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LT1725IGN#PBF

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1
LT1725
1725fa
LT1725
3V
OUT
FB
SFST
VC
OSCAP
t
ON
ENDLY
MENAB
R
OCMP
R
CMPC
V
CC
UVLO
GATE
I
SENSE
SGND PGND
1nF
0.1µF
47pF
51k
51k
51k
2.7k
35.7k
1%
3.01k
1%
+
15µF
150µF
1µF
1.5µF
47k
820k
100pF
33k
68Ω
150pF
22Ω
BAS16
V
IN
36V TO 72V
+
IRF620
6
1
2
4
9
10
12
11
18Ω
51Ω
1W
470pF
12CWQ06
V
OUT
= 5V
I
OUT
= 0 to 2A
CTX02-14989
1725 TA01a
0.18Ω
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
General Purpose
Isolated Flyback Controller
The LT
®
1725 is a monolithic switching regulator control-
ler specifically designed for the isolated flyback topology.
It drives the gate of an external MOSFET and is generally
powered from a third transformer winding. These features
allow for an application input voltage limited only by
external power path components. The third transformer
winding also provides output voltage feedback informa-
tion, such that an optoisolator is not required. Its gate
drive capability coupled with a suitable external MOSFET
can deliver load power up to tens of watts.
The LT1725 has a number of features not found on most
other switching regulator ICs. By utilizing current mode
switching techniques, it provides excellent AC and DC line
regulation. Its unique control circuitry can maintain regu-
lation well into discontinuous mode in most applications.
Optional load compensation circuitry allows for improved
load regulation. An optional undervoltage lockout pin
halts operation when the application input voltage is too
low. An optional external capacitor implements a soft-
start function. A 3V output is available at up to several mA
for powering primary side application circuitry.
■
Drives External Power MOSFET with External
I
SENSE
Resistor
■
Application Input Voltage Limited Only by
External Power Components
■
Senses Output Voltage Directly from Primary Side
Winding—No Optoisolator Required
■
Accurate Regulation Without User Trims
■
Regulation Maintained Well into Discontinuous Mode
■
Switching Frequency from 50kHz to 250kHz with
External Capacitor
■
Optional Load Compensation
■
Optional Undervoltage Lockout
■
Available in 16-Pin SO and SSOP Packages
■
Telecom Isolated Converters
■
Offline Isolated Power Supplies
■
Instrumentation Power Supplies
Output Load Regulation
48V to Isolated 5V Converter
I
LOAD
(A)
0
V
OUT
(V)
5.00
1725 F10b
4.75
0.5
1.0
1.5
2.0
5.25
V
IN
= 36V
V
IN
= 72V
V
IN
= 48V
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
U
2
LT1725
1725fa
(Note 1)
V
CC
Supply Voltage ................................................. 22V
UVLO Pin Voltage .................................................... V
CC
I
SENSE
Pin Voltage .................................................... 2V
FB Pin Current ..................................................... ±2mA
Operating Junction
Temperature Range
LT1725C .............................................. 0°C to 100°C
LT1725I ........................................... –40°C TO 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
PACKAGE/ORDER I FOR ATIO
UU
W
ABSOLUTE AXI U RATI GS
WWWU
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 14V, GATE open, V
C
= 1.4V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Supply
V
CC
V
CC
Turn-On Voltage ● 14.0 15.1 16.0 V
V
CC
Turn-Off Voltage ● 8 9.7 11 V
V
CC
Hysteresis (Note 3) (V
TURN-ON
– V
TURN-OFF
) ● 4.0 5.4 6.5 V
I
CC
Supply Current V
C
= Open ● 61015mA
Start-Up Current
● 120 280 µA
Feedback Amplifier
V
FB
Feedback Voltage 1.230 1.245 1.260 V
● 1.220 1.270 V
I
FB
Feedback Pin Input Current 500 nA
g
m
Feedback Amplifier Transconductance ∆l
C
= ±10µA ● 400 1000 1800 µmho
I
SRC
, I
SNK
Feedback Amplifier Source or Sink Current ● 30 50 80 µA
V
CL
Feedback Amplifier Clamp Voltage 2.5 V
Reference Voltage/Current Line Regulation 12V ≤ V
IN
≤ 18V ● 0.01 0.05 %/V
Voltage Gain V
C
= 1V to 2V 2000 V/V
Soft-Start Charging Current V
SFST
= 0V 25 40 50 µA
Soft-Start Discharge Current V
SFST
= 1.5V, V
UVLO
= 0V 0.8 1.5 mA
ORDER PART NUMBER
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
LT1725CGN
LT1725IGN
LT1725CS
LT1725IS
T
JMAX
= 125°C, θ
JA
= 110°C/W (GN)
T
JMAX
= 125°C, θ
JA
= 100°C/W (SO)
TOP VIEW
S PACKAGE
16-LEAD PLASTIC SO
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PGND
I
SENSE
SFST
R
OCMP
R
CMPC
OSCAP
V
C
FB
GATE
V
CC
t
ON
ENDLY
MINENAB
SGND
UVLO
3V
OUT
1725
1725I
GN PART MARKING
3
LT1725
1725fa
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: Component value range guaranteed by design.
Note 3: The V
CC
turn-on/turn-off voltages and hysteresis voltage are
proportional in magnitude to each other-guaranteed by design.
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 14V, GATE open, V
C
= 1.4V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Gate Output
V
GATE
Output High Level I
GATE
= 100mA ● 11.5 12.1 V
I
GATE
= 500mA ● 11.0 11.8 V
Output Low Level I
GATE
= 100mA ● 0.3 0.45 V
I
GATE
= 500mA ● 0.6 1.0 V
I
GATE
Output Sink Current in Shutdown, V
UVLO
= 0V V
GATE
= 2V ● 1.2 2.5 mA
t
r
Rise Time C
L
= 1000pF 30 ns
t
f
Fall Time C
L
= 1000pF 30 ns
Current Amplifier
V
C
Control Pin Threshold Duty Cycle = Min 0.90 1.12 1.25 V
● 0.80 1.35 V
V
ISENSE
Switch Current Limit Duty Cycle ≤ 30% 220 250 270 mV
Duty Cycle ≤ 30%
● 200 280 mV
Duty Cycle = 80% 220 mV
∆V
ISENSE
/∆V
C
0.30 mV
Timing
f Switching Frequency C
OSCAP
= 100pF 90 100 115 kHz
● 80 125 kHz
C
OSCAP
Oscillator Capacitor Value (Note 2) 33 200 pF
t
ON
Minimum Switch On Time R
tON
= 50k 200 ns
t
ED
Flyback Enable Delay Time R
ENDLY
= 50k 200 ns
t
EN
Minimum Flyback Enable Time R
MENAB
= 50k 200 ns
R
t
Timing Resistor Value (Note 2) 24 200 kΩ
Maximum Switch Duty Cycle ● 85 90 %
Load Compensation
Sense Offset Voltage 25mV
Current Gain Factor 0.80 0.95 1.05 mV
UVLO Function
V
UVLO
UVLO Pin Threshold ● 1.21 1.25 1.29 V
I
UVLO
UVLO Pin Bias Current V
UVLO
= 1.2V –0.25 + 0.1 + 0.25 µA
V
UVLO
= 1.3V –4.50 – 3.5 – 2.50 µA
3V Output Function
V
REF
Reference Output Voltage I
LOAD
= 1mA ● 2.8 3.0 3.2 V
Output Impedance 10 Ω
Current Limit ● 815 mA
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LT1725IGN#PBF

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Buy LT1725IGN#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators General Purpose Iso Fly Cntr
Lifecycle:
New from this manufacturer.
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