LTC3705_15 Datasheet, PDF (1/20 Pages) Linear Technology – 2-Switch Forward Controller and Gate Driver

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
V_IN+
1µF
100V
x3
V_IN–
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
V_CC
SS/FLT
LTC3705
FS/IN^–
15k
33nF
GND PGND VSLMT
162k
33nF
1.2Ω
L1
1.2µH
Si7336ADP
×2
CMPSH1-4
V_OUT+
330µF
6.3V
×3
10µF
CZT3019
I_S– ^FG
I_S+
PT⁺
SW SG V_IN
LTC3706
NDRV V_CC
FS/SYNC
FB
ITH
PT^–
RUN/SS GND PGND PHASE SLP MODE REGSD
V_OUT–
2.2µF 102k
680pF
20k 22.6k
3705 TA01
3705fb
1