LTC3766
High Efficiency,
Secondary-Side Synchronous
Forward Controller
FEATURES DESCRIPTION
n
Direct Flux Limit Guarantees No Saturation
The LTC 3766 is a PolyPhase-capable secondary-side
n
Fast and Accurate Average Current Limit
controller for synchronous forward converters. When used
n
Clean Start-Up Into Pre-Biased Output
in conjunction with the LTC3765 active-clamp forward
n
Secondary-Side Control for Fast Transient Response
controller and gate driver, the part creates a complete
n
Simple, Self-Starting Architecture
isolated power supply that combines the power of multi-
n
Synchronous MOSFET Reverse Current Limit
phase operation with the speed of secondary-side control.
n
PolyPhase Operation Eases High-Power Design
The LTC3766 has been designed to simplify the design of
n
True Remote Sense Differential Amplifier
active clamp forward converters. Working in concert with
n
Remote Sense Reverse Protection
the LTC3765, the LTC3766 forms a robust, self-starting
n
High Voltage Linear Regulator Controller
converter that eliminates the need for the separate bias
n
Internal LDO Powers Gate Drive from V
OUT
regulator that is commonly used in secondary-side control
n
Overtemperature/Overvoltage Protection
applications. A precision current-limit coupled with clean
n
Low Profile 4mm 5mm QFN and Narrow 28-Lead
start-up into a pre-biased load make the LTC3766 an excel-
SSOP Packages
lent choice for high-power battery charger applications.
APPLICATIONS
The LTC3766 provides extensive remote sensing and output
protection features, while Direct Flux Limit guarantees no
n
Isolated 48V Telecommunication Systems
transformer saturation without compromising transient
n
Isolated Battery Chargers
response. A linear regulator controller and internal bypass
n
Automotive and Military Systems
LDO are also provided to simplify the generation of the
n
Industrial, Avionics and Heavy Equipment
secondary-side bias voltage.
L, LT, LTC, LTM, PolyPhase, Linear Technology and the Linear logo are registered and Direct
Flux Limit is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 7200014 and 6144194.
Other patents pending.
TYPICAL APPLICATION
36V 72V to 5V/15A Active Clamp Isolated Forward Converter
1.4H
+V
OUT
+V
IN 6:2
5V
36V TO 72V
15A
EFFICIENCY: 94% AT 48V /15A
IN OUT
2.2F 220F
100V FDMS86201 6.3V
BSC0901NS
SiR414DP
3 33nF 100nF 2
200V 200V
15m 3m
168
0.5W 2W
V
IN V
OUT
2.2nF
Si3437DV
200k
(SOT23) 250VAC
Si3440DV
+
1 FG SW SG RUN V NDRV V FS/SYNC V V
IN CC S S
4.42k
I
S
+
365k 0.1F 1.0F +
NDRV PG I I
AG I I FB
S S SMAG
S
2:1
+ + LTC3766
RUN IN PT ITH
604
LTC3765 PT
V
CC IN
SS
SSFLT FS/UV
470pF
4.7F GND PGND I SGD FGD MODE
PK
R
CORE DELAY SGND PGND
33nF 26.1k 15k 22.1k 17.8k
47pF
15.0k 33nF 10.5k 14k 18.2k
3766 TA01
3766fc
1
For more information www.linear.com/LTC3766LTC3766
ABSOLUTE MAXIMUM RATINGS (Note 1)
V Voltage .................................................0.3V to 12V V Voltage ................................................ 0.3V to 3V
CC
SEC
V Voltage ................................................. 0.3V to 33V I , SS Voltages ........................................... 0.3V to 4V
IN
PK
RUN Voltage............................................... 0.3V to 33V Operating Junction Temperature Range (Notes 2,3)
SW LTC3766E, LTC3766I ......................... 40C to 125C
Low Impedance Source ............................ 5V to 40V LTC3766H .......................................... 40C to 150C
Current Fed .......... 2mA DC or 0.2A for <1s Into Pin* LTC3766MP ....................................... 55C to 150C
+
V , V , V , V , NDRV Voltages ...... 0.3V to 16V Storage Temperature Range .................. 65C to 150C
AUX S S SOUT
+
ITH, I , REGSD Voltages ............................ 0.3V to 6V Lead Temperature (Soldering, 10 sec )
S
PHASE Voltage ............................................. 0.3V to 6V GN Package .....................................................300C
I , SGD, FGD Voltages ...............................0.3V to 12V
S
*The LTC3766 contains an internal 50V clamp that limits the voltage on the
FS/SYNC, FB, MODE Voltages .....................0.3V to 12V SW pin.
PIN CONFIGURATION
TOP VIEW
TOP VIEW
1 28 V
SG
CC
2 27 PGND
FG
28 27 26 25 24 23
+
3 26 PT
V
SEC
MODE 1 22 PT
4 25 PT
MODE
PHASE 2 21 V
AUX
5 24 V
PHASE
AUX
FB 3 20 SW
6 23 SW
FB
ITH 4 19
V
29 IN
7 22 V
ITH GND
IN
RUN 5 18 NDRV
8 21 NDRV
RUN
SS 6 17 FGD
9 20 FGD
SS
I 7 16 SGD
PK
+
10 19 SGD
I V 8 15 I
PK
SOUT S
+
11 18 I 9 10 11 12 13 14
V
SOUT S
+
12 17 I
V
S S
13 16 REGSD
V
S
14 15 FS/SYNC
GND
UFD PACKAGE
28-LEAD (4mm 5mm) PLASTIC QFN
GN PACKAGE
T = 125C, = 43C/W
JMAX JA
28-LEAD NARROW PLASTIC SSOP
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
T = 125C, = 95C/W
JMAX JA
3766fc
2
For more information www.linear.com/LTC3766
+
V
V
S SEC
V FG
S
GND SG
FS/SYNC V
CC
REGSD
PGND
+
I
PT
S