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dc2658af
DEMO MANUAL DC2658A
Description
LT8643S
42V, 6A Synchronous
Step-Down Silent Switcher 2
Demonstration circuit 2658A is a 42V, 6A synchronous
step-down second generation SILENT SWITCHER with
spread spectrum frequency modulation featuring the
LT
®
8643S. The demo board is designed for 5V output
from a 5.8V to 42V input. The wide input range allows a
variety of input sources, such as automotive batteries and
industrial supplies. The LT8643S is a compact, ultralow
emission, high efficiency, and high speed synchronous
monolithic 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. Fast minimum
on-time of 30ns enables high VIN to low VOUT conversion
at high frequency.
The LT8643S switching frequency can be programmed
either via oscillator resistor or external clock over a
200kHz to 3MHz range. The default frequency of demo
circuit 2658A 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 forced
continuous 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 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
the LT8643S temperature rising on DC2658A demo board
under different load conditions. The rated maximum load
current is 6A, while derating is necessary for certain input
voltage and thermal conditions.
The demo board has an EMI filter installed. The EMI perfor-
mance of the board (with EMI filter) is shown on Figure 3.
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 3, the input EMI filter is required and
the input voltage should be applied at VIN_EMI 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 LT8643S 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 DC2658A. The LT8643S is assembled in a
4mm × 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 and Peak Output Current.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2658A
Specifications are at TA = 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN_EMI Input Supply Range with EMI Filter 5.8 42 V
VOUT Output Voltage 4.85 5 5.15 V
IOUT Maximum Output Current Derating Is Necessary for Certain VIN and
Thermal Conditions
6 A
fSW Switching Frequency 1.85 2 2.15 MHz
EFF Efficiency VIN = 12V , IOUT = 3A 94.2 %
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DEMO MANUAL DC2658A
POWER LOSS
f
SW
= 2MHz
SYNC/MODE = GND
V
OUT
= 5V
V
IN
= 12V
V
IN
= 24V
LOAD CURRENT (A)
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
60
65
70
75
80
85
90
95
100
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
EFFICIENCY (%)
POWER LOSS (W)
DC2658A F01
f
SW
= 2MHz
I
OUT
= 6A
I
OUT
= 5A
I
OUT
= 4A
V
OUT
= 5V
INPUT VOLTAGE (V)
6
12
18
24
30
36
42
0
10
20
30
40
50
60
70
80
90
100
CASE TEMPERATURE RISING (°C)
DC2658A F02
Figure 1. LT8643S DC2658A Efficiency
vs Load Current (Input from VIN Terminal)
Figure 2. LT8643S DC2658A Case
Temperature Rising vs Input Voltage
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DEMO MANUAL DC2658A
Radiated EMI Performance
(CISPR25 Radiated Emission Test with Class 5 Peak Limits)
Conducted EMI Performance
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, f
SW
= 2MHz
SPREAD SPECTRUM MODE
FIXED FREQUENCY 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)
DC2658 F03a
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)
DC2658 F03b
(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)
DC2658 F03c
Figure 3. LT8643S Demo Circuit DC2658A EMI Performance
(14V Input from VIN_EMI, with EMI Filter, IOUT = 4A)
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dc2658af
DEMO MANUAL DC2658A
Quick start proceDure
Demonstration circuit 2658A is easy to set up to evalu-
ate the performance of the LT8643S. Refer to Figure 4
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 5 for the proper scope technique. Figure 6
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
VIN_EMI 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
42V.
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 LT8643S switching frequency equal to or below the
lowest SYNC frequency. JP1 can also set LT8643S in
spread spectrum mode (JP1 on the SPREAD-SPEC-
TRUM position) or forced continuous mode (JP1 on
the FCM position).
POWER
SUPPLY
IIN IOUT
VOUT
VIN_EMI
+
–
+
–
LOAD
+
–
+–
+
–
+
–
Figure 4. Proper Measurement Equipment Setup
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DEMO MANUAL DC2658A
Quick start proceDure
DC2658A F06
500ns/DIV
VOUT
5mV/DIV
AC-COUPLED
Figure 5. Measuring Output Ripple at Output Capacitor C9
Figure 6. LT8643S Demo Circuit DC2658A Output Voltage Ripple
(12V Input, IOUT = 6A, Full BW)
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DEMO MANUAL DC2658A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 2 C2, C12 CAP., X5R, 1μF, 50V, 10%, 0603 MURATA, GRM188R61H105KAALD
2 1 C5 CAP., C0G, 330pF, 50V, 5%, 0603 MURATA, GRM1885C1H331JA01D
3 1 C6 CAP., X5R, 100μF, 10V, 20% 1210 MURATA, GRM32ER61A107ME20L
4 1 C8 CAP., X7R, 0.1μF, 16V, 10%, 0603 MURATA, GRM188R71C104KA01D
5 1 C9 CAP., X5R, 22μF, 10V, 20%, 0603 SAMSUNG, CL10A226MPMNUBE
6 1 C16 CAP., C0G, 4.7pF, 50V, ±0.1pF, 0603 MURATA, GRM1885C1H4R7BA01D
7 1 C17 CAP., X7R, 10μF, 50V, 10%, 1210 MURATA, GRM32ER71H106KA12L
8 1 C20 CAP., X7R, 1μF, 10V, 10%, 0603 MURATA, GRM188R71A105KA61D
9 1 L1 INDUCTOR,1.5μH COILCRAFT, XEL6030-152ME
10 2 R1, R5 RES., CHIP, 100k, 1/10W, 1% 0603 VISHAY, CRCW0603100KFKEA
11 1 R2 RES., CHIP, 17.8k, 1/10W, 1% 0603 VISHAY, CRCW060317K8FKEA
12 1 R3 RES., CHIP, 243k, 1/10W, 1%, 0603 VISHAY, CRCW0603243KFKEA
13 1 R4 RES., CHIP, 8.45k, 1/10W, 1%, 0603 VISHAY, CRCW06038K45FKEA
14 1 R7 RES., CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA
15 1 U1 I.C., STEP-DOWN SWITCHER, 4mm × 4mm LQFN LINEAR TECH., LT8643SEV#PBF
Additional Demo Board Circuit Components
1 1 C1 CAP., ALUM 22μF, 63V SUN ELECT., 63CE22BS
2 2 C3, C10 CAP., X7R, 10μF, 50V, 10%, 1210 MURATA, GRM32ER71H106KA12L
3 2 C14, C21 CAP., X7R, 0.1μF, 50V, 10%, 0402 MURATA, GRM155R71H104KE14D
4 0 C15, C18 (OPT) CAP., OPTION, 0603
5 1 FB1 BEAD, FERRITE, 100Ω, 1812 WURTH ELEKTRONIK, 74279226101
6 0 R6 (OPT) RES., OPTION, 0603
7 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, .094" MILL-MAX, 2501-2-00-80-00-00-07-0
2 4 E2, E10, E12, E13 TESTPOINT, TURRET, .064" MILL-MAX, 2308-2-00-80-00-00-07-0
3 1 JP1 2×4, 0.079 DOUBLE ROW HEADER WURTH ELEKTRONIK, 62000821121
4 1 XJP1 SHUNT, .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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dc2658af
DEMO MANUAL DC2658A
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.
SYNC
BURST
SPREAD-SPECTRUM
FCM
*
*SEE DEMO MANUAL
R2
17.8K
C17
10uF
50V
1210
E11 EN
FB1
74279226101
E9
GND
C21
0.1uF
0402
50V R8
0
E2
GND
C2
1uF
50V
R6
OPT
JP1
1 2
3
5
7
4
6
8
C14
0.1uF
0402
50V
E8 PG
E5
SYNC
R7
1M
R3
243K
+
C1
22uF
63V
63CE22BS C6
100uF
10V
1210
J1
C12
1uF
50V
C5
330pF
C3
10uF
1210
50V
E7
TR/SS
J3
VOUT
5V / 6A
C20
1uF
10V
E1
VIN
5.8V - 42V
C16
4.7pF
J4 GND
C10
10uF
1210
50V
E10
VIN_EMI
C15
OPT
C8
0.1uF
C9
22uF
10V
L1
XEL6030
1.5uH
C18
OPT
J2
R5
100K
E6 CLKOUT
E12
U1
LT8643SEV
EN
17
SYNC
20
VCC
2
RT
18
FB
24
PG
23
BIAS
1
BST
7
GND
3
TR/SS
21
GND
16
VIN
5
VIN
6
VIN
13
VIN
14
VC
22
CLKOUT
19
SW
8
SW
9
SW
10
SW
11
SW
12
NC
4
NC
15
GND
25
GND
26
GND
27
GND
28
R1
100K
R4
8.45K
E13
VC
E14
VIN
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dc2658af
DEMO MANUAL DC2658A
© LINEAR TECHNOLOGY CORPORATION 2017
LT 0817 • 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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Copyright © 2004, Linear Technology Corporation