The TCA9537 device is a 4-bit I/O expander for the I²C bus and is designed for 1.65-V to 5.5-V V_CC operation. It provides general-purpose remote I/O expansion for most microcontroller families via the I²C interface.

The TCA9537 consists of a configuration (input or output selection), Input Port, Output Port, and Polarity Inversion (active-high or active-low operation) registers. At power-on, the I/Os are configured as inputs. 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 Input Port register can be inverted with the Polarity Inversion register. All registers can be read by the system controller.

The TCA9537 open-drain interrupt output (INT) is activated when any input differs from its corresponding Input Port register state and is used to indicate to the system controller that an input state has changed.

The system processor can reset the TCA9537 in the event of a timeout or other improper operation by using an I²C soft reset command, which puts the registers in their default state, or with the use of the RESET pin.

The device outputs (latched) have high-current drive capability for directly driving LEDs.