LT1425
Isolated Flyback Switching Regulator
FEATURES
DESCRIPTION
The LT®1425 is a monolithic high power switching regula-
tor specifically designed for the isolated flyback topology.
No “third winding” or optoisolator is required; the inte-
grated 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.
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No Transformer “Third Winding” or Optoisolator
Required
5ꢀ ꢁAAurate Output Voltage Without User Trims
(See CirAuit Below)
Resistor Programmable Output Voltage
Regulation Maintained Well Into DisAontinuous
Mode (Light Load)
Optional Load Compensation
Operating Frequency: 285kHz
Easily Synchronized to External Clock
Available in 16-Pin Narrow SO Package
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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.
APPLICATIONS
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
shutdown mode reduces total supply current to 15µA for
standby operation.
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Isolated Flyback Switching Regulators
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Ethernet Isolated 5V to –9V Converters
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Medical Instruments
Isolated Telecom Supplies
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All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
Load Regulation
5V to Isolated –9VOUT
ꢑ.ꢐ
ꢑ.ꢔ
ꢑ.ꢕ
ꢑ.ꢖ
500V
ISOLATION BARRIER
5V
T1*
–
V
+
C1
100μF
10V
C2
ISOLATED
D1
1N5819
12
47μF
–9V 5% AT
ꢑ.ꢗ
ꢑ.ꢋ
ꢏ.ꢑ
ꢏ.ꢏ
ꢏ.ꢒ
ꢏ.ꢓ
ꢏ.ꢐ
+
16V
20mA TO 200mA
V
IN
11
3
•
•
V
SW
R1
22.6k
1%
F
LT1425
*DALE LPE 4841-330MB
15
R
SHDN
FB
R2
3.01k
1%
6
SYNC
5
4
R
V
C
REF
C3
1000pF
14
13
ꢋ
ꢐꢋ
ꢗꢋꢋ
ꢗꢐꢋ
ꢖꢋꢋ
R
OCOMP
ꢀꢁꢂꢃꢁꢂ ꢄꢁRRꢅꢆꢂ ꢇꢈꢉꢊ
R3
15k
R
CCOMP
C4
0.1μF
ꢗꢔꢖꢐ ꢂꢉꢋꢖ
SGND PGND
10
7
1425 TA01
Rev. B
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