1
dc1726f
DEMO MANUAL DC1726
DESCRIPTION
LTC3618EUF
Dual ±3A Synchronous Buck
Regulator for DDR Termination
Demonstration circuit 1726 is a dual high efficiency
monolithic step-down (buck) DC/DC switching regulator
designed for double-data-rate (DDR) memory termina-
tion in computer systems. The VDDQ output is capable
of sourcing and sinking up to 3A with output voltages of
1.5V, 1.8V, 2.5V plus an optional voltage, selected using
jumpers. The VTT output can also source and sink up
to 3A with an output voltage equal to half of the VDDQ
voltage, half of the input voltage or half of an externally
applied voltage, selected using a jumper. An additional low
current output (VTTR) equal to the VTT voltage capable of
sourcing and sinking up to 10mA is included. Input voltage
range is from 2.25V to 5.5V with overvoltage protection
for transients exceeding 6.5V. Switching frequency is set
to 1MHz although it can be programmed up to 4MHz and
can be synchronized to an external clock for noise sensi-
tive applications.
Jumpers are included for selecting either internal or exter-
nal compensation and jumpers for low quiescent current
shutdown for each regulator. Other jumpers allow select-
ing internal or external soft-start, selecting the switching
L
, LT, LTC, LTM, μModule, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
phase between the two regulators and selecting external
frequency synchronizing, and forced continuous or pulse
skipping modes of operation for the VDDQ regulator only.
Terminals are provided for connecting an input supply,
output loads and voltmeters. Other terminals include
external sync input, external reference input, external
tracking input, and separate power good outputs that
pull low at start-up and when the VDDQ or VTT output is
outside a voltage window.
The LTC
®
3618 used on this board is housed in a 24-pin 4mm
×
4mm thermally enhanced QFN package. The LTC3618
is also available in a 24-pin TSSOP package.
The LTC3618 data sheet gives a complete description of
the part, operation and application information and should
be read in conjunction with this quick start guide.
Design files for this circuit board are available at
http://www.linear.com/demo
(T
A
= 25°C)
PARAMETERS
CONDITION
TYPICAL VALUE
Input Voltage Range (VIN)
2.25V to 5.5V
VDDQ Output Voltages (1.5V, 1.8V, 2.5V)
VIN = 3.3V
±2.5%
VTTR Output Voltage
VIN = 3.3V
VDDQIN • 0.5 ±2%
VTT Output Voltage
VIN = 3.3V
VTTR ±6mV
Load Regulation (Each Regulator)
VIN = 3.3V, 0 to 3A Load
5mV
Maximum Output Current (Each Regulator)
VIN = 3.3V
±3A
Switching Frequency
1MHz ±20%
Output Voltage Ripple
VIN = 3.3V, 0 to 3A Load
10mV
P-P
Efficiency
VIN = 3.3V, VDDQ = 1.8V, 2A Load
88%
Efficiency
VIN = 3.3V, VTT = 900mV, 2A Load
80.5%
