Mobile Processor Core-Voltage RegulatorThe 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
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