Linear Technology DC1848A User manual

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dc1848af
DEMO MANUAL DC1848A
Description
LT3976
40V, 5A, 2MHz Step-Down Switching Regulator
with 3.3µA Quiescent Current
Demonstrationcircuit1848Ais amonolithicstep-downDC/
DC switching regulator featuring the LT3976. The LT3976
is a compact, high efficiency, high speed monolithic step-
down switching regulator that consumes only 3.3μA of
quiescent current. The demo circuit is designed for 3.3V,
5A output from a 4.3V to 40V input. The switching fre-
quency can be programmed either via oscillator resistor or
external clock up to 2MHz. To synchronize to an external
clock, move JP2 to SYNC and apply the external clock to
the SYNC turret. The RTresistor (R5) should be chosen
to set the LT3976 internal switching frequency at least
20% below the lowest synchronization input frequency.
Low ripple Burst Mode
®
operation increases the efficiency
at the light load while keeping the output ripple below
15mV. The SYNC pin on the demo board is grounded by
default for low ripple burst mode operation.
The LT3976 is in shutdown when 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 under
voltage lockout. A low dropout voltage of 500mV is main-
tainedwhen the input voltagedropsbelow the programmed
performance summary
output voltage. During a short circuit fault, the LT3976
has current limit foldback to limit the power dissipation.
The demo board has an EMI filter installed. The EMI per-
formance of the demo board is shown on Figure 2. The
limit in Figure 2 is EN55022 Class B. The figure shows
the circuit passes the test with a wide margin. To use the
EMI filter, the input should be tied to VEMI, not VIN. VEMI
pad is on the back of the demo board.
The LT3976 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 1848A. The LT3976 is assembled in a
16-lead plastic MSOP and 24-lead 5mm × 3mm QFN
packages with an exposed pad for low thermal resistance.
Proper board layout is essential for both proper operation
and maximum thermal performance. See the data sheet
sections for details.
Design files for this circuit board are available at
http://www.linear.com/demo
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.
Specifications are at TA= 25°C
PARAMETER CONDITIONS VALUE
Minimum Input Voltage 4.3V
Maximum Input Voltage 40V
Output Voltage VOUT VIN = 4.3V ~ 40V 3.3V ± 3%
Switching Frequency RT= 130k 400kHz ± 20%
Guaranteed Maximum Output Current IOUT VIN = 4.3V ~ 40V 5A
Typical Efficiency VIN = 12V, IOUT = 5A 82.1%
Typical Output Voltage Ripple VIN = 12V, IOUT = 5A 20mV

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DEMO MANUAL DC1848A
Quick start proceDure
Demonstration circuit 1848A is easy to set up to evalu-
ate the performance of the LT3976. Refer to Figure 3 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 4 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. Make sure that the input voltage does not
exceed 40V.
4. With power off, connect load from VOUT to GND.
5. Turn on the power at the input.
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 voltage is 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.
performance summary
LOAD CURRENT (A)
0
EFFICIENCY (%)
87
85
84
82
83
86
81
80 20.5
DC1848A F01
51.5 4.53 3.52.5 41
VIN = 12V
VOUT = 3.3V
fS= 400kHz
Figure 1. LT3976 Efficiency vs Load Current Figure 2. LT3976 Demo Board EMI Performance,
Switching Frequency 400kHz

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DEMO MANUAL DC1848A
Quick start proceDure
Figure 3. Proper Measurement Equipment Setup
Figure 4. Measuring Input or Output Ripple

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DEMO MANUAL DC1848A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Demo Board Circuit Components
1 2 C1, C8 Cap., X5R, 47µF, 10V, 20% 1210 TDK, C325X5R1A476MT
2 1 C2 Cap., X5R, 0.47µF, 25V, 10% 0603 TDK, C1608X5R1E474K
3 2 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 C7 Cap., C0G, 470pF, 50V, 10%, 0402 AVX, 04025A471KAT2A
7 1 D1 DIODE, Schottky, PowerDi5 DIODE INC., PDS540-13
8 1 L1 IND., 3.3µH VISHAY, IHLP2525CZER3R3M01
9 1 R1 Res., Chip, 1.00M, 1/16W, 1% 0402 NIC, NRC04F1004TRF
10 1 R2 Res., Chip, 576K, 1/16W, 1% 0402 VISHAY, CRCW0402576KFKED
11 1 R3 Res., Chip, 2, 1/16W, 1% 0402 VISHAY, CRCW04022R00FKED
12 1 R5 Res., Chip, 130k, 1/16W, 1% 0402 VISHAY, CRCW0402130KFKED
13 1 R6 Res., Chip, 200k, 1/16W, 1% 0402 VISHAY,CRCW0402200KFKED
14 1 U1 I.C., MSE16 LINEAR TECH., LT3976EMSE
Additional Demo Board Circuit Components
15 1 C11 Cap., X5R, 1µF 16V 20%, 0603 AVX, 0603YD105MAT
16 1 C4 Cap., Elect.,100µF, 50V, 10% SUN ELECT, 50CE100BS
17 1 C9 Cap., X5R, 10µF, 50V, 10%,1210 TDK, C3225X5R1H106K
18 1 C10 Cap., Alum. Electro., 33µF, 50V SUNCON, 50HVP33M
19 1 L2 Ind., 1.0µH XAL4020 COILCRAFT, XAL4020-102MEC
20 1 L3 Ind., 3.3µH XAL5030 COILCRAFT, XAL5030-332MEC
21 0 R7, R8 Res., 0402 OPT
Hardware/Components (for Demo Board Only)
22 7 E1, E2, E3, E4, E5, E6, E7 Turret, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0
23 2 JP1, JP2 JMP, 1X3-079 SAMTEC, TMM-103-02-L-S
24 2 XJP1, XJP2 SAMTEC, 2SN-BK-G

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DEMO MANUAL DC1848A
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
5 5
4 4
3 3
2 2
1 1
D D C C B B A A
ALL CAPACITORS ARE 0402.
NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTORS ARE 0402.
SUNCON 50CE100BS
VIN
VOUT
VIN
D1 PDS540 D1 PDS540
2 1
3
E7 SYNC E7 SYNC
C6 10nF C6 10nF
E4
GND
E4
GND
E5
EN E5 EN
VEMIVEMI
C3 10uF 50V 1210 C3 10uF 50V 1210
C5 10pF C5 10pF
C7
470pF
C7
470pF
R7
OPT 0603
R7
OPT 0603
R8
OPT 0603
R8
OPT 0603
C9
10uF
50V 1210 C9
10uF
50V 1210
E6
PG
E6
PG
L1
3.3uH
IHLP2525CZER3R3M01
L1
3.3uH
IHLP2525CZER3R3M01
L2
1.0uH
XAL4020-102ME
L2
1.0uH
XAL4020-102ME
JP1
ON
OFF
JP1
ON
OFF
1 3 2
R2 576k 1% R2 576k 1%
U1
LT3976EMSE
U1
LT3976EMSE
NC
9
OUT 3
FB 1
SS
2
EN
13
VIN
12
BOOST 4
SW 5
PG
15
SYNC 16
GND
17
VIN
11 VIN 10
SW 6 SW 7
RT 14
NC
8
L3
3.3uH
XAL5030-332ME
L3
3.3uH
XAL5030-332ME
C11 1uF
0603
16V C11 1uF
0603
16V
R5 130K 1% (400kHz) R5 130K 1% (400kHz)
C1 47uF 10V 1210 C1 47uF 10V 1210
+
C4 100uF 50V
+
C4 100uF 50V
R1 1.00M 1% R1 1.00M 1%
E2 GND E2 GND
R6 200K R6 200K
C2 0.47uF 0603 C2 0.47uF 0603
E1
VOUT
3.3V / 5A
E1
VOUT
3.3V / 5A
JP2
SYNC RT FREQ
JP2
SYNC RT FREQ
1 3 2
R3 2 R3 2
E3
VIN
4.3V - 40V E3
VIN
4.3V - 40V
+
C10
33uF
50V
50HVP33
+
C10
33uF
50V
50HVP33
C8 47uF 10V 1210 C8 47uF 10V 1210

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DEMO MANUAL DC1848A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2012
LT 1012 • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LT C ) 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 LT C 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 LT C 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. LT C assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LT C 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 LT C applica-
tion engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation