LT3825 Datasheet, PDF (1/32 Pages) Linear Technology – Isolated No-Opto Synchronous Flyback Controller with Wide Input Supply Range

LT3825
FEATURES
Isolated No-Opto
Synchronous Flyback Controller
with Wide Input Supply Range
DESCRIPTION
n _{Senses Output Voltage Directly from Primary Side}
Winding—No Optoisolator Required
n _{Synchronous Driver for High Efficiency}
n _{Input Voltage Limited Only by External}
Power Components
n _{Accurate Output Regulation Without User Trims}
n _{Switching Frequency from 50kHz to 250kHz}
n _{Synchronizable}
n _{Load Compensation}
n _{Programmable Undervoltage Lockout}
n _{Available in a Thermally Enhanced 16-Lead}
TSSOP Package
APPLICATIONS
n _{Isolated Medium Power (10W to 60W) Supplies}
n _{Isolated Telecom, Medical Converters}
n _{Instrumentation Power Supplies}
n _{Isolated Power over Ethernet Supplies}
The LT^®3825 is an isolated switching regulator controller
designed for medium power flyback topologies. A typical
application is 10W to 60W with input voltage limited only
by external power path components. A third transformer
winding provides output voltage feedback.
The LT3825 is a current mode controller that regulates
output voltage based on sensing secondary voltage via
a transformer winding during flyback. This allows for
tight output regulation without the use of an optoisolator,
improving dynamic response and reliability. Synchronous
rectification increases converter efficiency and improves
output cross regulation in multiple output converters.
The LT3825 operates in forced continuous conduction mode
which improves cross regulation in multiple winding ap-
plications. Switching frequency is user programmable and
can be externally synchronized. The part also has load com-
pensation, undervoltage lockout and soft-start circuity.
L, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 6948466, 5841643.
TYPICAL APPLICATION
V_IN+
36V TO 72V
2.2μF
48V to 3.3V at 12V Isolated Supply
28.7k
T1
•
3.01k
402k
FB
20Ω 47k
+
47μF
SG
V_CC
SG
100pF ^•
T1
20Ω
•
470μF
×4
47Ω
PG SENSE⁺
×2
SG
UVLO
0.02Ω
15k
LT3825
SENSE^–
330Ω
15Ω
PGDLY
V_C
0.1μF ^2.2nF
t_ON SYNC R_CMP ENDLY OSC GND SFST C_CMP
12k 100k
2.1k 150k
47pF
0.22μF
0.1μF
10nF
100k
••
10k
V_OUT+
3.3V
12A
1μF
3825 TA01a
Efficiency
92
90
36V_IN
88
86
48V_IN
72V_IN
84
82
80
78
2 3 4 5 6 7 8 9 10 11 12
LOAD CURRENT (A)
3825 TA01b
Regulation
3.43
3.38
36V_IN
3.33
48V_IN
72V_IN
3.28
3.23
3.18
3.13
2 3 4 5 6 7 8 9 10 11 12
LOAD CURRENT (A)
3825 TA01c
3825fa
1