The TOSHIBA TLP555 consists of an infrared emitting diode and integrated high gain, high speed photodetector. This unit is an 8−lead DIP package. The detector has a three state output stage that eliminates the need for a pull−up resistor, and built−in Schmitt trigger. The detector has a Schmitt trigger circuit and 3 State output circuit, so both-directions of source and sink drive can be performed. The detector IC has an internal shield that provides a guaranteed common mode transient immunity of 1000V / μs. TLP555 is a buffer logic type. When an inverter logic type is required, there is TLP558.