Mobile Processor Core-Voltage Regulator

The FAN5250 is a single output power controller to power mobile CPU cores. The FAN5250 includes a 5-bit digital-to- Analog converter (DAC) that adjusts the core PWM output voltage from 0.6VDC to 1.75VDC, and may be changed during operation. Special measures are taken to allow the output to transition with controlled slew rate to comply with Transmetas LongRun and Intels P3-M Speed-Step requirements. The FAN5250 includes a precision reference, and a proprietary architecture with integrated compensation providing excellent static and dynamic core voltage regula- tion. With nominal currents, the controller operates at a selectable frequency of 300kHz or 600kHz. At light loads, when the lter inductor current becomes discontinuous, the controller operates in a hysteretic mode dramatically improving system efciency. The hysteretic mode of operation CAN be inhibited by the FPWM control pin. The FAN5250 monitors the output voltage and issues a PGOOD (Power-Good) when soft start is completed and the output is in regulation. A built-in over-voltage protection (OVP) forces the lower MOSFET on to prevent output volt- ages from exceeding 1.9V. Undervoltage protection Latches the chip off when the output drops below 75% of the set value. The PWM controller's overcurrent circuitry monitors the converter load by sensing the voltage drop across the lower MOSFET The overcurrent threshold is set by an external resistor. If precision overcurrent protection is required, an optional external current-sense resistor may be used. By Fairchild Semiconductor