LTC3705 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC3705' PDF : 20 Pages View PDF
FEATURES
■ High-Speed Top and Bottom Gate Drivers for
2-Switch Forward Converter
■ On-Chip Rectifier and Self-Starting Architecture
Eliminate Need for Separate Gate Drive Bias
Supply
■ Wide Input Voltage Supply Range: 18V to 80V
■ Tolerant of 100V Input Voltage Transients
■ Linear Regulator Controller for Fast Start-Up
■ Precision UVLO with Adjustable Hysteresis
■ Overcurrent Protection
■ Volt-Second Limit Prevents Transformer Core
Saturation
■ Voltage Feedforward for Fast Transient Response
■ Available in 16-LeUad Narrow SSOP Package
APPLICATIO S
■ Isolated 48V Telecommunication Systems
■ Internet Servers and Routers
■ Distributed Power Step-Down Converters
■ Automotive and Heavy Equipment
LTC3705
2-Switch Forward
Controller and Gate Driver
DESCRIPTIO
The LTC®3705 is a controller for a 2-switch forward
converter and includes on-chip bottom and top gate
drivers that do not require external transformers.
For secondary-side control, combine the LTC3705 with
the LTC3706 PolyPhase® secondary-side synchronous
forward controller to create a complete forward converter
using a minimum of discrete parts. A proprietary scheme
is used to multiplex gate drive signals across the isolation
barrier through a tiny pulse transformer. The on-chip
rectifier and the same pulse transformer provide gate drive
bias power.
Alternatively, the LTC3705 can be used as a standalone
voltage mode controller in a primary-side control architec-
ture with optoisolator feedback. Voltage feedforward pro-
vides excellent line regulation and transient response.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
PolyPhase is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Patent Pending
TYPICAL APPLICATIO
36V –72V to 3.3V/20A Isolated 2-Switch Forward Converter
VIN+
1µF
100V
x3
VIN–
Si7852DP
MURS120
T1
••
Si7852DP
Si7336ADP
30mΩ
1W
MURS120
2mΩ
2W
FQT7N10
100k
BAS21 0.22µF
L1: COILCRAFT SER2010-122
T1: PULSE PA0807
T2: PULSE PA0297
365k
NDRV
UVLO
BOOST TG TS BG IS
FB/IN+
1µF
T2
••
2.2µF
VCC
SS/FLT
LTC3705
FS/IN–
15k
33nF
GND PGND VSLMT
162k
33nF
1.2Ω
L1
1.2µH
Si7336ADP
×2
CMPSH1-4
VOUT+
330µF
6.3V
×3
10µF
CZT3019
IS– FG
IS+
PT+
SW SG VIN
LTC3706
NDRV VCC
FS/SYNC
FB
ITH
PT–
RUN/SS GND PGND PHASE SLP MODE REGSD
VOUT–
2.2µF 102k
680pF
20k 22.6k
3705 TA01
3705fb
1
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