LT3825
Isolated No-Opto
Synchronous Flyback Controller
with Wide Input Supply Range
FEATURES DESCRIPTION
n
Senses Output Voltage Directly from Primary Side The LT 3825 is an isolated switching regulator controller
designed for medium power flyback topologies. A typical
WindingNo Opto-Isolator Required
n
application is 10W to 60W with input voltage limited only
Synchronous Driver for High Efficiency
n by external power path components. A third transformer
Input Voltage Limited Only by External
winding provides output voltage feedback.
Power Components
n
Accurate Output Regulation without User Trims
The LT3825 is a current mode controller that regulates
n
Switching Frequency from 50kHz to 250kHz
output voltage based on sensing secondary voltage via a
n
Synchronizable
transformer winding during flyback. This allows for tight
n
Load Compensation
output regulation without the use of an opto-isolator,
n
Programmable Undervoltage Lockout
improving dynamic response and reliability. Synchronous
n
Available in a Thermally Enhanced 16-Lead
rectification increases converter efficiency and improves
TSSOP Package output cross regulation in multiple output converters.
The LT3825 operates in forced continuous conduction
APPLICATIONS
mode which improves cross regulation in multiple winding
n
applications. Switching frequency is user programmable
Isolated Medium Power (10W to 60W) Supplies
n and can be externally synchronized. The part also has load
Isolated Telecom, Medical Converters
n compensation, undervoltage lockout and soft-start circuity.
Instrumentation Power Supplies
n L, LT, LTC, LTM, Burst Mode, SwitcherCAD, Linear Technology and the Linear logo are registered
Isolated Power over Ethernet Supplies
trademarks and No R , ThinSOT are trademarks of Linear Technology Corporation. All other
SENSE
trademarks are the property of their respective owners. Protected by U.S. Patents, including
6948466, 5841643.
Efficiency
92
TYPICAL APPLICATION
90
36V
IN 48V
IN
88
72V
IN
86
48V to 3.3V at 12A Isolated Supply
84
+
V
+ OUT
V
IN
82
3.3V
36V TO 72V
470F
12A
100pF
4
T1
80
28.7k
T1
20
20 47k
78
47
2 3 4 5 6 7 8 9 10 11 12
3.01k
+
LOAD CURRENT (A) 3825 TA01b
47F
SG
402k
2 Regulation
+
FB V SG PG
SENSE 3.43
CC
2.2F SG
1F
0.02
UVLO
3.38
330 15
LT3825
SENSE
15k
36V
IN
48V
2.2nF IN
PGDLY V
C 0.1F 3.33
72V
IN
t SYNC R ENDLY OSC GND SFST C
ON CMP CMP
10nF
3.28
0.22F 10k
12k 100k 2.1k 150k
100k
47pF 0.1F
3.23
3825 TA01a
3.18
3.13
2 3 4 5 6 7 8 9 10 11 12
LOAD CURRENT (A) 3825 TA01c
3825fe
1
OUTPUT (V) EFFICIENCY (%)LT3825
ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION
(Note 1)
TOP VIEW
V to GND
CC
Low Impedance Source ........................ 0.3V to 18V
SG 1 16 PG
Current Fed V 2 15 PGDLY
CC
t 3 14 R
(V Has Internal 19.5V Clamp) ...........30mA Into V ON CMP
CC CC
ENDLY 4 13 C
CMP
UVLO, SYNC Pin Voltage ........................... 0.3V to V 17
CC
GND +
+
SYNC 5 12 SENSE
SENSE , SENSE Pin Voltage ......................0.5V, +0.5V
SFST 6 11 SENSE
FB Pin Current ........................................................2mA
OSC 7 10 UVLO
V Pin Current ....................................................... 1mA
C
FB 8 9 V
C
Operating Junction Temperature Range
FE PACKAGE
(Notes 2, 3, 4) ........................................ 40C to 125C
16-LEAD PLASTIC TSSOP
Storage Temperature Range ................. 65C to 150C
T = 125C, = 40C/W, = 10C/W
JMAX JA JC
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
Lead Temperature (Soldering, 10 sec) ...................300C
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3825EFE#PBF LT3825EFE#TRPBF 3825EFE 16-Lead Plastic 4.4mm TSSOP 40C to 125C
LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3825EFE LT3825EFE#TR 3825EFE 16-Lead Plastic 4.4mm TSSOP 40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: