LT1737 Datasheet, PDF (1/28 Pages) Linear Technology – High Power Isolated Flyback Controller

LT1737
High Power
Isolated Flyback Controller
FEATURES
s _{Drives External Power MOSFET}
s _{Supply Voltage Range: 4.5V to 20V}
s _{Flyback Voltage Limited Only by}
External Components
s _{Senses Output Voltage Directly from Primary Side}
Winding—No Optoisolator Required
s _{Switching Frequency from 50kHz to 250kHz}
with External Capacitor
s _{Moderate Accuracy Regulation Without User Trims}
s _{Regulation Maintained Well into Discontinuous Mode}
s _{External ISENSE Resistor}
s _{Optional Load Compensation}
s _{Optional Undervoltage Lockout}
s _{Shutdown Feature Reduces IQ to 50µA Typ}
s _{Available in 16-Pin GN and SO Packages}
U
APPLICATIO S
s _{Isolated Flyback Switching Regulators}
s _{Medical Instruments}
s _{Instrumentation Power Supplies}
DESCRIPTIO
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.
TYPICAL APPLICATIO
Q1
2N3906
D2
BAS16
R2
35.7k
1%
240k
33k
12V-18V to Isolated 15V Converter
V_IN
C1 ⁺
22µF
T1
D1
COILTRONICS _MBRS1100
CTX150-4
C3
0.1µF
•
150µH
150µH
•
+ _C2
33µF
V_OUT = 15V
I_OUT = 300mA
R4
7.5k
R3
3.01k
1%
FB
V_C
OSCAP
UVLO
V_CC
LT1737
t_ON ENDLY MINENAB R_OCMP R_CMPC
SGND
GATE
I_SENSE
PGND
1nF
47pF 75k 150k 100k 4.7k
0.1µF
M1
IRFL014
R1
0.27Ω
NOTE: SEE APPLICATIONS
INFORMATION FOR ADDITIONAL
COMPONENT SPECIFICATIONS
1737 TA01
1737f
1