FAN5236 — Dual Mobile-Friendly DDR / Dual-Output PWM Controller
November 2010
FAN5236
Dual Mobile-Friendly DDR / Dual-Output PWM Controller
Features
Highly Flexible, Dual Synchronous Switching PWM
Controller that Includes Modes for:
Description
The FAN5236 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 notebook
computers,
PDAs,
and
Internet
appliances.
Synchronous rectification and hysteretic operation at
light loads contribute to high efficiency over a wide
range of loads. The Hysteretic Mode can be disabled
separately on each PWM converter if PWM Mode is
desired for all load levels. Efficiency is enhanced by
using MOSFET R
DS(ON)
as a current-sense component
.
Feedforward ramp modulation, average-current-mode
control scheme, 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 FAN5236 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. 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 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.
-
-
-
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
V
TT
Tracks V
DDQ/2
V
DDQ/2
Buffered Reference Output
Complete DDR Memory Power Solution
-
-
Lossless Current Sensing on Low-side MOSFET or
Precision Over-Current Using Sense Resistor
V
CC
Under-Voltage Lockout
Converters can Operate from +5V or 3.3V or
Battery Power Input (5V to 24V)
Excellent Dynamic Response with Voltage
Feedforward and Average-Current-Mode Control
Power-Good Signal
Supports DDR-II and HSTL
Light-Load Hysteretic Mode Maximizes Efficiency
TSSOP28 Package
Applications
DDR V
DDQ
and V
TT
Voltage Generation
Mobile PC Dual Regulator
Server DDR Power
Hand-held PC Power
Related Resources
Application Note — AN-6002 Component
Calculations and Simulation Tools for FAN5234 or
FAN5236
Application Note — AN-1029 Maximum Power
Enhancement Techniques for SO-8 Power
MOSFET
© 2002 Fairchild Semiconductor Corporation
FAN5236 • Rev. 1.3.2
www.fairchildsemi.com
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
