Multiphase, Fixed-Frequency Controller for AMD Hammer CPU Core Power Supplies

The MAX8707 is a multiphase (3-/4-phase), interleaved, fixed-frequency, step-down controller for AMD Hammer CPU core supplies. Interleaved multiphase operation reduces the input ripple current and output voltage ripple while easing component selection and layout placement. The MAX8707 includes active voltage positioning with adjustable gain and offset, reducing power dissipation and bulk output-capacitance requirements.

The MAX8707 is intended for two different notebook CPU core applications: stepping down the battery directly or stepping down the +5V system supply to create the core voltage. The single-stage conversion method allows these devices to directly step down high-voltage batteries for the highest possible efficiency. Alternatively, 2-stage conversion (stepping down the +5V system supply instead of the battery) at higher switching frequency provides the minimum possible physical size.

The MAX8707 features dedicated differential currentsense inputs for each phase and includes a fifth pair of current-sense inputs to provide an accurate voltagepositioning slope and average current-limit protection using a single current-sense resistor. The MAX8707 also has two dedicated inputs that provide differential remote voltage sensing.

The MAX8707 provides an analog input for setting the suspend voltage and a slew-rate controller for transitions between VID codes or the suspend voltage. The controllers reduce the transition slew rate during startup and shutdown, providing soft-start with minimal input surge current and damped soft-shutdown without negative output undershoot. The MAX8707 includes output fault protectionundervoltage, nonlatched overvoltage, and thermal overloadand an independent voltageregulator power-OK (VROK) output.

The MAX8707 has a selectable switching frequency, allowing 200kHz, 300kHz, or 600kHz per-phase operation. The MAX8707 is available in the low-profile, 40-pin, 6mm x 6mm thin QFN package. Refer to the MAX8702/MAX8703 for compatible drivers.

Applications

* AMD Hammer Desknote Computers * Multiphase CPU Core Supplies * Notebook and Desktop Computers * Servers * Voltage-Positioned Step-Down Converters

* 3-/4-Phase Interleaved Fixed-Frequency Controller

* ±0.75% VOUT Accuracy Over Line, Load, and Temperature

* 5-Bit On-Board Digital-to-Analog Converter (DAC)—0.80V to 1.55V

* Adjustable Suspend Voltage Input

* Active Voltage Positioning with Adjustable Gain and Offset

* Accurate Lossless Current Balance

* Accurate Droop and Current Limit

* Remote Output and Ground Sense

* Output Slew-Rate Control

* Power-Good Window Comparator

* Selectable 200kHz/300kHz/600kHz Switching Frequency

* Output Overvoltage and Undervoltage Protection

* Thermal Fault Protection

* 2V ±0.7% Reference Output

* Soft-Startup and Shutdown