Linear Technology DC1736A Quick setup guide

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DEMO MANUAL DC1736A
DESCRIPTION
LT3975
42V, 2.5A, 2.7µA Micropower
Buck Regulator
Demonstration circuit 1736A is a monolithic step-down
DC/DC switching regulator featuring the LT
®
3975. The
demo circuit is designed for 3.3V, 2.5A output from a 4.3V
to 42V input. The wide input range of the LT3975 allows
a variety of input sources, such as automotive batteries
and industrial supplies. The switching frequency can be
programmed either via oscillator resistor or external clock
up to 2MHz. When the circuit is synchronized to an external
clock connected to the SYNC terminal, the RTresistor (R5)
should be chosen to set the LT3975 internal switching
frequency at least 20% below the lowest synchroniza-
tion input frequency. Low ripple Burst Mode
®
operation
increases the efficiency at the light load while keeping the
output ripple below 15mV.
The circuit consumes only 2.7A of quiescent current.
The LT3975 internal boost diode and loop compensation
reduce the components count and solution size. The cur-
rent mode control scheme creates fast transient response
and good loop stability. The LT3975 is in shutdown when L, LT, LTC, LTM, µModule, 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.
PERFORMANCE SUMMARY
the EN pin is low and active when the pin is high. The
threshold of the EN pin is accurate at 1.02V with 60mV
of hysteresis. Users can populate R7 and R8 to provide a
programmable undervoltage lockout. Duringa short-circuit
fault, the LT3975 has current limit foldback to limit the
power dissipation.
The LT3975 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this demo manual
for demo circuit 1736A. The LT3975 is assembled in a
16-lead plastic MSOP package with an exposed pad for
low thermal resistance. Proper board layout is essential
for both proper operation and maximum thermal perfor-
mance. See the data sheet section PCB Layout and High
Temperature Considerations.
Design files for this circuit board are available at
http://www.linear.com/demo
TA= 25°C
PARAMETER CONDITIONS VALUE
Minimum Input Voltage 4.3V
Maximum Input Voltage 42V
Output Voltage, VOUT VIN = 4.3V ~ 42V 3.3V ± 3%
Switching Frequency RT= 78.7k 600kHz ±20%
Maximum Output Current, IOUT VIN = 4.3V ~ 42V 2.5A
Typical Efficiency VIN = 12V, IOUT = 2.5A 82.1%
Typical Output Voltage Ripple VIN = 12V, IOUT = 2.5A, 25MHz BW 20mV

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DEMO MANUAL DC1736A
QUICK START PROCEDURE
Demonstration circuit 1736A is easy to set up to evalu-
ate the performance of the LT3975. 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 the proper
scope technique.
1. Place JP1 on the ON position.
2. Place JP2 on the RT FREQ position.
3. With power off, connect the input power supply to VIN
and GND.
4. With power off, connect load from VOUT to GND.
5. Turn on the power at the input.
NOTE.Makesurethattheinputvoltagesdonotexceed42V.
6. Check for the proper output voltage (3.3V).
NOTE.If there is no output, temporarily disconnect the load
to make sure that the load is not set too high or is shorted.
7. Once the proper output voltages are established, adjust
the load within the operating ranges and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
8. An external clock can be added to the SYNC terminal
when SYNC function is used (JP2 on the SYNC posi-
tion). Please make sure that the SYNC frequency is at
least 20% higher than the set switching frequency. See
the data sheet section Synchronization.
LOAD CURRENT (A)
0
EFFICIENCY (%)
65
70
75
1.5 2.5
DC1735A F01
60
55
50 0.5 1 2
80
85
90
VOUT = 3.3V
VIN = 12V
fSW = 600kHz
Figure 1. Efficiency vs Load Current

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DEMO MANUAL DC1736A
QUICK START PROCEDURE
Figure 2. Proper Measurement Equipment Setup
Figure 3. Measuring Output Ripple
V
+
–
+
–
A
–+
VOUT LOAD
V
+
–
VIN
+
–
A
–+

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DEMO MANUAL DC1736A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 C1 Cap., X5R, 47µF 10V 20% 1210 TDK, C3225X5R1A476M
2 1 C2 Cap., X5R, 0.47µF 25V 10% 0603 TDK, C1608X5R1E474K
3 1 C3 Cap., X5R, 10µF 50V 10%, 1210 TDK, C3225X5R1H106K
4 1 C5 Cap., C0G, 10pF 50V 10%, 0402 TDK, C1005C0G1H100D
5 1 C6 Cap., X7R, 10nF 25V 10%, 0402 TDK, C1005X7R1E103K
6 1 D1 Diode, Scholtky, PowerDi5 DIODE INC, PDS360-13
7 1 L1 IND, 3.3µH VISHAY, IHLP2020CZER3R3M01
8 1 R1 Res., Chip, 1.00M 1/16W 1% 0402 VISHAY, CRCW04021M00FKED
9 1 R2 Res., Chip, 576k 1/16W 1% 0402 VISHAY, CRCW0402576KFKED
10 1 R5 Res., Chip, 78.7k 1/16W 1% 0402 VISHAY, CRCW040278K7FKED
11 1 R6 Res., Chip, 200k 1/16W 1% 0402 VISHAY, CRCW0402200KFKED
12 1 U1 I.C., MSE16 LINEAR TECH., LT3975EMSE
Additional Circuits
13 1 C4 Cap., Elect.,100µF 50V 10% SUN ELECT, 50CE100BS
14 1 C7 Cap., X5R, 1µF 16V 20% 0603 AVX, 0603YD105MAT
15 0 R7, R8 Res., 0402 OPT
Hardware—For Demo Board Only
16 7 E1, E2, E3, E4, E5, E6, E7 Turret, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0
17 2 JP1, JP2 JMP, 1X3-079 SAMTEC, TMM-103-02-L-S
18 2 Shunt Shunt, 2mm Ctrs. SAMTEC, 2SN-BK-G

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DEMO MANUAL DC1736A
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 DC1736A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2012
LT 0712 • 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.).
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 applica-
tion engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation

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