DC448A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448
DUAL OUTPUT ISOLATED POWER SUPPLY
LT3710
DESCRIPTION
Demonstration circuit 448 is a dual output high efficiency isolated DC/DC power supply with 36V to 72V
input range. It has two outputs: 3.3V at 10A max and
1.8V or 2.5V at 10A max. LT3710, a secondary side synchronous post regulator controller, is used to generate a
tightly regulated second output directly from the transformer secondary winding, thus minimizing the size of
the output inductor and capacitor at the first output
stage. Synchronous MOSFETs significantly improve efficiency, making it suitable for low output voltage applications. The complete design is mounted within a standard
half brick PCB area with about half inch height.
Design files for this circuit board are available. Call
the LTC factory.
Table 1. Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
36V
Maximum Input Voltage
72V
VOUT1
VIN = 36V to 72V, IOUT1 = 0A to 10A,
3.3V ±2%
IOUT2 = 0A to 10A
VIN = 36V to 72V, IOUT1 = 0A to 10A,
1.83V ±2% (JP1, JP2: 1.8V position)
IOUT2 = 0A to 10A
or 2.53V ±2% (JP1, JP2: 2.5V position)
Typical Output Ripple VOUT1
VIN = 48V, IOUT1 = 10A (20MHz BW)
70mVP–P
Typical Output Ripple VOUT2
VIN = 48V, IOUT2 = 10A (20MHz BW)
50mVP–P for 1.8Vo
VOUT2
60mVP–P for 2.5Vo
Output Regulation
Line
±0.1%
Load
±0.2%
Nominal Switching Frequency
Efficiency
Output Voltage VOUT1 Trim
On/Off Control
Isolation Voltage
230kHz
VIN = 48V, VOUT1 =3.3V, VOUT2 =1.8V, IOUT1 =IOUT2 =10A
86% Typical
VIN = 48V, VOUT1 =3.3V, VOUT2 =2.5V, IOUT1 =IOUT2 =10A
87% Typical
VO1 TRIM =3.3V
5% Typical
VO1 TRIM =0V
–5% Typical
Logic Low Voltage-Off
0.6V Max
Logic High Voltage-On
1V Min
Basic Insulation
1500VDC
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448
DUAL OUTPUT ISOLATED POWER SUPPLY
OPERATING PRINCIPLES
Demonstration circuit 448A features the LT3710, LT3781
and LTC1698 controllers. The basic power stage topology is a two-switch forward converter with synchronous
rectification. The primary side controller uses the
LT3781, a current mode two-switch forward controller
with built-in MOSFET drivers. On the secondary side, an
LTC1698 is used to provide the voltage feedback for the
3.3V output, as well as the gate drive for the synchronous MOSFETs in the 3.3V output stage. The error amplifier output of the 3.3V circuit is fed into the optocoupler and then relayed to LT3781 on the primary side to
complete the 3.3V regulation. The second 1.8V/2.5V
output is directly regulated by the LT3710 circuit.
A planar transformer PA0191 built by Pulse Engineering
is employed as the power transformer in this design.
This transformer is constructed on a PQ20 core with
nine turns of primary windings, two turns of secondary
windings and seven turns of auxiliary windings for the
LT3781 bias supply. A Vishay Si7892DP is used due to
its low RDS(ON), 30V VDSS rating and its compact and
thermally enhanced PowerPak SO-8 package.
The switching frequency of the circuit is about 230KHz.
1500V input to output isolation is provided. Additional
features of this demo board include primary side on/off
control, ±5% secondary side trimming on the 3.3V output, input overvoltage protection, under voltage lockout,
3.3V output overvoltage protection, 1.8V/2.5V output
current limit and board overtemperature shutdown.
The demo board can deliver the full rated currents (10A
at both outputs) at room temperature without airflow.
The hottest spot on the demo board (T1 transformer)
has a temperature rise of 50°C at 48V input and full
loads (without airflow).
QUICK START PROCEDURE
Demonstration circuit DC448 is easy to set up to evaluate the performance of the LT3710, LT3781 and
LTC1698. Refer to Figure 1 for proper measurement
equipment setup and follow the procedure below:
NOTE: When measuring the input or output voltage rip-
ple, 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 2 for
proper scope probe technique.
Default jumper setting: both jumpers at 1.8V position
1. Select Vout2 1.8V (or 2.5V): Place both jumpers JP1
and JP2 at 1.8V (or 2.5V) position.
3. The on/off control pin should be left open for normal
operation. (Connecting the on/off pin to the –Vin
turns off the converter.)
4. For normal 3.3V output, Vo1 Trim pin should be left
open.
5. Connect the 3.3V load (Load 1 in Figure 1) between
+Vo1 and Vo RTN; connect the 1.8V/2.5V load
(Load 2 in Figure 1) between +Vo2 and Vo RTN.
6. Connect the DVMs to the input and outputs.
7. Turn on the input power supply and check for the
proper output voltages. Vo1 should be 3.3V ±2%. Vo2
should be 1.83V ±2% if 1.8Vo is selected (or Vo2
should be 2.53V ±2% if 2.5Vo is selected).
2. With power off, connect the input power supply to
+Vin (36V–72V) and –Vin (input return).
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448
DUAL OUTPUT ISOLATED POWER SUPPLY
+
+
+
+
–
–
+
LOAD 2
–
–
LOAD 1
+
–
+
–
–
–
+
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448
DUAL OUTPUT ISOLATED POWER SUPPLY
90
VIN = 36V
85
EFFICIENCY (%)
80
VIN = 48V
75
70
VIN = 72V
65
VOUT1 = 3.3V
VOUT2 = 1.8V
LOAD CURRENT = IVOUT1 = IVOUT2
60
55
0
1
2
3 4 5 6 7
LOAD CURRENT (A)
8
9
10
Figure 3. Efficiency vs load current: Vout1=3.3V and Vout2=1.8V
90
VIN = 36V
85
EFFICIENCY (%)
80
VIN = 48V
75
VIN = 72V
70
65
VOUT1 = 3.3V
VOUT2 = 2.5V
LOAD CURRENT = IVOUT1 = IVOUT2
60
55
0
1
2
3 4 5 6 7
LOAD CURRENT (A)
8
9
10
Figure 4. Efficiency vs load current: Vout1=3.3V and Vout2=2.5V
4
5
4
3
2
1
REVISIONHISTORY
N O T E S : UNLESS OTHERWISE SPECIFIED,
L T C CONFIDENTIAL - For Customer Use Only
ECO
[1]
DESCRIPTION
DATE
APPROVED
OPTIONAL.
0
36V-72V
REV
5
PROTO
<
??
Vi
L1
1.2uH
P1
VIN
+Vin
DO1813P-122HC
R1
1
5 6 7 8
2
Q1
Si7456DP
5 6 7 8
2
0
4
Q2
1
MMBT3906LT1
[1]
1 2 3
SEC
T1
Pulse
PA0191
1 2 3
1
3
D
Q15
Si7456DP
[1]
4
L3
CEP125-2R5
D
Vout
P8
7
Vout
+Vo1
D2
D1
[email protected]
B2100
1.5uF
1.5uF
100V
B2100
5 6 7 8
R2
100V
1
2
5 6 7 8
Q3
Si7456DP
4
4
5
Q16
Si7456DP
[1]
2
4
1 2 3
2
0
Q8
1
8 7 6 5
Q4
1 2 3
8 7 6 5
Q5
Si7892DP
4
Si7892DP
4
C9
1000pF
100V
R3
10
1/4W
R4
10
1/4W
8 7 6 5
C4
+ 470uF
4V
POSCAP
C5
+ 470uF
4V
POSCAP
C18
10uF
6.3V
Q6
Si7892DP
4
3
R9
C8
1000pF
100V
C7
+ 470uF
4V
[1]
2
C3
1
C2
3 2 1
MMBT3906LT1
[1]
3 2 1
3 2 1
P2
Vo RTN
C10
R6
-Vin
L2
1mH
P7
3
0.020 1 %
1/2W
Vout
3.3
2200pF
D3
D18
C6
250VAC
Vcc
1uF
DO1608C-105
COILCRAFT
Vi
B0540W
BAS21TA
D6
D4
BAS21TA
Q10
B0540W
R16
2K
0.25W
ZVN3310F
2
R25
20K
1
D7
R18
100
2
C
VccS
Q12
FZT690B
Q7
FZT853
C13
C
0.22uF
1
0.25W
2
3
Vcc
BAT54
D20
R17
R8
10
B0540W
1
3
Vcc
D19
5241B
11V
D12
2
10K
D10
10V
MMBZ5240B
C15
4.7uF
16V
2
1
3
C14
330pF
1
BAT54S
Vi
2
0.01uF
LT3781EG
1
8
4 3
5Vref
1
2
5
6
CG
VCOMP
2
16
11
FG
R33
3.01K
1%
B
8
MARGIN
VAUX
4700pF
3
ICOMP
1
[1]
R46
1K
13
R47
1.24K
1%
R48
1.78K
1%
C33
0.1uF
2
2
Vout
Vo1 Trim
2
1
0
0.01uF
C30
0.1uF
2
C32
82pF
R40
2
C11
1
C31
1uF
C29
8
3300pF
PWRGGD
C26
GND
C22
7
10
6
5
R42
2.43K
1%
9
P5
OPTODRV
PGND
VC
SGND
SS
R41
10
R45
1.24K
1%
OVPIN
1K
1
1
2
ISNSGND
2
1
4
R37
52.3K 1 %
R43
10K
R34
2.43K
1%
LTC1698EGN
MOC207
14
100K
C28
1000pF
Vout
U4
ISO1
9
R39
C25
4.7uF
16V
SYNC
VFB
7
1uF
15
2
470
R35
10
4
8
VFB
3K
C27
1
VDD
14
11
15
SYNC
FSET
5Vref
RT1
3
5
SHDN
6
1
12
220pF
THERM
D17
MMBD4148
5VREF
P9
ON OFF
SG
R31
1
0.022uF
R32
470
OVLO
7
2
7
C17
PGND
TG
U3
SENSE
VCC
VBST
13
B
18
100V
19
0.1uF
20
BAS21TA
1000pF
C19
T2
PULSE ENG.
P2033
4
1
C20
BG
D13
C16
C21
1uF
16V
1
C1
12
R26
73.2K
1%
BSTREF
R24
270K
0.25W
ISNS
Vcc
A
A
CONTRACTNO.
U N LESS OTHERWISE SPECIFIED
D IMENSIONS ARE IN INCHES
TOLERANCE ON ANGLE - - 2 PLACES - - 3 PLACES - - INTERPRET DIM AND TOL
PER ASME Y14.5M -1994
APPROV ALS
D R A W N MEI
DATE
07/15/02
TECHNOLOGY
TITLE
CHECKED
THIRD ANGLE PROJECTION
APPROVED
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
SCH, LT3710EFE/LT3781EG/LTC1698EGN DUAL OUTPUT
ISOLATED POWER SUPPLY
ENGINEER
DESIGNER
SIZE CAGE CODE
C
Friday, October 25, 2002
DO NOT SCALE DRAWING
5
4
3
2
SCALE:NONE
DWG NO
REV
5
DC448A
FILENAME: 448A-5.DSN
SHEET
1
1
OF
2
5
4
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1
REVI SION HISTORY
ECO
REV
>
DESCRIPTION
5
DATE
Proto
APPROVED
<
?
D
D
C37
4
680pF
14
2
C35
1
1
2
6
SW
CSET
BGATE
PGND
BGS
ILCOMP
10K
CL+
1
2
1
1 2 3
2
15
R7
9
L4
CEP125-1R8
R49
0.004 1%
P10
D15 CMDSH-3
5 6 7 8
0 [1]
1
Q14
Si7892DP
4
2
11
D16
Q17
Si7892DP
[1]
1 2 3
1 2 3
+Vo2
2512
C46
1000pF
5 6 7 8
4
12
C42
[1]
B340A
R64
10 [1]
1/4W
R59
100
4700pF
C12
+ 680uF
4V
[1]
C40
C41
+ 680uF
+ 680uF
4V
4V
POSCAP
POSCAP
[email protected]
C
C23
10uF
6.3V
R53
220
C43
8
CL-
R56
10
16
3
5 6 7 8
4
2
TGATE
10
180pF
50V
R57
2
Q13
Si7892DP
2
C
C47
1uF
GBIAS
LT3710EFE
VCC
C44
0.1uF
16V
1
1
VccS
SS
D14
CMDSH-3
1
13
SYNC
VFB
7
0.01uF
BOOST
C34
5
VAOUT
10K
1
2
C36
4.7uF
16V
1
2
2
U5
1
R58
1
SEC
[NOT USED]
R5
1
C45
10pF
2
2
Vout
0.01uF
R50
1
C38
R51
3.01K
1%
2
3.30K
.033uF
C39
330pF
JP2
R60
B
9.1K
1
2 . 5V
2
3
4
R61
R52
2.32K
1%
6.2K
R54
3.40K
1%
B
1 . 8V
JP1
1
2 . 5V
2
Vo2 SELECT
3
4
1 . 8V
UNLESS OTHERWISE SPECIFIED
DIMENSIONS ARE IN INCHES
TOLERANCE ON ANGLE - - 2 PLACES - - - 3 PLACES - - INTERPRET DIM AND TOL
PER ASME Y14.5M -1994
A
THIRD ANGLE PROJECTION
CONTRACT NO.
APPROVALS
DRAWN MEI
DATE
08-02-01
CHECKED
TECHNOLOGY
TITLE
APPROVED
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
A
SCH, LT3710EFE/LT3781EG/LTC1698EGN DUAL OUTPUT
ISOLATED POWER SUPPLY
ENGINEER
SIZE CAGE CODE
DESIGNER
B
DO NOT SCALE DRAWING
5
4
3
Friday, October 25, 2002
SCALE:NONE
2
DWG NO
REV
5
DC448A
FILENAME: 448A-5.PCB
SHEET
1
2
OF
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