16-bit I2C-bus/SMBus I/O Expander with Interrupt and Agile I/O in TSSOP24 package

The PCAL9555A is a low-voltage 16-bit General Purpose Input/Output (GPIO) expander

with interrupt and weak pull-up resistors for I²C-bus/SMBus applications. NXP® I/O

expanders provide a simple solution when additional I/Os are needed while keeping

interconnections to a minimum, for example, in ACPI power switches, sensors, push

buttons, LEDs, fan control, etc.

In addition to providing a flexible set of GPIOs, the wide VDD range of 1.65 V to 5.5 V

allows the PCAL9555A to interface with next-generation microprocessors and

microcontrollers where supply levels are dropping down to conserve power.

The PCAL9555A contains the PCA9555 register set of four pairs of 8-bit Configuration,

Input, Output, and Polarity Inversion registers, and additionally, the PCAL9555A has

Agile I/O, which are additional features specifically designed to enhance the I/O. These

additional features are programmable output drive strength, latchable inputs,

programmable pull-up/pull-down resistors, maskable interrupt, interrupt status register,

programmable open-drain or push-pull outputs.

The PCAL9555A is a pin-to-pin replacement to the PCA9555, however, the PCAL9555A

powers up with all I/O interrupts masked. This mask default allows for a board bring-up

free of spurious interrupts at power-up.

The PCAL9555A open-drain interrupt (INT) output is activated when any input state differs

from its corresponding Input Port register state and is used to indicate to the system

leader that an input state has changed.

INT can be connected to the interrupt input of a microcontroller. By sending an interrupt

signal on this line, the remote I/O can inform the microcontroller if there is incoming data

on its ports without having to communicate via the I²C-bus. Thus, the PCAL9555A can

remain a simple follower device.

The device outputs have 25 mA sink capabilities for directly driving LEDs while consuming

low device current.

The power-on reset sets the registers to their default values and initializes the device state

machine.

The device powers on with weak pull-up resistors enabled that can replace external

components.

Three hardware pins (A0, A1, A2) select the fixed I²C-bus address and allow up to eight

devices to share the same I²C-bus/SMBus.