www.fairchildsemi.com
FAN5236
Dual Mobile-Friendly 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
– V
TT
Tracks VDDQ/2
– VDDQ/2 Buffered Reference Output
• 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 (5 to 24V)
• Excellent dynamic response with Voltage Feed-Forward
and Average Current Mode control
• Power-Good Signal
• Also supports DDR-II and HSTL
• Light load Hysteretic mode maximizes efficiency
• QSOP28, TSSOP28
General Description
The FAN5236 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 notebook comput-
ers, PDAs and Internet appliances. Synchronous rectification
and hysteretic operation at light loads contribute to a high
efficiency over a wide range of loads. The hysteretic mode of
operation can be disabled separately on each PWM converter
if PWM mode is desired for all load levels. Efficiency is even
further enhanced by using MOSFET’s R
DS(ON)
as a current
sense component.
Feed-forward ramp modulation, average current mode con-
trol 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 con-
troller can be transformed into a complete DDR memory
power supply solution by activating a designated pin. In
DDR mode of operation one of the channels tracks the out-
put 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 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 its set point. A built-in
over-voltage protection prevents the output voltage from
going above 120% of the set point. Normal operation is auto-
matically restored when the over-voltage conditions go
away. Under-voltage 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 cur-
rent-sensing is required, an external current-sense resistor
may optionally be used.
Applications
•
•
•
•
DDR V
DDQ
and V
TT
voltage generation
Mobile PC dual regulator
Server DDR power
Hand-Held PC power
REV. 1.1.7 4/4/03
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
