Linear Technology DC1771A Quick setup guide

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DEMO MANUAL DC1771A
DESCRIPTION
LTC3867EUF
Synchronous Buck Converter
with Remote Sensing
Demonstration circuit 1771A is a single output synchro-
nous buck converter featuring the LTC
®
3867EUF with a
24-lead 4mm ×4mm QFN package.
The DC1771A is configured with a sense resistor. DCR
sensing circuit is optional. Using the inductor’s DCR as
the sense element instead of the on-board sense resistor
saves cost and board space while improving full-load
efficiency over 2%, though the sense resistor provides a
more accurate current limit.
The board has a lot of features including an internal 5V
linear regulator for bias, output voltage remote sense,
programmable nonlinear control to improve load tran-
sient performance, programmable thermal shutdown,
L, LT, LTC, LTM, Burst Mode, 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
optional temperature compensated DCR sense circuit, a
mode selector that allows the converter to run in CCM,
pulse-skippingorBurstMode
®
operation.Synchronization
to an external clock is also possible.
The input voltage range is from 4.5V to 14V. The LTC3867
data sheet gives a complete description of the part, op-
eration and application information and must be read in
conjunction with this demo manual for DC1771A.
Design files for this circuit board are available at
http://www.linear.com/demo
(TA= 25°C)
PARAMETER CONDITIONS/NOTES VALUE
Input Voltage Range 4.5V ~ 14V
Output Voltage VOUT VIN = 4.5V ~ 14V, IOUT = 0A ~ 15A, JP3: CCM 1.5V ±2% (1.470V ~ 1.530V)
Default Operating Frequency 400kHz
External Clock Sync. Frequency Range 400kHz to 780kHz
Typical Full-Load Efficiency (See Figure 4) VIN = 12V, VOUT = 1.5V, IOUT1 = 15A, fSW = 400kHz 88.3%

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DEMO MANUAL DC1771A
QUICK START PROCEDURE
Figure 1. Test Setup of the DC1771A
Demonstration circuit DC1771A is easy to set up to evalu-
ate the performance of the LTC3867EUF. Please refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
1. Place jumpers in the following positions for a typical
application:
JP2 On
JP3 CCM
2. With power off, connect the input power supply, load
and meters as shown in Figure 1. Preset the load to 0A
and VIN supply to 12V.
3. Turn on the power supply at the input.
NOTE: Make surethat the inputvoltage does notexceed 14V.
4. Check the output voltage. The output voltage should
be between 1.470V and 1.530V.
Once the proper output voltage is established, adjust the
load within the operating range and observe the output
voltage regulation, output voltage ripple, efficiency and
other parameters.
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 2 for proper scope
probe technique.
5. Change JP3 jumper position to select different opera-
tion modes. Set jumper to CCM, BURST or P.S. position
toe set forced continuous conduction, burst or pulse-
skipping mode respectively. For synchronizing to an
external clock source, set the jumper to BURST position
and apply the clock signal to MODE/PLLIN turret.

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DEMO MANUAL DC1771A
RAIL TRACKING
Figure 2. Measuring Input or Output Ripple Across Terminals or Directly Across Bulk Capacitor
Figure 3. Measured Efficiency
Demonstration circuit 1771A is configured for an onboard
soft-start circuit. The soft-start ramp rate can be adjusted
by changing the value of C24. Demonstration circuit 1771A
can also be modified to track an external reference. Refer
to Table 1 for tracking options and to the data sheet for
more details.
Table 2. Output Tracking Options
TRK/SS RESISTORS AND CAPACITOR RAIL TRACKING
CONFIGURATION R32 R35 C24 TRK/SS PIN
Soft-Start Without Tracking (Default) 0Ω Open 0.1μF OPEN
VOUT Equals External Ramp 0Ω Open Open External Reference Applied
VOUT Tracking Scaled External Ramp Resistor Divider Open External Reference Applied
LOAD CURRENT (A)
0
EFFICIENCY (%)
40
50
60
915
30
20
10 36 12
70
80
90
CCM
BURST
P. S.
VIN = 12V
VOUT = 1.5V
fSW = 400kHz

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DEMO MANUAL DC1771A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 2 CIN3, CIN6 CAP, X5R 22μF 20% 25V 1210 TAIYO YUDEN TMK325BJ226MM-T
2 2 COUT1, COUT3 CAP, 330μF 20% 2.5V POSCAP 7343 SANYO 2R5TPE330MF
3 2 COUT4, COUT9 CAP, X5R 100μF 20% 6.3V 1210
4 2 C19, C33 CAP, X5R 1μF 10% 25V 0603 TDK C1608X5R1E105K
5 2 C24, C30 CAP, X7R 1nF 10% 25V 0603 AVX 06033C102KAT
6 1 C25 CAP, X5R 0.1μF 10% 10V 0603 AVX 0603ZD104KAT
7 1 C28 CAP, C0G 100pF 5% 50V 0603 TDK C1608C0G1H101J
8 1 C32 CAP, C0G 10pF 5% 50V 0603 TDK C1608C0G1H100J
9 1 C27 CAP, X5R 4.7μF 10% 10V 0603
10 1 C26 CAP, C0G 470pF 5% 50V 0603 TDK C1608C0G1H471J
11 1 D2 DIODE, CMDSH-3 SOD-323 CENTRAL SEMI CMDSH-3-LTC
12 1 L1 IND., 0.4μH VITEC 59PR9875
13 1 Q1 XSTR, MOSFET LFPAK RENESAS RJK0305DPB
14 1 Q3 XSTR, MOSFET LFPAK RENESAS RJK0329DPB
15 1 RSNSE RES, 0.002Ω 5% 1/4W 2512 PANASONIC ERJM1WTJ2MOU
16 1 U1 IC, LTC3867EUF,QFN 4mm x 4mm
17 4 R32, R36, R56, R58 RES, 0Ω JUMPER 0603 VISHAY CRCW06030000Z0EA
18 2 R9, R10 RES, 100Ω 1%, 1/10W 0603 VISHAY CRCW0603100RFKEA
19 1 R33 RES, 100k 1% 1/10W 0603 VISHAY CRCW0603100KFKEA
20 1 R37 RES, 2.2Ω 5% 1/10W 0603 VISHAY CRCW06032R20JNEA
21 1 R38 RES, 49.9k 1% 1/10W 0603 VISHAY CRCW060349K9FKED
22 1 R39 RES, 75k 1% 1/10W 0603 VISHAY CRCW060375KFKEA
23 1 R40 RES, 10k 1% 1/10W 0603 VISHAY CRCW060310KFKEA
24 1 R51 RES, 37.4KΩ 1% 1/10W 0603 VISHAY CRCW060337K4FKEA
25 6 R49, R50, R53, R57, R59, PTC RES, 10Ω 1% 1/10W 0603 VISHAY CRCW060310R0FKEA
Additional Demo Board Circuit Components
1 1 CIN1 CAP, 150μF 20% 16V SANYO 16SVP150M
2 8 E1, E2, E4-E11 TESTPOINT, TURRET, 0.094" PBF MILL-MAX, 2501-2-00-80-00-00-07-0
3 4 E3, E12-E14 JACK BANANA KEYSTONE, 575-4
Hardware-For Demo Board Only
1 1 JP3 HEADER 4-PIN 0.079 SINGLE ROW SAMTEC, TMM104-02-L-S
2 1 JP2 HEADER 3-PIN 0.079 SINGLE ROW SAMTEC, TMM103-02-L-S
3 2 XJP2, XJP3 SHUNT, 0.079" CENTER SAMTEC, 2SN-BK-G
4 4 (STAND-OFF) STAND-OFF, NYLON 0.50" KEYSTONE, 8832(SNAP ON)

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DEMO MANUAL DC1771A
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
SCHEMATIC DIAGRAM

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DEMO MANUAL DC1771A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2011
LT 0811 • PRINTED IN USA
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in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
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