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DEMO MANUAL DC1781A
DESCRIPTION
LT3507A
Triple Monolithic Step-Down
Regulator with LDO
Demo circuit 1781A is a Triple Monolithic Step-Down Regu-
lator with LDO featuring the LT3507A. The demo circuit
is designed for 1.8V, 3.3V, 5.0V and 2.5V outputs from a
7V to 36V input. The current capability of each channel
is 2.7A, 1.5A, 1.8A and 0.3A respectively. Independent
input voltage, feedback, soft-start and power good pins
for each channel simplify complex power supply tracking/
sequencing requirements.
All three converters are either synchronized to a common
external clock input or single-resistor programmable from
250kHz to 2.5MHz using internal oscillator. At all frequen-
cies, a 180° phase shift between VOUT1 and the other two
outputs is maintained, reducing input voltage ripple and L, LT, LTC, LTM, 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
component size. Programmable frequency allows for opti-
mization between efficiency and external component size.
Each output can be independently disabled using its own
soft-start pin, or by using the SD terminal the entire part
can be placed in a low quiescent current shutdown mode.
The LT3507A data sheet 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 1781A.
Design files for this circuit board are available at
http://www.linear.com/demo
(TA = 25°C)
PARAMETER CONDITIONS VALUE
Minimum Input Voltage 7V
Maximum Input Voltage 36V
Output Voltage VOUT1 V
IN = 7~36V 1.80V ±3%
Output Voltage VOUT2 VIN = 7~36V 3.33V ±3%
Output Voltage VOUT3 VIN = 7~36V 5.0V ±3%
Output Voltage VOUT4 VIN = 7~36V 2.52V ±3%
Switching Frequency 450kHz ±10%
Maximum Output Current IOUT1 VIN = 7~36V 2.7A
Maximum Output Current IOUT2 VIN = 7~36V 1.5A
Maximum Output Current IOUT3 VIN = 7~36V 1.8A
Maximum Output Current IOUT4 VIN = 7~36V 0.3A
Voltage Ripple VOUT1 VIN = 12V, IOUT1 = 2.7A <20mV
Voltage Ripple VOUT2 VIN = 12V, IOUT2 = 1.5A <20mV
Voltage Ripple VOUT3 VIN = 12V, IOUT3 = 1.8A <20mV
Voltage Ripple VOUT4 VIN = 12V, IOUT4 = 0.3A <10mV
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DEMO MANUAL DC1781A
QUICK START PROCEDURE
Demo circuit 1781A is easy to set up to evaluate the
performance of the LT3507A. Refer to Figure 2 for proper
measurement equipment setup and follow the procedure
below:
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 3 for
proper scope probe technique.
1. With power off, connect the input power supply to VIN
and GND.
2. Turn on the power at the input.
NOTE. Make sure that the input voltage does not ex-
ceed 36V.
3. Check for the proper output voltages.
NOTE. If there is no output, temporarily disconnect
the load to make sure that the load is not set too high.
4. Once the proper output voltages are established, adjust
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
Figure 1. DC1781A Buck Channel Efficiency at VIN = 12V, f = 450kHz
LOAD CURRENT (A)
0.3
0
EFFICIENCY (%)
90
80
70
60
50
40
30
20
10
100
0.6 1.8 2.1 2.4 2.70.9 1.2
DC1781A F01
1.5
VOUT1 = 5.0V
VOUT1 = 3.3V
VOUT1 = 1.8V
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DEMO MANUAL DC1781A
QUICK START PROCEDURE
Figure 2. DC1781A Proper Equipment Setup
Figure 3. Measuring Input or Output Ripple
V
IN
GND
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DEMO MANUAL DC1781A
QUICK START PROCEDURE
SYNC FUNCTION
Install a 10k R20 resistor if the board is synchronized from
an external signal generator.
Figure 4. Cut Line for the EMI Filter Installation
EMI FILTER
Install EMI filters on the backside of the DC1781A, how-
ever, a trace cut is required for the insertion of the option
circuit. See Figure 4 for the cut line.
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DEMO MANUAL DC1781A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 3 CIN1, CIN2, CIN3 CAP., X7R, 2.2μF, 50V, 10%, 1210 TDK, C3225X7R1H225K
2 1 C1 CAP., X7R, 0.47μF, 25V, 10%, 0603 MURATA, GRM188R71E474KA12D
3 2 C2, C9 CAP., X7R, 0.22μF, 25V, 10%, 0603 TDK, C1608X7R1E224K
4 2 C3, C10 CAP., X5R, 47μF, 10V, 20%, 1206 TAIYO YUDEN, LMK316BJ476ML-T
5 1 C4 CAP., X5R, 22μF, 6.3V, 20%, 1206 TAIYO YUDEN, JMK316BJ226ML
6 3 C5, C6, C11 CAP., X7R, 680pF, 50V, 10%, 0402 AVX, 04025C681KAT
7 4 C7, C8, C13, C20 CAP., X5R, 0.1μF, 10V, 10%, 0402 AVX, 0402ZD104KAT
8 1 C12 CAP., X5R, 2.2μF, 6.3V, 20%, 0603 TAIYO YUDEN, JMK107BJ225MA
9 3 C15, C17, C19 CAP., NPO, 47pF, 50V, 5%, 0402 AVX, 04025A470JAT
10 1 D4 DIODE, SCHOTTKY, B340A, SMA-DIODE DIODES INC., B340A
11 2 D5, D6 DIODE, SCHOTTKY, B240A, SMA-DIODE DIODES INC., B240A
12 3 D7, D8, D9 DIODE, SCHOTTKY, CMDSH-4E, SOD323 CENTRAL SEMI., CMDSH-4E
13 1 L1 IND., 4.7μH NIC, NPIM74C4R7MTRF
14 1 L2 IND., 8.2μH NIC, NPIM74C8R2MTRF
15 1 L3 IND., 10μH NIC, NPIM74C100MTRF
16 1 Q1 XTOR, NPN, 50V LOW SATURATION, MLP322 ZETEX, ZXTCM322TA
17 5 R1, R2, R3, R15, R22 RES., CHIP, 100k, 1/16W, 1%, 0402 YAGEO, RC0402FR-07100KL
18 1 R4 RES., CHIP, 12.4k, 1/16W, 1%, 0402 VISHAY, CRCW040212K4FKEA
19 1 R5 RES., CHIP, 31.6k, 1/16W, 1% 0402 VISHAY, CRCW040231K6FKEA
20 3 R6, R7, R11 RES., CHIP, 20k, 1/16W, 1% 0402 VISHAY, CRCW040220K0FKEA
21 3 R8, R9, R23 RES., CHIP, 10k, 1/16W, 1% 0402 YAGEO, RC0402FR-0710KL
22 1 R10 RES., CHIP, 53.6k, 1/16W, 1% 0402 VISHAY, CRCW040253K6FKEA
23 1 R12 RES., CHIP, 10.2k, 1/16W, 1% 0402 NIC, NRC04F1022TRF
24 1 R13 RES., CHIP, 1.07k, 1/16W, 1% 0402 YAGEO, RC0402FR-071K07L
25 1 R14 RES., CHIP, 49.9k, 1/16W, 1% 0402 VISHAY, CRCW040249K9FKEA
26 1 R16 RES., CHIP, 499, 1/16W, 1% 0402 AAC, CR05-4990FM
27 1 R17 RES., CHIP, 18.2k, 1/16W, 1% 0402 VISHAY, CRCW040218K2FKEA
28 1 R18 RES., CHIP, 3.32k, 1/16W, 1% 0402 VISHAY, CRCW04023K32FKEA
29 1 R19 RES., CHIP, 107k, 1/16W, 1% 0402 AAC, CR05-1073FM
30 1 U1 I.C., LT3507EUHF, QFN38UHF LINEAR TECH., LT3507EUHF
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DEMO MANUAL DC1781A
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Additional Demo Board Circuit Components
1 1 CIN4 CAP., ELECTROLYTIC, 22μF, 50V SANYO, 50CE22LX
2 0 C14, C16, C18, C28 CAP., 0402 OPT
3 0 C21 CAP., X7R, 0.01μF, 50V, 10%, 0603 OPT
4 0 C22 CAP., X7R, 2.2μF, 50V, 10%, 1210 OPT
5 0 C23 CAP., ELECTROLYTIC, 22μF 50V OPT
6 4 C24-C27 CAP., X5R, 1μF, 10V, 10%, 0603 MURATA, GRM188R61A105K
7 0 C29 CAP., 1206 OPT
8 0 D1, D2, D3 DIODE, SCHOTTKY, CMDSH-4E, SOD323 OPT
9 0 FB1 BEAD, 1206 OPT TAIYO YUDEN, FB MJ3216HS800
10 0 L4 IND., 22μH, OPT VISHAY, IHLP4040DZER220-M01
11 0 R20 RES., CHIP, 0402 OPT
12 0 R21 RES., CHIP, 0603 OPT
Hardware-For Demo Board Only:
1 10 E1, E2, E6-E9, E12-E15 TP, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0
2 9 E3, E4, E5, E10, E11, E16-E19 TP, TURRET, 0.064" MILL-MAX, 2308-2-00-44
PARTS LIST
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DEMO MANUAL DC1781A
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 DC1781A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2011
LT 0711 • PRINTED IN USA
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.).
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customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
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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 applica-
tion engineer.
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Copyright © 2004, Linear Technology Corporation
