NXP’s GPIO expanders are classified in different groups according to the output structure type: quasi output, totem-pole (or push-pull) output, and open-drain output. Quasi output ports are easy to use since they can be configured as an input or output without the need of a Port Configuration Register. However, they only have a weak current-source pull-up to keep the port HIGH and cannot source more than 100 µA per output. Totem-pole outputs consist of upper and lower transistors, and are ideal for fast switching applications. They have steep HIGH-to-LOW and LOW-to-HIGH transitions, where each output stage is required to source or sink 10 mA to 25 mA current. Open-drain outputs are only capable of sinking current and rely on an external pull-up resistor to drive the line HIGH. Under heavy capacitive loading conditions, they have slower LOW-to-HIGH transitions compared to the totem-pole and quasi outputs, which have steep LOW-to-HIGH transitions.