DEMO MANUAL DC1537A
LT3992A
Monolithic Dual Tracking 3A
Step-Down Switching Regulator
DESCRIPTION
The demo circuit 1537A is a dual current mode PWM
step-down DC/DC converter featuring LT
®
3992. The demo
circuit is designed for 5V and 3.3V outputs from a 7V to
60V input. The current capability of each channel is up to 3A
when running individually and 2A when both are sourcing
the same current without special heat sinking. Individual
soft-start, current limit, comparator, input voltage for each
output as well as frequency division and synchronous
and clock output functions simplify the complex design
of dual-output power converters
Both converters are synchronized to either a common
external clock input or a resistor programmable 250kHz to
2MHz internal oscillator. At all frequencies, a 180° phase
shift between channels is maintained, reducing voltage
ripple. Programmable frequency allows optimization be-
tween efficiency and external component size. Each output
can be independently disabled using its own SHDN pin
and be placed in a low quiescent current shutdown mode.
The LT3992 data sheet gives complete description of the
device, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 1537A.
Design files for this circuit board are available at
http://www.linear.com/demo
100
95
90
EFFICIENCY (%)
85
80
75
70
65
V
OUT1
= 5V
V
OUT2
= 3.3V
60
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0
LOAD CURRENT FOR SIGNAL CHANNEL (A)
DC1537a F01
Figure 1. Single Channel Efficiency at V
IN
= 24V,
f = 300kHz
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
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Specifications are at T
A
= 25°C.
VALUE
7V
60V (For Transient. Continuous Operation
if D3 and D4 Are Replaced with Higher
Voltage Rated Schottky Diodes)
CONDITIONS
Output Voltage V
OUT1
Output Voltage V
OUT2
Switching Frequency
Maximum Output Current I
OUT1
Maximum Output Current I
OUT2
Voltage Ripple V
OUT1
Voltage Ripple V
OUT2
V
IN
= 7~ 60V
V
IN
= 7~ 60V
V
IN
= 7~ 60V
V
IN
= 7~ 60V
V
IN
= 12V, I
OUT1
= 3A
V
IN
= 12V, I
OUT2
= 3A
5.0V ±3%
3.3V ±3%
300kHz ±10%
3A Individually, 2A Both Running
3A Individually, 2A Both Running
<20mV
<20mV
dc1537af
1
DEMO MANUAL DC1537A
DESCRIPTION
100
95
0.8
T
J
PIN VOLTAGE (V)
85
80
75
70
0.5
65
60
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT FOR BOTH CHANNELS (A)
DC1537a F02
0.9
V
OUT1
= 5V/3A, V
OUT2
NO LOAD
V
OUT2
= 3.3V/3A, V
OUT1
NO LOAD
T
J
PIN VOLTAGE (V)
20
25
35
40
0.9
0.8
90
EFFICIENCY (%)
0.7
0.7
0.6
0.6
0.5
0.4
5
10
15
30
V
IN
(V)
DC1537a F03
0.4
5
10
15
20
25
30
35
40
V
IN
(V)
DC1537a F04
Figure 2. Dual Channel Efficiency
at V
IN
= 24V, f = 300kHz
Figure 3. DC1537A T
J
Pin Voltage
When Channels Running Individually
at 3A Load (T
A
= 25°C)
Figure 4. DC1537A T
J
Pin Voltage
When Both Channels Sourcing 2A
Current at Meantime (T
A
= 25°C)
QUICK START PROCEDURE
Demo circuit 1537A is easy to set up to evaluate the
performance of the LT3992. 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. Measure the input or output
voltage ripple by touching the probe tip directly across
the VIN or VOUT and GND terminals. See Figure 6 for
proper scope probe technique.
1. Place JP1 on the SINGLE position.
2. With power off, connect the input power supply to VIN1
and GND. (Connect another input power supply to VIN2
and GND if DUAL is selected.)
3. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed
60V (Due to part selection on D3 and D4, 60V is for
transient purpose. Continuous operation can be avail-
able after D3 and D4 are replaced with higher voltage
rated schottky diodes).
dc1537af
4. Check for the proper output voltages.
NOTE. If there is no output, temporarily disconnect
the load to make sure that the load is not set too high.
5. Once the proper output voltages are established, adjust
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
ADDITIONAL NOTES
If an EMI filter is desirable on VIN1, it can be feasibly
installed on the back of the board in the optional circuit
area. However, a trace cut is required for the insertion of
the optional circuit. See Figure 7 for the cut line.
2
DEMO MANUAL DC1537A
QUICK START PROCEDURE
Figure 5. DC1537A Proper Equipment Setup
Figure 6. Measuring Input or Output Ripple
VIN
GND
Figure 7. Cut Line for the EMI Filter Installation
dc1537af
3
DEMO MANUAL DC1537A
PARTS LIST
ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
1
2
3
4
5
6
7
8
9
10
11
1
2
3
4
QTY
4
2
2
2
2
2
2
1
2
2
1
1
2
1
1
2
2
2
2
1
1
1
1
2
0
0
0
0
0
0
0
0
0
0
1
8
9
1
REFERENCE
C2, C3, C22, C23
C4, C5
C7, C8
C10, C11
C12, C13
C14, C15
C16, C17
C24
D1, D5
D2, D4
L1
L2
R1, R2
R5
R6
R7, R8
R9, R10
R11, R12
R13, R14
R15
R16
R17
U1
C1, C21
C6, C9
C18
C19
C20
C25
D3, D6
D7, D8
R18
FB1
L3
JP1
TP1, TP2, TP5 TO TP8,
TP16, TP17
JP1
PART DESCRIPTION
CAP 1210 2.2μF 10% 100V X7R
,
CAP 0603 0.47μF 10% 25V X7R
,
CAP 1210 100μF 20% 10V X5R
,
CAP 0402 22pF 10% 25V NPO
,
CAP 0402 0.1μF 10% 16V X7R
,
CAP 0402 680pF 10% 25V X7R
,
CAP 0402 33pF 10% 25V NPO
,
CAP 0402 10nF 10% 16V X7R
,
DIODE, SCHOTTKY BARRIER SOD123
DIODE, SCHOTTKY RECTIFIER SMB
IND, 22μH
IND, 10μH
RES, 0603 1kΩ 1% 1/16W
RES, 0402 42.2kΩ 1% 1/16W
RES, 0402 24.9kΩ 1% 1/16W
RES, 0402 100kΩ 5% 1/16W
RES, 0402 8.06kΩ 1% 1/16W
RES, 0402 100kΩ 1% 1/16W
RES, 0402 30kΩ 1% 1/16W
RES, 0402 7.32kΩ 1% 1/16W
RES, 0402 20kΩ 1% 1/16W
RES, 0402 40.2kΩ 1% 1/16W
IC, STEP-DOWN REGULATOR
CAP 22μF 20% 100V OSCON
,
CAP 0805 10μF 10% 16V X5R OPTION
,
CAP 22uF 20% 100V OSCON OPTION
,
CAP 0603 0.01μF 10% 100V X7R OPTION
,
CAP 1210 2.2μF 10% 100V X7R OPTION
,
CAP 0402 10nF 10% 16V X7R OPTION
,
DIODE, SCHOTTKY BARRIER SOD123 OPTION
DIODE, OPT
RES, 0603 0Ω JUMPER OPTION
FERRITE BEAD OPTION
IND, 22μH OPTION
HEADER, 4-PIN
TURRET
MANUFACTURER/PART NUMBER
AVX 12101C225KAT2A
MURATA GRM188R71E474KA12D
TAIYO YUDEN LMK325ABJ107MM-T
AVX 04023A220KAT2A
TDK C1005X7R1C104K
AVX 04023C681KAT2A
AVX 04023A330KAT
MURATA GRM155R71C103KA01D
ON SEMICONDUCTOR MMSD701T1G
DIODES INC. B360B
NIC NPIM104B220MTRF
NIC NPIM104B100MTRF
NIC NRC06F1001TRF
VISHAY CRCW040242K2FKED
VISHAY CRCW040224K9FKED
VISHAY CRCW0402100KJNED
VISHAY CRCW04028K06FKED
VISHAY CRCW0402100KFKED
NIC NRC04F3002TRF
VISHAY CRCW04027K32FKED
VISHAY CRCW040220K0FKED
VISHAY CRCW040240K2FKED
LINEAR TECHNOLOGY LT3992EFE
SUNCON 100CE22BS
MURATA GRM21BR61C106KE15L OPTION
SANYO 100CE22BS OPTION
AVX 06031C103KAT OPTION
AVX 12101C225KAT2A OPTION
MURATA GRM155R71C103KA01D OPTION
ON SEMICONDUCTOR MMSD701T1G OPTION
OPTION
VISHAY CRCW06030000Z0EA OPTION
TAIYO YUDEN FBMJ3216HS800 OPTION
VISHAY IHLP4040DZ-01 OPTION
SAMTEC TMM-104-02-L-S
MILL-MAX 2501-2-00-80-00-00-07-0
MILL-MAX 2308-2-00-80-00-00-07-0
SAMTEC 2SN-BK-G
dc1537af
Required Circuit Components
Additional Demo Board Circuit Components
Hardware/Components (For Demo Board Only)
TP3, TP4, TP9 TO TP15 TURRET
SHUNT, 2mm
4
5
4
3
2
1
REVISION HISTORY
INPUT MODE
1
ECO
REV
DESCRIPTION
DATE
APPROVED
SINGLE
2
EDWIN L.
PRODUCTION
01-17-12
CASCADE
DUAL
JP1
[1]
VIN2
D
2
VOUT1
3
4
D
VIN1
VIN2
7V - 60V
VIN1
+
TP1
VOUT2
U1
36
22
7V - 60V
VOUT1
VIN2
C23
2.2uF
100V
1210
C3
2.2uF
100V
1210
+
C1
22uF
100V
C2
2.2uF
100V
1210
R1
1k
1%
LT3992EFE
0603
VIN1
SHDN1
BST1
SW1
SW2
20
BST2
14
VIN2
35
SHDN2
6
23
0603
C22
2.2uF VIN1
100V
1210
D6
MMSD701T1G
OPT
D3
MMSD701T1G
OPT
R2
1k
1%
TP16
C21
22uF
100V
GND
GND
TP17
TP2
SHDN1
D7
OPT
38
SCHEMATIC DIAGRAM
SHDN2
TP4
TP3
D8
OPT
L2
10uH
B360B
2
IND1
VOUT1
FB1
CMPI1
CMPO1
SS1
ILIM1
VC1
RT/SYNC
DIV
NC
NC
NC
NC
PGND
NC
39
NC
17
NC
19
NC
21
NC
31
NC
37
TJ
28
CLKOUT
29
VC2
26
ILIM2
25
SS2
24
CMPO2
13
CMPI2
12
FB2
11
VOUT2
16
IND2
4
9
18
D1
MMSD701T1G
B360B
C4 0.47uF
0603
D2
L1
22uH
D4
C5 0.47uF
0603
D5
MMSD701T1G
C
C
VOUT1
C10
8
7
34
33
VOUT1
C11
22pF
VOUT2
C8
100uF
10V
1210
R8
100K
TP6
VOUT2
5V/2A
R5
42.2K
1%
22pF
R6
24.9K
1%
*
R7
100K
TP5
GND
C6
10uF
16V
OPT
0805
C7
100uF
10V
1210
C9
10uF
16V
OPT
0805
*
TP7
R9 8.06K 1%
32
30
TP8
R10 8.06K 1%
TP10
R12 100K 1%
R14 30k 1% C15 680pF
C17 33pF
R18
OPT
C24
10nF
R17
40.2k
1%
TP14
TP15
C13
0.1uF
TP12
GND
CMPO2
SS2
CMPO1
R11 100K 1%
27
1
3
5
10
15
TP9
SS1
C14 680pF R13 30k 1%
C16 33pF
TP11
C12
0.1uF
B
SYNC
C25
10nF
OPT
R15
7.32k
1%
R16
20k
1%
(300kHz)
TP13
CLKOUT
TEMP
B
VIN1
VIN1
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.
+
FB1 BEAD
C18
22uF
100V
OPT
L3 22uH
C19
0.01uF
100V
OPT
0603
OPT
OPT
C20
2.2uF
100V
OPT
1210
A
NOTES: UNLESS OTHERWISE SPECIFIED,
JW
EDWIN L.
TECHNOLOGY
A
[1] SEE QUICK START GUIDE FOR DETAILS ON JP1 SETTING
AND INPUT VOLTAGE IMPLEMENTATION ORDER.
2. ALL CAPACITORS ARE 0402.
ALL RESISTORS ARE 0402.
SEE QUICK START GUIDE FOR DETAILS ON
CURRENT CAPABILITY.
4
3
*
DUAL MONOLITHIC STEP-DOWN
CONVERTER
LT3992EFE
DEMO CIRCUIT 1537A
Tuesday, January 17, 2012
2
1
5
DEMO MANUAL DC1537A
dc1537af
5
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