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LT3781EG#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
1
LT3781
3781f
FEATURES
APPLICATIO S
U
DESCRIPTIO
U
TYPICAL APPLICATIO
U
V
CC
13
2
1
5
1µF 150pF
OVLO
SHDN
73.2k
1%
20k
10k
270k
0.25W
68µF
20V
5V
REF
6
FSET
4.7nF
8
SS
10
14
BAT54
ZVN3310F
9
V
C
PGND
V
FB
374
THERM
LT3781
SYNC SGND
52.3k
100Ω
1k
1%
100Ω
2k
FZT690
4.7µF
16V
0.22µF
50V
CMPZ5242B
12V
3.3k
6.8k
10k
0.01µF
12
SG
+
0.1µF
11
SENSE
15
BG
18
BSTREF
19
TG
20
BAS21
0.1µF
100V
V
BST
C4
1.5µF
100V
C3
1.5µF
100V
L1
4.7µH
R9
0.025Ω
1/2W
Q3
1nF
100V
1nF
100V
Q5
Q6
MURS120T3
MURS120T3
Q1
T1
V
IN
+
V
IN
–
C2
22µF
100V
V
OUT
+
V
OUT
–
C5
330µF
10V
10Ω
0.25W
10Ω
0.25W
L2
4.7µH
330pF
+
1.24k
1%
•
•
•
•
V
CC1
IN2
IN1
GND2
V
CC2
OUT2
OUT1
GND1
8
3
1
4
6
5
7
2
LTC1693-2
1OV
BIAS
1OV
BIAS
V
OUT
= 5V
I
OUT
= 7A
MBR-
0540T1
MMBD914LT1
5V
OUT
3.01k
1%
51Ω
0.047µF
6
7
5
8
4
9
1
2
3
10
11
12
1nF
4.7Ω
+
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
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
High Voltage Operation up to 72V
■
Synchronizable Operating Frequency and Output
Switch Phase for Multiple Controller Systems
■
Synchronous Switch Output
■
Undervoltage Lockout Protection with 6V Hysteresis
for Self-Biased Power
■
Fixed Frequency Operation to 350kHz
■
Local ±1% Voltage Reference
■
Input Overvoltage Protection
■
Low Start-Up Current
■
Programmable Start Inhibit for Power Supply
Sequencing and Protection
■
Optocoupler Support
■
Soft-Start Control
“Bootstrap” Start Dual
Transistor Synchronous Forward Controller
36V-72V to 5V/7A DC/DC
Synchronous Forward Converter (Quarter-Brick Footprint)
■
Isolated Telecommunication Systems
■
Personal Computers and Peripherals
■
Distributed Power Step-Down Converters
■
Lead Acid Battery Backup Systems
■
Automotive and Heavy Equipment
The LT
®
3781 controller simplifies the design of high
power synchronous dual transistor forward DC/DC con-
verters. The part employs fixed frequency current mode
control and supports both isolated and nonisolated to-
pologies. The IC
drives external N-channel power MOSFETs
and operates with input voltages up to 72V.
The LT3781 is ideal for output derived power schemes,
through the use of a large undervoltage lockout hysteresis
range. The part is also equipped with an 18V V
CC
shunt
regulator, which prevents exceeding absolute maximum
ratings while in trickle start applications.
The LT3781’s operating frequency is programmable and
can be synchronized up to 350kHz. Switch phase is also
controlled during synchronized operation to accommo-
date multiple-converter systems. Internal logic guaran-
tees 50% maximum duty cycle operation to prevent trans-
former saturation.
The LT3781 is available in a 20-lead SSOP package.
2
LT3781
3781f
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
CC
= V
BST
= 12V, V
BSTREF
= 0V, V
VC
= 2V, V
FB
= V
REF
= 1.25V, C
TG
= C
BG
= C
SG
= 1000pF.
ELECTRICAL CHARACTERISTICS
Power Supply (V
CC
)
Low Impedance Source Voltage .............–0.3V to 20V
Shutdown Mode:
(Supply Self-Regulates to 18V)
Maximum Input Current ............................... 20mA
Topside Supply (V
BST
) ....................................................
V
BSTREF
– 0.3V to V
BSTREF
+20V (V
BST(MAX)
= 90V)
Topside Reference Pin (V
BSTREF
) ...............–0.6V to 75V
SHDN Pin Voltage........................... –0.3V to V
CC
+ 0.3V
All Other Input Voltages.............. –0.3V to 5V
REF
+ 0.3V
5V
REF
Pin Sink Current ......................................... 10mA
FSET Pin Current ...................................... –2mA to 5mA
All Other Input Pin Currents......................–2mA to 2mA
Operating Ambient
Temperature Range (Note 4) ...............–40°C to 85°C
Operating Junction
Temperature Range ...............................–40°C to 125°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
T
JMAX
= 125°C, θ
JA
= 90°C/W
LT3781EG
LT3781IG
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Note 1)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1
2
3
4
5
6
7
8
9
10
TOP VIEW
G PACKAGE
20-LEAD PLASTIC SSOP
20
19
18
17
16
15
14
13
12
11
SHDN
OVLO
THERM
SGND
5V
REF
FSET
SYNC
SS
V
FB
V
C
V
BST
TG
BSTREF
NC
NC
BG
PWRGND
V
CC
SG
SENSE
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Supply and Protection
V
CCUVLO
Undervoltage Lockout Threshold Falling Edge ● 8.0 8.4 8.6 V
Rising Edge
● 13 14.5 16 V
V
CCSHDN
Shutdown Mode Shunt Regulator 100µA < I
VCC
≤ 10mA ● 16.5 18 19.9 V
I
CC
DC Active Supply Current (Note 2) 17 22 mA
● 25 mA
DC Active UVLO Supply Current V
SHDN
= 1.35V, V
CC
= 8V ● 800 1200 µA
DC Standby Supply Current V
SHDN
< 0.3V ● 16 30 µA
V
BST
DC Active Supply Current TG Logic High (Note 2) ● 5.0 8.5 mA
DC Standby Supply Current V
SHDN
< 0.3V 0.1 µA
V
SHDN
Shutdown Rising Threshold ● 1.15 1.25 1.35 V
Shutdown Threshold Hysteresis 100 150 200 mV
I
SS
Soft-Start Charge Current V
SS
= 2V ● –14 –10 –6 µA
V
SS
Soft-Start Reset Threshold 225 mV
V
BSTUVLO
Boost Undervoltage Lockout Falling Edge ● 5.7 6.4 7.1 V
(V
BST
-BSTREF) Rising Edge ● 6.5 7.0 7.5 V
Boost UVLO Hysteresis ● 0.3 0.6 V
5V External Reference
V
5VREF
5V Reference Voltage 0 ≤ (I
5VREF
– I
VC
) < 20mA 4.85 5.0 5.10 V
● 4.80 5.15 V
I
5VREFSC
Short-Circuit Current Source, I
VC
= 0 ● 20 45 mA
R
5VREF
Output Impedance 0 ≤ (I
5VREF
– I
VC
) < 20mA 1 Ω
3
LT3781
3781f
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
CC
= V
BST
= 12V, V
BSTREF
= 0V, V
VC
= 2V, V
TS
= 0V, V
FB
= V
REF
= 1.25V, C
TG
= C
BG
= C
SG
= 1000pF.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Error Amp
V
FB
Error Amplifier Reference Voltage Measured at Feedback Pin 1.242 1.250 1.258 V
● 1.225 1.265 V
I
FB
Feedback Input Current V
FB
= V
REF
–50 nA
A
V
Error Amplifier Voltage Gain 72 dB
I
VC
Error Amplifier Current Limit Source ● 10 25 mA
Sink
● 0.5 1 mA
V
VC
Zero Current Output Voltage 1.4 V
Maximum Output Voltage 3.2 V
GBW Gain Bandwidth Product (Note 3) 1 MHz
Current Sense
A
V
Amplifier DC Gain 12 V/V
I
SENSE
Input Bias Current –275 µA
V
SENSE
Current Limit Threshold Measured at SENSE Pin 135 150 165 mV
● 130 170 mV
t
D
Current Sense to Switch Delay 175 ns
t
MIN
Switch Minimum On Time Measured at BG Output 250 ns
THERM and OVLO Fault Detectors
V
THERM
/ Threshold (Rising Edge) ● 1.2 1.25 1.3 V
V
OVLO
Threshold Hysteresis ● 20 40 60 mV
t
D
Fault Delay to Output Disable >50mV Overdrive 650 ns
Oscillator and Synchronization Decoder
f
OSC
Oscillator Frequency, Free Run Measured at F
SET
Pin 700 kHz
Frequency Programming Error f
OSC
≤ 500kHz (Note 3) ● –10 5 %
I
FSET
FSET Input Bias Current F
SET
Charging, V
FSET
= 2V 50 nA
V
SYNC
SYNC Logic High Input Threshold Positive-Going Edge ● 1.4 2 V
SYNC Logic Low Input Threshold Negative-Going Edge ● 0.8 1.4 V
f
SYNC
SYNC Frequency ● f
OSC
/2 350 kHz
t
H, L
Maximum SYNC Pulse Width f
OSC
= Oscillator Free-Run Frequency 1/f
OSC
s
(Logic High or Logic Low)
Output Drivers
V
TG
TG On Voltage ● 11 11.5 V
TG Off Voltage
● 0.1 0.5 V
t
TGr/f
TG Rise/Fall Time 10% to 90%/90% to 10% 35 ns
V
BG
BG On Voltage ● 11 11.5 12 V
BG Off Voltage
● 0.1 0.5 V
t
BGr/f
BG Rise/Fall Time 10% to 90%/90% to 10% 35 ns
V
SG
SG On Voltage ● 11 11.5 12 V
SG Off Voltage
● 0.1 0.5 V
t
SGr/f
SG Rise/Fall Time 10% to 90%/90% to 10% 35 ns
t
SG-BG
SG to BG Enable Lag Time 4V On/Off Thresholds ● 80 150 300 ns
t
TG-BG
TG to BG Enable Lag Time 4V On/Off Thresholds 100 ns
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20

LT3781EG#TRPBF

Mfr. #:
Buy LT3781EG#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Bootstrap Start 2x Trans Sync For Cntr
Lifecycle:
New from this manufacturer.
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