Controller. LT1681 Datasheet

LT1681 Datasheet PDF

Part LT1681
Description Dual Transistor Synchronous Forward Controller
Feature U U LT1681 Dual Transistor Synchronous Forward Controller FEATURES s High Voltage: Operation Up t.
Manufacture Linear
Datasheet
Download LT1681 Datasheet





LT1681
LT1681
Dual Transistor
Synchronous Forward Controller
FEATURES
s High Voltage: Operation Up to 72V
s Synchronizable Operating Frequency and Output
Switch Phase for Multiple Controller Systems
s Fixed Frequency Operation to 350kHz
s Adaptive and Adjustable Blanking
s Synchronous Rectifier Driver
s Local 1% Voltage Reference
s Undervoltage Lockout Protection with Hysteresis
s Input Overvoltage Protection
s Programmable Start Inhibit
s Transformer Primary Saturation Protection
s Optocoupler Feedback Support
s Soft-Start Control
U
APPLICATIO S
s Isolated Telecommunication Systems
s Personal Computers and Peripherals
s Lead Acid Battery Backup Systems
s Automotive and Heavy Equipment
DESCRIPTIO
The LT®1681 controller simplifies the design of high power
synchronous dual transistor forward DC/DC converters. The
part employs fixed frequency current mode control and
supports both isolated and nonisolated topologies. The IC
drives external N-channel power MOSFETs and operates with
input voltages up to 72V.
The LT1681’s operating frequency is programmable and can
be synchronized up to 350kHz. Switch phase is also con-
trolled during synchronized operation to accommodate mul-
tiple converter systems. Internal logic guarantees 50% maxi-
mum duty cycle operation to prevent transformer saturation.
The LT1681 incorporates a soft-start feature that provides a
controlled increase in supplied current during start-up and
after an undervoltage lockout or overvoltage/overcurrent
event.
The part is available in a 20-lead wide SO package to support
high voltage pin-to-pin clearance.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
36V-72V DC to 5V/7A Synchronous Forward Converter (Half-Brick Footprint)
L1
4.7µH
VIN+
+ C2
22µF
100V
C4
1.5µF
100V
C3
1.5µF
100V
MURS120T3
Q1
MURS120T3
Q3 0.025
1/2W
6
1
7 2 10
3 0.25W
5
1nF
8 10 1nF 100V
4
11 100V 10
12 0.25W
9
T1 Q5
Q6
VIN–
C2:SANYO 100MV22AX
C3, C4: VITRAMON VJ1825Y155MXB
C5: 4X KEMET T510X337KO10AS
L1: COILCRAFT DO1608C-472
L2: PANASONIC ETQP6F4R1LF4
Q1,Q3:100V SILICONIX SUD40N10-25
Q5,Q6: SILICONIX Si4450
T1:COILTRONICS VP5-1200
Q10: ON SEMI MMBT3906LTI
73.2k
270k 1%
0.25W
20k
CMPZ5248B
18V
CMPZ-
5248B
15V
0.1µF
68µF +
20V
10k 56k
1.24k
1nF 24k 1%
ZVN3310F BAT54
1OV
BIAS
MMBD914LT1
0.1µF
100V
10k
330pF
BAS21
20 17 19 18 16 11 12 15
14
2
VCC
VBST
BLKSENS
TG
BSTREF
BG
SENSE
TMAX
PGND
SG
13
OVLO
LT1681
1 SHDN 5VREF FSET THERM SYNC SGND SS VC VFB 9
56
3 7 4 8 10
Q10 52.3k
100
5V
OUT
3.3
0.047µF
3.01k 51
1%
1µF
150pF
4.7nF
0.01µF
1k
1%
1OV
BIAS FZT690
100
4.7µF
16V
CMPZ5242B
12V
8 LTC1693-2 6
VCC1
VCC2
35
IN2 OUT2
1
IN1
7
OUT1
4
GND2
2
GND1
2k
0.22µF
50V
L2
4.1µH
VOUT = 5V
IOUT = 7A
VOUT+
MBR- +
0540T1
C5
330µF
10V
4.7
VOUT–
1681 TA01
1681f
1



LT1681
LT1681
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltages
Power Supply (VCC) ............................. – 0.3V to 20V
Topside Supply (VBST) ................... VBSTREF – 0.3V to
VBSTREF + 20V (VBST(MAX) = 90V)
Topside Reference Pin (VBSTREF) .......... – 0.6V to 75V
Input Voltages
SHDN Pin .................................. – 0.3V to VCC + 0.3V
All Other Inputs ..................... – 0.3V to 5VREF + 0.3V
Maximum Currents
5VREF Pin ........................................ – 85mA to 10mA
FSET Pin ............................................. – 2mA to 5mA
All Other Inputs .................................. – 2mA to 2mA
Operating Ambient Temperature Range
LT1681E (Note 4) .............................. – 40°C to 85°C
LT1681I ............................................. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
SHDN 1
OVLO 2
THERM 3
SGND 4
5VREF 5
FSET 6
SYNC 7
SS 8
VFB 9
VC 10
20 VBST
19 TG
18 BSTREF
17 BLKSENS
16 BG
15 PWRGND
14 VCC
13 SG
12 IMAX
11 SENSE
SW PACKAGE
20-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 85°C/ W
ORDER PART
NUMBER
LT1681ESW
LT1681ISW
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VCC = VBST = 12V, VBSTREF = 0V, VVC = 2V, VFB = VREF = 1.25V, CTG = CBG = CSG = 1000pF.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX
Supply and Protection
VCC Operating Supply Voltage Range
ICC DC Active Supply Current
(Note 2)
q 9 12 18
17 22
q 25
IBST
VSHDN
DC Active UVL Supply Current
DC Standby Supply Current
DC Active Supply Current
DC Standby Supply Current
Shutdown Rising Threshold
Shutdown Threshold Hysteresis
VSHDN > 1.35V, VCC = 8V
VSHDN < 0.3V
TG Logic High (Note 2)
VSHDN < 0.3V
q 800 1200
0.5
q 5 8.5
0.1
q 1.15 1.25 1.35
q 100 150 200
ISS
VSS
VCCUVLO
Soft-Start Charge Current
Soft-Start Reset Threshold
Undervoltage Lockout Threshold
VSS = 2V
Falling Edge
Rising Edge
q –14 – 10 – 6
225
q 8.0 8.40 8.60
q 8.3 8.75 8.95
Undervoltage Lockout Hysteresis
q 0.25 0.35
VBSTUVLO Boost Undervoltage Lockout
(VBST-BSTREF)
Boost UVLO Hysteresis
Falling Edge
Rising Edge
q 5.7 6.4 7.1
q 6.5 7.0 7.5
q 0.3 0.6
UNITS
V
mA
mA
µA
µA
mA
µA
V
mV
µA
mV
V
V
V
V
V
V
1681f
2




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