www.fairchildsemi.com

REV. 1.1.7 8/29/02

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

• AMD Mobile Duron

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.

FAN5240

Multi-Phase PWM Controller for AMD Mobile