14

TCA9538

SCPS199D – AUGUST 2014 – REVISED OCTOBER 2016

www.ti.com

Product Folder Links: TCA9538

Submit Documentation Feedback

Copyright © 2014–2016, Texas Instruments Incorporated

8 Detailed Description

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

VCC 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.