LT3573 Datasheet, PDF (1/24 Pages) Linear Technology – Isolated Flyback Converter Without an Opto-Coupler

FEATURES
n _{3V to 40V Input Voltage Range}
n _{1.25A, 60V Integrated NPN Power Switch}
n _{Boundary Mode Operation}
n _{No Transformer Third Winding or}
Optoisolator 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 _{Thermally Enhanced 16-Lead MSOP}
APPLICATIONS
n _{Industrial, Automotive, Medical}
n _{Low Power PoE}
LT3573
Isolated Flyback Converter
Without an Opto-Coupler
DESCRIPTION
The LT^®3573 is a monolithic switching regulator specifi-
cally designed for the isolated flyback topology. No third
winding or optoisolator is required for regulation. The
part senses the isolated output voltage directly from the
primary side flyback waveform. A 1.25A, 60V NPN power
switch is integrated along with all control logic into a 16-
lead MSOP package.
The LT3573 operates with input supply voltages from
3V to 40V, and can deliver output power up to 7W with
no external power devices.The LT3573 utilizes boundary
mode operation to provide a small magnetic solution with
improved load regulation.
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patents pending.
TYPICAL APPLICATION
V_IN
12V TO 24V
10μF _357k
51.1k
5V Isolated Flyback Converter
V_IN
SHDN/UVLO
TC
R_ILIM
SS
VC
LT3573
R_FB
R_REF
SW
GND TEST BIAS
0.22μF
1N4148
80.6k
B340A
3:1
2k
24μH
2.6μH
6.04k
28.7k 10k
20k
10nF
1nF
4.7μF
V_OUT+
5V, 0.7A
47μF
V_OUT–
3573 TA01
Load Regulation
3
2
1
0
V_IN = 24V
V_IN = 12V
–1
–2
–3
0 200 400 600 800 1000 1200 1400
I_OUT (mA)
3573 TA01b
3573f
1