DEMO MANUAL DC1750A
LT8611
42V, 2.5A Micropower Synchronous
Step-Down Regulator with Current Sense
DESCRIPTION
Demonstration circuit 1750A is a 42V, 2.5A micropower
synchronous step-down regulator with current sense
featuring the LT®8611. The LT8611 is a compact, high efficiency, high speed synchronous monolithic step-down
switching regulator that consumes only 2.5μA of quiescent
current when output is regulated at 3.3V. Top and bottom
power switches, compensation components and other
necessary circuits are inside of the LT8611 to minimize
external components and simplify design.
The demonstration circuit has output current limit set at
2.5A by default. The current limit can be moved to the input
side for application where input supply current is limited,
such as energy harvesting application. ICTRL and IMON on
the board set and monitor the regulated current respectively.
The SYNC pin on the demo board is grounded by default
for low ripple Burst Mode® operation. To synchronize to an
external clock, move JP1 to SYNC and apply the external
clock to the SYNC turret. Once JP1 is on SYNC position,
a DC voltage of higher than 2V or INTVCC can be applied
to the SYNC turret for pulse skipping operation. Figure 1
shows the efficiency of the circuit at 12V input.
The demo board has an EMI filter installed. The EMI
performance of the board is shown on Figure 2. Figure 3
shows the EMI performance of the board running at 1MHz
switching frequency. The limit in Figure 2 and Figure 3 is
EN55022 Class B. Both figures show the circuit passes
the test with a wide margin. To use the EMI filter, the input
should be tied to VEMI, not VIN.
The LT8611 datasheet gives a complete description of the
part, operation and application information. The data sheet
must be read in conjunction with this quick start guide for
demo circuit 1750A.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
12VIN to 3.3VOUT Efficiency
100
EFFICIENCY (%)
95
90
85
80
0
0.5
1
1.5
LOAD CURRENT (A)
2
2.5
1750 F01
Figure 1. LT8611 Efficiency from 12V to 3.3V (R5 = 0)
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DEMO MANUAL DC1750A
DESCRIPTION
Figure 2. LT8611 Demo Circuit EMI Performance,
Switching Frequency = 700kHz
Figure 3. LT8611 Demo Circuit EMI Performance,
Switching Frequency = 1MHz
PERFORMANCE SUMMARY
(TA = 25°C)
SYMBOL
PARAMETER
CONDITIONS
VIN
Input Supply Range
VOUT
Output Voltage
IOUT
Maximum Output Current
FSW
Switching Frequency
EFE
Efficiency at DC
MIN
TYP
3.8
3.168
MAX
42
3.3
3.465
2.5
630
IOUT = 1A, R5 = 0
700
93
UNITS
V
V
A
770
kHz
%
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DEMO MANUAL DC1750A
QUICK START PROCEDURE
Demonstration circuit 1750A is easy to set up to evaluate the performance of the LT8611. Refer to Figure 4 and
Figure 5 for proper measurement equipment setup and
follow the procedure below:
2. With power off, connect the load VOUT and GND.
1. With power off, connect the input power supply to VIN
and GND.
5. Carefully evaluate other design parameters as needed.
3. Check JP1 setting
4. Turn on the power at the input.
Figure 4. Proper Measurement Equipment Setup
Figure 5. Measure Output Ripple
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DEMO MANUAL DC1750A
PARTS LIST
ITEM
QTY
REFERENCE
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Required Circuit Components
1
1
C2
CAP, CER 4.7μF 50V 1206
TAIYO YUDEN UMK316BJ475KL
2
1
C4
CAP, CER 0.22μF 16V 0603
TAIYO YUDEN EMK107BJ224KA-T
3
1
C6
CAP, CER 47μF 10V 1210
MURATA, GRM32ER71A476K
4
1
C7
CAP, CER 1.0μF 25V 0603
MURATA GRM188R71E105K
5
1
C8
CAP, CER 0.1μF 0402
AVX, 0402YD104KAT2A
6
1
C9
CAP, CER 4.7pF 25V 0402
AVX, 04023A4R7CAT
7
1
L1
IND, 4.7μH
COILTRONICS HCM0703-4R7-R
8
1
R5
RES, 0.02Ω 1% 1206
VISHAY, WSL1206R0200FEA
9
1
R8
RES, 60.4k 1% 0402
VISHAY, CRCW040260K4FKED
10
1
R9
RES, 49.9k 1% 0402
VISHAY, CRCW040249K9FKED
11
2
R10, R12
RES, 1M 1% 0402
VISHAY, CRCW04021M00FKED
12
1
R11
RES, 412k 1% 0402
VISHAY, CRCW0402412KFKED
13
1
U1
IC, LT8611EUDD QFN24EUDD
LINEAR TECH.CORP. LT8611EUDD
Additional Demo Board Circuit Components
1
1
C1
CAP, ALUM 22μF 63V
SUNCON 63CE22BS
2
1
C10
CAP, CER 4.7μF 50V 1206
TAIYO YUDEN UMK316BJ475KL
3
1
C3
CAP, CER 4.7μF 50V 1206
MURATA, GRM31CR71H475K
4
0
C5
CAP, OPT 0402
OPT
5
1
FB1
FERRITE BEAD 0805
TDK, MPZ2012S221A
6
1
L2
IND, 4.7μH
VISHAY, IHLP2020BZ-ER4R7M01
7
1
R1
RES, 0Ω 1206
AAC CJ18-000M
8
0
R2, R3, R4
RES, OPT 0402
OPT
9
2
R6, R7
RES, 0Ω 0402
AAC, CJ05-000M
Hardware/Components (For Demo Board Only)
1
9
E1-E7, E9, E10
TESTPOINT TURRET 0.094"
MILL-MAX-2501-2
2
1
JP1
HEADER 1X3 0.079"
SAMTEC, TMM-103-02-L-S
3
1
XJP1
SHUNT, 0.079" CENTER
SAMTEC, 2SN-BK-G
4
4
MH1-MH4
STAND-OFF, NYLON 0.50" TALL
KEYSTONE, 8833 (SNAP ON)
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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 DC1750A
SCHEMATIC DIAGRAM
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DEMO MANUAL DC1750A
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
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Linear Technology Corporation
LT 0512 • PRINTED IN USA
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●
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