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LT1681ESW#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
1
LT1681
1681f
APPLICATIO S
U
DESCRIPTIO
U
FEATURES
TYPICAL APPLICATIO
U
Dual Transistor
Synchronous Forward Controller
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.
■
Isolated Telecommunication Systems
■
Personal Computers and Peripherals
■
Lead Acid Battery Backup Systems
■
Automotive and Heavy Equipment
■
High Voltage: Operation Up to 72V
■
Synchronizable Operating Frequency and Output
Switch Phase for Multiple Controller Systems
■
Fixed Frequency Operation to 350kHz
■
Adaptive and Adjustable Blanking
■
Synchronous Rectifier Driver
■
Local 1% Voltage Reference
■
Undervoltage Lockout Protection with Hysteresis
■
Input Overvoltage Protection
■
Programmable Start Inhibit
■
Transformer Primary Saturation Protection
■
Optocoupler Feedback Support
■
Soft-Start Control
, LTC and LT are registered trademarks of Linear Technology Corporation.
36V-72V DC to 5V/7A Synchronous Forward Converter (Half-Brick Footprint)
V
CC
14
2
1
5
1µF 150pF
OVLO
SHDN
73.2k
1%
20k
10k
270k
0.25W
68µF
20V
5V
REF
6
F
SET
4.7nF
8
SS
10
15
BAT54
ZVN3310F
9
V
C
PGND
V
FB
374
THERM
LT1681
SYNC SGND
52.3k
100Ω
1k
1%
100Ω
2k
FZT690
4.7µF
16V
0.22µF
50V
CMPZ5242B
12V
3.3Ω
10k
0.01µF
13
SG
+
0.1µF
11
SENSE
16
BG
18
BSTREF
19
TGBLKSENS T
MAX
20
BAS21
0.1µF
100V
V
BST
C4
1.5µF
100V
C3
1.5µF
100V
L1
4.7µH
0.025Ω
1/2W
Q3
1nF
100V
1nF
100V
Q5
Q6
MURS120T3
MURS120T3
Q1
V
IN
+
V
IN
–
C2
22µF
100V
V
OUT
+
V
OUT
–
C5
330µF
10V
10Ω
0.25W
10Ω
0.25W
L2
4.1µH
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
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
+
1681 TA01
56k
1217
CMPZ5248B
18V
CMPZ-
5248B
15V
Q10
24k
T1
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
V
OUT
= 5V
I
OUT
= 7A
2
LT1681
1681f
Supply Voltages
Power Supply (V
CC
)............................. –0.3V to 20V
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
Input Voltages
SHDN Pin .................................. –0.3V to V
CC
+ 0.3V
All Other Inputs ..................... –0.3V to 5V
REF
+ 0.3V
Maximum Currents
5V
REF
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
(Note 1)
ORDER PART
NUMBER
LT1681ESW
LT1681ISW
T
JMAX
= 125°C, θ
JA
= 85°C/W
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.
ABSOLUTE MAXIMUM RATINGS
W
WW
U
PACKAGE/ORDER INFORMATION
W
U
U
ELECTRICAL CHARACTERISTICS
1
2
3
4
5
6
7
8
9
10
TOP VIEW
SW PACKAGE
20-LEAD PLASTIC SO
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
BLKSENS
BG
PWRGND
V
CC
SG
I
MAX
SENSE
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Supply and Protection
V
CC
Operating Supply Voltage Range ● 91218 V
I
CC
DC Active Supply Current (Note 2) 17 22 mA
● 25 mA
DC Active UVL Supply Current V
SHDN
> 1.35V, V
CC
= 8V ● 800 1200 µA
DC Standby Supply Current V
SHDN
< 0.3V 0.5 µA
I
BST
DC Active Supply Current TG Logic High (Note 2) ● 5 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
CCUVLO
Undervoltage Lockout Threshold Falling Edge ● 8.0 8.40 8.60 V
Rising Edge
● 8.3 8.75 8.95 V
Undervoltage Lockout Hysteresis ● 0.25 0.35 V
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
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LT1681
1681f
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
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
5V External Reference
V
5VREF
5V Reference Voltage 0 ≤ (I
5VREF
– I
VC
) < 20mA 4.85 5 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
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 and Blanking
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
V
BLKSENS
Blanking Input Threshold ● 4.5 5 5.5 V
I
BLKSENS
Blanking Input Bias Current –2 µA
t
MIN
Switch Minimum On Time V
BLKSENS
= V
BG
, Measured at BG Output 250 ns
I
MAX
Sense
I
IMAX
Input Bias Current –250 µA
V
IMAX
I
MAX
Threshold (Rising Edge) Measured at I
MAX
Input ● 320 360 400 mV
I
MAX
Threshold Hysteresis Measured at I
MAX
Input 140 mV
t
P
I
MAX
Output Switch Disable Delay Measured at BG Output 130 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
P
Fault Delay to Output Disable 50mV Overdrive 650 ns
Oscillator and Synchronization Decoder
f
OSC
Oscillator Frequency, Free Run Measured at FSET Pin 700 kHz
Frequency Programming Error, Free Run f
OSC
≤ 500kHz (Note 3) ● –10 5 %
I
FSET
FSET Input Bias Current FSET 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)
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LT1681ESW#TRPBF

Mfr. #:
Buy LT1681ESW#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Primary Sync. Forward Sw Controller
Lifecycle:
New from this manufacturer.
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