lt3781 Linear Technology Corporation, lt3781 Datasheet
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lt3781
Manufacturer Part Number
lt3781
Description
Bootstrap Start Dual Transistor Synchronous Forward Controller
Manufacturer
Linear Technology Corporation
Datasheet
1.LT3781.pdf
(20 pages)
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Linear Technology
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LT/凌特
Quantity:
20 000
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Part Number:
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FEATURES
APPLICATIO S
V
V
TYPICAL APPLICATIO
68 F
IN
IN
20V
+
–
0.1 F
High Voltage Operation up to 72V
Synchronizable Operating Frequency and Output
Switch Phase for Multiple Controller Systems
Synchronous Switch Output
Undervoltage Lockout Protection with 6V Hysteresis
for Self-Biased Power
Fixed Frequency Operation to 350kHz
Local 1% Voltage Reference
Input Overvoltage Protection
Low Start-Up Current
Programmable Start Inhibit for Power Supply
Sequencing and Protection
Optocoupler Support
Soft-Start Control
Isolated Telecommunication Systems
Personal Computers and Peripherals
Distributed Power Step-Down Converters
Lead Acid Battery Backup Systems
Automotive and Heavy Equipment
+
0.25W
270k
1nF
+
10k
73.2k
20k
4.7 H
C2
22 F
100V
1%
L1
BIAS
1.24k
1%
1OV
13
U
MMBD914LT1
2
1
C3
1.5 F
100V
BAS21
V
OVLO
SHDN
CC
1 F
V
BST
5V
20
C4
1.5 F
100V
REF
5
52.3k
0.1 F
100V
Transistor Synchronous Forward Controller
FSET
6
TG
150pF
19
U
Synchronous Forward Converter (Quarter-Brick Footprint)
BSTREF
THERM
LT3781
18
3
BG
SYNC SGND
15
SENSE
7
4.7nF
11
ZVN3310F
4
SS
MURS120T3
8
PGND
36V-72V to 5V/7A DC/DC
V
C
14
10
100
Q3
V
BAT54
SG
10k
FB
330pF
0.01 F
12
9
MURS120T3
OUT
5V
0.047 F
3.01k
1%
1%
1k
0.025
1/2W
DESCRIPTIO
R9
The LT
power synchronous dual transistor forward DC/DC con-
verters. The part employs fixed frequency current mode
control and supports both isolated and nonisolated to-
pologies. The IC drives external N-channel power MOSFETs
and operates with input voltages up to 72V.
The LT3781 is ideal for output derived power schemes,
through the use of a large undervoltage lockout hysteresis
range. The part is also equipped with an 18V V
regulator, which prevents exceeding absolute maximum
ratings while in trickle start applications.
The LT3781’s operating frequency is programmable and
can be synchronized up to 350kHz. Switch phase is also
controlled during synchronized operation to accommo-
date multiple-converter systems. Internal logic guaran-
tees 50% maximum duty cycle operation to prevent trans-
former saturation.
The LT3781 is available in a 20-lead SSOP package.
Q1
3.3k
6.8k
, LTC and LT are registered trademarks of Linear Technology Corporation.
51
8
3
1
4
®
3781 controller simplifies the design of high
V
IN2
IN1
GND2
6
7
5
8
4
9
LTC1693-2
CC1
“Bootstrap” Start Dual
T1
BIAS
1OV
GND1
OUT2
OUT1
V
CC2
Q5
10
11
12
1
2
3
6
5
7
2
C2:SANYO 100MV22AX
C3, C4: VITRAMON VJ1825Y155MXB
C5: 4X KEMET T510X337KO10AS
L1: COILCRAFT DO1608C-472
4.7 F
100V
U
FZT690
1nF
16V
100V
0.25W
0.25W
1nF
10
10
CMPZ5242B
100
12V
Q6
2k
0.22 F
50V
4.7 H
4.7
L2: PANASONIC ETQP6F4R1LF4
Q1,Q3:100V SILICONIX SUD40N10-25
Q5,Q6: SILICONIX Si4450
T1:COILTRONICS VP5-1200
L2
MBR-
0540T1
+
LT3781
C5
330 F
10V
CC
V
I
OUT
OUT
V
V
OUT
OUT
shunt
= 7A
= 5V
+
–
1
3781f