LT1425_15 Datasheet, PDF (1/20 Pages) Linear Technology – Isolated Flyback Switching Regulator

LT1425
Isolated Flyback
Switching Regulator
FEATURES
s _{No Transformer “Third Winding” or Optoisolator}
Required
s _{±5% Accurate Output Voltage Without User Trims}
(See Circuit Below)
s _{Resistor Programmable Output Voltage}
s _{Regulation Maintained Well Into Discontinuous}
Mode (Light Load)
s _{Optional Load Compensation}
s _{Operating Frequency: 285kHz}
s _{Easily Synchronized to External Clock}
s _{Available in 16-Pin Narrow SO Package}
U
APPLICATIONS
s _{Isolated Flyback Switching Regulators}
s _{Ethernet Isolated 5V to – 9V Converters}
s _{Medical Instruments}
s _{Isolated Telecom Supplies}
, LTC and LT are registered trademarks of Linear Technology Corporation.
DESCRIPTION
The LT^®1425 is a monolithic high power switching regu-
lator specifically designed for the isolated flyback topol-
ogy. No “third winding” or optoisolator is required; the
integrated circuit senses the isolated output voltage
directly from the primary side flyback waveform. A high
current, high efficiency switch is included on the die along
with all oscillator, control and protection circuitry.
The LT1425 operates with input supply voltages from 3V
to 20V and draws only 7mA quiescent current. It can
deliver output power up to 6W with no external power
devices. By utilizing current mode switching techniques, it
provides excellent AC and DC line regulation.
The LT1425 has a number of features not found on other
switching regulator ICs. Its unique control circuitry can
maintain regulation well into discontinuous mode in most
applications. Optional load compensation circuitry allows
for improved load regulation. An externally activated shut-
down mode reduces total supply current to 15µA for
standby operation.
TYPICAL APPLICATION
5V to Isolated – 9V_OUT
500V
ISOLATION BARRIER
5V
+ C1
100µF
10V
T1*
12
V_IN
11
•
V_SW
R1
D1
1N5819
•
C2
47µF
16V
V^–
ISOLATED
–9V ± 5% AT
20mA TO 200mA
LT1425
22.6k
F
15
3 ^1%
*DALE LPE 4841-330MB
SHDN R_FB
6
R2
SYNC
3.01k
4
C3
V_C
1000pF
R_REF ⁵
14
R_OCOMP
R_CCOMP ¹³
SGND PGND
1%
R3
C4
15k
0.1µF
7
10
1425 TA01
9.5
9.4
9.3
9.2
9.1
9.0
8.9
8.8
8.7
8.6
8.5
0
Load Regulation
50
100
150
OUTPUT CURRENT (mA)
200
1425 TA02
1