The MAX1661/MAX1662/MAX1663 serial-to-parallel/ parallel-to-serial converters are intended to control external power MOSFETs in power-plane switching applications. These small, low-cost devices can be used on a system motherboard to control point-of-load switching from a 2wire SMBusTM serial interface. Each device has three highvoltage open-drain outputs that double as TTL-level logic inputs, giving them bidirectional capabilities. The I/O pins can withstand +28V, so they can control battery voltagedistribution switches in notebook computers. The MAX1661 is intended for driving N-channel MOSFETs and its outputs are low upon power-up. The MAX1662/ MAX1663 are intended for P-channel MOSFETs, and their outputs are high-impedance upon power-up. This ensures that the MOSFETs are off at power-up, so the system can enforce power-plane sequencing.