LTC3725_15 Datasheet, PDF (1/20 Pages) Linear Technology – Single-Switch Forward Controller and Gate Driver

FEATURES
■ _{High Speed Gate Driver for Forward Converter}
■ _{On-Chip Rectifier and Self-Starting Architecture}
Eliminates Need for Separate Gate Drive Bias
Supply
■ _{Wide Input Voltage Supply Range: 9V and Up}
■ _{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 10-Lead MSOP Package}
U
APPLICATIO S
■ _{Isolated 48V Telecommunication Systems}
■ _{Internet Servers and Routers}
■ _{Distributed Power Step-Down Converters}
■ _{Automotive and Heavy Equipment}
LTC3725
Single-Switch Forward
Controller and Gate Driver
DESCRIPTIO
The LTC^®3725 is a controller for a single-switch forward
converter and includes an on-chip gate driver.
For secondary-side control, combine the LTC3725 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 LTC3725 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
V_IN+
36V TO 72V
1µF
100V
×2
V_IN–
36V-72V to 3.3V/30A Isolated Single-Switch Forward Converter
T1
•
•
L1
0.85µH
Si7450DP
0.030Ω
1W
•
2.2nF
200V
HAT2165
×2
0.0012Ω
1W
HAT2165
×2
B0540W
1.2Ω
1/4W
100µF
6.3V
×2
10µF
365k
15k
100k
FDC2512
NDRV GATE I_S
V_CC
FB/IN⁺
UVLO LTC3725
1µF
SSFLT
FS/IN^–
V_{SLMT PGND GND}
33nF
0.1µF
T2
••
5.1k
162k
L1: PULSE PA1294.910
T1: PULSE PA0815
T2: PULSE PA0297
FCX491A
2.2µF
1µF
FG SW I_S–
I_S+
PT⁺
SG V_IN NDRV V_CC MODE
LTC3706
FB
PT^–
GND PGND RUN/SS SLP REGSD FS/SYNC PHASE I_TH
33nF
100k
470pF
3.3k
47nF
V_OUT+
3.3V
30A
+
220µF
6.3V
V_OUT–
2.74k
604Ω
3725 TA01
3725fa
1