Linear Technology LT8614 Quick setup guide

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dc2019bfb
DEMO MANUAL DC2019B
DESCRIPTION
LT8614
42V, 4A Micropower
Synchronous Step-Down
Silent Switcher
Demonstration circuit 2019B is a 42V, 4A micropower
synchronous step-down Silent Switcher™ featuring the
LT
®
8614. 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 LT8614 is a compact, ultralow
emission, high efficiency and high speed synchronous
monolithic step-down switching regulator. The integrated
power switches and inclusion of all necessary circuitry
reduce the components count and solution size. Special
Silent Switcher architecture minimizes EMI/EMC emis-
sions. Ultralow 2.5µA quiescent current in Burst Mode
®
operation achieves high efficiency at very light loads. Fast
minimum on-time of 30ns enables high VIN to low VOUT
conversion at high frequency.
TheLT8614switching frequencycanbe programmedeither
via oscillator resistor or external clock over a 200kHz to
3MHz range. The SYNC pin on the demo board is grounded
by default for low ripple Burst Mode operation. To syn-
chronize to an external clock, move JP1 to SYNC and
apply the external clock to the SYNC turret. Once JP1 is
on SYNC position, a DC voltage of higher than 3V can be
applied to the SYNC turret for pulse-skipping operation.
Figure 1 shows the efficiency of the circuit at 12V input in
Burst Mode operation (input from VIN turret pin). Figure 2
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and Silent Switcher is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
PERFORMANCE SUMMARY
shows the LT8614 temperature rising on DC2019B demo
board under different load conditions. The rated maximum
load current is 4A, while derating is necessary for certain
VIN and thermal conditions.
The demo board has an EMI filter installed. The EMI perfor-
mance of the board (with EMI filter) is shown in Figure 3.
The red line in Figure 3 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 VEMI turret pin.
The LT8614 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 2019B. The LT8614 is assembled in a 3mm
×4mm plastic QFN package with exposed pads for low
thermalresistance. Properboard layoutis essential for both
low EMI operation and maximum thermal performance.
See the data sheet sections, “Low EMI PCB Layout” and
“High Temperature Considerations.”
Design files for this circuit board are available at
http://www.linear.com/demo/DC2019B
Specifications are at TA= 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input Supply Range 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
4 A
fSW Switching Frequency 1.85 2 2.15 MHz
EFE Efficiency at DC VIN = 12V, IOUT = 3A 91.3 %

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DEMO MANUAL DC2019B
PERFORMANCE
Figure 1. Efficiency vs Load Current
(Input from VIN Turret Pin)
Figure 3. LT8614 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test (14V Input from VEMI Turret Pin, IOUT = 4A)
Figure 2. Temperature Rising vs Input Voltage
FREQUENCY (MHz)
0
AMPLITUDE (dBµV/m)
30
40
50
800
20
10
0100 200 300 400 500 600 700 900 1000
DETECTOR: +PEAK
dc2019a F03
CLASS 5 PEAK
DATA
60
EFFICIENCY (%)
70
80
90
100
65
75
85
95
LOAD CURRENT (A)
0 1 22.5
0.5 1.5 3.53 4
dc2019a F01
VIN = 12V
VOUT = 5V
fSW = 2MHz
INPUT VOLTAGE (V)
6
TEMPERATURE RISING (°C)
70
80
90
60
50
12 2418 30 36 42
20
10
40
100
30
dc2019a F02
IOUT = 4A
IOUT = 3.5A
I
OUT
= 3A
IOUT = 2.5A
IOUT = 2A
VOUT = 5V
fSW = 2MHz

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dc2019bfb
DEMO MANUAL DC2019B
QUICK START PROCEDURE
Demonstration circuit 2019B is easy to set up to evalu-
ate the performance of the LT8614. 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 input or output voltage
ripple by touching the probe tip directly across the VEMI
or VOUT and GND terminals. See Figure 5 for the proper
scope technique.
1. Place JP1 on GND position.
2. With power off, connect the input power supply to VEMI
and GND. If the EMI/EMC performance is not important,
the input EMI filter can be bypassed by connecting 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 termi-
nal when SYNC function is used (JP1 on the SYNC
position). Please ensure that the chosen RT sets the
LT8614 switching frequency to equal or below the
lowest SYNC frequency. See the data sheet section,
“Synchronization.”
Figure 4. Proper Measurement Equipment Setup
Figure 5. Measuring Output Ripple

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dc2019bfb
DEMO MANUAL DC2019B
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 2 C2, C12 CAP., X5R, 1µF, 50V, 10%, 0603 TDK, C1608X5R1H105K
2 2 C4,C8 CAP., X7R, 0.1µF, 16V, 10%, 0603 MURATA, GRM188R71C104KA01D
3 1 C5 CAP., C0G, 4.7pF, 25V, ±0.25p, 0603 AVX, 06033A4R7CAT2A
4 1 C6 CAP., X7R, 47µF, 10V, 10%, 1210 MURATA, GRM32ER71A476KE15L
5 2 C7, C13 CAP., X7R, 1µF, 25V, 10%, 0603 MURATA, GRM188R71E105KA12D
6 1 C9 CAP., X5R, 4.7μF, 25V, 10%, 0603 MURATA, GRM188R61E475KE11D
7 1 C11 CAP., X5R, 10µF, 50V, 10%, 1206 MURATA, GRM31CR61H106KA12L
8 1 L1 IND, 1.5µH, IHLP2020CZ-01 VISHAY, IHLP2020CZER1R5M01
9 2 R1, R3 RES., CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA
10 1 R2 RES., CHIP, 18.2k, 1/10W, 1%, 0603 VISHAY, CRCW060318K2FKEA
11 1 R4 RES., CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA
12 1 R5 RES., CHIP, 243k, 1/10W, 1%, 0603 VISHAY, CRCW0603243KFKEA
13 1 U1 IC, REGULATOR, 20-QFN, UDC LINEAR TECHNOLOGY, LT8614EUDC#PBF
Additional Demo Board Circuit Components
1 1 C1 CAP., ALUM, 22µF, 63V SUN ELECT., 63CE22BS
2 1 C3 CAP., X7R, 4.7µF, 50V, 10%, 1206 MURATA, GRM31CR71H475KA12L
3 1 C10 CAP., X7R, 10µF, 50V, 10%, 1210 MURATA, GRM32ER71H106KA12L
4 1 C14 CAP., X7R, 0.1µF, 50V, 10%, 0402 TDK, C1005X7R1H104K
5 1 FB1 CHIP BEAD, MPZ2012 TDK, MPZ2012S300AT
6 1 L2 IND., 0.22µH,IHLP1616AB-01 VISHAY, IHLP1616ABERR22M01
7 0 R6 (OPT) RES., 0603
8 1 R7 RES., CHIP, 0, 1/10W, 0603 VISHAY, CRCW06030000Z0EA
Hardware: For Demo Board Only
1 10 E1-E10 TESTPOINT, TURRET, 0.094" pbf MILL-MAX, 2501-2-00-80-00-00-07-0
2 1 JP1 HEADER, 3 PIN, 0.079", SINGLE ROW SULLINS, NRPN031PAEN-RC
3 1 XJP1 SHUNT, 0.079", CENTER SAMTEC, 2SN-BK-G
4 4 MH1-MH4 STAND-OFF, NYLON, 0.50" TALL KEYSTONE, 8833 (SNAP-ON)

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dc2019bfb
DEMO MANUAL DC2019B
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.
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SCHEMATIC DIAGRAM

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dc2019bfb
DEMO MANUAL DC2019B
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2013
LT 0515 REV B • 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
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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.
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