DEMO MANUAL DC1726
LTC3618EUF
Dual ±3A Synchronous Buck
Regulator for DDR Termination
DESCRIPTION
Demonstration circuit 1726 is a dual high efficiency
monolithic step-down (buck) DC/DC switching regulator
designed for double-data-rate (DDR) memory termination 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 sensitive applications.
Jumpers are included for selecting either internal or external compensation and jumpers for low quiescent current
shutdown for each regulator. Other jumpers allow selecting internal or external soft-start, selecting the switching
PERFORMANCE SUMMARY
PARAMETERS
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
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.
(TA = 25°C)
CONDITION
Input Voltage Range (VIN)
TYPICAL VALUE
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
10mVP-P
Efficiency
VIN = 3.3V, VDDQ = 1.8V, 2A Load
88%
Efficiency
VIN = 3.3V, VTT = 900mV, 2A Load
80.5%
dc1726f
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DEMO MANUAL DC1726
QUICK START PROCEDURE
Demonstration circuit 1726 allows the user to quickly
evaluate the performance of the LTC3618. Refer to Figure 2
for proper measurement equipment setup and follow the
procedure below
7. Verify that the VTT output voltage is equal to the VTTR
voltage ±6mV. The error voltage can be read differentially
by placing the meter leads between the VTTR and VTT
terminals
1. Place jumpers in the following positions.
8. To evaluate sourcing current from VDDQ or VTT outputs,
connect a suitable 10W load in series with an ammeter
between each output terminal and ground. Resistor.
See Figure 2 for resistor connections and resistor value
equation. Verify that the output voltages still meet the
specifications shown in the Performance Summary
section.
JP1
VOUT 1 Select
1.5V
JP5
Track/SS
INT SS
JP6
PHASE
180°
JP8
MODE
FCM
JP9
COMP 1
INT
JP10
COMP 2
INT
JP11
RUN 1
ON
JP12
RUN 2
ON
JP13
VDDQIN
VDDQ
2. With the input power supply turned down and switched
off, connect the supply and digital voltmeters as shown
in Figure 2.
3. Switch on the input supply and adjust for approximately
3.3V on VIN.
4. Verify that the VDDQ output voltage is within the limits shown in the table on page 1 for each of the three
output voltages as selected by JP1, JP2 and JP2. Note:
moving the jumper to JP3 sets VDDQ to the internal
reference voltage of 600mV. Other output voltages can
be programmed by selecting a suitable resistor for R9.
5. To verify VDDQ output voltage tracking. Move JP5 to the
TRACK position (upper) and remove all VOUT1 SELECT
jumpers. Apply an external reference voltage between
100mV and 600mV to TRACK1 terminal. Verify that the
VDDQ output is within ±11mV of the external reference
voltage.
6. Move JP5 to the INT SS position (lower) and place
a jumper on JP2 (1.8V). Verify that the VTTR output
voltage is equal to VDDQ • 0.5 ±2%. Additional VDDQ
voltages can be selected using JP1 or JP3.
9. To evaluate sinking current into the VTT output, connect
a suitable 10W load resistor in series with an ammeter
between the VTT output and the VIN terminals. Verify
that the output voltages meet the specifications in the
Performance Summary section.
The many jumpers on this board allow the user to evaluate
the various features of the LTC3618. Jumpers are used to
select VDDQ output voltages, switch phasing, soft-start,
tracking, on/off, operating mode and compensation. Refer
to the data sheet for information on these functions.
Extra pads are located on the top and bottom of the board
for adding additional input and output capacitors if desired.
NOTE. When measuring the input or output voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. Measure the input or output voltage
ripple by touching the probe tip directly across the VIN or
VOUT and GND terminals. See Figure 1 for proper scope
probe technique.
Figure 1.
dc1726f
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DEMO MANUAL DC1726
QUICK START PROCEDURE
VIN - VTT
Rsinking = ––––––––
ILOAD
Connection for VTT Sinking Current
VTT
Rsourcing = –––––
ILOAD
Sourcing
10W Load
Resistor
VTT
Output
-
R
+
A
V
-
+ +
-
-
V
5V @ 5A
Input Power Supply
- (set to 3.3V)
V VDDQ Output
+
+
+
VTTR V
Output
-
GND
Figure 2. Proper Measurement Equipment Setup
VTT COMP
VDDQ COMP
Ext Sync Input
PHASE Select
Ext REF Input
GND
MODE Select
Tracking Input
+VIN
GND
GND
GND
VTT Output
VDDQ Output
GND
VDDQ Vout Select
VDDQ ON/OFF
VDDQ Power Good
VTTR Output
VTT ON/OFF
VTT Power Good
Figure 3. Jumper and Terminal Descriptions
VDDQ
Output
VDDQ
Regulator
±3A
VDDQ
TRACK
/SS
VTTR
Output
JP13
SVIN
FB1
1%
VTTR
±10mA
VDDQIN
600mV, ±1.3% Ref
TRACK
Input
EXT
REF
Input
Program
VDDQ
R
VTT
Regulator
±3A
VTT
Output
R
9775RXWSXW 9''4±2%
VTT output = VTTR ±6mV
VDDQ output = VTRACK ±11mV
P9WRP9
VDDQ output = programmed voltage ±
Figure 4. Simplified Block Diagram of Demo Board Showing Output Voltages and Tolerances
dc1726f
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DEMO MANUAL DC1726
PARTS LIST
ITEM
QTY
REFERENCE
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Required Circuit Components
1
1
C3
CAP., X7R, 0.01μF, 50V, 20% 0603
AVX, 06035C103MAT2A
2
4
CIN1, CIN2, CIN3, CIN4
CAP., X7R, 22μF, 6.3V, 20% 1206
AVX, 12066C226MAT2A
3
2
COUT1, COUT2
CAP., X5R, 47μF, 6.3V, 20% 1210
AVX, 12106D476MAT2A
4
2
L1, L2
INDUCTOR, 1μH
COILCRAFT, XFL4020-102MEB
5
1
RT
RES., CHIP, 402k, 1/16W, 5% 0603
VISHAY, CRCW0603402KFKEA
6
1
R1
RES., CHIP, 845k, 1/16W, 1% 0603
VISHAY, CRCW0603845KFKEA
7
1
R3
RES., CHIP, 562k, 1/16W, 1% 0603
VISHAY, CRCW0603562KFKEA
8
1
U1
IC., LTC3618EUF UF-24
LINEAR TECH., LTC3618EUF#PBF
CAP., C0G, 10pF, 25V, 20% 0603
AVX, 06033A100MAT2A
Additional Demo Board Circuit Components
1
3
C1, C2, CFFW1
2
1
C4
CAP., X7R, 0.1μF, 50V, 20% 0603
AVX, 06035C104MAT2A
3
1
CIN6
CAP., TANT., 100μF 10V, 20% 7343
AVX, TPSW107M010Y0150
4
0
COUT5, COUT6, CIN5 (OPT)
CAP., 7343
5
1
CITH1
CAP., NPO, 470pF, 25V, 20% 0805
AVX, 08053A471MAT2A
6
1
CITH2
CAP., NPO, 680pF, 25V, 20% 0805
AVX, 08053A681MAT2A
7
2
COUT3, COUT4
CAP., X7R, 10μF, 6.3V, 20% 0805
AVX, 08056C106MAT2A
8
0
COUT7, COUT8 (OPT)
CAP., 1210
9
1
CSS1
CAP., X7R, 0.01μF, 50V, 20% 0603
AVX, 06035C103MAT2A
10
1
CFILT
CAP., X7R, 1μF, 10V, 20% 0603
AVX, 0603ZD105MAT2A
11
1
RFILT
RES., CHIP, 24Ω, 1/16W, 5% 0603
VISHAY, CRCW060324R0JNEA
12
1
RITH1
RES., CHIP, 15.4k, 1/16W, 1% 0805
VISHAY, CRCW080515K4FKEA
13
1
RITH2
RES., CHIP, 10k, 1/16W, 1% 0805
VISHAY, CRCW080510K0FKEA
14
1
RTR1
RES., CHIP, 100k, 1/16W, 1% 0603
VISHAY, CRCW0603100KFKEA
15
2
RPG1, RPG2
RES., CHIP, 100k, 1/16W, 5% 0603
VISHAY, CRCW0603100KJNEA
16
1
RSS1
RES., CHIP, 4.7M, 1/16W, 5% 0603
VISHAY, CRCW06034M70JNEA
17
0
RTR3, R9, RM1, RM2 (OPT)
RES., 0603
18
1
R5
RES., CHIP, 422k, 1/16W, 1% 0603
VISHAY, CRCW0603422KFKEA
19
1
R7
RES., CHIP, 267k, 1/16W, 1% 0603
VISHAY, CRCW0603267KFKEA
Hardware/Components (For Demo Board Only)
1
2
JP11, JP12
HEADER, 3 PIN 0.079 SINGLE ROW
SAMTEC, TMM-103-02-L-S
2
4
JP5, JP6, JP8, JP13
HEADER, 2x3 PIN 0.079 DOUBLE ROW
SAMTEC, TMM-103-02-L-D
3
2
JP9, JP10
HEADER, 2x2 PIN 0.079 DOUBLE ROW
SAMTEC, TMM-102-02-L-D
4
4
JP1-JP4
HEADER, 2 PIN 0.079 SINGLE ROW
SAMTEC, TMM-102-02-L-S
5
9
XJP1, XJP5, XJP6, XJP8-XJP13
SHUNT, .079" CENTER
SAMTEC, 2SN-BK-G
6
14
E1-E14
TESTPOINT, TURRET, 0.094" pbf
MILL-MAX, 2501-2-00-80-00-00-07-0
7
4
MH1-MH4
STANDOFF, NYLON, 0.25, 1/4"
KEYSTONE, 8831 (SNAP ON)
dc1726f
4
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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DEMO MANUAL DC1726
SCHEMATIC DIAGRAM
dc1726f
5
DEMO MANUAL DC1726
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union
directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims
arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.
Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
dc1726f
6
Linear Technology Corporation
LT 0811 • PRINTED IN USA
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(408) 432-1900
●
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