LT1737
High Power
Isolated Flyback Controller
U
FEATURES
DESCRIPTIO
■
Drives External Power MOSFET
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.
■
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 ISENSE Resistor
The LT1737 has a number of features not found on other
isolated flyback controller ICs. By utilizing current mode
switchingtechniques, itprovidesexcellentACandDCline
regulation. Its unique control circuitry can maintain regu-
lation well into discontinuous mode in most applications.
Optionalloadcompensationcircuitryallowsforimproved
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.
■
Optional Load Compensation
■
Optional Undervoltage Lockout
■
Shutdown Feature Reduces IQ to 50µA Typ
■
Available in 16-Pin GN and SO Packages
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APPLICATIO S
■
Isolated Flyback Switching Regulators
Medical Instruments
Instrumentation Power Supplies
■
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
12V-18V to Isolated 15V Converter
R2
35.7k
1%
V
IN
+
C1
22µF
T1
D1
COILTRONICS
CTX150-4
D2
MBRS1100
BAS16
Q1
2N3906
V
= 15V
= 300mA
OUT
OUT
I
•
+
240k
33k
R4
7.5k
C2
33µF
150µH
150µH
•
C3
0.1µF
UVLO
V
CC
M1
FB
GATE
IRFL014
LT1737
ENDLY MINENAB R
V
C
I
SENSE
R3
3.01k
1%
OSCAP
t
R
SGND
PGND
R1
0.27Ω
ON
OCMP
CMPC
NOTE: SEE APPLICATIONS
75k
150k 100k
4.7k
0.1µF
1nF
47pF
INFORMATION FOR ADDITIONAL
COMPONENT SPECIFICATIONS
1737 TA01
1737f
1