LT1737
High Power
Isolated Flyback Controller
FEATURES
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DESCRIPTIO
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Drives External Power MOSFET
Supply Voltage Range: 4.5V to 20V
Flyback Voltage Limited Only by
External Components
Senses Output Voltage Directly from Primary Side
Winding—No Optoisolator Required
Switching Frequency from 50kHz to 250kHz
with External Capacitor
Moderate Accuracy Regulation Without User Trims
Regulation Maintained Well into Discontinuous Mode
External I
SENSE
Resistor
Optional Load Compensation
Optional Undervoltage Lockout
Shutdown Feature Reduces I
Q
to 50µA Typ
Available in 16-Pin GN and SO Packages
The LT
®
1737 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 DC supply voltage. Output voltage feed-
back information may be supplied by a variety of methods
including a third transformer winding, the primary wind-
ing or even direct DC feedback (see Applications Informa-
tion). Its gate drive capability, coupled with a suitable
external MOSFET and other power path components, can
deliver load power up to tens of Watts.
The LT1737 has a number of features not found on other
isolated flyback controller 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Isolated Flyback Switching Regulators
Medical Instruments
Instrumentation Power Supplies
TYPICAL APPLICATIO
R2
35.7k
1%
D2
BAS16
12V-18V to Isolated 15V Converter
V
IN
C1
22µF
+
Q1
2N3906
T1
COILTRONICS
CTX150-4
240k
33k
C3
0.1µF
•
150µH
150µH
•
UVLO
FB
V
C
R3
3.01k
1%
1nF
OSCAP
47pF
LT1737
V
CC
GATE
I
SENSE
M1
IRFL014
R1
0.27Ω
t
ON
ENDLY MINENAB R
OCMP
75k
150k
100k
4.7k
R
CMPC
SGND
PGND
0.1µF
U
D1
MBRS1100
U
U
+
C2
33µF
R4
7.5k
V
OUT
= 15V
I
OUT
= 300mA
NOTE: SEE APPLICATIONS
INFORMATION FOR ADDITIONAL
COMPONENT SPECIFICATIONS
1737 TA01
1737f
1
LINER [ LINEAR TECHNOLOGY ]
