The ISL6504 and ISL6504A complement 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 16-pin wide-body SOIC or 20-pin QFN 6x6 package. The ISL6504, ISL6504A operating mode (active outputs 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. 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 ISL6504 5VDUAL output is shut down. In the ISL6504A, the 5VDUAL output stays on during S4/S5 sleep states. This is the only difference between the two parts; see Table 1.