TCA9538 Datasheet, PDF (14/37 Pages) Texas Instruments – Low Voltage 8-Bit I2C and SMBus Low-Power I/O Expander

TCA9538
SCPS199C – AUGUST 2014 – REVISED OCTOBER 2015
8 Detailed Description
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8.1 Overview
The TCA9538 is an 8-bit I/O expander for the two-line bidirectional bus (I²C) is designed for 1.65-V to 5.5-V
V_CC operation. It provides general-purpose remote I/O expansion for most micro-controller families via the
I²C interface (serial clock, SCL, and serial data, SDA, pins).
The TCA9538 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. The INT pin can be connected to the interrupt input of a micro-controller. By sending an interrupt
signal on this line, the remote I/O can inform the micro-controller if there is incoming data on its ports without
having to communicate via the I2C bus. Thus, the TCA9538 can remain a simple slave device. The device
outputs (latched) have high-current drive capability for directly driving LEDs.
Two hardware pins (A0 and A1) are used to program and vary the fixed I²C slave address and allow up to
four devices to share the same I²C bus or SMBus.
The system master can reset the TCA9538 in the event of a timeout or other improper operation by asserting
a low on the RESET input pin or by cycling the power supply and causing a power-on reset (POR). A reset
puts the registers in their default state and initializes the I²C /SMBus state machine. The RESET feature and
a POR cause the same reset/initialization to occur, but the RESET feature does so without powering down
the part.
The TCA9538 consists of one 8-bit Configuration (input or output selection), Input Port, Output Port, and
Polarity Inversion (active high or active low) registers. At power on, the I/Os are configured as inputs.
However, 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 Port or Output Port
register. The polarity of the Input Port register can be inverted with the Polarity Inversion register. All
registers can be read by the system master.
The TCA9538 is identical to the TCA9554 except for the removal of the internal I/O pull-up resistors, which
greatly reduces power consumption when the I/Os are held LOW, the replacement of A2 with RESET, and
different slave address range.
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