DC1439A - Demo Manual

DEMO MANUAL DC1439A
LT3688 Dual 800mA Step-Down
Switching Regulator with Power-On
Reset and Watchdog Timer
DESCRIPTION
Demonstration circuit 1439A is an adjustable dual monolithic step-down switching regulator with two power-on
reset timers and a watchdog timer. The regulator operates
off inputs up to 36V and withstands transients up to 60V.
The two buck outputs are capable of generating up to
800mA each and both of them have independent RUN/SS
function. The reset and watchdog timeout periods are both
adjustable using external capacitors.
The LT3688 is available in 24-Pin TSSOP and 4mm ×
4mm QFN packages, each with an exposed pad for low
thermal resistance.
PERFORMANCE SUMMARY
The LT3688 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 1439A.
Design files for this circuit board are available at
http://www.linear.com/demo
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.
Specifications are at TA = 25°C.
SYMBOL
PARAMETER
CONDITIONS
VIN
Input Supply Range
VOUT1 = 5V, IOUT1 = 800mA
VOUT2 = 3.3V, IOUT2 = 800mA
MIN
VOUT1
Output Voltage 1
VIN = 12V, IOUT1 = 800mA
4.85
VOUT2
Output Voltage 2
VIN = 12V, IOUT2 = 800mA
3.20
IOUT1
Output Current 1
IOUT2
Output Current 2
FSW
Switching Frequency
TYP
7
MAX
UNITS
36
V
5
5.15
V
3.3
3.40
V
0
800
mA
0
800
mA
1.1
MHz
0.9
1
tWDU
Watchdog Upper Boundary Period
C7 = 1000pF
20
ms
tWDL
Watchdog Lower Boundary Period
C7 = 1000pF
1.3
ms
tRST1
Programmed Reset Period 1
C8 = 1000pF
5
ms
tRST2
Programmed Reset Period 2
C9 = 1000pF
5
ms
dc1439af
1
DEMO MANUAL DC1439A
QUICK START PROCEDURE
Demonstration circuit 1439A is easy to set up to evaluate the performance of the LT3688. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
1.Place Jumper JP1 in the following position:
OFF: Watchdog Disabled
ON: Watchdog Enabled
2.With power off, connect the input power supply to VIN
and GND.
3. With power off, connect loads from VOUT1 to GND and
VOUT2 to GND.
4.Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed
36V.
5.Check for the proper output voltages:
VOUT1 = 5V, VOUT2 = 3.3V
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 voltages are established, adjust
the loads within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
7. To test the watchdog timer, connect a clock input to the
WDI terminal. Observe the output at the WDO terminal
while the clock parameters are adjusted.
8.To test Power-On Reset, observe output at the RESET
terminals: RST1 and RST2.
dc1439af
2
DEMO MANUAL DC1439A
QUICK START PROCEDURE
+
A
–
LOAD
–
+ +
V
–
–
V
+
+
A
+
–
POWER SUPPLY
+
+
A
–
+
V
LOAD
DC1439a F01
–
–
Figure 1. DC1439A Proper Equipment Setup
100
VOUT1 = 5V
EFFICIENCY (%)
90
80
VOUT2 = 3.3V
70
60
50
VIN = 12V
fSW = 1MHz
0
100
200
300
400 500
IOUT (mA)
600
700
800
DC1439a F02
Figure 2. Buck Efficiency vs Output Load
dc1439af
3
DEMO MANUAL DC1439A
PARTS LIST
ITEM QUANTITY
REFERENCE
DESCRIPTION
MANUFACTURER/PART NUMBER
Required Circuit Components:
1
2
C1, C2
CAP, X7R 22µF 10V 10% 1206
MURATA GRM31CR71A226ME15K
2
1
C3
CAP, X7R 4.7µF 50V 10% 1206
MURATA GRM31CR71H475K
3
2
C4, C6
CAP, X5R 0.22µF 6.3V 20% 0402
AVX 04026D224MAT2A
4
2
C5, C10
CAP, X7R 1000pF 25V 20% 0402
AVX 04023C102MAT2A
5
3
C7, C8, C9
CAP, NPO 1000pF 25V 5% 0402
AVX 04023A102JAT2A
6
2
C15, C16
CAP, NPO 22pF 25V 10% 0402
AVX 04023A220KAT2A
7
2
D1, D2
SCHOTTKY DIODE 1A/40V, PowerDI-123
DIODES INC. DFLS140
8
2
L1, L2
INDUCTOR, 10µH, NPIS43LS
NIC COMPONENTS CORP. NPIS43LS100MTRF
9
1
R3
RES, CHIP 562k 0.06W 1% 0402
VISHAY CRCW0402562KFKED
10
1
R4
RES, CHIP 107k 0.06W 1% 0402
VISHAY CRCW0402107KFKED
11
5
R5, R6, R9, R11, R12
RES, CHIP 100k 0.06W 5% 0402
VISHAY CRCW0402100KJNED
12
1
R7
RES, CHIP 316k 0.06W 1% 0402
VISHAY CRCW0402316KFKED
13
1
R8
RES, CHIP 49.9k 0.06W 1% 0402
VISHAY CRCW040249K9FKED
14
1
R10
RES, CHIP 100k 0.06W 1% 0402
VISHAY CRCW0402100KFKED
15
1
U1
IC, VOLTAGE REGULATOR TSSOP24-FE/AA
LINEAR TECHNOLOGY CORPORATION LT3688EFE
SANYO 63CE22BS
Additional Demo Board Circuit Components:
1
1
C11
CAP, ALUM 22µF 63V 25%, OSCON-CE-6.3
2
0
C12 (OPT)
CAP, 0603
3
0
C13 (OPT)
CAP, 1210
4
1
C14
CAP, NPO 1000pF 50V 5% 0402
AVX 04025A102JAT2A
5
1
R1
RES/JUMPER, CHIP 0Ω 1/16W 1A 0402
VISHAY CRCW04020000ZOEA
6
0
R2 (OPT)
RES, 0402
7
0
L3 (OPT)
INDUCTOR, 3.3µH, CDRH4D22
COILCRAFT LPS4018-332ML
8
0
E12 (OPT)
TURRET, TESTPOINT 0.062 THICK BRD. 0.094”
MILL MAX 2501-2-00-80-00-00-07-0
9
0
FB1 (OPT)
FERRITE BEAD, FBMJ4516HS720NB(BEAD), 1206
Hardware for Demo Board Only:
1
11
E1 to E11
TURRET, TESTPOINT 0.062 THICK BRD. 0.094”
MILL MAX 2501-2-00-80-00-00-07-0
2
2
JP1, JP2
HEADERS, 3 PINS 2mm CTRS.
SAMTEC TMM-103-02-L-S
3
2
XJP1, XJP2
SHUNT, 2mm CTRS.
SAMTEC 2SN-BK-G
dc1439af
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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 representation
that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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REVISION HISTORY
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TECHNOLOGY
2. INSTALL SHUNTS AS SHOWN.
1. ALL RESISTORS ARE IN OHMS, 
ALL CAPACITORS ARE IN MICROFARADS, 
NOTE: UNLESS OTHERWISE SPECIFIED.
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REV
ECO
DEMO MANUAL DC1439A
SCHEMATIC DIAGRAM
dc1439af
5
DEMO MANUAL DC1439A
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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
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Linear Technology Corporation
LT 0111 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2011
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