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FAN5026 — Dual DDR / Dual-Output PWM Controller
March 2011
FAN5026
Dual DDR / Dual-Output PWM Controller
Features
Highly Flexible, Dual Synchronous Switching PWM
Controller that Includes Modes for:
Description
The FAN5026 PWM controller provides high efficiency
and regulation for two output voltages adjustable in the
range of 0.9V to 5.5V required to power I/O, chip-sets,
and memory banks in high-performance computers,
set-top boxes, and VGA cards. Synchronous
rectification and hysteretic operation at light loads
contribute to high efficiency over a wide range of loads.
Efficiency is enhanced by using MOSFET R
DS(ON)
as a
current-sense component.
Feedforward ramp modulation, average-current mode
control, and internal feedback compensation provide
fast response to load transients. Out-of-phase operation
with 180-degree phase shift reduces input current
ripple. The controller can be transformed into a
complete DDR memory power supply solution by
activating a designated pin. In DDR Mode, one of the
channels tracks the output voltage of another channel
and provides output current sink and source capability
— essential for proper powering of DDR chips. The
buffered reference voltage required by this type of
memory is also provided. The FAN5026 monitors these
outputs and generates separate PGx (power good)
signals when the soft-start is completed and the output
is within ±10% of the set point.
Over-voltage protection prevents the output voltage
from exceeding 120% of the set point. Normal operation
is automatically restored when over-voltage conditions
cease. Under-voltage protection latches the chip off
when output drops below 75% of the set value after the
soft-start sequence for this output is completed. An
adjustable over-current function monitors the output
current by sensing the voltage drop across the lower
MOSFET. If precision current-sensing is required, an
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