controller for synchronous forward converters. When used
in conjunction with the LTC3765 active-clamp forward
controller and gate driver, the part creates a complete
isolated power supply that combines the power of multi-
phase operation with the speed of secondary-side control.
The LTC3766 has been designed to simplify the design of
active clamp forward converters. Working in concert with
the LTC3765, the LTC3766 forms a robust, self-starting
converter that eliminates the need for the separate bias
regulator that is commonly used in secondary-side control
applications. A precision current-limit coupled with clean
start-up into a pre-biased load make the LTC3766 an excel-
lent choice for high-power battery charger applications.
The LTC3766 provides extensive remote sensing and output
protection features, while Direct Flux Limit guarantees no
transformer saturation without compromising transient
response. A linear regulator controller and internal bypass
LDO are also provided to simplify the generation of the
secondary-side bias voltage.
Direct Flux Limit™ Guarantees No Saturation
Fast and Accurate Average Current Limit
Clean Start-Up Into Pre-Biased Output
Secondary-Side Control for Fast Transient Response
Simple, Self-Starting Architecture
Synchronous MOSFET Reverse Current Limit
PolyPhase
®
Operation Eases High-Power Design
True Remote Sense Differential Amplifier
Remote Sense Reverse Protection
High Voltage Linear Regulator Controller
Internal LDO Powers Gate Drive from V
OUT
Overtemperature/Overvoltage Protection
Low Profile 4mm
×
5mm QFN and Narrow 28-Lead
SSOP Packages
APPLICATIONS
n
n
n
n
Isolated 48V Telecommunication Systems
Isolated Battery Chargers
Automotive and Military Systems
Industrial, Avionics and Heavy Equipment
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
+V
IN
36V TO 72V
2.2µF
100V
×3
36V – 72V to 5V/15A Active Clamp Isolated Forward Converter
•
6:2
1.4µH
•
EFFICIENCY: 94% AT 48V
IN
/15A
OUT
+V
OUT
5V
15A
220µF
6.3V
×2
FDMS86201
33nF
200V
15m
0.5W
168
100nF
200V
3m
2W
BSC0901NS
SiR414DP
–V
IN
Si3440DV
200k
–V
OUT
Si3437DV
(SOT23)
1
365k
NDRV PG
RUN
V
CC
4.7µF
15.0k
SSFLT
R
CORE
33nF
10.5k
LTC3765
DELAY
14k
I
S+
I
S–
AG
I
SMAG
0.1µF
1.0µF
2.2nF
250VAC
FG SW SG RUN V
IN
NDRV V
CC
FS/SYNC V
S+
V
S–
I
S–
I
S+
PT
+
PT
–
SS
33nF
GND
PGND
I
PK
SGD
15k
FGD
MODE
47pF
LTC3766
FB
ITH
604
470pF
17.8k
3766 TA01
4.42k
IN
+
IN
–
•
2:1
•
FS/UV
SGND PGND
18.2k
26.1k
22.1k
3766fc
For more information
www.linear.com/LTC3766
1
LTC3766
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
CC
Voltage .................................................–0.3V to 12V
V
IN
Voltage ................................................. –0.3V to 33V
RUN Voltage............................................... –0.3V to 33V
SW
Low Impedance Source ............................ –5V to 40V
Current Fed .......... 2mA DC or 0.2A for <1μs Into Pin*
V
AUX
, V
S+
, V
S –
, V
SOUT
, NDRV Voltages ...... –0.3V to 16V
ITH, I
S+
, REGSD Voltages ............................ –0.3V to 6V
PHASE Voltage............................................. –0.3V to 6V
I
S –
, SGD, FGD Voltages ...............................–0.3V to 12V
FS/SYNC, FB, MODE Voltages .....................–0.3V to 12V
V
SEC
Voltage ................................................ –0.3V to 3V
I
PK
, SS Voltages ........................................... –0.3V to 4V
Operating Junction Temperature Range (Notes 2,3)
LTC3766E, LTC3766I ......................... –40°C to 125°C
LTC3766H .......................................... –40°C to 150°C
LTC3766MP ....................................... –55°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec )
GN Package ..................................................... 300°C
*The LTC3766 contains an internal 50V clamp that limits the voltage on the
SW pin.
PIN CONFIGURATION
TOP VIEW
V
SEC
SG
FG
V
SEC
MODE
PHASE
FB
ITH
RUN
SS
1
2
3
4
5
6
7
8
9
28 V
CC
27 PGND
26 PT
+
25 PT
–
24 V
AUX
23 SW
22 V
IN
21 NDRV
20 FGD
19 SGD
18 I
S+
17 I
S–
16 REGSD
15 FS/SYNC
MODE 1
PHASE 2
FB 3
ITH 4
RUN 5
SS 6
I
PK
7
V
SOUT
8
9 10 11 12 13 14
FS/SYNC
GND
REGSD
V
S+
V
S–
I
S
–
TOP VIEW
PGND
V
CC
PT
+
22 PT
–
21 V
AUX
20 SW
29
GND
19 V
IN
18 NDRV
17 FGD
16 SGD
15 I
S+
SG
FG
28 27 26 25 24 23
I
PK
10
V
SOUT
11
V
S+
12
V
S–
13
GND 14
GN PACKAGE
28-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
2
3766fc
For more information
www.linear.com/LTC3766
LTC3766
ORDER INFORMATION
http://www.linear.com/product/LTC3766#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3766EGN#PBF
LTC3766EGN#TRPBF
LTC3766GN
28-Lead Narrow Plastic SSOP
–40°C to 125°C
LTC3766IGN#PBF
LTC3766IGN#TRPBF
LTC3766GN
28-Lead Narrow Plastic SSOP
–40°C to 125°C
LTC3766HGN#PBF
LTC3766HGN#TRPBF
LTC3766GN
28-Lead Narrow Plastic SSOP
–40°C to 150°C
LTC3766MPGN#PBF
LTC3766MPGN#TRPBF
LTC3766GN
28-Lead Narrow Plastic SSOP
–55°C to 150°C
LTC3766EUFD#PBF
LTC3766EUFD#TRPBF
3766
28-Lead (4mm
×
5mm) Plastic QFN
–40°C to 125°C
LTC3766IUFD#PBF
LTC3766IUFD#TRPBF
3766
28-Lead (4mm
×
5mm) Plastic QFN
–40°C to 125°C
LTC3766HUFD#PBF
LTC3766HUFD#TRPBF
3766
28-Lead (4mm
×
5mm) Plastic QFN
–40°C to 150°C
LTC3766MPUFD#PBF
LTC3766MPUFD#TRPBF 3766
28-Lead (4mm
×
5mm) Plastic QFN
–55°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
Main Control Loop
Regulated Feedback Voltage
V
FB
Feedback Input Current
I
FB
Feedback Voltage Line Regulation
ΔV
FB(LINREG)
ΔV
FB(LOADREG)
Feedback Voltage Load Regulation
Average Current Sense Threshold
V
ISAVG
V
ISADJ
Current Sense Ripple Compensation
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. (Note 2) V
IN
= 15V, GND = PGND = 0V, unless otherwise noted.
CONDITIONS
(Note 4) ITH = 1.2V
(Note 4)
V
IN
= 5V to 32V, ITH = 1.2V
Measured in Servo Loop, ITH = 0.5V to 2V
Resistor Sense (RS) Mode
Current Transformer (CT) Mode
RS Mode
CT Mode
V
SW
= 10V, V
S+
= 5V, FS/SYNC = V
CC
,
R
IPK
= 23.7k
RS Mode: V
IS–
= 0V
CT Mode: V
IS–
= V
CC
l
MIN
0.592
TYP
0.600
2
0.001
–0.01
55
0.73
10
140
100
1.33
280
2.7
5
5
3
1.22
1.17
3.0
200
79
MAX
0.608
50
–0.1
63
0.80
UNITS
V
nA
%/V
%
mV
V
mV
mV
mV
V
nA
mS
MΩ
μA
μA
V
V
μA
ns
%
%
%
Ω
V
%
l
47
0.66
V
ISOC
I
SIN
g
m
R
EA
I
SOFT(C)
I
SOFT(D)
V
RUNR
V
RUNF
I
RUN
t
ON(MIN)
D
MAX
ΔV
SEC(TH)
R
VSDN
V
SWCL
ΔV
FB(OV)
Overcurrent Shutdown Threshold
I
S+
and I
S–
Input Current
Error Amplifier g
m
Error Amplifier Output Resistance
Soft-Start Charge Current
Soft-Start Discharge Current
RUN Pin On Threshold
RUN Pin Off Threshold
RUN Pin Hysteresis Current
Minimum Controllable On Time
Maximum Duty Cycle
Volt-Second Limit Threshold Accuracy
Volt-Second Discharge Resistance
SW Clamp Voltage
Output Overvoltage Threshold
86
1.22
2.2
113
1.44
500
3.2
6
1.26
1.21
3.6
81
6
4
60
19
(Note 7)
V
SS
= 2V
V
SS
= 2V
V
RUN
Rising
V
RUN
Falling
V
RUN
= 0.5V
FGD = SGD = GND
2V ≤ V
SW
< 5V
5V ≤ V
SW
≤ 40V
I
SW
= 1mA
V
FB
Rising
4
l
l
1.18
1.13
2.2
77
–6
–4
43
15
75
51
17
3766fc
For more information
www.linear.com/LTC3766
3
LTC3766
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
Drivers and Control
FG, SG Driver Pull-Up On-Resistance
FG, SG R
UP
FG, SG R
DOWN
FG, SG Driver Pull-Down On-Resistance
PT
+
, PT
–
Driver Pull-Up Resistance
PT
+
, PT
–
R
UP
PT
+
,PT
–
R
DOWN
PT
+
, PT
–
Driver Pull-Down Resistance
FGD Delay
t
FGD
t
SGD
V
SW(REV)
I
SW(REV)
V
CC
Supply
V
CCOP
I
CC
V
UVLOR
V
UVLOF
V
REGSD
I
REGSD(C)
I
REGSD(D)
V
AUX
Supply
V
AUXOP
V
CCVAUX
V
AUXLR
V
AUXSWP
V
AUXSWN
R
AUX
R
PSL
V
IN
Supply
V
INOP
V
INCL
I
CLMAX
V
CCVIN
I
IN
V
INUVLO
SGD Delay
SG Reverse Overcurrent SW Threshold
SG Reverse Overcurrent Adjust Current
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. (Note 2) V
IN
= 15V, GND = PGND = 0V, unless otherwise noted.
CONDITIONS
MIN
TYP
1.5
1.0
1.5
1.5
65
545
75
230
73
148
–103
–42
MAX
UNITS
Ω
Ω
Ω
Ω
ns
ns
ns
ns
mV
mV
µA
µA
V
mA
µA
V
V
V
V
V
μA
μA
V
V
V
%
V
V
V
V
Ω
Ω
V
V
mA
V
V
µA
µA
V
R
FGD
= 10kΩ
R
FGD
= 100kΩ
R
SGD
= 15kΩ
R
SGD
= 50kΩ
LV MODE
HV MODE
LV MODE
HV MODE
50
436
60
195
66
140
–86
–34.5
5
80
654
90
265
79
156
–120
–49
10
V
CC
Operating Voltage Range
Supply Current
Normal Mode
Shutdown
UV Lockout Rising
UV Lockout Falling
REGSD Threshold Voltage
REGSD Charge Current
REGSD Discharge Current
V
AUX
Operating Voltage Range
Regulated V
CC
Output Voltage
V
CC
Load Regulation
V
AUX
Switchover Voltage Rising
V
AUX
Switchover Voltage Falling
V
AUX
Dropout Resistance
V
AUX
Pre-Switchover Load
V
IN
Operating Voltage Range
V
IN
Clamp Voltage
V
IN
Clamp Current Limit
Regulated V
CC
Output Voltage
Supply Current
Operating
Shutdown
V
IN
Undervoltage Lockout
V
FS/SYNC
= V
CC
= 7V (Note 5)
V
RUN
= GND
V
CC
Rising, LV MODE
V
CC
Rising, HV MODE
V
CC
Falling, LV MODE
V
CC
Falling, HV MODE
V
REGSD
Rising
V
REGSD
= 0.7V
V
REGSD
= 0.7V
l
l
l
l
4.6
7.7
3.8
6.7
5
210
4.7
7.9
3.9
6.9
1.21
13
3
4.8
8.1
4.0
7.1
V
AUX
= 15V, LV MODE
V
AUX
= 15V, HV MODE
I
CC
= 0mA to 120mA, V
AUX
= 8V, LV MODE
V
AUX
Ramping Positive, LV MODE
V
AUX
Ramping Positive, HV MODE
V
AUX
Ramping Negative, LV MODE
V
AUX
Ramping Negative, HV MODE
I
CC
= 120mA, V
AUX
= 4.9V
V
AUX
= 4V
5
6.7
8.1
4.50
7.65
4.30
7.35
7.0
8.5
0.8
4.70
8.00
4.50
7.70
1.7
920
15
7.3
8.9
2
4.88
8.35
4.70
8.05
2.5
I
VIN
= 2mA, V
RUN
= GND
V
IN
= 33V, V
RUN
= GND
LV MODE (Note 6)
HV MODE (Note 6)
V
FS/SYNC
= V
CC
V
RUN
= GND
V
IN
Rising
5
28
3.8
6.7
8.1
30
5.5
7.2
8.5
900
450
3.2
32
32
7.2
7.3
8.9
1200
3.8
2.6
4
3766fc
For more information
www.linear.com/LTC3766
LTC3766
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
Oscillator and Phase-Locked Loop
FS/SYNC Pin Sourcing Current
I
FS/SYNC
Oscillator High Frequency Set Point
f
HIGH
Oscillator Resistor Set Accuracy
Δf (R
FS/SYNC
)
PLL Sync Frequency Range
f
PLL(RANGE)
Differential Amplifier
Gain
A
DA
Common Mode Rejection Ratio
CMRR
DA
V
S+
Input Resistance
R
INP
V
S–
Input Resistance
R
INM
Output Sourcing Current
I
OH
Output High Fault Threshold
V
IN
-V
OHST
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. (Note 2) V
IN
= 15V, GND = PGND = 0V, unless otherwise noted.
CONDITIONS
MIN
TYP
20
275
MAX
UNITS
μA
kHz
%
kHz
V/V
dB
kΩ
kΩ
mA
V
V
FS/SYNC
= V
CC
18.75kΩ < R
FS/SYNC
< 125kΩ
l
234
–12
100
0.99
316
12
500
1.01
1.5V ≤ V
SOUT
≤ 15V, V
IN
= 20V
V
IN
= 20V
V
IN
= 20V
V
IN
= 20V
V
IN
= 20V, V
S+
= 5V, V
SOUT
= 2.5V
V
S+
Rising
l
0.8
1
75
120
160
3.0
1.2
1.5
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3766E is guaranteed to meet specifications from 0°C
to 85°C with specifications over the –40°C to 125°C operating junction
temperature range assured by design, characterization and correlation with
statistical process controls. The LTC3766I is guaranteed over the –40°C to
125°C operating junction temperature range, the LTC3766H is guaranteed
over the –40°C to 150°C operating junction temperature range, and the
LTC3766MP is tested and guaranteed over the –55°C to 150°C operating
junction temperature range. High junction temperatures degrade operating
lifetimes; operating lifetime is derated for junction temperatures greater
than 125°C. Note that the maximum ambient temperature consistent with
these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance and
other environmental factors.
Note 3:
T
J
is calculated from the ambient temperature, T
A
, and power
dissipation, P
D
, according to the following formula:
T
J
= T
A
+ (P
D
•
θ
JA
°C/W)
where
θ
JA
is 95°C/W for the SSOP and 43°C/W for the QFN package.
Note 4:
The LTC3766 is tested in a feedback loop that servos V
FB
to a
voltage near the internal 0.6V reference voltage to obtain the specified ITH
voltage (V
ITH
= 1.2V).
Note 5:
Operating supply current is measured in test mode. Dynamic
supply current is higher due to the internal gate charge being delivered at
the switching frequency. See Typical Performance Characteristics.
Note 6:
The V
IN
Regulator employs an external pass device to produce the
regulated V
CC
output voltage. The LTC3766 is tested using a 2N3904 NPN
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