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PCF8574AT

8-bit I2C I/O expander, quasi-bidirectional, INT pin, SOIC-16

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Manufacturer Part：

PCF8574AT

Package：

SOIC-16 (10.3 x 10.3 x 2.35mm, 1.27mm pitch)

Brand：

Product Categories：

Integrated Circuits ICs, Interface ICs

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Description

Product Overview

The PCF8574AT is a remote 8-bit I/O expander for the I2C bus from NXP Semiconductors with quasi-bidirectional ports, interrupt output, and 100kHz I2C interface in an SOIC-16 package.

Key Specifications

Number of I/O	8 (quasi-bidirectional)
Interface	I2C (standard-mode, 100kHz max)
Supply Voltage	2.5V to 6V
Standby Current	2.5µA typical (static)
I2C Addresses	8 programmable (3 address pins A0, A1, A2)
Slave Address (PCF8574A)	0x38 – 0x3F
Slave Address (PCF8574)	0x20 – 0x27
Max Sink Current per I/O	25mA
Total Package Sink Current	80mA
Source Current per I/O	0.1mA (weak internal pull-up)
Interrupt Output	Active-low, open-drain (INT)
Port Default (Power-On)	Inputs (HIGH with 100µA weak pull-up)
Operating Temperature	-40°C to +85°C
Package	SOIC-16 (10.3 x 10.3mm)

Features

8 quasi-bidirectional I/O pins (no direction register needed)
I2C bus interface up to 100kHz
Active-low open-drain interrupt output (INT)
3 hardware address pins for 8 device addresses
2.5µA static standby current
Latched outputs directly drive LEDs
25mA sink current per I/O pin
PCF8574A has different I2C base address from PCF8574
Up to 16 devices (8 PCF8574 + 8 PCF8574A) on one I2C bus = 128 I/Os

Applications

LED signs and displays
Keypad and button matrix scanning
GPIO expansion for microcontrollers
Industrial control and PLC
Mobile device peripheral control

Product Introduction:PCF8574AT Product Introduction

The PCF8574AT from NXP Semiconductors is a remote 8-bit I/O expander that communicates via the I2C bus, adding 8 general-purpose I/O pins to any I2C-capable microcontroller. The eight quasi-bidirectional ports can each serve as an input or output without requiring a data-direction register—writing a 1 to a port configures it as an input (weak 100µA pull-up active), while writing a 0 drives the pin LOW with a strong sink transistor. The active-low open-drain interrupt output (INT) signals the host when any input pin changes state, eliminating the need for continuous I2C polling. The PCF8574A variant has a different I2C base address (0x38-0x3F) from the PCF8574 (0x20-0x27), allowing up to 16 devices (128 I/Os) on a single bus. The 2.5µA static current makes it ideal for battery-powered designs. The T suffix denotes the SOIC-16 package.

Working Principle:PCF8574AT Working Principle

The PCF8574AT uses quasi-bidirectional I/O ports that simplify interface design by eliminating the need for a direction register. Each port pin has three components: a weak 100µA current source pulling to VDD, a strong pulldown transistor that activates when the output latch is 0, and a momentary strong pull-up that activates briefly when the output latch transitions from 0 to 1 (to accelerate rising edges). When used as an output, writing 0 turns on the strong pulldown (sinking up to 25mA), and writing 1 allows the weak pull-up to hold the pin HIGH. When used as an input, the port must first be written to 1 (default after power-on reset). An external device then pulls the pin LOW or lets it remain HIGH. Reading the port returns the actual pin state regardless of the output latch value. The interrupt output (INT) is an open-drain active-low signal that activates whenever any input pin state differs from the last-read value. This allows the host MCU to connect INT to an interrupt pin and only perform I2C reads when the I/O state has actually changed. Communication uses standard I2C: the master sends START + 7-bit slave address + R/W bit. For a write, the next byte is latched to the output port. For a read, the slave returns the current port pin states.

Pin Description:PCF8574AT Pin Definition and Functions

Pin	Name	Type	Description
1	A0	Input	I2C address bit 0
2	A1	Input	I2C address bit 1
3	A2	Input	I2C address bit 2
4	P0	I/O	Quasi-bidirectional I/O port bit 0
5	P1	I/O	Quasi-bidirectional I/O port bit 1
6	P2	I/O	Quasi-bidirectional I/O port bit 2
7	P3	I/O	Quasi-bidirectional I/O port bit 3
8	VSS	Power	Ground
9	P4	I/O	Quasi-bidirectional I/O port bit 4
10	P5	I/O	Quasi-bidirectional I/O port bit 5
11	P6	I/O	Quasi-bidirectional I/O port bit 6
12	P7	I/O	Quasi-bidirectional I/O port bit 7
13	INT	Output	Interrupt output (active-low, open-drain)
14	SCL	Input	I2C serial clock
15	SDA	I/O	I2C serial data (open-drain)
16	VDD	Power	Supply (2.5V to 6V)

Application Scenarios:In which products and applications isPCF8574AT used

LED Matrix: 8 pins sink 25mA each to drive 8 LEDs directly; add more PCF8574 for larger displays
Keypad Scan: 4 outputs + 4 inputs scan a 4×4 matrix; INT pin interrupts MCU on any key press
GPIO Expansion: Add 8 I/O to an MCU with only 2 pins (SDA, SCL); 16 devices per bus = 128 I/O from 2 MCU pins
Relay Driver: 25mA sink per pin directly drives 5V relay coils through ULN2803 darlington array
Low-Power Design: 2.5µA static current; INT eliminates polling, reducing MCU wake time in battery systems

Alternative Models:What chips are recommended as replacements for PCF8574AT

Model	Manufacturer	Key Difference	Package	Specs
PCF8574T	NXP	Same but different I2C base address (0x20), SOIC-16	–	–
PCF8574AP	TI	TI’s equivalent, DIP-16 through-hole	–	–
PCA9557PW	NXP	Drop-in replacement, TSSOP-20, with config registers	–	–
MCP23008-E/SO	Microchip	8-bit I2C expander, config registers, SOIC-18	–	–
MAX7317ATG+T	ADI/Maxim	10-bit I2C expander, PWM, TSSOP-24	–	–

PCF8574AT is an 8-bit I2C I/O expander from NXP in SOIC-16 with address 0x38-0x3F. The PCF8574T provides address 0x20-0x27. The PCF8574AP uses DIP-16 with address 0x38-0x3F. The MCP23008-E/SO from Microchip provides 8-bit I2C I/O with configurable interrupt in SOIC-18. The MAX7311 from ADI/Maxim offers 16-bit I2C I/O. The PCA8574 from NXP provides a newer I/O expander with improved ESD. The TCA9554 from TI offers 8-bit I2C I/O with interrupt in VQFN-16.