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 master 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 PCAL9554B or PCAL9554C can remain a simple slave 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 the most complex system.