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FAN5026

Dual DDR/Dual-Output PWM Controller

Fairchild Semiconductor 

October 2005

FAN5026

Dual DDR/Dual-Output PWM Controller

Features

■ Highly flexible dual synchronous switching PWM

controller includes modes for:

– DDR mode with in-phase operation for reduced

channel interference

– 90° phase shifted two-stage DDR Mode for reduced

input ripple

– Dual Independent regulators 180° phase shifted

■ Complete DDR Memory power solution

– VTT Tracks VDDQ/2

– VDDQ/2 Buffered Reference Output

■ Lossless current sensing on low-side MOSFET or

Precision current sensing using sense resistor

■ VCC Under-voltage Lockout

■ Wide power input range: 3 to 16V

■ Excellent dynamic response with Voltage

Feed-Forward and Average Current Mode control

■ Power-Good Signal

■ Supports DDR-II and HSTL

■ TSSOP28 package

Applications

■ DDR VDDQ and VTT voltage generation

■ Desktop computer

■ Graphics cards

General Description

The FAN5026 PWM controller provides high efficiency

and regulation for two output voltages adjustable in the

range from 0.9V to 5.5V that are required to power I/O,

chip-sets, and memory banks in high-performance com-

puters, set top boxes, and VGA cards. Synchronous rec-

tification contributes to high efficiency over a wide range

of loads. Efficiency is even further enhanced by using

MOSFET’s RDS(ON) as a current sense component.

Feed-forward ramp modulation, average current mode

control scheme, and internal feedback compensation

provide fast response to load transients. Out-of-phase

operation with 180° phase shift reduces input current

ripple. The controller can be transformed into a com-

plete DDR memory power supply solution by activating a

designated pin. In DDR mode of operation one of the

channels tracks the output voltage of another channel

and provides output current sink and source capability —

features essential for proper powering of DDR chips. The

buffered reference voltage required by this type of mem-

ory is also provided. The FAN5026 monitors these out-

puts and generates separate PGx (power good) signals

when the soft-start is completed and the output is within

±10% of its set point. A built-in over-voltage protection

prevents the output voltage from going above 120% of

the set point. Normal operation is automatically restored

when the over-voltage conditions go away. Under-volt-

age protection latches the chip off when either output

drops below 75% of its 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 external cur-

rent-sense resistor may optionally be used.

Ordering Information

Part Number

FAN5026MTC

FAN5026MTCX

Temperature Range

-40°C to 85°C

-40°C to 85°C

Package

TSSOP-28

TSSOP-28

Packing

Rails

Tape and Reel

©2005 Fairchild Semiconductor Corporation

1

FAN5026 Rev. 1.0.5

www.fairchildsemi.com

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