The PCA9574 is a CMOS device that provides 8 bits of General Purpose parallel
Input/Output (GPIO) expansion in low voltage processor and handheld battery powered
mobile applications and was developed to enhance the NXP family of I2C-bus I/O
expanders. The improvements include lower supply current, lower operating voltage of
1.1 V to 3.6 V, dual and separate supply rails to allow voltage level translation anywhere
between 1.1 V and 3.6 V, 400 kHz clock frequency, and smaller packaging. Any of the
eight I/O ports can be configured as an input or output independent of each other and
default on start-up to inputs. I/O expanders provide a simple solution when additional I/Os
are needed while keeping interconnections to a minimum; for example in battery powered
mobile applications and clamshell devices for interfacing to sensors, push buttons,
keypad, etc. In addition to providing a flexible set of GPIOs, it simplifies interconnection of
a processor running at one voltage level to I/O devices operating at a different (usually
higher) voltage level. PCA9574 has built-in level shifting feature that makes these devices
extremely flexible in mixed signal environments where communication between
incompatible I/Os is required. The core of PCA9574 can operate at a voltage as low as
1.1 V while the I/O bank can operate in the range 1.1 V to 3.6 V. Bus-hold with
programmable on-chip pull-up or pull-down feature for I/Os is also provided.
The system controller can enable the I/Os as either inputs or outputs by writing to the I/O
configuration register 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 (active HIGH or active LOW operation). Either a bus-hold function or
pull-up/pull-down feature can be selected by programming corresponding registers. The
bus-hold provides a valid logic level when the I/O bus is not actively driven. When
bus-hold feature is not selected, the I/O ports can be configured to have pull-up or
pull-down by programming the pull-up/pull-down configuration register.
An open-drain interrupt output pin (INT) allows monitoring of the input pins and is asserted
each time a change occurs on an input port unless that port is masked
(default = masked). A ‘GPIO All Call’ command allows programming multiple PCA9574s
at the same time even if they have different individual I2C-bus addresses. This allows
optimal code programming when more than one device needs to be programmed with the
same instruction or if all outputs need to be turned on or off at the same time. The internal
Power-On Reset (POR) or hardware reset pin (RESET) initializes the eight I/Os as inputs,
sets the registers to their default values and initializes the device state machine. The I/O
bank is held in its default state when the logic supply (VDD) is off.
One address select pin allows up to two PCA9574 devices to be connected with two
different addresses on the same I2C-bus.
The PCA9574 is available in TSSOP16 and HVQFN16 packages and is
specified over the -40 °C to +85 °C industrial temperature range.