FAN5026 Dual-Output/DDR PWM Controller0 pages

March 2011
© 2005 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5026 • Rev. 1.0.8
FAN5026 — Dual DDR / Dual-Output PWM Controller
FAN5026
Dual DDR / Dual-Output PWM Controller
Features
Highly Flexible, Dual Synchronous Switching PWM
Controller that 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 Over-Current Using Sense Resistor
VCC Under-Voltage Lockout
Wide Input Range: 3V to 16V
Excellent Dynamic Response with Voltage
Feedforward and Average Current-Mode Control
Power-Good Signal
Supports DDR-II and HSTL
28-Lead Thin-Shrink Small-Outline Package
Applications
DDR VDDQ and VTT Voltage Generation
PC Dual Power Supply
Server DDR Power
Desktop Computer
Graphics Cards
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 RDS(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
external current-sense resistor may be used.
Related Resources
Application Note — AN-6002 Component
Calculations and Simulation Tools
Ordering Information
Part Number
Operating
Temperature
Range
Package Packing Method
FAN5026MTCX -40 to +85°C 28-Lead Thin-Shrink Small-Outline Package (TSSOP) Tape and Reel