LTC3706_15 Datasheet, PDF (1/22 Pages) Linear Technology – Secondary-Side Synchronous Forward Controller with PolyPhase Capability

FEATURES
n _{Secondary-Side Control for Fast Transient Response}
n _{Self-Starting Architecture Eliminates Need for}
Separate Bias Regulator
n _{Proprietary Gate Drive Encoding Scheme Reduces}
System Complexity
n _PolyPhase^® _{Operation Reduces CIN Requirements}
n _{Current Mode Control Ensures Current Sharing}
n _{PLL Fixed Frequency: 100kHz to 500kHz}
n _{±1% Output Voltage Accuracy}
n _{True Remote Sense Differential Amplifier}
n _{Power Good Output Voltage Monitor}
n _{High Voltage Linear Regulator Controller}
n _{Wide Supply Range: 5V to 30V}
n _{Available in a Narrow 24-Lead SSOP Package}
APPLICATIONS
n _{Isolated 48V Telecommunication Systems}
n _{Internet Servers and Routers}
n _{Distributed Power Step-Down Converters}
n _{Automotive and Heavy Equipment}
L, LT, LTC, LTM, PolyPhase, Burst Mode, Linear Technology and the Linear logo are registered
trademarks and No R_SENSE and ThinSOT are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents
including 6144194, other patents pending.
LTC3706
Secondary-Side Synchronous
Forward Controller with
PolyPhase Capability
DESCRIPTION
The LTC^®3706 is a PolyPhase capable secondary-side
controller for synchronous forward converters. When used
in conjunction with the LTC3705 gate driver and primary-
side controller, the part creates a complete isolated power
supply that combines the power of PolyPhase operation
with the speed of secondary-side control.
The LTC3706 has been designed to simplify the design
of highly efficient, secondary-side forward converters.
Working in concert with the LTC3705, the LTC3706 forms
a robust, self-starting converter that eliminates the need
for the separate bias regulator that is commonly used in
secondary-side control applications. In addition, a pro-
prietary scheme is used to multiplex gate drive signals
and DC bias power across the isolation barrier through a
single, tiny pulse transformer.
The LTC3706 provides remote sensing, accurate power
good and overvoltage monitoring circuits to support preci-
sion, high current applications. A linear regulator controller
with thermal protection is also provided to simplify the
generation of secondary-side bias voltage.
The LTC3706 is available in a 24-lead SSOP package.
TYPICAL APPLICATION
36V-72V to 3.3V/20A Isolated Forward Converter
V_IN+
T1
Si7852DP
MURS120
••
1.2Ω
L1
1.2µH
V_OUT+
1µF
100V
×3
V_IN–
Si7852DP
Si7336ADP
30mΩ
1W
MURS120
2mΩ
2W
FQT7N10
100k
BAS21 ^0.22µF
L1: COILCRAFT SER2010-122
T1: PULSE PA0807
T2: PULSE PA0297
365k
1%
NDRV
UVLO
BOOST TG TS BG IS
FB/IN⁺
T2
••
2.2µF
25V
V_CC
SS/FLT
LTC3705
FS/IN^–
15k
1%
33nF
GND PGND VSLMT
162k
1µF
33nF
Si7336ADP
×2
CMPSH1-4
330µF
6.3V
×3
10µF
25V
CZT3019
V_OUT–
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
2.2µF 102k
16V
1%
680pF
20k
22.6k
1%
3706 TA01
3706fd
1