1. General description
The PCA9555 is a 24-pin CMOS device that provides 16 bits of General Purpose parallel
Input/Output (GPIO) expansion for I
2
C-bus/SMBus applications and was developed to
enhance the NXP Semiconductors family of I
2
C-bus I/O expanders. The improvements
include higher drive capability, 5 V I/O tolerance, lower supply current, individual I/O
configuration, and smaller packaging. I/O expanders provide a simple solution when
additional I/O is needed for ACPI power switches, sensors, push buttons, LEDs, fans, etc.
The PCA9555 consists of two 8-bit Configuration (Input or Output selection); Input, Output
and Polarity Inversion (active HIGH or active LOW operation) registers. The system
master can enable the I/Os as either inputs or outputs by writing to the I/O configuration
bits. The data for each Input or Output is kept in the corresponding Input or Output
register. The polarity of the read register can be inverted with the Polarity Inversion
register. All registers can be read by the system master. Although pin-to-pin and I
2
C-bus
address compatible with the PCF8575, software changes are required due to the
enhancements, and are discussed in Application Note AN469.
The PCA9555 open-drain interrupt 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. The power-on reset sets the registers to their default values
and initializes the device state machine.
Three hardware pins (A0, A1, A2) vary the fixed I
2
C-bus address and allow up to eight
devices to share the same I
2
C-bus/SMBus. The fixed I
2
C-bus address of the PCA9555 is
the same as the PCA9554, allowing up to eight of these devices in any combination to
share the same I
2
C-bus/SMBus.
2. Features and benefits
Operating power supply voltage range of 2.3 V to 5.5 V
5 V tolerant I/Os
Polarity Inversion register
Active LOW interrupt output
Low standby current
Noise filter on SCL/SDA inputs
No glitch on power-up
Internal power-on reset
16 I/O pins which default to 16 inputs
0 Hz to 400 kHz clock frequency
ESD protection exceeds 2000 V HBM per JESD22-A114, 200 V MM per
JESD22-A115, and 1000 V CDM per JESD22-C101
PCA9555
16-bit I
2
C-bus and SMBus I/O port with interrupt
Rev. 10 — 8 November 2017 Product data sheet
