The PCAL9554B and PCAL9554C are a low-voltage 8-bit General Purpose Input/Output
(GPIO) expanders with interrupt and weak pull-up for I²C-bus/SMBus applications. The
only difference between the PCAL9554B and PCAL9554C is their I²C-bus fixed address,
allowing a larger number of the same device on the I²C-bus with no chance of address
conflicts. 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 PCAL9554B/PCAL9554C to interface with next-generation microprocessors
and microcontrollers where supply levels are dropping down to conserve power.
The PCAL9554B/PCAL9554C contains the PCA9554A register set of four 8-bit
Configuration, Input, Output, and Polarity Inversion registers, and additionally, the
PCAL9554B/PCAL9554C 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 PCAL9554B is a pin-for-pin replacement for the PCA9554, while the PCAL9554C
replaces the PCA9554A, however both versions power-up with all I/O interrupted masked.
This mask default allows for a board bring-up free of spurious interrupts at power-up.
The PCAL9554B/PCAL9554C 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
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 PCAL9554B or
PCAL9554C can remain a simple follower device.
The device outputs have 25 mA sink capabilities for directly driving LEDs while consuming
low device current.
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. The PCAL9554B and PCAL9554C differ only
in their base I²C-bus addresses permitting a total of 16 of the same devices on the
I²C-bus, minimizing the chance of address conflict, even in a complex system.