The ISL6505 complements other power building blocks (voltage regulators) in ACPI-compliant designs for microprocessor and computer applications. The IC integrates three linear controllers/regulators, switching, monitoring and control functions into a 20-pin wide-body SOIC or 20-pin QFN (also known as MLF) 5x5 package. The ISL6505's operating mode (active or sleep outputs) is selectable through two digital control pins, S3 and S5. One linear controller generates the 3.3VDUAL/3.3VSB voltage plane from the ATX supply's 5VSB output, powering the south bridge and the PCI slots through an external NPN pass transistor during sleep states (S3, S4/S5). In active state (during S0 and S1/S2), the 3.3VDUAL/3.3VSB linear regulator uses an external N-channel pass MOSFET to connect the outputs directly to the 3.3V input supplied by an ATX power supply, for minimal losses. The 3.3VDUAL/3.3VSB output is active for as long as the ATX 5VSB voltage is applied to the chip. A controller powers up the 5VDUAL plane by switching in the ATX 5V output through an NMOS transistor in active states, or by switching in the ATX 5VSB through a PMOS (or PNP) transistor in S3 sleep state. In S4/S5 sleep states, the ISL6505 5VDUAL output is either shut down or stays on, based on the state of the EN5 pin.