International Rectifier’s (IR) XPhase™ is an extremely flexible and scalable architecture for multiphase, interleaved buck dc-dc converters requiring one or more phases. The first XPhase chip set consists of the IR3081 Control IC and the IR3086 Phase IC, and provides a high-performance solution that exceeds the VRM or VRD/EVRD 10.0 requirements for the most advanced microprocessors used in servers and high-end desktop computers.
Unlike other multiphase solutions, which are limited in the number of phases they drive, the IR XPhase architecture enables a scalable multiphase design that accommodates the constant change and unpredictable nature of advanced CPU power requirements.
The architecture consists of a Control IC, which communicates with the Phase IC using a simple 5-wire bus scheme. Phases can be added or removed without changing the fundamental design. The 5-wire analog bus consists of bias voltage, phase timing, average current, error amplifier output, and VID voltage. By eliminating point-to-point wiring between the Control and the Phase ICs, the 5-wire bus shortens interconnections, cutting parasitic inductance and noise and thus improves PCB layout.
The IR3081 Control IC in the 28-lead MLPQ package contains all one-per-converter circuitry, including voltage identification (VID) pull-up resistors, PWM ramp oscillator, error amplifier, bias voltage, fault detection, and other necessary functions.
The IR3086 Phase IC in the 20-lead MLPQ package drives and monitors a single phase in a multiphase converter. The IR3086 Phase IC includes all one-per-phase circuitry that includes gate drivers, PWM comparator and latch, overvoltage protection, and current sensing and sharing and programmable overtemperature detection.
A patent-pending body braking control feature achieves nearly two times improvement in inductor slew rate, improving transient response time and efficiency. This control technique turns off the synchronous rectifier MOSFET in response to a significant decrease in load current. In addition to permitting the use of larger inductor values, body braking also helps to decrease output capacitor requirements--reducing solution cost and size.
The XPhase Control IC implements feed-forward voltage mode control with modified Type 3 load line terminal compensation and trailing edge modulation in conjunction with adaptive voltage positioning. Because accurate current sharing is critical to multiphase designs, XPhase architecture implements average output inductor current sensing to accomplish very accurate current sharing with support for 100% duty cycle and over-lapping phases. In addition, it supports single-cycle transient response.
A 100A, 6-phase, VRM 10.0-compliant converter using the IR3081 and IR3086 XPhase chipset and IR's DirectFET(tm) MOSFETs (IRF6602 control FET and IRF6601 synchronous FET) yields 84% efficiency with less than 4% variation in phase current and average current per phase.
For more information, visit www. irf.com.