Linear Technology LT8608 User manual

1
dc2458af
DEMO MANUAL DC2458A
DESCRIPTION
LT8608
42V, 1.5V Micropower Synchronous
Step-Down Regulator
Demonstration circuit 2458A is a 42V, 1.5A micropower
synchronous step-down regulator featuring the LT
®
8608.
The demo board is designed for 5V output from a 5.5V to
42V input. The wide input range allows a variety of input
sources, such as automotive batteries and industrial sup-
plies. The LT8608 is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 2.5μA of quiescent current when
output is regulated at 5V. Top and bottom power switches,
compensation components and other necessary circuits
are inside of the LT8608 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
SKIPPINGpositioncanchangetheoperationmodetopulse-
skipping operation. Once JP1 is on SPREAD SPECTRUM
position, VCC is applied to the SYNC pin for low EMI spread
spectrum operation. To synchronous to an external clock, L, LT, LTC, LTM, Linear Technology, 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
move JP1 to SYNC and apply the external clock to the
SYNC turret. Figure 1 shows the efficiency of the circuit.
The demo board has an EMI filter installed. The radiated
EMI performances of the board (with EMI filter) are shown
in Figures 2 and 3. The red lines in Figures 2 and 3 are
CISPR25 class 5 peak limit. To use the EMI filter, the input
should be tied to VEMI, not VIN. An inductor L2, which is
a 0Ω jumper on the board by default now, can be added
in the EMI filter to further reduce the conducted emission.
The LT8608 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 DC2458A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2458A
Specifications are at TA= 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input Voltage Range 5.5 42 V
VOUT Output Voltage 4.8 5 5.2 V
IOUT Maximum Output Current 1.5 A
fSW Switching Frequency 1.85 2 2.15 MHz
EFE Efficiency at DC VIN = 12V, IOUT = 0.75A 92.2 %

2
dc2458af
DEMO MANUAL DC2458A
QUICK START PROCEDURE
DC2458A is easy to set up to evaluate the performance
of the LT8608. 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. See Figure 5 for the proper scope
technique.
1. Setan inputpowersupply thatis capableof 42V/1.5A.
Then turn off the supply.
2. With power off, connect the supply to the input
terminals VIN and GND.
3. Turn on the power at the input.
NOTE: Make sure that the input voltage never exceeds
42V.
4. Check for the proper output voltage of 5V. Turn off
the power at the input.
5. Once the proper output voltage is established, con-
nect a variable load capable of sinking 1.5A at 5V to
the output terminals VOUT and GND. Set the current
for 0A.
a. If efficiency measurements are desired, an am-
meter can be put in series with the output load in
order to measure the DC2458A’s output current.
b. A voltmeter can be placed across the output ter-
minals in order to get an accurate output voltage
measurement.
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 established again,
adjust the load and/or input within theoperatingrange
and observe the output voltage regulation, ripple
voltage, efficiency and other desired parameters.
8. 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 RTsets the
LT8608 switching frequency to equal or below the
lowest SYNC frequency. See the data sheet section,
Synchronization.
Figure 1. Efficiency vs Load Current at 2MHz Switching Frequency
IOUT (A)
0
EFFICIENCY (%)
100
95
85
75
90
80
55
60
65
70
50 0.5
DC2458a F01
1.5
1
12V INPUT
24V INPUT

3
dc2458af
DEMO MANUAL DC2458A
QUICK START PROCEDURE
Figure 2. LT8608 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test,
Antenna Polarization: Vertical (VIN = 14V, VOUT = 5V, IOUT = 1.5A, 2MHz Switching Frequency)

4
dc2458af
DEMO MANUAL DC2458A
Figure 3. LT8608 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test,
Antenna Polarization: Horizontal (VIN = 14V, VOUT = 5V, IOUT = 1.5A, 2MHz Switching Frequency)
QUICK START PROCEDURE

5
dc2458af
DEMO MANUAL DC2458A
QUICK START PROCEDURE
Figure 4. Proper Measurement Equipment Setup
Figure 5. Measuring Output Ripple

6
dc2458af
DEMO MANUAL DC2458A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 C2 CAP, X7R, 4.7µF, 50V, 10% 1206 MURATA, GRM31CR71H475K
2 1 C4 CAP, X7R, 0.22µF, 16V, 10%, 0603 AVX, 0603YC224KAT2A
3 1 C5 CAP, C0G, 10pF, 25V, 5%, 0603 AVX, 06033A100JAT2A
4 1 C6 CAP, X7R, 47µF, 10V, 10%, 1210 MURATA, GRM32ER71A476KE20L
5 1 C7 CAP, X7R, 1µF, 25V, 10%, 0603 MURATA, GRM188R71E105KA12D
6 1 C8 CAP, X7R, 0.01µF, 16V, 10%, 0603 AVX, 0603YC103KAT2A
7 1 L1 IND, 2.2µH COILCRAFT, XFL4020-222MEC
8 1 R2 RES, CHIP, 18.2k, 1/10W, 1%, 0603 VISHAY, CRCW060318K2FKEA
9 1 R3 RES, CHIP, 49.9k, 1/10W, 1%, 0603 VISHAY, CRCW060349K9FKEA
10 2 R1, R4 RES, CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA
11 1 R5 RES, CHIP, 187k, 1/10W, 1%, 0603 VISHAY, CRCW0603187KFKEA
12 1 U1 IC, REGULATOR, MSE10 LINEAR TECHNOLOGY, LT8608EMSE#PBF
Additional Demo Board Circuit Components
1 1 C1 CAP, ALUM 22µF 63V SUN ELECT, 63CE22BS
2 2 C3, C10 CAP, X7R, 4.7µF, 50V, 10% 1206 MURATA, GRM31CR71H475K
3 1 C9 CAP, X7R, 4.7µF, 16V, 10%, 0805 MURATA, GRM21BR71C475K73L
4 1 C11 CAP, X7R, 1µF, 50V, 10%, 0805 TDK, C2012X7R1H105K
5 2 C12, C13 CAP, X7R, 0.1µF, 50V, 10%, 0603 MURATA, GRM188R71H104KA93D
6 1 FB1 FERRITE BEAD 0805 TDK, MPZ2012S221AT000
7 1 L2 RES, CHIP, 0Ω, 3/4W, 2010 VISHAY, CRCW20100000Z0EF
8 0 R6 (OPT) RES, 0603
Hardware: For Demo Board Only
1 9 E1 TO E9 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0
2 1 E10 (OPT) TESTPOINT, TURRET, 0.094"
3 1 JP1 DOUBLE ROW HEADER 2 × 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)

7
dc2458af
DEMO MANUAL DC2458A
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
DD C C
B B
A A
ALL CAPACITORS ARE 0603.
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL RESISTORS ARE 0603.
SUNCON 63CE22BS
(2MHz)
SYNC SPREAD SPECTRUM PULSE SKIPPING BURST
VOUT
VCC
VCC
E6
EN/UV
R2
18.2k
E5
SYNC
R4
1.00M
+
C1 22µF 63V
L1
2.2µH
XFL4020-222MEC
E9
GND
E7
TR/SS
C6
47µF 10V 1210
C11 1µF
50V
0805
C8
0.01µF
C10 4.7µF 50V 1206
C4
0.22µF
R6 (Opt)
C7
1µF
E8 PG
R3 49.9k
JP1
1 2
3 5
7
4 6
8
E3
VOUT
5V / 1.5A
E4
GND
C5
10pF
R5 187k
R1 1.00M
L2
0 2010
C13 0.1µF 50V
C3 4.7µF 50V 1206
E1
VEMI
5.5V - 42V
FB1
MPZ2012S221AT000
C2 4.7µF 50V 1206
C12 0.1µF 50V
U1 LT8608EMSE
VIN
9
EN/UV
10
SYNC
5
VCC
3
TR/SS
7
RT
4
FB 6
PG 8
SW 2
BST 1
GND
11
E10
VIN
5.5V - 42V
E2
GND
C9 4.7µF 16V 0805

8
dc2458af
DEMO MANUAL DC2458A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2016
LT 0516 • 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:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation

Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Analog Devices Inc.:
DC2458A