ON Semiconductor – I/O expander provides 16 channels of I2C or SMBus signals


The PCA9655E from ON Semiconductor is a 16-bit parallel I/O expander for systems using an I2C bus or SMBus.

The device includes two 8-bit configuration registers. At power- on, all 16 I/Os operate as inputs by default. Each I/O may be configured as either an input or an output by writing to its corresponding I/O configuration bit.

The data for each input or output is kept in its corresponding input or output register. All registers can be read by the system master.

The PCA9655E provides an open-drain interrupt output which is activated when any input state differs from the register state of its corresponding input port. An Interrupt output may be used to indicate to the system master that an input state has changed.

The chip’s power-on reset function sets the registers to their default values and initialises the device’s state machine.

Three hardware pins are used to configure the device’s I2C slave address. Up to 64 PCA9655E devices can share the same I2C bus or SMBus.


  • Operating-voltage range: 1.65V to 5.5V
  • 5.5V-tolerant I/Os
  • Low stand-by current
  • Input noise filter
  • No glitch on power-up
  • Supports I2C in Standard mode, Fast mode and Fast mode+


  • Keyboards
  • Human-machine interface devices