The PCA9673 is a drop in upgrade for the PCF8575 providing higher Fast-mode Plus (Fm+) I2C-bus speeds (1 MHz versus 400 kHz) so that the output can support PWM dimming of LEDs, higher I2C-bus drive (30 mA versus 3 mA) so that many more devices can be on the bus without the need for bus buffers, higher total package sink capacity (400 mA versus 100 mA) that supports having all 25 mA LEDs on at the same time and more device addresses (16 versus 8) are available to allow many more devices on the bus without address conflicts.