Analog Devices DC2468A Quick setup guide

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dc2468af
DEMO MANUAL DC2468A
DESCRIPTION
LT8645S
65V, 8A Micropower Synchronous
Step-Down Silent Switcher 2
Demonstration circuit 2468A is a 65V, 8A micropower syn-
chronous step-down second generation Silent Switcher
®
with spread spectrum frequency modulation featuring the
LT8645S. The demo board is designed for 5V output from
a 5.6V to 65V input. The wide input range allows a variety
of input sources, such as automotive batteries and indus-
trial supplies. The LT8645S is a compact, ultralow emis-
sion, high efficiency, and high speed synchronous mono-
lithic step-down switching regulator. The integrated bypass
capacitors optimize all the fast current loops and make it
easier to minimize EMI/EMC emissions by reducing layout
sensitivity. Selectable spread spectrum mode can further
improve EMI/EMC performance. Ultralow quiescent cur-
rent in Burst Mode
®
operation achieves high efficiency at
very light loads. Fast minimum on-time of 40ns enables
high VIN to low VOUT conversion at high frequency.
The LT8645S switching frequency can be programmed
either via oscillator resistor or external clock over a
200kHz to 2.2MHz range. The default frequency of demo
circuit 2468A is 2MHz. The SYNC pin on the demo board
is grounded (JP1 at BURST position) 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 terminal. Spread spectrum mode and pulse
skipping mode can be selected respectively by moving
JP1 shunt. Figure 1 shows the efficiency of the circuit at
12V input and 24V input in Burst Mode operation (input
from VIN terminal to bypass the EMI filter). Figure 2 shows
the LT8645S temperature rising on DC2468A demo board
under different load conditions. The rated maximum load
L, LT, LTC, LTM, Linear Technology, the Linear logo, Silent Switcher and Burst Mode are
registered trademarks of Analog Devices, Inc. All other trademarks are the property of their
respective owners.
current is 8A, while derating is necessary for certain input
voltage and thermal conditions. Low switching frequency
can extend the output load capability by reducing the
power dissipations. Figure 3 shows the temperature ris-
ing at 500kHz switching frequency.
The demo board has an EMI filter installed. The EMI
performance of the board (with EMI filter) is shown on
Figure 4. The red line in Radiated EMI Performance is
CISPR25 Class 5 peak limit. The figure shows that the
circuit passes the test with a wide margin. To achieve EMI/
EMC performance as shown in Figure 4, the input EMI
filter is required and the input voltage should be applied
at VEMI terminal. An inductor can be added in the EMI
filter to further reduce the conducted emission. The EMI
filter can be bypassed by applying the input voltage at
VIN terminal.
The LT8645S 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 2468A. The LT8645S is assembled in a
6mm × 4mm LQFN package with exposed pads for low
thermal resistance. The layout recommendations for low
EMI operation and maximum thermal performance are
available in the data sheet section Low EMI PCB Layout
and Thermal Considerations.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2468A
PERFORMANCE SUMMARY
Specifications are at TA= 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN_EMI Input Supply Range with EMI Filter 5.6 65 V
VOUT Output Voltage 4.85 5 5.15 V
IOUT Maximum Output Current Derating is Necessary for Certain VIN and Thermal Conditions 8 A
fSW Switching Frequency 1.85 2 2.15 MHz
EFF Efficiency VIN = 12V, IOUT = 4A 93.8 %

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DEMO MANUAL DC2468A
DESCRIPTION
Figure 1. LT8645S Demo Circuit DC2468A Efficiency vs
Load Current (Input from VIN Terminal)
Figure 3. LT8645S Demo Circuit DC2468A
Temperature Rising vs Input Voltage (500kHz)
Figure 2. LT8645S Demo Circuit DC2468A
Temperature Rising vs Input Voltage (2MHz)
V
OUT
= 5V
POWER LOSS
f
SW
= 2MHz
SYNC/MODE = GND
EFFICIENCY
V
IN
= 12V
V
IN
= 24V
LOAD CURRENT (A)
1
2
3
4
5
6
7
8
60
65
70
75
80
85
90
95
100
0
0.8
1.6
2.4
3.2
4.0
4.8
5.6
6.4
EFFICIENCY (%)
POWER LOSS (W)
dc2468a F01
V
OUT
= 5V
f
SW
= 500kHz
I
OUT
= 8A
I
OUT
= 6A
I
OUT
= 4A
INPUT VOLTAGE (V)
12
18
24
30
36
42
48
54
60
0
10
20
30
40
50
60
70
80
90
100
TEMPERATURE RISING (°C)
dc2468a F03
V
OUT
= 5V
f
SW
= 2MHz
I
OUT
= 8A
I
OUT
= 6A
I
OUT
= 4A
INPUT VOLTAGE (V)
12
18
24
30
36
42
48
54
60
0
10
20
30
40
50
60
70
80
90
100
TEMPERATURE RISING (°C)
dc2468a F02

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DEMO MANUAL DC2468A
DC2468A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, f
SW
= 2MHz
FIXED FREQUENCY MODE
SPREAD SPECTRUM MODE
FREQUENCY (MHz)
0
3
6
9
12
15
18
21
24
27
30
–40
–30
–20
–10
0
10
20
30
40
50
60
AMPLITUDE (dBµV/m)
dc2468 F04a
Conducted EMI Performance
Radiated EMI Performance
(CISPR25 Radiated Emission Test with Class 5 Peak Limits)
VERTICAL POLARIZATION
PEAK DETECTOR
CLASS 5 PEAK LIMIT
SPREAD SPECTRUM MODE
FIXED FREQUENCY MODE
FREQUENCY (MHz)
0
100
200
300
400
500
600
700
800
900
1000
–5
0
5
10
15
20
25
30
35
40
45
50
AMPLITUDE (dBµV/m)
dc2468 F04b
DC2468A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, f
SW
= 2MHz
HORIZONTAL POLARIZATION
PEAK DETECTOR
CLASS 5 PEAK LIMIT
SPREAD SPECTRUM MODE
FIXED FREQUENCY MODE
FREQUENCY (MHz)
0
100
200
300
400
500
600
700
800
900
1000
–5
0
5
10
15
20
25
30
35
40
45
50
AMPLITUDE (dBµV/m)
dc2468 F04c
Figure 4. LT8645S Demo Circuit DC2468A EMI Performance (14V Input from VEMI, with EMI Filter, IOUT = 4A)
DESCRIPTION

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DEMO MANUAL DC2468A
IN_EMI
QUICK START PROCEDURE
Demonstration circuit 2468A is easy to set up to evalu-
ate the performance of the LT8645S. Refer to Figure 5
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 output voltage ripple by
touching the probe tip directly across the output capaci-
tor. See Figure 6 for the proper scope technique. Figure 7
shows the output voltage ripple measured at the output
capacitor C9.
1. Place JP1 on BURST position.
2. With power off, connect the input power supply to
VEMI and GND. If the input EMI filter is not desired,
connect the input power supply to VIN and GND.
3. With power off, connect the load from VOUT to GND.
4. Turn on the power at the input.
NOTE:Make sure that the input voltage does not
exceed 65V.
5. Check for the proper output voltage (VOUT = 5V).
NOTE:If there is no output, temporarily disconnect the
load to make sure that the load is not set too high or
is shorted.
6. 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.
7. An external clock can be added to the SYNC terminal
when SYNC function is used (JP1 on the SYNC posi-
tion). Please make sure that R2 should be chose to set
the LT8645S switching frequency equal to or below the
lowest SYNC frequency. JP1 can also set LT8645S in
spread spectrum mode (JP1 on the SPREAD-SPEC-
TRUM position) or pulse skipping mode (JP1 on the
PULSE-SKIPPING position).
Figure 5. Proper Measurement Equipment Setup

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DEMO MANUAL DC2468A
QUICK START PROCEDURE
Figure 6. Measuring Output Ripple at Output Capacitor C9
Figure 7. LT8645S Demo Circuit DC2468A Output Voltage Ripple
(12V Input, IOUT = 8A, Full BW)
VOUT
GND
C9
500ns/DIV
VOUT
5mV/DIV
AC-COUPLED
dc2468a F07

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DEMO MANUAL DC2468A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 2 C2, C12 CAP., X7R, 0.47μF, 100V, 10%, 0805 MURATA, GRM21BR72A474KA73L
2 1 C6 CAP., X5R, 100μF, 10V, 20%, 1210 MURATA, GRM32ER61A107ME20L
3 1 C8 CAP., X7R, 0.1μF, 25V, 10%, 0603 MURATA, GRM188R71E104KA01D
4 1 C9 CAP., X5R, 10μF, 25V, 20%, 0603 MURATA, GRM188R61E106MA73D
5 1 C16 CAP., C0G, 4.7pF, 50V, ±0.25pF, 0603 MURATA, GRM1885C1H4R7CA01D
6 1 C17 CAP., X7S, 4.7μF, 100V, 10%, 1210 MURATA, GRJ32DC72A475KE11L
7 1 C20 CAP., X7R, 1μF, 16V, 10%, 0603 MURATA, GRM188R71C105KA12D
8 1 L1 INDUCTOR, 1.0μH, XEL6030 COILCRAFT, XEL6030-102MEC
9 2 R1, R5 RES., CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA
10 1 R2 RES., CHIP, 17.8k, 1/10W, 1%, 0603 VISHAY, CRCW060317K8FKEA
11 1 R3 RES., CHIP, 243k, 1/10W, 1%, 0603 VISHAY, CRCW0603243KFKEA
12 1 R7 RES., CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA
13 1 U1 I.C., STEP-DOWN SWITCHER, 6mmX4mm LQFN LINEAR TECH., LT8645SEV#PBF
Additional Demo Board Circuit Components
1 1 C1 CAP., ALUM 22μF, 100V, 10% SUNCON, 100CE22BS
2 2 C3, C10 CAP., X7R, 2.2μF, 100V, 10%, 1210 MURATA, GRM32ER72A225KA35L
3 1 C4 CAP., X7R, 0.1μF, 100V, 10%, 0603 MURATA, GRM188R72A104KA35D
4 1 C14 CAP., X5R, 0.1μF, 100V, 10%, 0402 MURATA, GRM155R62A104KE14D
5 0 C18 (OPT) CAP., 0603
6 0 C19 (OPT) CAP., 1210
7 1 FB1 FERRITE BEAD 100Ω 8A SMD 1812 WURTH ELEKTRONIK, 74279226101
8 0 R6 (OPT) RES., OPTION, 0603
9 1 R8 RES., CHIP, 0Ω, 1/10W, 1%, 0603 VISHAY, CRCW06030000Z0EA
Hardware: For Demo Board Only
1 8 E1, E5-E9, E11, E14 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0
2 4 E2, E10, E12, E13 TESTPOINT, TURRET, 0.061" MILL-MAX, 2308-2-00-80-00-00-07-0
3 1 JP1 2X4, 0.079" DOUBLE ROW HEADER WURTH ELEKTRONIK, 62000821121
4 1 XJP1 SHUNT, 0.079" CENTER WURTH ELEKTRONIK, 60800213421
5 4 J1-J4 JACK BANANA KEYSTONE, 575-4
6 4 MH1-MH4 STAND-OFF, NYLON 0.50" TALL WURTH ELEKTRONIK, 702935000

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DEMO MANUAL DC2468A
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 0603.
NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTORS ARE 0603.
100CE22BS
SYNC
BURST
SPREAD-SPECTRUM
PULSE-SKIPPING
*
*
SEE DEMO MANUAL
R2
17.8K
E9
GND
FB1
74279226101 E11
EN
C2
0.47uF 100V 0805
E2
GND
R6
OPT
C17 4.7uF
100V
1210
C14 0.1uF
0402
100V
JP1
1 2 3 5 7
4 6 8
R8
0
E5
SYNC
E8 PG
C12 0.47uF
100V 0805
J1
C6
100uF 10V 1210
+
C1 22uF 100V
R3
243K
R7
1M
C4 0.1uF
100V
C3
2.2uF
1210
100V
J3
VOUT
5V / 8A
E7
TR/SS
E1
VIN
5.6V - 65V
J4 GND
C16
4.7pF
C18
OPT
C20 1uF
16V
L1
1.0uH
XEL6030-102
C9
10uF
25V
C8 0.1uF
E10
VEMI
C10
2.2uF
1210
100V
E6 CLKOUT
J2
R5 100K
E12
U1 LT8645S
VIN
4
EN
25
SYNC
28
VCC
2
RT
26
FB
32
PG
31
BIAS
1
BST
11
GND1
8
GND2
10
TR/SS
29
GND1
9
GND2
17
VIN
5
VIN
6
VIN
21
VIN
22
VIN
23
GND2
18
GND2
19
GND
30
CLKOUT
27
SW
12
SW
13
SW
14
SW
15
SW
16
NC
3
NC
7
NC
20
NC
24
GND
33
GND
34
GND
35
GND
36
GND
37
GND
38
C19 OPT
1210
E14 BIAS
E13
R1
100K
VIN

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DEMO MANUAL DC2468A
 LINEAR TECHNOLOGY CORPORATION 2017
LT 0517 • 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 application
engineer.
Mailing Address:
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Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation

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