Current-Max	0.1mA
Interrupt Output	Yes
Current - Output Source/Sink	1mA / 25mA
Features	POR
Height	1.2mm
Length	6.5mm
Width	4.4mm
Thickness	1mm
REACH SVHC	No SVHC
Radiation Hardening	No
RoHS Status	ROHS3 Compliant
Lead Free	Lead Free

Technical Specifications of PCF8574

Technical specifications, features, characteristics, and components with comparable specifications of Texas Instruments PCF8574.

Type	Parameter
Lifecycle Status	ACTIVE (Last Updated: 6 days ago)
Factory Lead Time	6 Weeks
Contact Plating	Gold
Mounting Type	Surface Mount
Package / Case	20-TSSOP (0.173, 4.40mm Width)
Surface Mount	YES
Number of Pins	20
Weight	76.997305mg
Number of I/Os	8
Operating Temperature	-40°C ~ 85°C
Packaging	Tube
JESD-609 Code	e4
Pbfree Code	Yes
Part Status	Active
Moisture Sensitivity Level (MSL)	1 (Unlimited)
Number of Terminations	20
ECCN Code	EAR99
Voltage - Supply	2.5V ~ 6V
Terminal Position	DUAL
Terminal Form	GULL WING
Peak Reflow Temperature (°C)	260
Supply Voltage	5V
Terminal Pitch	0.65mm
Base Part Number	PCF8574
Pin Count	20
Number of Outputs	8
Output Type	Push-Pull
Power Supplies	3/5V
Interface	I2C
Number of Ports	1
Number of Bits	8
Clock Frequency	100kHz
Supply Current-Max	0.1mA
Interrupt Output	Yes
Current - Output Source/Sink	1mA / 25mA
Features	POR
Height	1.2mm
Length	6.5mm
Width	4.4mm
Thickness	1mm
REACH SVHC	No SVHC
Radiation Hardening	No
RoHS Status	ROHS3 Compliant
Lead Free	Lead Free

PCF8574 Features

Low Standby-Current Consumption

The PCF8574 has a standby mode with low current consumption, only up to 10 µA. This allows it to save power, which can be especially helpful for battery-operated devices.

I2C to Parallel-Port Expander

This device acts as an I2C interface, converting signals for parallel port use. This feature makes it easier for microcontrollers to connect with additional I/O devices, expanding the possibilities of your design.

Open-Drain Interrupt Output

With an open-drain interrupt output, this device can signal the system when an event occurs. This feature is useful for managing events without requiring constant attention from the microcontroller, which can save processing power.

Compatibility with Most Microcontrollers

The PCF8574 is designed to work with a variety of microcontroller types. This compatibility lets you use it in multiple types of projects, regardless of the microcontroller family you choose.

High-Current Drive for Direct LED Control

Equipped with high-current drive capabilities, this device can directly control LEDs without extra components. This feature provides flexibility in design and reduces the need for additional circuitry.

Latch-Up Resistance

The device is designed to resist latch-up up to 100 mA, making it reliable in various operating conditions. This resistance helps maintain stability and reduces the chances of failure during operation.

Applications of PCF8574

Telecom Shelters and Filter Units

The PCF8574 is suitable for telecom shelters where filter units may require remote control or expansion. Its I/O capabilities allow easy integration into systems needing more control options.

Servers

Used in server applications, this device can expand the I/O availability for server monitoring and management. It provides an efficient way to control and manage peripheral devices.

Routers and Telecom Switching Equipment

In routers and telecom switches, the PCF8574 provides expanded I/O capabilities that can be used to control different parts of the equipment. Its compatibility with I2C makes it easy to integrate and manage within these complex systems.

Personal Computers

The device can also be used in personal computers for additional control over peripherals and other I/O expansion needs. Its ability to work with most microcontrollers ensures ease of integration.

Personal Electronics

The PCF8574 is a great fit for personal electronic devices where additional I/O ports are required. It allows you to expand control options in gadgets like smart home devices, adding flexibility without increasing size or complexity.

Industrial Automation

In industrial automation, the PCF8574 provides essential remote control and monitoring capabilities. This feature helps to expand control options, making it suitable for large-scale automated systems that require robust and versatile I/O management.

Devices with Limited GPIO Options

For products with microcontrollers that have limited GPIO, the PCF8574 can provide needed I/O expansion. It’s ideal for small devices that require more I/O ports than are natively available, allowing for added functionality in compact designs.

• Connect the SCL and SDA pins directly to VCC. If they’re connected to an auxiliary power source that could be on while VCC is off, it may increase the supply current (ICC).

• For this example, the device address is set to 0100000.

• Configure P0, P2, and P3 as outputs.

• Set P1, P4, and P5 as inputs.

• P6 and P7 are unused and should be configured as outputs.