FAN5240 Datasheet, PDF (1/19 Pages) Fairchild Semiconductor – Multi-Phase PWM Controller for AMD Mobile Athlon TM and Duron TM

www.fairchildsemi.com
FAN5240
Multi-Phase PWM Controller for AMD Mobile
Athlon^TM and Duron^TM
Features
• CPU Core power: 0.925V to 2.0V output range
• ±1% reference precision over temperature
• Dynamic voltage setting with 5-bit DAC
• 5V to 24V input voltage range
• 2 phase interleaved switching
• Active droop to reduce output capacitor size
• Differential remote voltage sense
• High efficiency:
>90% efficiency over wide load range
>80% efficiency at light load
• Excellent dynamic response with Voltage Feed-Forward
and Average Current Mode control
• Dynamic duty cycle clamp minimizes inductor current
build up
• Lossless current sensing on low-side MOSFET or
Precision current sensing using sense resistor
• Fault protections: Over-voltage, Over-current, and
Thermal Shut-down
• Controls: Enable, Forced PWM, Power Good, Power
Good Delay
• QSOP28, TSSOP28
Applications
• AMD Mobile Athlon CPU VCORE Regulator
• AMD Mobile Duron CPU VCORE Regulator
General Description
The FAN5240 is a single output 2-Phase synchronous buck
controller to power AMD’s mobile CPU core. The FAN5240
includes a 5-bit digital-to-analog converter (DAC) that
adjusts the core PWM output voltage from 0.925VDC to
2.0VDC, which may be changed during operation. Special
measures are taken to allow the output to transition with
controlled slew rate to comply with AMD’s Power Now
technology. The FAN5240 includes a precision reference,
and a proprietary architecture with integrated compensation
providing excellent static and dynamic core voltage regula-
tion. The regulator includes special circuitry which balances
the 2 phase currents for maximum efficiency.
At light loads, when the filter inductor current becomes
discontinuous, the controller operates in a hysteretic mode,
dramatically improving system efficiency. The hysteretic
mode of operation can be inhibited by the FPWM control
pin.
The FAN5240 monitors the output voltage and issues a
PGOOD (Power-Good) when soft start is completed and the
output is in regulation. A pin is provided to add delay to
PGOOD with an external capacitor.
A built-in over-voltage protection (OVP) forces the lower
MOSFET on to prevent the output from exceeding a set
voltage. The PWM controller's overcurrent circuitry moni-
tors the converter load by sensing the voltage drop across the
lower MOSFET. The overcurrent threshold is set by an exter-
nal resistor. If precision overcurrent protection is required,
an optional external current-sense resistor may be used.
REV. 1.1.7 8/29/02