FAN5240 Datasheet, PDF (7/19 Pages) Fairchild Semiconductor – Multi-Phase PWM Controller for AMD Mobile Athlon TM and Duron TM

PRODUCT SPECIFICATION
FAN5240
Circuit Description
Overview
The FAN5240 is a 2-phase, single output power management
IC, which supplies the low-voltage, high-current power to
modern processors for notebook PCs. Using very few exter-
nal components, the IC controls a precision programmable
synchronous buck converter driving external N-Channel
power MOSFETs. The output voltage is adjustable from
0.925V to 2.0V by changing the DAC (VID) code settings
(see Table 2). The output voltage of the core converter can be
changed on-the-fly with programmable slew rate, which
meets a key requirement of AMD's Mobile Athlon/Duron
processors.
The converter can operate in two modes: fixed frequency
PWM, and variable frequency hysteretic depending on the
load. At loads lower than the point where filter inductor cur-
rent becomes discontinuous, hysteretic mode of operation is
activated. Switchover from PWM to hysteretic operation at
light loads improves the converter's efficiency and prolongs
battery run time. As the filter inductor resumes continuous
current, the PWM mode of operation is restored.
Output Voltage Programming
The output voltage of the converter is programmed by an
internal DAC in discrete steps of 25mV from 0.925V to
1.300V and then in 50mV steps from 1.300V to 2.00V:
Table 2. Output voltage VID
VID4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
VID3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
VID2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
VID1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
VID0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
VOUT to CPU
0.000
0.925
0.950
0.975
1.000
1.025
1.050
1.075
1.100
1.125
1.150
1.175
1.200
1.225
1.250
1.275
0.000
1.300
1.350
1.400
1.450
1.500
1.550
1.600
1.650
1.700
1.750
1.800
1.850
1.900
1.950
2.000
1 - Logic High or open, 0 = Logic Low
VID0–4 pins will assume a logic 1 level if left open as each
input is pulled up with a 1µA internal current source.
REV. 1.1.7 8/29/02
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