Linear Technology 2373A Quick setup guide

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DEMO MANUAL DC2373A
Description
LT8641
65V, 3.5A Micropower Synchronous
Step-Down Silent Switcher
Demonstration circuit 2373A is a 65V, 3.5A micropower
synchronous step-down Silent Switcher
®
with spread
spectrum frequency modulation featuring the LT
®
8641.
The demo board is designed for 5V output from a 5.5V to
65V input. The wide input range allows a variety of input
sources, such as automotive batteries and industrial sup-
plies. The LT8641 is a compact, ultralow emission, high
efficiency, high speed synchronous monolithic step-down
switchingregulatorthat consumesonly 2.5μAof quiescent
current when output is regulated at 5V. Top and bottom
power switches, compensation components and other
necessary circuits are inside of the LT8641 to minimize
external components and simplify design.
The SYNC pin on the demo board is grounded by default
for low ripple burst mode operation. Move JP1 to PULSE
SKIPPING position can change the operation mode to
pulse-skipping operation. Once JP1 is on SPREAD SPEC-
TRUM position, VCC is applied to the SYNC pin for low
EMI spread spectrum operation. To synchronous to an
external clock, move JP1 to SYNC and apply the external
clock to the SYNC turret. Figure 1 shows the efficiency of
the circuit at 12V and 24V input in Burst Mode
®
operation
(input from VIN turret pin). Figure 2 shows the LT8641
L, LT, LTC, LTM, Linear Technology, Silent Switcher, Burst Mode and the Linear logo are
registered trademarks of Linear Technology Corporation. All other trademarks are the property
of their respective owners.
performance summary
temperature rising on DC2373A demo board under differ-
ent load conditions. The rated maximum load current is
3.5A, while derating is necessary for certain input voltage
and thermal conditions.
The demo board has an EMI filter installed. Under burst
and spread spectrum operation, the EMI performances of
the board (with EMI filter) are shown in Figure 3 and 4. The
red lines in Figure 3 and 4 are CISPR25 Class5 peak limit.
To achieve EMI/EMC performance as shown in Figure 3
and 4, the input EMI filter is required and the input voltage
should be applied at VEMI turret pin.
This board is suitable for a wide range of automotive,
telecom, industrial, and other applications.
The LT8641 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 DC2373A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2373A
Specifications are at TA= 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input Voltage Range 5.5 65 V
VOUT Output Voltage 4.8 5 5.2 V
IOUT Maximum Output Current Derating Is Necessary for Certain VIN and
Thermal Conditions
3.5 A
fSW Switching Frequency 1.85 2 2.15 MHz
EFF Efficiency VIN = 12V, IOUT = 1A 94 %

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DEMO MANUAL DC2373A
Quick start proceDure
DC2373A is easy to set up to evaluate the performance
of the LT8641. 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. See Figure 6 for the proper scope
technique.
1. Set an input power supply that is capable of 65V/3.5A.
Then turn off the supply.
2. With power off, connect the supply tothe input terminals
VEMI and GND.
3. Turn on the power at the input.
NOTE: Make sure that the input voltage never exceeds 65V.
4. Check for the proper output voltage of 5V. Turn off the
power at the input.
5. Once the proper output voltage is established, connect a
variable load capable of sinking 3.5A at 5V to the output
terminals VOUT and GND. Set the current for 0A.
a. If efficiency measurements are desired, an ammeter
can be put in series with the output load in order to
measure the DC2373A’s output current.
b. A voltmeter can be placed across the output terminals
in order to get an accurate output voltage measure-
ment.
6. Turn on the power at the input.
NOTE: If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
7. Once the proper output voltage is again established,
adjust the load and/or input within the operating range
and observe the output voltage regulation, ripple volt-
age, efficiency and other desired parameters.
8. An external clock can be added to the SYNC terminal
when SYNC function is used (JP1 on the SYNC posi-
tion). Please ensure that the chosen RT sets the LT8641
switching frequency to equal or below the lowest SYNC
frequency. See the data sheet section, Synchronization.

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DEMO MANUAL DC2373A
Quick start proceDure
Figure 1. Efficiency vs Load Current at 2MHz Switching Frequency
Figure 2. DC2373A Temperature Rising vs Load Current
IOUT (A)
0
EFFICIENCY (%)
100
95
85
75
90
80
70
65
60
55
50 21 3
DC2373a F01
3.5
1.50.5 2.5
12V INPUT
24V INPUT
LOAD CURRENT (A)
0
CASE TEMPERATURE RISE (°C)
60
40
30
50
20
10
021 3
DC2373a F02
3.5
1.50.5 2.5
VIN = 12V, fSW = 1MHz
VIN = 24V, fSW = 1MHz
VIN = 12V, fSW = 2MHz
VIN = 24V, fSW = 2MHz

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DEMO MANUAL DC2373A
Figure 3. LT8641 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test, Antenna Polarization:
Vertical (VIN = 14V, VOUT = 5V, IOUT = 3.5A, 2MHz Switching Frequency)
Figure 4. LT8641 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test, Antenna Polarization:
Horizontal (VIN = 14V, VOUT = 5V, IOUT = 3.5A, 2MHz Switching Frequency)
Quick start proceDure
FREQUENCY (MHz)
AMPLITUDE (dBµV/m)
DC2373a F03
FREQUENCY (MHz)
AMPLITUDE (dBµV/m)
DC2373a F04

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DEMO MANUAL DC2373A
V
OUT
GND
Figure 5. Proper Measurement Equipment Setup
Figure 6. Measuring Output Ripple
Quick start proceDure

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DEMO MANUAL DC2373A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 2 C2, C12 CAP, X7R, 0.1µF, 100V, 10%, 0603 MURATA, GRM188R72A104KA35D
2 2 C4, C8 CAP, X7R, 0.1µF, 16V, 10%, 0603 MURATA, GRM188R71C104KA01D
3 1 C5 CAP, C0G, 10pF, 25V, 5%, 0603 AVX, 06033A100CAT2A
4 1 C6 CAP, X5R, 100µF, 10V, 20%, 1210 MURATA, GRM32ER61A107ME20L
5 1 C7 CAP, X7R, 1µF, 25V, 10%, 0603 MURATA, GRM188R71E105KA12D
6 1 C11 CAP, X7S, 4.7µF, 100V, 10%, 1206 AVX, 12061Z475KAT2A
7 1 L1 IND, 2.2µH VISHAY, IHLP2525CZER2R2M01
8 2 R1, R4 RES, CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA
9 1 R2 RES, CHIP, 18.2k, 1/10W, 1%, 0603 VISHAY, CRCW060318K2FKEA
10 1 R3 RES, CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA
11 1 R5 RES, CHIP, 191k, 1/10W, 1%, 0603 VISHAY, CRCW0603191KFKEA
12 1 R7 RES, CHIP, 0, 1/10W, 1%, 0604 VISHAY, CRCW06030000Z0EA
13 1 U1 IC, REGULATOR, 20-QFN, UDC LINEAR TECH,LT8641EUDC#PBF
Additional Demo Board Circuit Components
1 1 C1 CAP, ALUM 22µF, 100V SUN ELECT, 100CE22BS
2 2 C3, C10 CAP, X7S, 4.7µF, 100V, 10%, 1210 TDK, C3225X7S2A475K200AB
3 1 C9 CAP, X7R, 1µF, 25V, 10%, 0603 MURATA, GRM188R71E105KA12D
4 1 C13 CAP, X7R, 10µF, 10V, 10%, 0805 MURATA, GRM21BR71A106KE51L
5 1 C14 CAP, X7R, 0.1µF, 100V, 10%, 0603 MURATA, GRM188R72A104KA35D
6 1 FB1 FERRITE BEAD, 0805 TDK, MPZ2012S300A
7 1 L2 IND, 0.22µH VISHAY, IHLP1212BZERR22M11
8 0 R6 (OPT) RES, 0603
Hardware: For Demo Board Only
1 9 E2 TO E10 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0
2 1 E1 (OPT) TESTPOINT, TURRET, 0.094"
3 1 JP1 DOUBLE ROW HEADER 2 x 4 0.079" SULLINS NRPN042PAEN-RC
4 1 XJP1 SHUNT, 0.079" CENTER SAMTEC 2SN-BK-G
5 4 MH1 TO MH4 STAND-OFF, NYLON 0.50" TALL KEYSTONE, 8833 (SNAP ON)

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DEMO MANUAL DC2373A
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 DC2373A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2016
LT 0216 • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
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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
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