LT3574_15 Datasheet, PDF (1/24 Pages) Linear Technology – Isolated Flyback Converter Without an Opto-Coupler

Features
n _{3V to 40V Input Voltage Range}
n _{0.65A, 60V Integrated NPN Power Switch}
n _{Boundary Mode Operation}
n _{No Transformer Third Winding or}
Opto-Isolator Required for Regulation
n _{Improved Primary-Side Winding Feedback}
Load Regulation
n _{VOUT Set with Two External Resistors}
n _{BIAS Pin for Internal Bias Supply and Power}
NPN Driver
n _{Programmable Soft-Start}
n _{Programmable Power Switch Current Limit}
n _{16-Lead MSOP Package}
Applications
n _{Industrial, Automotive and Medical Isolated}
Power Supplies
LT3574
Isolated Flyback Converter
Without an Opto-Coupler
Description
The LT^®3574 is a monolithic switching regulator specifi-
cally designed for the isolated flyback topology. No third
winding or opto-isolator is required for regulation. The
part senses the isolated output voltage directly from the
primary side flyback waveform. A 0.65A, 60V NPN power
switch is integrated along with all control logic into a
16‑lead MSOP package.
The LT3574 operates with input supply voltages from
3V to 40V, and can deliver output power up to 3W with
no external power switch. The LT3574 utilizes boundary
mode operation to provide a small magnetic solution with
improved load regulation.
The output voltage is easily set with two external resistors
and the transformer turns ratio. Off-the-shelf transformers
are available for many applications.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and No R_SENSE and ThinSOT are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
Typical Application
V_IN
12V TO 24V
5V Isolated Flyback Converter
10µF
357k
V_IN
SHDN/UVLO
51.1k
0.22µF
PMEG6010
B340A
2k ^3:1
•
50µH
5.6µH
•
TC
R_ILIM
SS
VC
LT3574
R_FB
R_REF
SW
GND TEST BIAS
80.6k
6.04k
28.7k 10k
59k
10nF
1nF
4.7µF
3574 TA01
V_OUT+
5V
0.35A
22µF
V_OUT–
Load Regulation
1.0
V_IN = 24V
0.5
V_IN = 12V
0
–0.5
–1.0
0
100 200 300 400 500 600 700
I_OUT (mA)
3574 TA01b
3574f